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#### Revomal of specific gases from a mixture of gas

 Posted on January 7, 2013 at 8:30 PM comments ()

How do you remove a specific gas from a mixture of gases?

It is not very difficult to remove a certain from a mixture, you simply need to know how to do it from it's reactivity and nature point of view.

With regards to the GCE O levels, the most common gases that we can remove, falls under the follow categories.

1. Acidic gases - Which comprises of gases like hydrogen chloride, carbon dioxide, nitrogen dioxide and sulfur dioxide.
2. Soluble gases - Which comprises of hydrogen chloride, nitrogen dioxide, sulfur dioxide, ammonia
3. Alkaline gases - ammonia
4. Oxygen gas

In order to remove acidic, soluble and alkaline gases, all these require this apparatus to work.

The whole idea is to bubble the mixture into the solution so that the solution can absorb the unwanted gas away. For the acidic gases, the solution will consist of an alkaline solution such as sodium hydroxide or calcium hydroxide (also known as limewater). This is because the acidic gases will be neutralized by the alkaline solution, hence the acidic gas will be removed.

For the soluble gases, all we need to use is to use water, as the water soluble gases will dissolved into it and disappear!

You may also notice that the delivery tube on the left is actually longer and is inserted into the solution. Pretty self explanatary, the tube needs to guide the gases into the solution. If the tube is above the liquid, do you think, it will bubble nicely into the liquid? Hence watch out for the drawing of the 2 delivery tubes.

Finally, to remove oxygen from a mixture of gases, a hot metal typically copper is used to remove it. When the metal is heated, it has enough energy to react with the oxygen gas to form a metal oxide, typically copper (II) oxide, if we used copper metal.

So that's it, these are methods to remove gases from mixture of gases.

#### Final Physics Reminders

 Posted on October 31, 2012 at 3:45 AM comments ()

Kinetic Particle Theory

1. The air molecules move in random direction. They collide on the smoke particles in all directions with uneven forces. The smoke particles will move in the direction of the resultant force.

2. See above.

3. Standard, temperature increases, kinetic energy increases.

4. During melting, heat energy is taken in increases the potential energy of the particles. The increase in potential energy causes particles to move apart. Since the kinetic energy remains unchanged, the temperature remains constant.

Transfer of thermal energy

1. When heat is applied, the particles gain energy and vibrate faster. This causes the particles to collide on neighbouring particle and thus transferring the energy to them. This process of collision and vibration continues till the whole solid is heated up.

2. When heat is applied, the particles gain energy and vibrate faster. This causes the particles to collide on neighbouring particle and thus transferring the energy to them. Good conductors like metals also contain free moving electrons. When the electrons gain energy, it moves faster and collide with other particles quickly, thus transferring the energy.

3. When the liquid is heated, it gains energy and expands. The volume of the liquid increases and for the same mass of liquid, it becomes less dense. The less dense liquid will rise and the cooler and denser liquid at the top will sink to the bottom to be heated. This sets up a convection current that heats up the entire liquid.

4. Simply, the transfer of heat is by electromagnetic radiation.

5. During the day, the land, being a better conductor of heat, gains heat faster than the sea. The warmer air above the land rises and the cooler air from the sea moves in to create the sea breeze. During the night, the land, being a better conductor of heat, loses heat faster than the sea. The warmer air above the water rises and the cooler air from the land moves in to create the land breeze.

6. Dark coloured, dull and rough surfaces are better absorber and emitter of radiation.

7. Insert rods of same dimension but different materials into a hot water tub. Stick a piece wax at the end of each rod, the rod that is the best conductor will be the rod that melts the wax first.

8. Place equal amount of water at 20˚C in 2 cups, 1 painted black, the other white. Place the 2 cups under the hot sun and insert a thermometer in each of the cup. The cup with the black surface will have a faster increase in temperature indicating that a black surface is a better absorber of heat. (For emitter use, hot water at 80˚C in a cool room, check that the black surface cools faster)

9. Heat some water in a beaker to boil. When it boils, add in a potassium manganate crystal at the bottom of the beaker. The crystal will dissolve to form a purple streak indication the path of the convection current.

10. The lid is to reduce heat loss by convection.

11. The vacuum flask has 3 features that keeps a liquid hot. First there is a vacuum layer between the walls of the container which prevents heat loss by conduction and convection. Secondly, its shiny inner walls will reflect heat back into the liquid to keep it hot. The bottle also has a plastic stopper at the top to reduce heat loss by convection.

12. The doubled layer window has a layer of air between them. Since the air is a poor conductor of heat, it keeps the room cool when temperature is high and keeps it warm when outside temperature is cold.

Temperature (Pure)

1. Volume of a fixed mass of liquid, pressure of a fixed volume of gas

2. 0 and 100˚C

3. -

4. Place an uncalibrated liquid in glass in pure melting ice. Measure the length of mercury in melting ice. Place the thermometer in steam just above the boiling water, measure the length of mercury. Finally place the thermometer in the unknown substance, measure its length. Find the temperature of the unknown by using the formula _______.

5. Use thinner bulb of thermometer.

6. Use thinner capillary tube.

Thermal Properties

1. Specific heat capacity measures the amount of energy needed to raise the temperature of a unit mass of substance by 1 ˚C while heat capacity measures the amount of energy needed to raise the temperature of a substance by 1˚C. (Pure)

2. See above

3. The more energetic particles on the surface gains sufficient energy and overcomes the forces of attraction holding the particles together. The average kinetic energy of the liquid decreases after the evaporation, hence energy decreases.

4. Evaporation occurs at all temperature and boiling occurs only at boiling point. Evaporation occurs on the surface and boiling occurs throughout the liquid. Evaporation results in cooling but boiling does not.

