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Chemistry > Topic 1: Fundamentals of Chemistry and Planet Earth > Flashcards

Topic 1: Fundamentals of Chemistry and Planet Earth Flashcards

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1
Q

What are the relationships between matter, pure substances, mixture, elements and compounds?

A

Matter - Pure substances + Mixture (separation, mixing)

Pure substances - Elements + Compounds (chemical reaction, breaking down)

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2
Q

What is matter made up of?

A

Matter is made up of elements in a variety of states and forms

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3
Q

Definition of an element.

A

An element is a pure substance which cannot be broken down into anything simpler by chemical methods, e.g. N₂ (g), O₂ (g), Br₂ (l), Hg (g), Na (s), Si (s).

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4
Q

What is an element made up of?

A

An element is made up of only one kind of atom.

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5
Q

What are the different types of elements? Give examples.

A

Monoatomic element: Helium (He), Copper (Cu), Krypton (Kr), Silver (Ag), Carbon (C)

Diatomic element: Hydrogen (H₂), Nitrogen (N₂), Fluorine (F₂), Oxygen (O₂), Iodine (I₂), Chlorine (Cl₂), Bromine (Br₂)

Triatomic element: Ozone (O₃)

Polyatomic element: Phosphorus (P₄), Sulphur (S₈)

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6
Q

What are most elements be like in the earth’s crust?

A

Most elements are in the form of compounds in the earth’s crust.

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7
Q

What are the most abundant elements in the earth’s crust?

A

50% Oxygen (non-metal), 26% Silicon (semi-metal), 7% Aluminium (metal), 4% Iron (metal)

*Approximate percentage by mass

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8
Q

What are the most abundant elements in the atmosphere?

A

78% Nitrogen (N₂), 21% Oxygen (O₂), 0.93% Argon (Ar)

*Approximate percentage by volume

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9
Q

Definition of a compound.

A

A compound is a pure substance made up of two or more elements chemically combined together.

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10
Q

Definition of a mixture.

A

A mixture consists of two or more pure substances (elements of compounds) which have not combined together chemically. They can be separated by physical or chemical methods.

*An impure substance is always a mixture.

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11
Q

What elements / compounds are presented in air, glucose solution, beer, sea water, concrete, cement, steel, stainless steel (mixture)?

A

Air: Nitrogen (N₂) + Oxygen (O₂) + Argon (Ar) + Carbon dioxide (CO₂) + Other noble gases (e.g. Helium (He), Neon (Ne))

Glucose solution: Glucose (C₆H₁₂O₆) + Water (H₂O)

Beer: Ethanol (CH₃CH₂OH) + Water (H₂O)

Sea water: Water (H₂O) + Sodium chloride (NaCl) + Magnesium chloride (MgCl₂) + Sodium sulphate (Na₂SO₄) + Calcium chloride (CaCl₂) + Other salts + Dissolved gases

Concrete: Calcium carbonate (CaCO₃) + Stone + Sand + Water (H₂O)

Cement: Calcium carbonate (CaCO₃) + Clay

Steel: Iron (Fe) + Carbon (C)

Stainless steel: Iron (Fe) + Carbon (C) + Chromium (Cr) + Nickel (Ni) + Manganese (Mn)

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12
Q

List 5 mixtures with special names, their description and examples.

A

Suspension: Solid particles dispersed in liquid, e.g. muddy water (soil + water), chalk powder in water

Smoke: Solid particles dispersed in gas, e.g. black smoke from cars and factories (carbon particles + air)

Emulsion: Liquid droplets dispersed in liquid (a mixture of two immiscible liquids), e.g. oil + water + detergent

Mist: Liquid droplets dispersed in gas, e.g. fog, aerosol spray

Foam: Gas bubbles dispersed in liquid, e.g. soapsuds, coffee cream foam

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13
Q

State the comparison between mixture and compound.

A

Composition by mass

  • Mixture: Variable (substances in the mixture can be mixed in any proportion)
  • Compound: Fixed

Melting point (m.p.) and boiling point (b.p.)

  • Mixture: Melts and boils over a wide range of temperatures (does not have a sharp m.p and b.p.)
  • Compound: Melts or boils at a definite temperature (has a sharp m.p and b.p.)

General properties

  • Mixture: Each constituent substance retains its own properties.
  • Compound: Properties are entirely different from those of its constituent elements.

