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Tambaya 1 Rahoto
(a)(i) What is an acid-base indicator?
(ii) Give one example of an acid-base indicator.
(b) State the property exhibited by nitrogen(IV) oxide in each of the following equations:,
(i) 4Cu + 2NO\(_2\) -> 4CuO + N\(_2\) (ii) H\(_2\)O + 2NO\(_2\) --> HNO\(_3\) + HNO\(_2\)
(c)(i) Define enthalpy of combustion..
(ii) State why the enthalpy of combustion is always negative.
(d)(i) Distinguish between a primary cell and a secondary cell.
(ii) Give an example of each of the cells stated in I (d)(i).
(e) Define the term mole.
(f) Calculate the amount of hydrochloric acid in 40.0 cm\(^3\) of 0.40 moldm\(^{-3}\) dilute HCl.
(g) Name two substances which can be used as electrodes during the electroylsis of acidified water.
(h) List two forces of attraction that can exist between covalent molecules.
(i) Name the products formed when butane undergoes incomplete combustion.
(j) Write the electron configuration of \(_{26}\)Fe\(^{3+}\)
(a)(i) An acid-base indicator is a substance (usually a weak acid or weak base) that shows different colours in acidic and alkaline media and is used to detect the end point of a neutralization.
(ii) Example: litmus (or methyl orange, or phenolphthalein).
(b)(i) In \(4Cu + 2NO_2 \rightarrow 4CuO + N_2\), nitrogen(IV) oxide acts as an oxidizing agent (it is reduced and oxidizes the copper).
(ii) In \(H_2O + 2NO_2 \rightarrow HNO_3 + HNO_2\), nitrogen(IV) oxide undergoes disproportionation, acting as both an oxidizing and a reducing agent (N goes from +4 to +5 and to +3).
(c)(i) Enthalpy of combustion is the heat change when one mole of a substance is completely burnt in excess oxygen under standard conditions.
(ii) It is always negative because combustion is exothermic - heat is released to the surroundings.
(d)(i) A primary cell cannot be recharged; its chemical reaction is irreversible. A secondary cell can be recharged because its reaction is reversible.
(ii) Primary cell: dry (Leclanche) cell. Secondary cell: lead-acid accumulator.
(e) A mole is the amount of a substance that contains as many elementary entities as there are atoms in 12 g of carbon-12 (that is, \(6.02 \times 10^{23}\) entities).
(f) Amount of HCl \(= C \times V = 0.40 \times \dfrac{40.0}{1000} = 0.016\ \text{mol}\).
(g) Platinum and carbon (graphite) - inert electrodes.
(h) Van der Waals (dispersion) forces and hydrogen bonds.
(i) Carbon(II) oxide (carbon monoxide) and water (with some carbon/soot).
(j) \(_{26}\)Fe is \(1s^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^2\); Fe3+ loses the two 4s and one 3d electron:
\[1s^2 2s^2 2p^6 3s^2 3p^6 3d^5\]
Bayanin Amsa
(a)(i) An acid-base indicator is a substance (usually a weak acid or weak base) that shows different colours in acidic and alkaline media and is used to detect the end point of a neutralization.
(ii) Example: litmus (or methyl orange, or phenolphthalein).
(b)(i) In \(4Cu + 2NO_2 \rightarrow 4CuO + N_2\), nitrogen(IV) oxide acts as an oxidizing agent (it is reduced and oxidizes the copper).
(ii) In \(H_2O + 2NO_2 \rightarrow HNO_3 + HNO_2\), nitrogen(IV) oxide undergoes disproportionation, acting as both an oxidizing and a reducing agent (N goes from +4 to +5 and to +3).
(c)(i) Enthalpy of combustion is the heat change when one mole of a substance is completely burnt in excess oxygen under standard conditions.
(ii) It is always negative because combustion is exothermic - heat is released to the surroundings.
(d)(i) A primary cell cannot be recharged; its chemical reaction is irreversible. A secondary cell can be recharged because its reaction is reversible.
(ii) Primary cell: dry (Leclanche) cell. Secondary cell: lead-acid accumulator.