Waves

1. definition

2. definition

3. Period is the time taken for a complete oscillation. Frequency measures the number of complete oscillation in 1 sec.

4. -

5. Longitudinal wave - particles vibrate parallel to wave motion but for transverse it is perpendicular.

#### Periodic Table Hints

 Posted on August 13, 2012 at 6:35 AM comments ()

Everything Periodic Table

1 What are the horizontal rows and vertical column in a periodic table known as?

A: The horizontal rows are called period and the vertical column are called group.

2 What information does the group number of an element tells us?

A: It tells us the number of valence electrons that an atom has. For example, group 1 elements have 1 valence electron and group 7 elements have 7 electrons on the outer shell.

3 What information does the period number of an element tells us?

A: It tells us the number of electrons an atoms has. For example, sodium has an electronic configuration of 2,8,1. It is in period 3 hence it has 3 electron shells.

4 How do metals react and how do non-metals react?

A: Metals react by losing electrons and non-metals react by gaining electron.

5 What are some common physical properties of metals?

A: Metals are ductile (able to be stretched into wires), malleable (able to form and shape easily), good conductors of electricity, good conductors of heat, sonorous (produce a tickling sound when struck), generally high melting and boiling points (except for group 1 metals and mercury which have low melting point).

6 What are the common chemical properties of metals?

A: Metals generally react with acids to form salt and hydrogen gas. They also form ionic compounds when reacted with non-metals. The more reactive metals like the group 1 metals can react with cold water to form aqueous group 1 hydroxide and hydrogen gas.

7 What is the name given to group 1 elements?

A: Group 1 elements are collectively called alkali metals.

8 What are some properties that are unique to group 1 elements only?

A: Group 1 metals are soft metal. Group 1 metals unlike most metals have low melting and boiling point. Group 1 metals can react with water to form a metal hydroxide and hydroxide.

9 Write the word and chemical equations, with state symbol, for sodium's reaction with water.

A: Sodium + water --> sodium hydroxide + hydrogen gas.

2Na(s) + 2H2O(l) --> 2NaOH(aq) + H2(g).

10 Describe the reactions of group 1 metals.

A: Alkali metals react with water to form metal hydroxide and hydrogen gas. They also react with acid to form salt and hydrogen gas. Group 1 metals react with halogens (group 7 element) to form metal halide. For example, sodium reacts with chlorine to form sodium chloride and potassium reacts with bromine to form potassium bromine.

11 What is the name given to elements in group 7?

A. Halogens.

12 What is the name given to elements in group 0?

A: Noble gas.

13 What is the name given to elements between group 2 and 3?

A: Transition metals.

14 How many valence electrons does group 1, group 2 and group 3 elements has?

A. Group 1 has 1, group 2 has 2 and group 3 has 3 valence electrons. (This is the safest way to determine the number of valence electrons, do not do the 2,8,8,8.... it will be wrong).

15 What is the ionic charge expected of group 1, group 2 and group 3 ions?

A: Group 1 ions is +1, group 2 is +2 and group 3 is +3.

16 What are some of the common properties of group 1 metal? (state only properties possessed by group 1 metals.

A: Soft metal, low melting boiling point (as opposed to most metals which are high) and low density.

17 State the trends of properties of group 1 elements down the group.

A: Melting and boiling point decreases down the group, reactivity increases down the group and density increases down the group.

18 Explain VERY briefly why melting point of group 1 metals decreases down the group.

A: The metal bonds holding the positive ions and negative sea of electrons weakens. So lesser energy is needed to overcome the forces of attraction and hence melting and boiling point decreases.

19 Explain in detail why the melting point of group 1 metals decreases down the group.

A: As the metals moved down the group, the atomic radius increases. The force of attraction between the positive nucleus and negative sea of electrons weakens. This weakens the metallic bonds and their melting point will decreases.

20 Explain why reactivity of metals increases down the group.

A: As the metals moved down the group, the atomic radius of the atoms increases. The shielding effect between the positive nucleus and the valence electrons increases. This weakens the force of attraction between the nucleus and the valence electrons. Since the metals react by losing electrons, it is easier to lose electrons down the group hence reactivity increases.

21 Describe a simple experiment to test the reactivity of lithium, sodium and potassium with a water.

A: Add same amount of the 3 metals into 3 separate beakers of water. Ensure all the water is identical and of the same temperature. It will be observed that lithium's reaction with water is fast, sodium is vigorous and potassium is explosive. This shows that potassium is the most reactive of the 3 metals and reactivity of metals increases down the group.

22 Describe what you will observe when sodium is added to water mixed with universal indicator. Explain the changes to the solution.

A: Bubbles of gas (effervescence) observed, gas produced extinguished light splint with a pop sound. Solution changes from green to violet. Water is a neutral substance therefore, it appears green with universal indicator. When sodium reacts with water, it forms sodium hydroxide and hydrogen gas. Since sodium hydroxide is a strong alkali, the universal indicator turns violet.

23 What are the states of the halogens at room temperature?

A: Both chlorine and flourine are gases at room temperature, bromine is a liquid at room temperature, iodine and astatine are both solids at room temperature.

24 What are the type colours of the halogens at room temperature?

A: Flourine is a pale yellow gas, chlorine is a greenish yellow gas, bromine is a reddish brown liquid, iodine is a black solid (sometime it can be BROWN SOLUTION) and astatine is a black solid.

25 State the trends of group 7 substances.

A: The colours of the molecules darkens down the group, the reactivity decreases down the group, the melting boiling point increases down the group.

26 What is a displacement reaction with regards to halogen?

A: A more reactive halogen can displace a less reactive element from its salt.

27 What are the colours of standard solutions?

A: Most of the solutions you will be encountering are colourless solutions. Solutions of group 1 and group 2 salts are all colourless. the coloured solutions are normally from transition metals. Like iron (II) salts are green, copper (II) salts are blue and iron (III) salts are yellow.

