WAEC SSCE - Chemistry - 2020 (Essay)
Question 1 Report
(a) In the laboratory preparation of dry chlorine gas, state the: I. reagents used; II. drying agent III. the mode of collection.
(i) Write the equation for the preparation of chlorine gas. (iii) Write an equation to show how chlorine reacts with hot concentrated NaOH.
(b)i). Name the main raw materials used for the extraction of iron in the blast furnace. (ii) Write the equations of the reactions taking place in the blast furnace.
(iii) What is the name given to the iron obtained directly from the blast furnace? (iv) State why the iron named in 4(b)(iii) have a relatively low melting point?
(c) The following equation represents one of the reaction steps involved in the contact process: \(2\mathrm{SO}_2 + \mathrm{O}_2 \;\text{⇌}\; 2\mathrm{SO}_3 \quad \Delta H = -395.7\ \text{kJ mo-l}\)
(i) Why is the \(\mathrm{SO}_3\) produced during the reaction not dissolved directly in water to form \(\mathrm{H}_2\mathrm{SO}_4\)? (ii) Why is the \(\mathrm{H}_2\mathrm{SO}_4\) regarded as a heavy chemical? (iii) State the property exhibited by tetraoxosulphate (VI) acid in each of the following reaction equations.
I. \(\mathrm{Pb}(\mathrm{NO}_3)_2 + \mathrm{H}_2\mathrm{SO}_4 \rightarrow \mathrm{PbSO}_4 + 2\mathrm{HNO}_3\) (d) Write a balanced chemical equation for the reaction between propanol and sodium
(a) Laboratory preparation of dry chlorine
- I. Reagents: concentrated hydrochloric acid and manganese(IV) oxide (\(MnO_2\)). (Warm together.)
- II. Drying agent: concentrated tetraoxosulphate(VI) acid (\(H_2SO_4\)).
- III. Mode of collection: upward delivery (downward displacement of air), because chlorine is denser than air.
(i) Equation for preparation:
\[MnO_{2(s)} + 4HCl_{(aq)} \to MnCl_{2(aq)} + Cl_{2(g)} + 2H_2O_{(l)}\](iii) Chlorine with hot concentrated NaOH:
\[3Cl_{2(g)} + 6NaOH_{(aq)} \to 5NaCl_{(aq)} + NaClO_{3(aq)} + 3H_2O_{(l)}\](b)(i) Main raw materials for iron extraction in the blast furnace
Iron ore (haematite, \(Fe_2O_3\)), coke (carbon), limestone (\(CaCO_3\)) and hot air (oxygen).
(b)(ii) Reactions in the blast furnace
\[C + O_2 \to CO_2\]\[CO_2 + C \to 2CO\]\[Fe_2O_3 + 3CO \to 2Fe + 3CO_2\]\[CaCO_3 \to CaO + CO_2\]\[CaO + SiO_2 \to CaSiO_3\ (\text{slag})\](b)(iii) The iron obtained directly from the blast furnace is called pig iron (cast iron).
(b)(iv) Pig iron has a relatively low melting point because it contains a high proportion of impurities, chiefly about 4% carbon, which lowers its melting point.
(c)(i) Why SO3 is not dissolved directly in water
Dissolving \(SO_3\) directly in water is violently exothermic and produces a dense, corrosive mist (fog) of tetraoxosulphate(VI) acid that is difficult to condense and escapes. Instead the \(SO_3\) is absorbed in concentrated \(H_2SO_4\) to form oleum, which is later diluted safely.
(c)(ii) \(H_2SO_4\) is regarded as a heavy chemical because it is manufactured and used industrially in very large quantities (tonnage).
(c)(iii) In \(Pb(NO_3)_2 + H_2SO_4 \to PbSO_4 + 2HNO_3\), the tetraoxosulphate(VI) acid acts as an acid (a less volatile acid displacing the more volatile trioxonitrate(V) acid and forming an insoluble sulphate).