Separation of constituents

  • Mixture: Constituents can be separated by physical and chemical methods.
  • Compound: Constituent elements can only be separated by chemical methods, not by physical methods.
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14
Q

What can elements be classified into?
What most elements are?

A

Elements can be classified into metals, non-metals and metalloids (semi-metals).
Most elements are metals.

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15
Q

List the properties of metals and non-metals.

A

1. Electrical conductivity

  • Metals: Good
  • Non-metals: Poor (except graphite)

2. Heat conductivity

  • Metals: Good
  • Non-metals: Poor (except graphite)

3. Melting point and boiling point

  • Metals: Usually high (except mercury)
  • Non-metals: Usually low (except those with giant covalent structures)

4. Appearance

  • Metals: Usually shiny
  • Non-metals: Usually dull for solids
    (Sulphur solid = yellow; Fluroine gas = pale yellow; Chlorine gas = pale yellowish green; Bromine liquid = brown)

5. Malleability and ductility

  • Metals: Malleable and ductile
  • Non-metals: Usually brittle in solid state

6. Mechanical properties

  • Metals: Usually hard and strong (not easily be broken apart)
  • Non-metals: Usually soft and brittle (except diamond)
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16
Q

Definition of ‘Malleability’ and ‘Ductility’.

A

Malleabiliy = ability to be hammered into a thin sheet
Ductility = ability to be pulled into a wire

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17
Q

What are the exception of metals and non-metals?

A

All metals are solids at room temperature and pressure, except mercury, which is a liquid.
All non-metals are gases or solids at room temperature and pressure, except bromine, which is a liquid.

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18
Q

What are compositions and properties of graphite?

A

Graphite is a form of carbon (non-metal) which can conduct electricity.

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19
Q

What are the properties of metalloids/semi-metals?

A

Metalloids/semi-metals, such as silicon and boron, have properties between those of metals and non-metals.

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20
Q

What is silicon, and what are uses of silicon?

A

Silicon (Si), a metalloid, is commonly used in the manufacture of integrated circuits/computer chips.

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21
Q

What elements are in liquid, gaseous, solid form at room temperature and pressure respectively?

A

Liquid form: Hg and Br₂
Gaseous form: 6 noble gases (He, Ne, Ar, Kr, Xe and Rn), H₂, N₂, O₂, F₂ and Cl₂
Solid form: All others

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22
Q

State the Particle Theory of Matter.

A
  • All matter is composed of small particles (e.g. atoms, molecules, or ions).
  • Particles are in constant motion and so they have kinetic energy.
  • An increase in temperature causes an increase in the speed of motion of particles and average kinetic energy of particles.
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23
Q

What are the three physical state of particles?
State their kinetic energy, speed of motion and packing of particles respectively.

A

Solid: Low - Slow - Closely packed in regular pattern (particles cannot move)

Liquid: Higher - Faster - Less closely packed (particles can move)

Gas: High - Fast - Widely separated (particles move freely)

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24
Q

How do matters change from one state to another?

A

Solid (sublimation) - Gas (condensation) - Liquid (freezing)
Solid (melting) - Liquid (vaporization) - Gas (deposition)

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25
Q

What are the state symbols of solid, liquid, gas and when a substance is dissolved in water (aqueous solution)?

A

Solid (s); Liquid (l); Gas (g); Aqueous solution (aq)

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26
Q

Definition of a physical change and a chemical change.

Note: What are the evidences for a chemical change?

A

Physical change is a change in which no new substance is formed.
Chemical change is a change in which new substance(s) is (are) formed (a chemical reaction is involved).

Evidences for a chemical change can be:

  • Change in odour
  • Change in colour
  • Change in temperature of the reaction mixture
  • Formation of gases, which often appears as bubbles in aqeuous solution
  • Formation of insoluble substances
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27
Q

Definition of chemical properties and physical properties of a substance.

Examples: What are some examples of physical properties?

A

Chemical properties of a substance are the properties of the substance in chemical reactions, e.g. chemical reactivites towards the reaction with water and oxygen.
Physical properties of a substance are the properties which can be measured/observed without chemically changing the substance into something else.