28. Describe and explain what happen when bromine is added to potassium chloride.

A: (First off bromine is reddish brown, potassium chloride is a group 1 salt so it is a colourless solution.) There is no visible reaction. Bromine is less reactive than chlorine so it is unable to displace chlorine from its salt.

29. Describe and explain what happen when chlorine is added to potassium bromide.

A: (Again potassium bromide is a group 1 salt so it is a colourless solution and chlorine is greenish yellow) When the greenish yellow gas is added to the colourless solution, solution turns reddish brown. Chlorine is more reactive than bromine hence it is able to displace bromine from potassium bromide. The displaced bromine is reddish brown, causing the solution to turn reddish brown.

30 Write the chemical equation for the reaction in question 29

A: Cl2 + 2KBr --> 2KCl + Br2. Ionic equation: Cl2 + 2Br- --> 2Cl- + Br2

31 Describe and explain what happen when chlorine is added to potassium iodide.

A: When greenish yellow gas is added to colourless solution, solution turns brown. Chlorine is more reactive than iodine so it is able to displace iodine from potassium iodide.

OR

A: When greenish yellow gas is added to colourless solution, black solid appears. Chlorine is more reactive than iodine so it is able displace iodine from potassium iodide.

#### Acids Bases and Salt Hints

 Posted on August 2, 2012 at 2:40 AM comments ()

Everything you want to know about acids

1. What is an acid?

A: An acid is a substance that ionizes in water to produce H+ as the only positive ion.

2. What is an alkali?

A: An alkali is a substance that ionizes in water to produce OH- as the only negative ion.

3. What causes a solution to be acidic?

A: Hydrogen ions, H+.

4. What causes a solution to be alkaline?

A: Hydroxide ions, OH-.

5. What is a strong acid?

A: Strong acids are acids that undergoes complete ionization of hydrogen ions in water.

6. What is a weak acid?

A: Weak acids are acids that undergoes partial ionization of hydroxide ions in water.

7. What are indicators?

A: An indicator is a chemical substance added to determine the pH of a substance.

8. What are the common indicators?

A: Universal indicator - Red at pH 1 for strong acids, Orange and yellow for weak acids, Green for neutral solution, blue for weak alkali and violet for strong alkali.

9. What exactly is neutralization?

A: Process where acids and bases react with form salt and water only.

10. What is a base?

A: A substance that reacts with acids to form salt and water. When it is soluble, it forms an alkali.

11. What are the products when acids react with metals?

A: Salt and hydrogen gas.

12. What are the products when acids react with metal carbonate?

A: Salt, water and carbon dioxide.

13. What are the products when acids react with metal oxide, also known as a base?

A: Salt and water.

14. What are the products when acids react with metal hydroxide, also known as a base?

A: Salt and water.

15. What is produced when bases dissolved in water?

A: Alkalis

16. Write the ionization equations of all common acids, including state symbols.

A: HCl --> H+ + Cl-, CH3COOH --> H+ + CH3COO-, HNO3 --> H+ + NO3-, H2SO4 --> 2H+ + SO42-. State symbols all aqueous

17. Write the ionization equations of common alkalis, including state symbols.

A: NaOH --> Na+ + OH- or Ca(OH)2 --> Ca2+ + 2OH- or NH4OH --> NH4+ + OH- and again all state symbols are aq.

18. Describe a simple test to prove that water is needed for the ionization of acids.

A: Dissolve nitric acid into water and ethanol separately. Connect a light bulb and a battery to the solution. The acid that dissolved into water will enable the light bulb to light up and the acid that dissolves into ethanol will not light up. It is because in the presence of water, acid dissociates to produce hydrogen ions. These ions are free to move to conduct electricity therefore the bulb that is connected to acid dissolved in water lights up. Ethanol is an organic solvent and therefore it will not allow acid to ionize.

19. Which oxides are non-metal oxides?

A: Acidic oxides and neutral oxide.

20. Which oxides are metal oxides?

A: Basic oxides and amphoteric oxide.

21. What is an acidic oxide?

A: Acidic oxides are non metal oxides when dissolved into water forms acids.

22. What is a neutral oxide?

A: Neutral oxides are non metal oxides that have no effect on the pH of a solution. All monoxides like carbon monoxides, nitrogen monoxide and water.

23. What is a basic oxide?

A: Basic oxide are metal oxides that, if soluble forms alkali. Bases also react with acids to form salt and water.

24. What is an amphoteric oxide?

A: Amphoteric oxides are metal oxides that react with both acids and alkalis to form salt and water. Common amphoteric oxides ZnO, Al2O3 and PbO. Collectively, they form the acronym ZAP.

25. When acid is spilled on the ground, suggest how they can be easily neutralized.

A: Calcium carbonate is used to neutralize spilled acid. As calcium carbonate is insoluble and neutral, when added in excess, will not cause the resulting mixture to be alkaline. Since it is insoluble, the excess calcium carbonate can be easily swept up.

26. Suggest a good substance to neutralized acidic soil.

A: Calcium oxide or lime can be used to neutralize acidic soil as it is a basic oxide. In some instance, calcium hydroxide is also used to neutralize the soil.

27. A farmer adds an alkali to neutralize acidic soil and ammonium sulfate to fertilize the soil. Explain why the farmer is wasting his time.

A: The alkali and ammonium sulfate reacts to produce ammonia gas and salt. The alkali thus fail to neutralize the acidic soil effectively. Ammonium salts are added to increase the nitrogen content of the soil. But the reaction produces ammonia gas, which causes the nitrogen to escape to the environment as a gas and thus unable to be absorbed by the plant.