(d) Propanol with sodium
\[2C_3H_7OH + 2Na \to 2C_3H_7ONa + H_{2}\](sodium propoxide and hydrogen gas).
Answer Details
(a) Laboratory preparation of dry chlorine
- I. Reagents: concentrated hydrochloric acid and manganese(IV) oxide (\(MnO_2\)). (Warm together.)
- II. Drying agent: concentrated tetraoxosulphate(VI) acid (\(H_2SO_4\)).
- III. Mode of collection: upward delivery (downward displacement of air), because chlorine is denser than air.
(i) Equation for preparation:
\[MnO_{2(s)} + 4HCl_{(aq)} \to MnCl_{2(aq)} + Cl_{2(g)} + 2H_2O_{(l)}\](iii) Chlorine with hot concentrated NaOH:
\[3Cl_{2(g)} + 6NaOH_{(aq)} \to 5NaCl_{(aq)} + NaClO_{3(aq)} + 3H_2O_{(l)}\](b)(i) Main raw materials for iron extraction in the blast furnace
Iron ore (haematite, \(Fe_2O_3\)), coke (carbon), limestone (\(CaCO_3\)) and hot air (oxygen).
(b)(ii) Reactions in the blast furnace
\[C + O_2 \to CO_2\]\[CO_2 + C \to 2CO\]\[Fe_2O_3 + 3CO \to 2Fe + 3CO_2\]\[CaCO_3 \to CaO + CO_2\]\[CaO + SiO_2 \to CaSiO_3\ (\text{slag})\](b)(iii) The iron obtained directly from the blast furnace is called pig iron (cast iron).
(b)(iv) Pig iron has a relatively low melting point because it contains a high proportion of impurities, chiefly about 4% carbon, which lowers its melting point.
(c)(i) Why SO3 is not dissolved directly in water
Dissolving \(SO_3\) directly in water is violently exothermic and produces a dense, corrosive mist (fog) of tetraoxosulphate(VI) acid that is difficult to condense and escapes. Instead the \(SO_3\) is absorbed in concentrated \(H_2SO_4\) to form oleum, which is later diluted safely.
(c)(ii) \(H_2SO_4\) is regarded as a heavy chemical because it is manufactured and used industrially in very large quantities (tonnage).
(c)(iii) In \(Pb(NO_3)_2 + H_2SO_4 \to PbSO_4 + 2HNO_3\), the tetraoxosulphate(VI) acid acts as an acid (a less volatile acid displacing the more volatile trioxonitrate(V) acid and forming an insoluble sulphate).
(d) Propanol with sodium
\[2C_3H_7OH + 2Na \to 2C_3H_7ONa + H_{2}\](sodium propoxide and hydrogen gas).
Question 2 Report
(a) In an equilibrium reaction between gases Q and R, to form QR, the energy content of the reactants is 100 KJ and that of the product is 54 kJ. The energy content of the activated complex is 210 KJ.
(i) Draw an energy profile diagram for the reaction. (ii) Determine the: I. activation energy of the reaction il. enthalpy change \( \Delta H \) of the reaction. (iii) Write a balanced equation for the reaction. (iv) Give a reason for the answer given in 3(C)(iv). (iv) State whether the reaction is exothermic or endothermic.
(b) Consider the following table:
| Element | E | F | G | H |
| Atomic number | 7 | 9 | 12 | 13 |
(i) Write the electron configuration for each of the elements. Element E, F, G, H 12 13 (ii) State: I. two elements that are metals; II. the elements(s) most likely to form an ion with a charge of \(+3\); III. the element(s) which belong(s) to group VII. on the periodic table; IV. the formula of the compound formed between F and G. Atomic
(c) Define the term isotopy (d) Name the three building blocks of matter.