Examples of physical properties:

  1. Appearance: It includes how a substance looks like and its physical state.
  2. Colour
  3. Odour
  4. Solubility: It describes whether and to what extent a substance is soluble in a particular solvent (e.g. water).
  5. Density: It is the mass of a substance per unit volume.
  6. Melting point: It is the temperature at which the substance changes state from solid to liquid (melting point = freezing point, which is the temperature at which the substance changes state from liquid to solid.
  7. Boiling point: It is the temperature at which the substance changes state from liquid to gas (boiling point = condensation point, which is the temperature at which the substance changes state from gas to liquid.
  8. Viscosity: It is the ease of a substance to flow.
  9. Electrical conductivity: It is the ability of a substance to conduct electric current.
  10. Thermal conductivity: It is the ability of a substance to conduct heat.
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28
Q

What are the steps to light the Bunsen burner?

A
  1. Place a Bunsen burner on an insulating mat.
  2. Turn the collar to close the air hole.
  3. Light a match and bring it over the burner. Then turn on the gas tap.
  4. Open the air hole.
  5. Adjust the height of the Bunsen flame by turning the gas tap.
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29
Q

When will striking back occur? What will happen? What should we do?

A

If the burner is lighted without closing the air hole, striking back will occur and it is dangerous. The flame burns inside the chimney with a hissing sound. The collar becomes very hot.
When it occurs, turn off the gas tap immediately and report to the teacher.

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30
Q

Comparison of Bunsen flames under different positions of air hole.

Note: What does a yellow flame contain and what will it do?

A

(left: When air hole is closed; right: When air hole is opened)

  1. Colour of the flame: yellow; blue
  2. Brightness of the flame: luminous; non-luminous
  3. Shape of the flame: irregular; regular
  4. Temperature of the flame: lower; higher
  5. Sound of the flame: quiet; noisy

Note:
A yellow flame contains unburnt carbon particles which will blacken glasswares.

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31
Q

List all the harzard warning labels and its corresponding precautions.

A

Explosive (e.g. hydrogen): /

Flammable (e.g. hydrogen, town gas, LPG, reactive metals): Fire extinguisher standby; No flame nearby

Oxidizing: Wear safety goggles and protective gloves

Toxic: Wear safety goggles and protective gloves; Carry out the experiment in a fume cupboard

Corrosive: Wear safety goggles and protective gloves

Carcinogenic: Wear safety goggles and protective gloves; Carry out the experiment in a fume cupboard

Harmful: Wear safety goggles and protective gloves; Carry out the experiment in a fume cupboard

Irritant (including dilute acids and alkalis): Wear safety goggles and protective gloves; Carry out the experiment in a fume cupboard

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32
Q

What is the composition of air?

Addition: is it an element, a compound or a mixture?

A

Air is a mixture of gases, which make up the atmosphere.

Composition of air:
78% Nitrogen (N₂), 21% Oxygen (O₂), 0.93% Argon (Ar), 0.03% Carbon dioxide (CO₂), 0.04% Other noble gases (e.g. helium and neon)

*Approximate percentage by volume

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33
Q

What are the uses of nitrogen (N₂) in air?

A
  1. N₂ gas (together with H₂ gas) is used to make ammonia (NH₃), which is then used to make fertilizers (e.g. ammonium sulphate and ammonium nitrate).
  2. N₂ gas is used to provide a chemically inert (unreactive) environment, e.g. food is packaged in gaseous nitrogen to increase its shelf life (potato chip packages are filled with N₂ gas to prevent oxidation of the chips).
  3. Liquid N₂ is used to provide a low temperature (-196°C) to store biological sample (e.g. cells) and freeze food.
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34
Q

What are the uses of oxygen (O₂) in air?

A
  1. O₂ gas is essential for respiration (i.e. making oxygen tanks for medical purpose, divers and firemen).
  2. O₂ gas supports combustions of fuels (e.g. hydrogen gas, coal, petrol, town gas).
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35
Q

What are the uses of carbon dioxide (CO₂) in air?

A
  1. CO₂ is the raw material for photosynthesis.
  2. Dry ice (solid CO₂) is used to provide a low temperature (-78°C) for different purposes (e.g. storing ice-creams).
  3. CO₂ can be used to make fire extinguisher because it does not support combustion and is denser than air.
  4. CO₂ can be used in soft drinks (a large amount of CO₂ dissolves in water at high pressure).
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36
Q

What are the uses of noble gases (He, Ne, Ar) in air?