28. Solution A has a pH of 1, B has a pH of 3, C has a pH of 7, D has a pH of 10 and E has a pH of 14. You are given potassium chloride, sodium hydroxide, nitric acid, ethanoic acid and aqueous ammonia. Assign the alphabets to the substances according to their pH.

A: pH 1- nitric acid. pH 3 - ethanoic acid. pH 7 - potassium chloride. pH 10 - aqueous ammonia, also known as ammonium hydroxide. pH 14 - sodium hydroxide.

29. Solution A has a pH of 1, B has a pH of 3, C has a pH of 14, D has a pH of 10. Which 2 solution when mixed together MUST produce an acidic solution.

A: Solution A and B since they are both acidic, the resulting mixture must be acidic.

30. Many plants do not grow well in acidic soil, calcium oxide is often used to solve this problem. What is the name of the chemical process?

A: Neutralization.

31. What is the difference between concentration of acids and the strength of acids?

A: Concentration measures the amount acid dissolved in the solvent but strength of acids measures the degree of ionization of the acid. So it is possible to have a high concentration acid and yet it is weak.

32. What are the products form when copper reacts with nitric acid?

A: Nothing. There is no reaction as copper is a non reactive metal. Together with silver and gold, they do not have reactions with acid. However, their carbonates, oxides or hydroxides still react with the acids.

33. Describe a reaction in which sulfuric acid is not acting as an acid.

A: In a precipitation reaction, sulfuric acid can react with barium nitrate to form barium sulfate precipitate. In order to at as an acid, sulfuric acid needs to react with metal, base or metal carbonate. In a precipitation reaction, it is merely acting as a soluble sulfate which caneasily be replaced by sodium sulfate.

34. Zinc oxide is added nitric acid and aqueous sodium hydroxide. State which reaction produce a salt. Explain why.

A: Both. Zinc oxide is amphoteric therefore is able to react with both acids and alkalis to form salt and water. The other possible oxides are aluminium oxides and lead (II) oxide.

35. The pH of sulfuric acid is 1. State and explain what happen to the pH of the acid when 20g of sodium chloride solution is added to it.

A: The solution remains at pH 1. Sodium chloride is a neutral salt and thus does not affect the pH of the solution.

36. There is an acid spill in the laboratory, state a reagent that can be added in excess without causing the resultant mixture to be alkaline.

A: Calcium carbonate.

37. State all the reactants that can be added to nitric acid to form silver nitrate.

A: Silver oxide, silver carbonate and silver hydroxide. Silver does not work as it is an unreactive metal and thus unable to react with acid.

38. State 2 ways to produce ammonia gas.

A: Heating a concentrate solution of ammonia. Warm an alkali with an ammonium salt.

39. Describe a simple to test distinguish between potassium carbonate and ammonium carbonate.

A: Since both salts contain carbonate, testing for carbonate will not be useful. Add sodium hydroxide to both solution, warm. The solution that produces a gas that turns moist litmus blue contains ammonium salt.

40. A substance known as potassium hydrogen phosphate is known as a salt and an acid. Explain why it is both an acid and salt.

A: It is a salt as it is made by the reaction between an acid, phosphoric acid and an alkali, sodium hydroxide. It is an acid as it is able to ionize to produce hydrogen ions in water.

41. When potassium hydroxide reacts with phosphoric, there are 3 possible salts formed. State the name and formula of the 3 salts.

A: Potassium phosphate, Na3PO4, potassium dihydrogen phosphate NaH2PO4, potassium hydrogen phosphate Na2HPO4.

42. Describe a simple experiment to test the strength of nitric acid and ethanoic acid. Explain why they display that way.

A: React both acids with magnesium metal, the reaction between nitric acid will be faster indicating that it is a stronger acid. As a strong acid, it undergoes complete ionization of hydrogen ions and thus with a higher concentration of hydrogen ions causes the reaction to be faster.

43. A titration between aqueous barium hydroxide against sulfuric acid is performed. A graph of electrical conductivity against volume of sulfuric acid is plotted. The shape of the graph is a V - shaped graph, at the lowest point of the V - shape graph, it corresponds to no electrical conductivity. Suggest the implication of the volume of sulfuric acid at the lowest point of the V - shape graph. Explain, in terms of ions, why the electrical conductivity of the mixture decreases to zero as more sulfuric is added and subsequently increases again when more sulfuric acid is added.

A: Initially, when there only barium hydroxide alkali in the solution, the solution has free moving hydroxide and barium ions, hence it conducts electricity. When sulfuric acid is added, it forms the insoluble barium sulfate and water. The number of free moving ions decreases and the electrical conductivity decreases. When all the barium hydroxide has been neutralized by the sulfuric acid, the mixture contain only barium sulfate precipitate and water. There are no free moving ions and electrical conductivity goes to zero. The ions in insoluble barium sulfate are held by strong electrostatic force of attraction and therefore cannot conduct electricity. When excess sulfuric acid is added to the mixture, it introduces free moving hydrogen ions, this causes the electrical conductivity to increase. Hence the shape of graph is a v shaped graph. The significance of the lowest point of the v shape graph is the point where the volume of sulfuric acid needed to neutralize the barium hydroxide. This volume can be used for mole calculation.

44. State, as many as you can, an oxide that can react with acid and alkali.

A: Aluminium oxide, zinc oxide and lead (II) oxide.

45. State an oxide which contribute to acid rain.

A: Sulfur dioxide, nitrogen dioxide and carbon dioxide. This is because they are non metal oxides and can dissolve in rain clouds to form acid rain.

46. Metals are basic oxide and are likely to react with acid to form salt and water. State 3 metal basic oxide which DO NOT react well with sulfuric acid.