(a)
(i) Energy profile diagram
(ii)
I. Activation energy, \(E_a\)
\[E_a=\text{energy of activated complex}-\text{energy of reactants}=210-100=110\ \text{kJ mol}^{-1}\]
II. Enthalpy change, \(\Delta H\)
\[\Delta H=H_{\text{products}}-H_{\text{reactants}}=54-100=-46\ \text{kJ mol}^{-1}\]
(iii) \[Q_2(g)+R_2(g)\rightleftharpoons 2QR(g)\]
(iv) The reaction is exothermic.
Reason: The products have lower energy than the reactants and \(\Delta H\) is negative; hence, \(46\ \text{kJ mol}^{-1}\) of energy is released.
(b)(i) Electron configurations
| Element | Atomic number | Electron configuration |
|---|---|---|
| E | 7 | \(1s^2\,2s^2\,2p^3\) |
| F | 9 | \(1s^2\,2s^2\,2p^5\) |
| G | 12 | \(1s^2\,2s^2\,2p^6\,3s^2\) |
| H | 13 | \(1s^2\,2s^2\,2p^6\,3s^2\,3p^1\) |
(ii)
- The metals are G and H.
- The element most likely to form a \(+3\) ion is H.
- The element in Group VII is F.
- G forms \(G^{2+}\) and F forms \(F^-\); therefore, the formula of the compound is \(GF_2\).
(c) Isotopy is the phenomenon in which atoms of the same element have the same atomic number but different mass numbers because they contain different numbers of neutrons.
(d) The three building blocks of matter are atoms, molecules and ions.
Answer Details
(a)
(i) Energy profile diagram
(ii)
I. Activation energy, \(E_a\)
\[E_a=\text{energy of activated complex}-\text{energy of reactants}=210-100=110\ \text{kJ mol}^{-1}\]
II. Enthalpy change, \(\Delta H\)
\[\Delta H=H_{\text{products}}-H_{\text{reactants}}=54-100=-46\ \text{kJ mol}^{-1}\]
(iii) \[Q_2(g)+R_2(g)\rightleftharpoons 2QR(g)\]
(iv) The reaction is exothermic.
Reason: The products have lower energy than the reactants and \(\Delta H\) is negative; hence, \(46\ \text{kJ mol}^{-1}\) of energy is released.
(b)(i) Electron configurations
| Element | Atomic number | Electron configuration |
|---|---|---|
| E | 7 | \(1s^2\,2s^2\,2p^3\) |
| F | 9 | \(1s^2\,2s^2\,2p^5\) |
| G | 12 | \(1s^2\,2s^2\,2p^6\,3s^2\) |
| H | 13 | \(1s^2\,2s^2\,2p^6\,3s^2\,3p^1\) |
(ii)
- The metals are G and H.
- The element most likely to form a \(+3\) ion is H.
- The element in Group VII is F.
- G forms \(G^{2+}\) and F forms \(F^-\); therefore, the formula of the compound is \(GF_2\).
(c) Isotopy is the phenomenon in which atoms of the same element have the same atomic number but different mass numbers because they contain different numbers of neutrons.
(d) The three building blocks of matter are atoms, molecules and ions.
Question 3 Report
(a)(i) State Faraday's first law of electrolysis. (ii) Distinguish between a strong electrolyte and a weak electrolyte
(b) State one chemical property of ethyne.
(c)( i) What is meant by the tern unsaturated hydrocarbon? (ii) Complete the following reaction equation: \(\mathrm{CH_3 + CH_3OH \rightarrow}\) (iii) Name the major product formed in the cation stated in 1(c)(ii).
(d) State one way by which the rate of esterification could be increased.
(e) Consider the reaction represented by the following equation: \(\mathrm{Zn + H_2SO_4 \rightarrow ZnOS_4 + H_2}\). If 3.75g of Zn dust was added to excess \(\mathrm{H_2SO_4}\). Calculate the number of molecules of hydrogen gas produced. [ \(\mathrm{Zn = 65.0,\ Na = 6.02 \times 10^{23}}\) ].