A

Helium (He) gas is used to fill balloons and airships as it is chemically inert / unreactive and lighter than air.

  • Exceptions: Hydrogen gas (H₂) cannot be used because it is flammable and explosive; Ne(g) and Ar(g) are not used. Although Ne(g) has a density lower than air, its density is not low enough for flying high. Ar(g) has a higher density than air.

Neon (Ne) is used to make neon light / advertising signs as it emits red light at a high temperature (when electricity passes through).

  • Notes: He(g) and Ar(g) can be used. Different noble gases give out lights of different colours.

Argon (Ar) is used to fill up the space in a light bulb to prevent air oxidation of the tungsten metal..

  • Exceptions: He(g) and Ne(g) cannot be used. Light bulb is cheap. He(g) and Ne(g) are more expensive that Ar.
37
Q

What is the common use of oxygen and nitrogen? What is their main source? How can they be separated from air?

A

Oxygen and nitrogen are useful industrial materials.
The main source of oxygen and nitrogen is air (O₂ = 21% and N₂ = 78% by volume).
Oxygen and nitrogen (together with argon) are separated from air by fractional distillation.

38
Q

Definition of fractional distillation.

A

Fractional distillation is a method used to separate a mixture of miscible liquids which have different boiling points (b.p.).

Note: Air must be liquefied / converted to liquid first before carrying out fractional distillation.

39
Q

What are the procedures of fractional distillation?

A
  1. The air is purified to remove dust, CO₂, water vapour and etc. (dust is filtered, CO₂ and water vapour are removed as solids at suitable temperature and pressure).
  2. The purified air is cooled to -200°C (by repeated compression and rapid expansion) - purified air is changed to liquid.
  3. The liquid air at -200°C is introduced to the lower part of the fractionating tower (or fractionating column).
  4. The liquid air is warmed slowly and the gases are collected on by one. At -190°C, nitrogen (b.p. = -196°C) vaporizes and is separated from the liquid mixture first. Argon (b.p. = -186°C) vaporizes next and oxygen (b.p. = -183°C) follows at a higher temperature and are then collected.
40
Q

What can we do to test for oxygen? Why?
How do we prepare for the test?

A

Since oxygen supports combustion, oxygen gas can relight a glowing splint.

Preparation of a glowing splint:
Light a wooden splint; Blow out the flame, but make sure that the splint has reddish, glowing tip.

41
Q

What is the composition of sea water?

Addition: is it an element, a compound or a mixture?

A

Sea water is a mixture containing salts, dissolved gases and water.

Composition of sea water:
96.5% Water, 2.4% Sodium chloride (NaCl), 0.5% Magnesium chloride (MgCl₂), 0.4% Sodium sulphate (Na₂SO₄), 0.1% Calcium chloride (CaCl₂), Other salts (Very small amount)

*Approximate % by mass

42
Q

What is the other names of NaCl?

A

NaCl is also known as common salt, rock salt or table salt.

43
Q

What are the solute and solvent of sea water (which is a solution)?

A

Solute = sodium chloride (NaCl), magnesium chloride (MgCl₂) … other dissolved gases
Solvent = water

44
Q

What are the three methods to extract sodium chloride (NaCl) from sea water?

A

Sodium chloride (NaCl) can be extracted from sea water by …
Method 1:

  1. Filtration: to remove large particle impurities.
  2. Evaporation by heating to dryness
  • NaCl(s) (impure)
    because it contains impurities (e.g. MgCl₂), which are originally presented in sea water

Method 2:

  1. Filtration: to remove large particle impurities.
  2. Evaporation of water by heating until a saturated solution is obtained: heat the filtrate to evaporate away some water to make sea water more concentrated and finally get a saturated solution.
  3. Crystallization: allow the saturated solution to cool down at room conditions; the solubility of NaCl in water decreases with decreasing temp. Thus, NaCl crystals are formed upon cooling.
  4. Filtration, wash and dry: NaCl crystals are filtered and washed with small amount of cold distilled water; NaCl crystals are allowed to dry on filter.
  • NaCl(s) (pure)

Method 3:

  1. Filtration: to remove large particle impurities.
  2. Slow evaporation of water at room temperature: the amount of water (the solvent) becomes less and less as a result of evaporation.
  3. Crystallization: when a saturated solution is formed, the amount of water is merely enough to dissolve all NaCl. Further evaporation of water causes crystallization to occur. Crystals are formed.
  4. Filtration, wash and dry: NaCl crystals are filtered and washed with small amount of cold distilled water; NaCl crystals are allowed to dry on filter.
  • NaCl(s) (pure)
45
Q

Draw the diagrams of decantation, filtration, evaporation and simple distillation.