Lead (II) oxide, barium oxide and calcium oxide. This is because the 3 oxides form insoluble sulfates. These insoluble sulfates forms an insoluble layer around the oxides preventing reaction with acids. The reaction comes to a premature end. In fact this also prevents their carbonates, hydroxides or metals to react well with acid. They are insoluble salts so can work well when made with the precipitation method. Similarly, silver chloride and lead (II) chlorides are insoluble too. Their oxides, hydroxides, carbonates and metals will have problem reaction with hydrochloric acid too.

47. State an oxide that do not change the colour of universal indicator.

A: Carbon monoxide, nitrogen dioxide. They are neutral oxides and so they have no reaction with an acid. On a side note, water is also a neutral oxide.

48. A student came up with a report detailing the steps to make silver nitrate solution. The following is his report. Add silver carbonate to a fixed amount of nitric acid. If the silver carbonate reacted, add more silver carbonate until no more silver carbonate dissolves. The mixture is then filtered. The filtrate is then heated to approximately to one third of its original volume and the hot solution is allowed to cool. The crystals are then filtered and washed with small amount of cold distilled water and dried by pressing between filter paper. Do not evaporate the solution to dryness. Explain the terms that are underlined and their roles in the salt making process.

A: More silver carbonate till no more dissolves is to ensure all the nitric acid is used up. Filtering is to remove excess unreacted silver carbonate. Heating to one third of solution is to obtain a saturated solution. Cooling is to allow crystals to form. Small amount of cold distilled water is to prevent soluble from dissolving in the distilled water since they are soluble. Crystals have poor solubility at cold temperature. Evaporating the solution to dryness will heat away the water of crystallization preventing the formation of the crystals.

49. Suggest a good indicator for titration for mixture that changes colour in the pH zone of 3 to 5.

Methyl orange - When alkali added to acid (with methyl orange), it changes from red to yellow. When acid added to alkali (with methyl orange), it changes from yellow to red.

50. Suggest a good indicator for titration for mixture that changes colour in the pH range of 9 to 11.

A: Phenolthalein. When alkali added to acid (with phenolthalein), it changes from pink to colourless. When acid added to alkali (with phenoolthalein), it changes from colourless to pink.

#### Chemistry Reminders

 Posted on October 29, 2011 at 8:25 AM comments ()

Dear A1 students, do scan through this set of questions. Part 2 incoming. Beep me if you have problem or leave your question in the comment section. Do look through the physics post below too.

Final Reminders Part 1

Kinetic Particle Theory

1 Do you know how to draw the cooling and heating curves?

2 Do you know the state of a substance at a stated temperature, given its MP and BP?

3 Do you know how to describe the 3 states of matter in terms of their arrangement, movement?

4 Do you know that energy is taken in during melting and boiling?

5 Do you know that energy is released during freezing and condensation?

6 Do you know how to explain why temperature remains constant during change of state?

7 Do you know which substances sublime?

8 Do you know how to draw particles in the 3 states?

9 Do you know how to draw particles during change of state?

Measurement, Experimental Techniques and Separation

1 Do you know how to decide which method of separation to use for a particular type of mixture?

2 Do you know why liquids can pass through the filter paper but solids cannot?

3 Do you know why water enters the condenser at the bottom and exit at the top?

4 Do you know why water enters the condenser at the bottom?

5 Do you know the role of fractionating column?

6 Do you know how do decide if a substance is pure?

7 Do you know the principle behind the chromatography separation?

8 Do you know how to calculate RF value for a substance? (PURE chem.)

9 Do you know how to remove carbon dioxide from a sample of gas?

10 Do you know how to remove acidic gases from a sample of gas?

11 Do you know how to remove soluble gases from a sample of gas?

12 Do you know which gases are soluble?

13 Do you know which gases are acidic?

14 Do you know ammonia is the most important alkaline gas?

15 Do you know when to use upward delivery of gas when to use downward delivery of gases?

16 Do you know the estimated Mr of air?

17 Do you know how to decide which gas has a higher rate of diffusion?

18 Do you know the different fractions of air can be separated using fractional distillation of liquid air?

19 Do you know a separating funnel is used to separate immiscible liquids?

20 Do you know pipette has fixed volumes of 10.0, 20.0 and 25.0cm3?

21 Do you know pipette and burette are only 2 equipment that is very accurate?

Element, compounds and mixtures

1 Do you know the difference between compounds and mixtures?

2 Do you know which are the common mixtures?

3 Do you know how to different mixtures, compounds and elements by looking at the particles drawn?

4 Do you know mixtures can be separated using the physical methods of separation?

Atomic Structure

1 Do you know that group number is the same as the number of valence electrons?

2 Do you know the number of electron shells is the same as the period number?

3 Do you know the proton number or the atomic number represents the number of electrons or protons?

4 Do you know mass number or nucleon represents the total number of protons and neutrons?

5 Do you know how to explain why elements like chlorine do not have a whole number for it’s relative atomic mass?

6 Do you know how to explain why noble gases are not reactive?

7 Do you know how to explain why a certain element is a metal?

8 Do you know how to explain why a certain element is a non-metal?

9 Do you know how to define an isotope?

10 Do you know the relative masses of the sub atomic particles?

11 Do you know the relative charges of the sub atomic particles?

12 Do you know where are the sub atomic particles located?

13 Do you know how to calculate the relative atomic mass of various isotopes based on their relative atomic masses? (Pure)