(f) State one effect of global warming.
(g) Consider the following reaction equation:
A. \(\mathrm{Pb(NO_3) + H_2S \rightarrow PbS + 2HNO_3}\);
B. \(\mathrm{H_2 + C_2H_4 \rightarrow C_2H_6}\).
C. \(\mathrm{Zn(OH)_2 + 2OH \rightarrow [Zn(OH)_4]^{2}}\).
(i) Which of the equations represent(s) redox process? (ii) State the change in Oxidation number of the species that are oxidized or reduced. (h)(i) State two of the main concepts of Bohr's model of the atom. (ii) State the limitations of Bohr's model. (i) List three factors that could influence the equilibrium position of a reversible reaction. (j) Calcium trioxocarbonate(iv) powder is added to separate equimolar solutions of hydrochloric acid and ethanoic acid. State one: (i) similarity in the observation in both reactions: (ii) difference in the observation in both reactions.
(a)(i) Faraday's first law of electrolysis
The mass of a substance liberated or deposited at an electrode during electrolysis is directly proportional to the quantity of electricity (charge) that passes through the electrolyte.
(a)(ii) Strong versus weak electrolyte
A strong electrolyte is almost completely ionized in aqueous solution, whereas a weak electrolyte is only partially ionized in aqueous solution.
(b) One chemical property of ethyne
Ethyne is unsaturated and undergoes addition reactions, e.g. it decolourizes bromine water; it also burns in air. \(C_2H_2 + 2Br_2 \to C_2H_2Br_4\).
(c)(i) Unsaturated hydrocarbon
A hydrocarbon that contains at least one carbon-carbon double or triple bond.
(c)(ii) and (iii) Esterification
Reading the reaction as an ethanoic acid and methanol esterification:
\[CH_3COOH + CH_3OH \overset{H_2SO_4}{\rightleftharpoons} CH_3COOCH_3 + H_2O\]The major product is the ester methyl ethanoate (\(CH_3COOCH_3\)).
(d) Increasing the rate of esterification
Use a small amount of concentrated tetraoxosulphate(VI) acid as catalyst (also warming the mixture increases the rate).
(e) Number of hydrogen molecules from 3.75 g Zn
\[Zn + H_2SO_4 \to ZnSO_4 + H_2\]Moles of Zn \(= 3.75/65 = 0.0577\,mol\). From the equation 1 mol Zn gives 1 mol \(H_2\), so moles of \(H_2 = 0.0577\,mol\).
\[\text{Number of molecules} = 0.0577 \times 6.02 \times 10^{23} = 3.47 \times 10^{22}\](f) One effect of global warming
Melting of polar ice caps leading to a rise in sea level (and flooding of low-lying areas). Other acceptable: climate change, drought, desertification.
(g) Redox analysis
- (i) Equation B (\(H_2 + C_2H_4 \to C_2H_6\)) is the redox process. (In A and C no oxidation number changes.)
- (ii) In B, hydrogen changes from oxidation number 0 (in \(H_2\)) to \(+1\) (in \(C_2H_6\)) so it is oxidized; carbon changes from \(-2\) (in \(C_2H_4\)) to \(-3\) (in \(C_2H_6\)) so it is reduced.
(h)(i) Two concepts of Bohr's model
- Electrons revolve round the nucleus only in certain fixed circular paths (orbits/shells) of definite (quantized) energy.
- An electron does not radiate energy while in a given orbit; it absorbs or emits energy only when it jumps from one energy level to another.
(h)(ii) Limitations of Bohr's model
It successfully explains only the hydrogen (one-electron) atom and fails for atoms with more than one electron; it cannot explain the fine structure/splitting of spectral lines and contradicts the Heisenberg uncertainty principle (an electron cannot have a fixed orbit and definite momentum simultaneously).