A

(Refer to notes p.33,36)

46
Q

Definition of filtration.

A

Filtration is a method used to separate (an) insoluble solid(s) (with large or small particle size) from a liquid/solution.

47
Q

Definition of evaporation.

A

Evaporation is a method used to separate dissolved solid(s) (solute), with higher boiling point than that of the solvent, from a solution. Upon heating, the solvent of the solution is lost as a result of evaporation and the high boiling solid(s) is/are left over.

Evaporation can also be used to remove some solvent (most commonly water) from a solution. The resulting solution will be more concentrated or become saturated.

48
Q

Definition of crystallization.

A

Crystallization is a method used to separate a dissolved solid (solute) from a solution.

  • A saturated solution is obtained by heating the solution to evaporate away some solvent (most commonly water).
  • Large crystals of the dissolved solid will form upon slow cooling of the saturated solution (e.g. standing in air). This is because the solubility of the solid in the solvent decreases with decreasing temperature.
49
Q

What is a crystal or crystalline solid?

A

Crystal or crystalline solid is a solid with particles (atoms, ions or molecules) arranged in an orderly repeating pattern.

50
Q

What is a saturated solution?

A

It is a solution containing the maximum amount of solute at a certain temperature.

51
Q

What are the two ways to decrease solubility of solid in a solution?

A
  1. Lower the temperature of the solution.
  2. Decrease the volume of solvent in the solution.
52
Q

What can we do to obtain a higher purity of solid (+ larger crystals)?

A
  • Obtain by crystallization instead of evaporation by heating to dryness
  • Slow cooling of the saturated solution (smaller and less pure crystals will form if cooled by ice-water bath)
53
Q

What can be done to check whether the solution is concentrated enough for crystallization?

A

Dip a glass rod into the solution, take it out to see if small crystals appear on the rod.

54
Q

What are the harzard warning labels of hydrogen and oxygen?

A

Hydrogen: flammable, explosive
Oxygen: oxidizing

55
Q

Definition of simple distillation.
Briefly explain the process.

A

Simple distillation is a method used to separate dissolved solid(s) (solute), with higher boiling point than that of the solvent, from a solution. Pure water can be isolated from the solution (sea water) by simple distillation.

  • The water from the solution (sea water) vaporizes (boiling point = 100°C) upon heating, the water vapour escapes and passes through the condenser. The vapour is cooled by the cold water flowing around the condenser. The water vapour condenses to form liquid water, which is then collected as distillate.
  • The dissolved solid(s) (i.e. NaCl) will not vaporize (NaCl has very high melting point and boiling point) and remain in the flask and eventually isolated as the solid residue.

^Remarks: A round bottomed flask is used, anti-bumping granules are added, water should enter the condenser from the bottom.

56
Q

What is the purpose of using a round-bottomed flask / pear-shaped flask in simple distillation?

A

A round-bottomed flask is used to ensure even heating.

57
Q

What is the purpose of adding anti-bumping granules into the solution (sea water) in simple distillation?

A

Anti-bumping granules are added to ensure smooth boiling.

58
Q

From which direction should water enter the condenser in simple distillation? and why?

A

Water should enter the condenser from the bottom to ensure the jacket of the condenser is fully filled with water. This results in a better cooling effect to condense water vapour.

59
Q

What can we do to test for different metal ions? and why?

A

Flame test (for identification of metal ions)
Many metal ions give characteristic flame colour upon heating over a Bunsen flame.

60
Q

What are the flame colours for sodium ion (Na+), potassium ion (K+), calcium ion (Ca2+), copper(II) ion (Cu2+)?

A

Sodium ion (Na+): Golden yellow
Potassium ion (K+): Lilac
Calcium ion (Ca2+): Brick-red
Copper(II) ion (Cu2+): Bluish green

61
Q

What are the procedures for carrying out a flame test?

What is the alternative way of carrying out the flame test?