14 Do you know difference in properties of different isotopes?

15 Do you know the similarities in properties of different isotopes?

16 Do you know when an atom loses electron, it becomes positively charged?

17 Do you know when an atom gains electron, it becomes negatively charged?

18 Do you know the motivation behind forming ions is to obtain a stable electronic configuration?

Ionic Bonding and Compounds

1 Do you know they are mainly formed from metal and non-metal chemically bonded to each other?

2 Do you know they are substances with high MP and BP?

3 Do you know they can conduct electricity in molten and liquid state?

4 Do you know they are generally soluble in water?

5 Do you know metals atoms loses electrons and the non-metals atoms gains electrons?

6 Do you know ionic bonds are the electrostatic force of attraction between oppositely charged ions?

7 Do you know during change of state electrostatic force of attraction between oppositely charged ions are broken?

8 Do you know that the electrostatic force of attraction between oppositely charged ions is strong?

9 Do you know giant ionic structure is also known as a lattice structure? (pure)

10 Do you know why MgO has higher melting point than NaCl?

Simple Covalent Bonding and compounds

1 Do you know they are formed mainly from non-metal sharing electrons to form a stable electronic configuration?

2 Do you know they have low MP and BP?

3 Do you know during change of state, simple covalent compounds overcome weak intermolecular forces of attraction between molecules (also known as Van Der Waals forces of attraction)

4 Do you know they are generally insoluble in water?

5 Do you know acids are the only simple covalent molecules that can conduct electricity?

6 Do you know the reason why they can conduct electricity is because acids ionizes to form hydrogen ions in water and hence can conduct electricity?

Giant Covalent Molecules (PURE)

1 Do you know that graphite, diamond and sand (silicon dioxide) are giant covalent molecules?

2 Do you know diamond and sand are tetrahedrally bonded, 1 atom bonded to 4 other atoms?

3 Do you know graphite atoms are hexagonally bonded in layers of carbon atoms?

4 Do you know graphite can conduct electricity because each carbon atom is only bonded to 3 other carbon atoms?

5 Do you know graphite can act as a lubricant because the layers of carbon atoms are bonded by weak intermolecular forces of attraction and hence can slide over each other?

6 Do you know diamond is hard because the atoms are arranged in a tetrahedral structure and is very rigd?

Acid, bases and salts

1 Do you know the 4 reactions of acids, namely with metals, metal hydroxides, metal oxides and metal carbonate?

2 Do you know the physical properties of acids?

3 Do you know all acids are good conductors of electricity in the aqueous state?

4 Do you know CaO is added to neutralize acidic soil?

5 Do you know sulfur dioxide and nitrogen dioxide causes acid rain?

6 Do you know you cannot add fertilizer and neutralize acidic soil at the same time?

7 Do you know bases are metal oxides and metal hydroxide?

8 Do you know alkalis are group 1 hydroxides, ammonium hydroxide (also known as aqueous ammonia) and calcium hydroxide (also known as limewater)?

9 Do you know when acid is spilt always use calcium carbonate because it is insoluble?

10 Do you know the middle point of the titration curve is pH of the solution?

11 Do you know sulfuric acid is known as a strong, dibasic acid?

12 Do you know hydrochloride and nitric acid are both strong and monobasic acid?

13 Do you know all other acids are weak?

14 Do you know strong acids undergoes complete ionization of hydrogen ions in water?

15 Do you know weak acids undergoes incomplete ionization of hydrogen ion?

16 Do you know basic oxide dissolves into water to form an alkali?

17 Do you know ammonium salts react with alkali to form salt, ammonia gas and water?

18 Do you know group 1 and ammonium salts are made by titration method?

19 Do you know titration salts require an acid and an alkali?

20 Do you know soluble (non group 1 and ammonium salt) are made by neutralization?

21 Do you know the easiest way to make the neutralization salts is by acid and metal carbonate?

22 Do you know in neutralization method we add excess metal carbonate to react with all the acid?

23 Do you know insoluble salts are made by precipitation?

24 Do you know precipitation salts are easily made by using a nitrate salt and sodium salt?

Periodic Table

1 Do you know down the group, reactivity of group 1 metals increases?

2 Do you know down the group, melting and boiling point of group 1 metal decreases?

3 Do you know down the group, group 1 metals’ density increases?

4 Do you know down the group, reactivity of group 7 elements decreases?

5 Do you know down the group, melting and boiling points of group 7 elements increase?

6 Do you know down the group, the states of group 7 elements are g,g,l,s,s states?

7 Do you know down the group, density of group 7 elements increases?

8 Do you know how to explain reactivity using the concept of atomic radius and screening effect? (more for pure)

9 Do you know group 1 elements are called alkali metals?

10 Do you know group 7 elements are called halogens?

11 Do you know halogens are only coloured when in diatomic form?

12 Do you know the colour of group 7 elements darkens down the group?

13 Do you know across the period, elements changes from a metal to a non-metal?

14 Do you know across the period, elements form basic oxide to amphoteric oxide to acidic oxide?

15 Do you know across the period it changes from metallic element to non-metallic element?

16 Do you know how to explain why noble gases are unreactive?

17 Do you know noble gases are used in cases where an inert environment is needed, for example Ar in the light bulb?

18 Do you know inert means unreactive?

19 Do you know transition metals lies between group 2 and group 3?

20 Do you know transition metals forms coloured compound?

21 Do you know transition metals have high melting boiling point?

22 Do you know transition metals can act as catalyst, eg like nickel in the addition of hydrogen, iron in the making of ammonia.

23 Do you know group 1 metals have low MP, BP?

24 Do you know group 1 metals are soft?

25 Do you know group 1 metals have low density?

26 Do you know halogens form diatomic molecule?

27 Do you know diatomic means 2 atoms chemically joined together?

Metals

1 Do you know only group 1 and calcium reacts with water to form metal hydroxide and hydrogen gas?

2 Do you know magnesium, zinc and iron reacts with steam to form metal oxide and hydrogen gas?

3 Do you know aluminium is excluded from most reaction because of it’s unreactive aluminium oxide layer which prevents most reaction from happening?