(i) Three factors influencing equilibrium position
Concentration of reactants/products, temperature, and pressure (for reactions involving gases). A catalyst does not shift the position of equilibrium.
(j) Calcium trioxocarbonate(IV) with HCl and with ethanoic acid
- (i) Similarity: in both, effervescence occurs and a colourless gas (carbon(IV) oxide) is evolved which turns limewater milky.
- (ii) Difference: the reaction with hydrochloric acid (a strong acid) is faster and more vigorous, while the reaction with ethanoic acid (a weak acid) is slower and less vigorous.
Answer Details
(a)(i) Faraday's first law of electrolysis
The mass of a substance liberated or deposited at an electrode during electrolysis is directly proportional to the quantity of electricity (charge) that passes through the electrolyte.
(a)(ii) Strong versus weak electrolyte
A strong electrolyte is almost completely ionized in aqueous solution, whereas a weak electrolyte is only partially ionized in aqueous solution.
(b) One chemical property of ethyne
Ethyne is unsaturated and undergoes addition reactions, e.g. it decolourizes bromine water; it also burns in air. \(C_2H_2 + 2Br_2 \to C_2H_2Br_4\).
(c)(i) Unsaturated hydrocarbon
A hydrocarbon that contains at least one carbon-carbon double or triple bond.
(c)(ii) and (iii) Esterification
Reading the reaction as an ethanoic acid and methanol esterification:
\[CH_3COOH + CH_3OH \overset{H_2SO_4}{\rightleftharpoons} CH_3COOCH_3 + H_2O\]The major product is the ester methyl ethanoate (\(CH_3COOCH_3\)).
(d) Increasing the rate of esterification
Use a small amount of concentrated tetraoxosulphate(VI) acid as catalyst (also warming the mixture increases the rate).
(e) Number of hydrogen molecules from 3.75 g Zn
\[Zn + H_2SO_4 \to ZnSO_4 + H_2\]Moles of Zn \(= 3.75/65 = 0.0577\,mol\). From the equation 1 mol Zn gives 1 mol \(H_2\), so moles of \(H_2 = 0.0577\,mol\).
\[\text{Number of molecules} = 0.0577 \times 6.02 \times 10^{23} = 3.47 \times 10^{22}\](f) One effect of global warming
Melting of polar ice caps leading to a rise in sea level (and flooding of low-lying areas). Other acceptable: climate change, drought, desertification.
(g) Redox analysis
- (i) Equation B (\(H_2 + C_2H_4 \to C_2H_6\)) is the redox process. (In A and C no oxidation number changes.)
- (ii) In B, hydrogen changes from oxidation number 0 (in \(H_2\)) to \(+1\) (in \(C_2H_6\)) so it is oxidized; carbon changes from \(-2\) (in \(C_2H_4\)) to \(-3\) (in \(C_2H_6\)) so it is reduced.
(h)(i) Two concepts of Bohr's model
- Electrons revolve round the nucleus only in certain fixed circular paths (orbits/shells) of definite (quantized) energy.
- An electron does not radiate energy while in a given orbit; it absorbs or emits energy only when it jumps from one energy level to another.
(h)(ii) Limitations of Bohr's model
It successfully explains only the hydrogen (one-electron) atom and fails for atoms with more than one electron; it cannot explain the fine structure/splitting of spectral lines and contradicts the Heisenberg uncertainty principle (an electron cannot have a fixed orbit and definite momentum simultaneously).
(i) Three factors influencing equilibrium position
Concentration of reactants/products, temperature, and pressure (for reactions involving gases). A catalyst does not shift the position of equilibrium.
(j) Calcium trioxocarbonate(IV) with HCl and with ethanoic acid
- (i) Similarity: in both, effervescence occurs and a colourless gas (carbon(IV) oxide) is evolved which turns limewater milky.