A
  1. A platinum (or nickel / nichrome) wire is cleaned by soaking in concentrated hydrochloric acid [HCl(aq)] and heated in a non-luminous flame until it does not give a characteristic coloured flame.
  2. The cleaned platinum wire is put into concentrated hydrochloric acid [HCl(aq)].
  3. It is then dipped into the solid sample.
  4. The wire with the bound solid sample is heated in a non-luminous flame and the flame colour is recorded.

Alternatively, the solid sample can be dissolved in concentrated hydrochloric acid [HCl(aq)] first and the cleaned platinum (or nickel) wire is put into the resulting solution and then heated in a non-luminous flame.

62
Q

Suggest a test for identifying chloride ion in sea water.
What are the procedures for testing chloride ion?
State the chemical equation of the above test.

A

Chloride ion (Cl-) in the sea water can be identified by addition of acidified silver nitrate solution [silver nitrate solution + nitric acid (not hydrochloric acid / sulphuric acid)]. After addition, white precipitate (沈澱物) will be formed.

Procedure:

  1. Dilute nitric acid (HNO₃) is added to the sample solution (sea water) until the solution is acidic (tested with pH paper or blue litmus paper).
  2. Silver nitrate (AgNO₃) solution is then added.

Chemical equation:

  • AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
    colourless, colourless, white precipitate, colourless
63
Q

What is the use of dilute nitric acid (HNO₃) in the test for chloride?

A

Dilute nitric acid (not hydrochloric acid / sulphuric acid) is used to remove carbonate ions (and other anions) which can also form white precipitate with silver nitrate.

64
Q

Suggest a test for water.

A
  1. Water can turn blue anhydrous cobalt(II) chloride (anhydrous CoCl₂) solid to pink.
  • Water can be identified by blue dry cobalt(II) chloride paper [colour change: blue → pink]
  1. Water can also turn white anhydrous copper(II) sulphate (anhydrous CuSO₄) solid to blue.
65
Q

Definition of electrolysis.

A

Electrolysis is the decomposition of an electrolyte by an electric current (a chemical method).

66
Q

Write a word equation for the electrolysis of sea water.
Draw a diagram of electrolysis of sodium chloride solution [NaCl(aq)] / sea water / brine in laboratory.

A

Sea water→ Hydrogen gas + Chlorine gas + Sodium hydroxide
Diagram: Refer to notes p.44

67
Q

What are the common uses of products from electrolysis of brine solution?

A

H₂(g):

  • NH₃(g) (for fertiliser production)
  • Making fuel (rocket fuel)

Cl₂(g) + H₂(g):

  • HCl(g) → HCl(aq): Hydrochloric acid

Cl₂(g):

  • Sterilization of drinking (/ swimming pool) water
  • Making PVC (a plastic)

NaOH(aq) + Cl₂(g):

  • Making bleaching solution

NaOH(aq):

  • Making soap, detergents
  • Making paper
  • Waste water treatment
68
Q

Definition of a rock.

A

A rock (岩石) is a solid containing one or more minerals. It needs not have a specific chemical composition.

  • e.g. Limestone = Calcium carbonate (mainly) + Silicon dioxide + Other constituents
69
Q

Definition of a mineral.
What are the different types of minerals?

A

A mineral (礦物) is a naturally occuring inorganic solid, which has a characteristic chemical composition and a highly ordered crystalline structure.

A mineral can be:

  1. an uncombined element (e.g. graphite and gold)
  2. a compound; made up of different elements (e.g. quartz = silicon dioxide, rock salt = sodium chloride, calcite = calcium carbonate)
70
Q

Definition of an ore.

A

An ore (礦石) is a rock from which a valuable constituent (usually metal) can be extracted through mining and refined for uses.

71
Q

Give examples of ores and the metals that can be extracted (Name of ore, Compound present, Extracted metal).

A

Name of ore, Compound present, Extracted metal:

  • Rock salt, Sodium chloride (NaCl), Sodium (Na)
  • Haematite, Iron(III) oxide (Fe₂O₃), Iron (Fe)
  • Bauxite, Aluminium oxide (Al₂O₃), Aluminium (Al)
  • Malachite, Copper(II) carbonate (CuCO₃), Copper (Cu)
  • Calcite, Calcium carbonate (CaCO₃), Calcium (Ca)
  • Iron pyrite, Iron(II) disulphide / Iron(II) persulphide (FeS₂), Iron (Fe)
  • Copper pyrite, Copper-iron sulphide (CuFeS₂), Copper (Cu)
  • Galena, Lead(II) sulphide (PbS), Lead (Pb)
  • Zinc blende, Zinc sulphide (ZnS), Zinc (Zn)
  • Cinnabar, Mercury(II) sulphide (HgS), Mercury (Hg)

^ Exceptions (non-metal) : Quartz; Silicon dioxide; Silicon

72
Q

What are the procedures for extraction of metals?