4 Do you know metals higher than hydrogen in the reactivity series reacts with acid to form salt and hydrogen gas?

5 Do you know how to describe displacement reaction observation?

6 Do you know most copper salts are blue?

7 Do you know group 1 carbonates are unable to break down upon strong heating?

8 Do you know the other metal carbonate when heated forms metal oxide and carbon dioxide gas?

9 Do you know green copper (II) carbonate breaks down to produce black copper (II) oxide and carbon dioxide gas?

10 Do you know alloys are stronger than pure metal due to the disruption of regularly arranged atoms in the metal by atoms of different sizes?

11 Do you know brass is zinc and copper?

12 Do you know bronze is tin and copper?

13 Do you know steel iron and carbon??

14 Do you know price of metals are dependent on the metal’s abundance and extraction method?

15 Do you know metals above aluminium is extracted from their ores by electrolysis?

16 Do you know metals below iron, extraction is by reduction using carbon.

17 Do you know the 5 equations of blast furnace?

18 Do you know the chemical name of the molten slag?

19 Do you know why newly extracted iron is too brittle?

20 Do you know why painting, applying oil prevents the rusting process?

21 Do you know how to explain sacrificial protection? (Pure)

22 Do you know zinc is used to prevent ship from rusting and magnesium for underground pipes? (Pure)

Rate of reaction

1 Do you know the 5 factors affecting rate of reaction?

2 Do you know how to explain each factor using collision theory?

3 Do you know how to draw the setup to measure rate of reaction?

4 Do you know how to draw the graphs to indicate rate of reaction?

5 Do you know gradient of the graphs shows you the rate of reaction?

6 Do you know how to explain why reactions are always fast at the beginning and slows down as reaction proceeds?

#### Physics 2010 Nagging

 Posted on October 31, 2010 at 2:28 AM comments ()

Dear all, i can't emphasis the importance of this. READ CAREFULLY.

Otherwise do remember the following pointers.

• Everything in 3sf. Don't waste your brain cells struggling the number of sf, just stick to 3. What happens if its exact value. E.g. 1.23N x 3.21m = 3.9483 Nm. So write that down its ok. But after this step, write this again. =3.95 Nm (3 s.f.)

• What to bring for your exams.

o Calculator that works

o Compass and projector (those pesky resultant force questions)

• Speed time graph questions when you are stucked, don’t forget for every section of your speed time graph label AVUTD.

• When does an object experience terminal velocity when it is free falling? Keep points include the weight of the object is the same as the air resistance of the object. When the object moves faster, the air resistance increases. When air resistance is the same as its weight, resultant force acting on the object is zero (this is the main thing i hope you will remember, any resultant force question, you have to phrase it as RF acting on object), therefore acceleration of the object is zero, object moves at constant speed.

• Angles always 1d.p.

• Friction depends on mass of object, surface texture and speed of object. Mass increase, friction increases. Speed increases, friction increases.

• How to calculate friction – a few formulae to calculate them

o Work done against friction = frictional force x distance moved

o Frictional force = mass x deceleration

o Resultant force = applied force - friction

• For pure physics people, becareful of the upthrust question when an object move upwards. When an object moves upwards, resultant force = upthrust – weight.

• There are questions that ask you whether an object will topple off the slope or not. E.g. in the 2009 paper the lorry question. You need to say something like the line of action of its weight is acting within the area of contact, The weight creates a moment that pushes the lorry onto the slope keeping it stable. Otherwise if it topples, say the line of action of its weight is outside the area of contact, therefore the weight creates a moment that topples the lorry.

• For those kind of slope questions, consider lifting an object of mass 10kg up this slope

• If question asks you about work done to lift the object up the answer is simply PE = mgh. In a way 10 x 10 x 3 = 300J. That’s work done to lift it up and i use 3m because the question gives us the mass.

• However if the question asks us for the pulling force to lift the object up the slope? Idea is that you still need 300J to pull it up. Therefore the pulling force is based on 5m length, work done = force x distance. 300 = f x 5 = 60N. So to pull the object

up the slope, a force of 60N is needed to pull the object up the slope over a distance of 5m. Supposed the pulling force is 80N instead of the required 60N. Work done due to the 80N force is 80 x 5 = 400J. You notice that 100J extra is needed instead of the 300J. That extra 100J is work done to overcome friction.

• Convert g/cm3 into kg/m3 simply x1000

• Moment remember to look out for PERPENDICULAR distance to pivot, not perpendicular to your view.

• Nervous, Nervous

• For pure Literature people i pity you, please endure.

• For light questions, if your light ray is moving from dense to less dense medium, never assume refraction occurs. Always check if the angle of incidence in the denser medium is more than critical angle. If it’s more than critical angle, it will undergo total internal reflection.

• Fat lens have short focal length, skinny lens have longer focal length.

• Magnification = image height/object height

• Magnification = image distance from lens / object distance from lens

• Speed of light 3 x 108m/s is defined as speed of light in VACUUM not air.

• EM waves, you need to memorized position of the waves. Note that high wavelength EM waves like radio,

• Sound moves fastest in solid, slowest in air, since sound energy is transmitted by vibration of particles, the closer they

are together, the faster it is transmitted.

• When doing sound calculations, make sure you account for distance x 2 or time x 2 since it’s echo thing.

• Stupid formulae

o Power = force x velocity

o V = J/C (Victoria jc), EMF = WD (energy)/Charge

• When doing questions on brightness of light bulbs, don’t worry if you have poor imagination, just assigned values to it. EMF let it be 12V, every resistors 2ohms, It should give you nice numbers.

• Calculating how much electricity used, units of electricity = power in kW x Time in hours

• Why must the fuse be in the live wire? When the fuse is in the live wire, it breaks the high potential in the live wire preventing electrical shocks to user. If it is in the neutral wire, although the circuit is broken, the live wire is still at high potential, this causes danger to the user if an electrical fault is present.