- (ii) Difference: the reaction with hydrochloric acid (a strong acid) is faster and more vigorous, while the reaction with ethanoic acid (a weak acid) is slower and less vigorous.
Question 4 Report
(a) Consider the following compounds: (i) What is the relationship between the compounds labeled A and B? (ii) Name each of compounds A and B. (iii) Will the chemical properties of compounds A and B be the same? (iv) Give the reason for the answer stated in 2(a)(ii).
(b)(i) Give two characteristic features of boiling, (ii) What would be the effect of each of the following conditions on the boiling point of water? I. Addition of crystals of sodium chloride. II. Reduction of the atmospheric pressure. (iii) State one way in which boiling differs from evaporation.
(c)(i) Differentiate between an unsaturated solution and a saturated Solution. (ii) State two ways by which a saturated solution could be made to dissolve more solute. (iii) State one factor that could affect the solubility of a solid in a liquid. (d)(i) Define the term mole .
(ii) Consider the following reaction equation: MgO + 2HCI ? MgCl\(_2\) + H\(_2\). What mass of magnesium Oxide is needed to neutralize 25.0 cm3 of 0.1 mol dm-3 hydrochloric acid? [O= 16.0; Mg = 24.0]. (e) State three physical properties of metals.
(a) Compounds A and B
- (i) Relationship: A and B are geometric (cis-trans) isomers. They have the same molecular formula and the same atoms joined in the same order, but differ in the spatial arrangement of the groups about the carbon-carbon double bond.
- (ii) Names: Compound A is trans-1,2-dichloroethene; Compound B is cis-1,2-dichloroethene.
- (iii) Chemical properties: Yes, the chemical properties of A and B are the same.
- (iv) Reason: They contain the same functional group (the carbon-carbon double bond) and the same type of atoms connected in the same way, so they undergo the same chemical reactions.
(b)(i) Two characteristic features of boiling
- Boiling takes place at a specific, constant temperature (the boiling point) at which the vapour pressure of the liquid equals the atmospheric pressure.
- Boiling takes place throughout the whole body of the liquid, with bubbles of vapour forming within it.
(b)(ii) Effect on the boiling point of water
- I. Addition of sodium chloride crystals: it increases the boiling point of the water.
- II. Reduction of atmospheric pressure: it lowers the boiling point of the water.
(b)(iii) One difference between boiling and evaporation
Boiling occurs throughout the whole liquid at a fixed temperature, whereas evaporation occurs only at the surface of the liquid and at all temperatures.
(c)(i) Unsaturated versus saturated solution
An unsaturated solution can still dissolve more solute at a given temperature and contains no undissolved solute, whereas a saturated solution cannot dissolve any more solute at that temperature and is in contact with undissolved solute.
(c)(ii) Making a saturated solution dissolve more solute
- By increasing the temperature of the solution.
- By increasing the volume of the solvent.
(c)(iii) One factor affecting solubility of a solid in a liquid
Temperature (also the nature of the solute and the nature of the solvent).
(d)(i) The mole
The mole is the amount of a substance that contains as many elementary particles as there are atoms in 12 g of carbon-12, that is, \(6.02 \times 10^{23}\) particles.
(d)(ii) Mass of magnesium oxide
\[ MgO + 2HCl \to MgCl_2 + H_2O \]
Moles of HCl \(= \dfrac{25.0}{1000} \times 0.1 = 2.5 \times 10^{-3}\,\text{mol}\).
From the equation, 2 mol HCl react with 1 mol MgO, so moles of MgO \(= \dfrac{2.5 \times 10^{-3}}{2} = 1.25 \times 10^{-3}\,\text{mol}\).
Molar mass of MgO \(= 24.0 + 16.0 = 40.0\).
\[ \text{Mass of MgO} = 1.25 \times 10^{-3} \times 40.0 = 0.05\,\text{g} \]
(e) Three physical properties of metals
- They are malleable and ductile.
- They are lustrous (shiny) and good conductors of heat and electricity.