A
  1. Mining of ore (by digging)
  2. Purification of ore (removal of waste)
  3. Extraction of metal by …
  • (i) Physical separation (e.g. platinum, gold)
  • (ii) Heating the ore (e.g. mercury, silver)
  • (iii) Heating the ore with carbon (e.g. zinc, iron, lead, copper)
  • (iv) Electrolysis (e.g. potassium, sodium, calcium, magnesium, aluminium)
  1. Purification of the impure metals extracted
73
Q

What are chalk, limestone and marble made up of?

A

Chalk, limestone and marble are rocks made up of mainly calcite / calcium carbonate (CaCO₃).

74
Q

Compare the process of formation, hardness and use of chalk, limestone and marble.

A

Chalk
Process of formation:

  • Sea animals with shells died → shells fell to sea bed and built up a deposit→ under high pressure, deposit is converted to chalk after millions of years.

Hardness: Soft
Use: White pigment in paper, plastics and paints

Limestone
Process of formation:

  • Under higher temperature and pressure, chalk is converted to limestone.

Hardness: Hard

Use: Materials for construction, e.g. limestone + clay = cement; limestone + water + sand + stone = concrete

Marble
Process of formation:

  • Under much higher temperature and pressure, chalk/limestone is converted to marble.

Hardness: Hardest
Use: Materials for construction, e.g. making floor, monuments

75
Q

What is the action of water on calcium carbonate (CaCO₃), include its chemical equation?

A

Calcium carbonate (CaCO₃) is insoluble in water.

Chemical equation: CaCO₃(s) + H₂O(l) → no reaction / insoluble

76
Q

What is the action of acid on calcium carbonate (CaCO₃)?

A

Calcium carbonate reacts with hydrochloric acid [HCl(aq)] to form calcium chloride [CaCl₂(aq)], water and carbon dioxide.

Chemical equation:

  • CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
    Calcium carbonate + Hydrochloric acid → Calcium chloride + Water + Carbon dioxide

Calcium carbonate also reacts with nitric acid to form calcium nitrate [Ca(NO₃)₂(aq)], water and carbon dioxide.

Chemical equation:

  • CaCO₃(s) + 2HNO₃(aq) → Ca(NO₃)₂(aq) + H₂O(l) + CO₂(g)
    Calcium carbonate + Nitric acid → Calcium nitrate + Water + Carbon dioxide
77
Q

What is the action of heat on calcium carbonate (CaCO₃)?

A

Calcium carbonate decomposes upon heating to give white calcium oxide [CaO(s)] and carbon dioxide.

Chemical equation:

  • CaCO₃(s) -heat→ CaO(s) + CO₂(g)
    Calcium carbonate -heat→ Calcium oxide + Carbon dioxide
78
Q

How can we identify calcium ion in calcium carbonate? Why?

A

The calcium ion in calcium carbonate can be identified by a flame test. This is because a calcium compound gives a characteristic brick-red flame colour upon heating over a Bunsen flame.

79
Q

How can we identify carbonate ion in calcium carbonate (state 2 solutions)? State the observations (if applicable) and chemical equations of the reactions.

A
  1. The carbonate ion in calcium carbonate can be identified by addition of dilute hydrochloric acid (HCl) [or dilute nitric acid (HNO₃), but not sulphuric acid (H₂SO₄) - CaSO₄ insoluble; stops reaction].
    After addition, colourless gas bubbles evolve / effervescene occurs (due to CO₂) and the CO₂ gas turns clear limewater [Ca(OH)₂(aq)] milky due to the formation of insoluble calcium carbonate [CaCO₃(s)].

Chemical equation:

  • CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
    Calcium carbonate + Hydrochloric acid → Calcium chloride + Water + Carbon dioxide
  • Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)
    Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
  1. The carbonate ion in calcium carbonate can also be identified by heating the solid in a test tube and put a lighted match / burning splint into the tube.
    Since calcium carbonate decomposes on heating to give CO₂ gas, which does not support combustion → the fire / flame will be extinguished.