• Don’t mixed up fuses and earth wire. Fuses prevent high current from damaging the equipment. When the current is higher than the fuse rating, the fuse will melt and breaks the circuit. For earth wire, it’s a safety feature to protect user in the event that the metal casing is live. If the casing becomes live due to the electrical fault that causes leakages of current to the metal casing. The earth wire will lead the current to the earth thus protecting user from electrical shocks. Hence do not blame SHORT CIRCUIT FOR EVERY OF YOUR PROBLEM, although most of the time sudden increase in current is due to short circuiting.

• Thin wires – Pro- cuts cost since less material is needed.

• Thin wires – Con – thin wire has high resistance, thus producing a lot of thermal energy lost due to heating effect of the wire. This is because power loss due to heating effect of wire can be calculated by P = I2R. Since R is higher for thin wire, the heat loss will also be greater.

• I against V, gradient is 1/R, while V against I, gradient is R.

• Electrical field lines – out of positive charge, going into negative charge ALWAYS

• Magnetic field lines – out of north, going into south

• For Fleming’s Left Hand Rule, make sure you write the following template. The interaction between the magnetic field and the current produces a force. Using FLHR, the force created is ___(in certain direct_____.

• AS OF THIS POINT, Kenneath & Edwin, Melvin, Jet, Grace, that’s it for you. If your name is not these 5, carry on reading.

• Positive static charges NEVER MOVED!!!!! Whenever you talk about induction of static always talk about the charges in your sphere, comb, paper, whatever, before you say electrons are attracted or repelled.

• What are the possible reasons why a transformer is not ideal? Standard answers will be heating effect of wires, eddy current produced on the soft iron core,

• Why transformer needs an a/c source? Remember its that changes in magnetic flux needed for a continued induction of EMF. Full story in template.

#### The Confusion of Vectors and Scalars

 Posted on May 31, 2010 at 11:46 PM comments ()

One of the more commonly asked question is the classification of vector and scalar quantities.

.

.

Basically we know that vector quantities has both magnitude (value like 2m/s, 400m etc) and direction (which means there is a possible of positive or negative figures like -5.2m/s).

.

Fortunately, an easy rule can help us to remember them.

Most of us can remember the 3 usual suspects

DISPLACEMENT, VELOCITY AND ACCELERATION.

The last member of this select group is FORCE.

Basically anything that has the unit of NEWTON, we can safely classify it under vector quatity. For example, friction, weight, pulling force, pushing force, contact force etc. The list can go on and on. You get the drift.

.

.

Which brings us to scalar, quatities which has magnitude and no direction. Since we are able to classify vectors, simply label the other components as scalar. Its that ez!

.

.

Json

www.oleveltuition.com

#### Acid Reactions

 Posted on April 30, 2010 at 8:25 PM comments ()

Dear all doing acids for this exam,

for reactions of acids, refer to this link.

http://olevelchemistry.blogspot.com/2009/08/acid-reactions-part-1.html

for oxide types

http://olevelchemistry.blogspot.com/2009/08/types-of-oxide.html

for salt making

http://olevelchemistry.blogspot.com/2009/08/salt-making-selection-of-method.html

Will be adding a more keep in view

Regards

Json

#### MCQs Answer for 21st Discussion

 Posted on April 14, 2010 at 9:23 AM comments ()

Chemistry

1-10

B C A A B D D B C D

11-20

A D C B C B B B D A

21-30

C D D C A A B D C B

31-40

D A C D D B D C B C

Physics

1-10

B C C B A D D B D A

11-20

A A D D A B C D B D

21-30

B D B D B D B A C A

31-40

C D C B A A B C D C

To er is human, if you suspect any wrong answers, dont struggle gimme a text i will check. Enjoy and remember 3 ilttle pigs.

A piece of history for all of you, why Raffles named our beloved Island City, Singapore ............ possibly.

#### Topics for Chemistry and Physics MCQ Test

 Posted on February 20, 2010 at 3:46 AM comments ()

Chemistry MCQ Topics, 10 Questions

1)Gas collection, Volume Measurement, Apparatus

2)Seperation Techniques, Kinetic Particle Theory

3)Atomic Structure, Bonding

4)Periodic Table

5)Metals

6)Mole Calculations

7)Acid Bases Salts

8)Rate of Reactions

9)Redox

10)Heat Changes

Physics MCQ Topics, 10 Questions

1)Kinetics

2)Dynamics

3)Moments

4)Pressure

5)Power, Energy

6)Heat Transfer

7)Heat Calculations, Thermometry

8,9)Electricity Calculations

10)Static Electricity

If the topics are not being taught yet, do worry just do whatever you can. Enjoy and have fun.

#### HCl, is it an ionic or covalent molecule?

 Posted on January 21, 2010 at 7:28 AM comments ()

From Nicole today, she asked if HCl should be considered an ionic or covalent substance, should it possess ionic or covalent properties.

The answer is very simple, HCl is a simple covalent molecule. It is bonded covalently so it has the standard properties of simple covalent molecules.

This link http://www.gcsescience.com/Hydrogen-Chloride-Molecule.gif shows you the dot and cross structure of HCl. Furthermore, its made up of 2 non-metal atoms. All these evidences points to simple covalent properties.

However, HCl being an acid, will ionize in water producing hydrogen and chloride ions. Hence despite being a covalent molecule, it is able to conduct electricity in the aqueous state. Hence acids hold the distinction of having and being covalent properties in nature but still conduct electricity.

Information correct as of O levels, A level chemistry has a different story all together

#### Wanton Recipe Part 2

 Posted on July 31, 2009 at 1:40 AM comments ()

#### Wanton Recipe Part 1

 Posted on July 24, 2009 at 1:44 AM comments ()

There has been a lot of queries about how to prepare the tasty! wanton i made for my tuition students. So this is the recipe revealed!!