- They have high melting and boiling points.
Answer Details
(a) Compounds A and B
- (i) Relationship: A and B are geometric (cis-trans) isomers. They have the same molecular formula and the same atoms joined in the same order, but differ in the spatial arrangement of the groups about the carbon-carbon double bond.
- (ii) Names: Compound A is trans-1,2-dichloroethene; Compound B is cis-1,2-dichloroethene.
- (iii) Chemical properties: Yes, the chemical properties of A and B are the same.
- (iv) Reason: They contain the same functional group (the carbon-carbon double bond) and the same type of atoms connected in the same way, so they undergo the same chemical reactions.
(b)(i) Two characteristic features of boiling
- Boiling takes place at a specific, constant temperature (the boiling point) at which the vapour pressure of the liquid equals the atmospheric pressure.
- Boiling takes place throughout the whole body of the liquid, with bubbles of vapour forming within it.
(b)(ii) Effect on the boiling point of water
- I. Addition of sodium chloride crystals: it increases the boiling point of the water.
- II. Reduction of atmospheric pressure: it lowers the boiling point of the water.
(b)(iii) One difference between boiling and evaporation
Boiling occurs throughout the whole liquid at a fixed temperature, whereas evaporation occurs only at the surface of the liquid and at all temperatures.
(c)(i) Unsaturated versus saturated solution
An unsaturated solution can still dissolve more solute at a given temperature and contains no undissolved solute, whereas a saturated solution cannot dissolve any more solute at that temperature and is in contact with undissolved solute.
(c)(ii) Making a saturated solution dissolve more solute
- By increasing the temperature of the solution.
- By increasing the volume of the solvent.
(c)(iii) One factor affecting solubility of a solid in a liquid
Temperature (also the nature of the solute and the nature of the solvent).
(d)(i) The mole
The mole is the amount of a substance that contains as many elementary particles as there are atoms in 12 g of carbon-12, that is, \(6.02 \times 10^{23}\) particles.
(d)(ii) Mass of magnesium oxide
\[ MgO + 2HCl \to MgCl_2 + H_2O \]
Moles of HCl \(= \dfrac{25.0}{1000} \times 0.1 = 2.5 \times 10^{-3}\,\text{mol}\).
From the equation, 2 mol HCl react with 1 mol MgO, so moles of MgO \(= \dfrac{2.5 \times 10^{-3}}{2} = 1.25 \times 10^{-3}\,\text{mol}\).
Molar mass of MgO \(= 24.0 + 16.0 = 40.0\).
\[ \text{Mass of MgO} = 1.25 \times 10^{-3} \times 40.0 = 0.05\,\text{g} \]
(e) Three physical properties of metals
- They are malleable and ductile.
- They are lustrous (shiny) and good conductors of heat and electricity.
- They have high melting and boiling points.
Question 5 Report
.(a)(i) Name two gases that can be used to perform the fountain experiment. (ii) What is the aim of he fountain experiment? (iii) Describe briefly the fountain experiment.
(b)(i) Name two chemical industries. (ii) State three effects of a chemical industry on the community in which it is sited.
(c)(i) Name three products of the destructive distillation of coal. (ii) Give one use each of any two of the products named in 5(c)(1).
(d)(i) Name two substances responsible for hardness in water. (ii) State two methods for the removal of hardness in water. (iii) State two advantages of hard water.
(a)(i) Two gases for the fountain experiment
Ammonia (\(NH_3\)) and hydrogen chloride (\(HCl\)); both are extremely soluble in water.
(a)(ii) Aim of the fountain experiment
To demonstrate the very high solubility of the gas in water.