Chemical equation:

  • CaCO₃(s) → CaO(s) + CO₂(g)
    Calcium carbonate → Calcium oxide + Carbon dioxide
80
Q

What will happen if excess CO₂(g) is bubbled into the milky suspension? State the chemical equation of the reaction.

A

If excess CO₂(g) is bubbled into the milky suspension, the mixture turns to colourless/clear.

Chemical equation:

  • CaCO₃(s) + CO₂(g) + H₂O(l) → Ca(HCO₃)₂(aq)
  • Calcium carbonate + Carbon dioxide + Water → Calcium hydrogencarbonate
81
Q

Draw a diagram to illustrate the test for carbon dioxide.

A

(Refer to notes p.50)

82
Q

Briefly explain the lime cycle (include chemical equations).

+remark: solubility of Ca(OH)₂(s), CaCO₃(s)

A

Lime cycle: Refer to notes p.52
(Remark: Ca(OH)₂(s) is only slightly soluble in water, CaCO₃(s) is insoluble in water)

Chemical equation:

  • Calcium carbonate(s) limestone / chalk / marble (^heat) → Calcium oxide(s) quicklime + Carbon dioxide(g)
  • Calcium oxide(s) quicklime + Water(l) → Calcium hydroxide(s) slaked lime
  • Calcium hydroxide(s) slaked lime (^water) → Calcium hydroxide(aq) limewater
  • Calcium hydroxide(aq) limewater + Carbon dioxide(g) → Calcium carbonate(s) + Water(l)
  • Calcium carbonate(s) + Water(l) + (excess) Carbon dioxide(g) → Calcium hydrogencarbonate(aq)
83
Q

How is clear limewater prepared?

A

Clear limewater is prepared by adding excess water to CaO(s) / Ca(OH)₂(s) followed by filtration to remove any undissolved Ca(OH)₂(s).

84
Q

Definition of weathering.

A

Weathering is the process where rock is dissolved, worn away or constantly broken down into smaller particles by physical and chemical processes.

85
Q

Definition of erosion.

A

Erosion is the process where weathered rock materials are carried away by water, wind or gravity.

86
Q

List some physical processes causing weathering.

(…after millions of years, underground limestone caves are formed)

A
  1. Change in temperature causes repeated cooling and expansion of rocks → Cracks are formed on rocks
  2. When water gets into the cracks of rocks, and is changed to ice at low temperature, it expands and causes further cracking of the rocks.
87
Q

List some chemical processes causing weathering.

(…after millions of years, underground limestone caves are formed)

A
  1. Normal rain water is acidic (pH = 5.6)
    ∵ CO₂(g) in air is dissolved in the rain water to form carbonic acid (H₂CO₃).
    Carbonic acid will react with calcium carbonate [CaCO₃(s)] limestone to form water-soluble calcium hydrogencarbonate [Ca(HCO₃)₂(aq)], calcium carbonate is thus broken down.

Chemical equations:

  • CO₂(g) + H₂O(l) → H₂CO₃(aq)
    Carbon dioxide + Water → Carbonic acid (碳酸)
  • H₂CO₃(aq) + CaCO₃(s) → Ca(HCO₃)₂(aq)
    Carbonic acid + Calcium carbonate → Calcium hydrogencarbonate
  1. Acid rain also causes breaking down of calcium carbonate.
  2. Calcium carbonate decomposes slowly at elevated temperature to form calcium oxide and carbon dioxide.

Chemical equations:

  • CaCO₃(s) (^heat) → CaO(s) + CO₂(g)
    Calcium carbonate (^heat) → Calcium oxide + Carbon dioxide
88
Q

How is acid rain formed?

A

Acid rain is formed as a result of presence of air pollutants nitrogen oxides (nitrogen monoxide (NO), and nitrogen dioxide (NO₂)) and sulphur oxides (SO₂) in air.

89
Q

How to separate a mixture of calcium carbonate and sodium chloride?

A

Shake a mixture of calcium carbonate and sodium chloride with water. [1M]
Filter the mixture using a funnel with filter paper and the residue is calcium carbonate. [1M]
Evaporate the filtrate and the solid formed is sodium chloride. [1M]

Chemistry (6 decks)

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