(a)(iii) Description of the fountain experiment
A dry round-bottomed flask is filled with the dry gas (e.g. ammonia) and fitted with a stopper carrying a jet tube that dips into a beaker of water (containing an indicator such as litmus) and a small dropper of water. A little water is squeezed from the dropper into the flask. The gas dissolves rapidly and almost completely, creating a partial vacuum (reduced pressure) inside the flask. The greater atmospheric pressure on the water in the beaker then forces water up the jet tube, and it spurts into the flask as a fountain. The indicator changes colour (turning blue for ammonia), showing the gas is alkaline.
(b)(i) Two chemical industries
Petrochemical (oil-refining) industry and cement industry. (Also acceptable: fertilizer, brewery, soap and detergent, pharmaceutical industries.)
(b)(ii) Three effects of a chemical industry on its community
- Provision of employment and improved standard of living (positive).
- Provision of social infrastructure such as roads, water and electricity (positive).
- Air and water pollution and health hazards from the disposal of wastes and emission of gases (negative).
(c)(i) Three products of the destructive distillation of coal
Coke, coal gas, coal tar (and ammoniacal liquor).
(c)(ii) One use each of two products
- Coke: used as a fuel and as a reducing agent in the extraction of metals.
- Coal gas: used as a gaseous fuel for heating and lighting. (Coal tar: source of organic chemicals and for surfacing roads.)
(d)(i) Two substances responsible for hardness in water
Calcium and magnesium hydrogencarbonates and sulphates (\(Ca^{2+}\) and \(Mg^{2+}\) salts).
(d)(ii) Two methods of removing hardness
Boiling (for temporary hardness) and addition of washing soda, \(Na_2CO_3\) (also ion exchange or distillation).
(d)(iii) Two advantages of hard water
- It supplies calcium salts needed for the formation of strong bones and teeth.
- It has a pleasant taste and helps prevent lead poisoning by coating lead pipes with an insoluble layer.
Answer Details
(a)(i) Two gases for the fountain experiment
Ammonia (\(NH_3\)) and hydrogen chloride (\(HCl\)); both are extremely soluble in water.
(a)(ii) Aim of the fountain experiment
To demonstrate the very high solubility of the gas in water.
(a)(iii) Description of the fountain experiment
A dry round-bottomed flask is filled with the dry gas (e.g. ammonia) and fitted with a stopper carrying a jet tube that dips into a beaker of water (containing an indicator such as litmus) and a small dropper of water. A little water is squeezed from the dropper into the flask. The gas dissolves rapidly and almost completely, creating a partial vacuum (reduced pressure) inside the flask. The greater atmospheric pressure on the water in the beaker then forces water up the jet tube, and it spurts into the flask as a fountain. The indicator changes colour (turning blue for ammonia), showing the gas is alkaline.
(b)(i) Two chemical industries
Petrochemical (oil-refining) industry and cement industry. (Also acceptable: fertilizer, brewery, soap and detergent, pharmaceutical industries.)
(b)(ii) Three effects of a chemical industry on its community
- Provision of employment and improved standard of living (positive).
- Provision of social infrastructure such as roads, water and electricity (positive).
- Air and water pollution and health hazards from the disposal of wastes and emission of gases (negative).
(c)(i) Three products of the destructive distillation of coal
Coke, coal gas, coal tar (and ammoniacal liquor).
(c)(ii) One use each of two products
- Coke: used as a fuel and as a reducing agent in the extraction of metals.
- Coal gas: used as a gaseous fuel for heating and lighting. (Coal tar: source of organic chemicals and for surfacing roads.)
(d)(i) Two substances responsible for hardness in water
Calcium and magnesium hydrogencarbonates and sulphates (\(Ca^{2+}\) and \(Mg^{2+}\) salts).
(d)(ii) Two methods of removing hardness
Boiling (for temporary hardness) and addition of washing soda, \(Na_2CO_3\) (also ion exchange or distillation).
(d)(iii) Two advantages of hard water
- It supplies calcium salts needed for the formation of strong bones and teeth.
- It has a pleasant taste and helps prevent lead poisoning by coating lead pipes with an insoluble layer.