(e) A mole is the amount of a substance that contains as many elementary entities as there are atoms in 12 g of carbon-12 (that is, \(6.02 \times 10^{23}\) entities).
(f) Amount of HCl \(= C \times V = 0.40 \times \dfrac{40.0}{1000} = 0.016\ \text{mol}\).
(g) Platinum and carbon (graphite) - inert electrodes.
(h) Van der Waals (dispersion) forces and hydrogen bonds.
(i) Carbon(II) oxide (carbon monoxide) and water (with some carbon/soot).
(j) \(_{26}\)Fe is \(1s^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^2\); Fe3+ loses the two 4s and one 3d electron:
\[1s^2 2s^2 2p^6 3s^2 3p^6 3d^5\]
Tambaya 2 Rahoto
(a)(i) 1. State the periodic law.
2. What is meant by the term periodic property of elements?
(ii) List three properties of an element which show periodicity.
(iii) Explain briefly how each of the properties listed in (a)(i) in varies across the period.
(b) Defulle relative atomic mass.
(c)(i) What phenomenon is exhibited by an element Z which exist as \(^{35}_{17}Z\) and \(^{37}_{17}X\)
(ii) What accounts for the difference in the mass numbers of the element Z?
(iii) Calculate the relative atomic mass of Z if the percentage abundance of \(^{37}_{17}Z\) is 75%
(d)(i) State the method used for collecting each of the following gases: I. CO II. HCI III. H\(_2\)
(ii) Give a reason for your answer stated in (d)(i) I and II
(a)(i) 1. The periodic law states that the properties of elements are a periodic function of their atomic numbers.
2. A periodic property is a property of elements that recurs at regular intervals (varies gradually and repeatedly) when the elements are arranged in order of increasing atomic number.
(ii) Three properties showing periodicity: atomic radius, ionization energy, electronegativity.
(iii) Across a period from left to right:
(b) Relative atomic mass is the ratio of the average mass of one atom of an element to one-twelfth of the mass of one atom of carbon-12.
(c)(i) The phenomenon is isotopy (Z exists as isotopes).
(ii) The difference in mass number is due to a different number of neutrons in the nuclei (17 protons each, but different neutron counts).
(iii) With 75% of \(^{37}Z\) and 25% of \(^{35}Z\):
\[\text{RAM} = \frac{(37 \times 75) + (35 \times 25)}{100} = \frac{2775 + 875}{100} = 36.5\]
(d)(i)
(ii) CO is collected over water because it is insoluble in water. HCl is collected by downward delivery of air because it is very soluble in water and is denser than air.
Bayanin Amsa
(a)(i) 1. The periodic law states that the properties of elements are a periodic function of their atomic numbers.
2. A periodic property is a property of elements that recurs at regular intervals (varies gradually and repeatedly) when the elements are arranged in order of increasing atomic number.
(ii) Three properties showing periodicity: atomic radius, ionization energy, electronegativity.
(iii) Across a period from left to right:
(b) Relative atomic mass is the ratio of the average mass of one atom of an element to one-twelfth of the mass of one atom of carbon-12.
(c)(i) The phenomenon is isotopy (Z exists as isotopes).
(ii) The difference in mass number is due to a different number of neutrons in the nuclei (17 protons each, but different neutron counts).
(iii) With 75% of \(^{37}Z\) and 25% of \(^{35}Z\):
\[\text{RAM} = \frac{(37 \times 75) + (35 \times 25)}{100} = \frac{2775 + 875}{100} = 36.5\]
(d)(i)
(ii) CO is collected over water because it is insoluble in water. HCl is collected by downward delivery of air because it is very soluble in water and is denser than air.
Tambaya 3 Rahoto
(a)(i) Describe briefly the industrial preparation of ammonia.
(ii) Write a balanced equation for the reaction in (a)(i).
(iii) State one way of increasing the yield of ammonia in 4(a)(i).
(iv) State two uses of ammonia.
(b) Describe briefly, one chemical test for each of the following gases in the laboratory: (i) hydrogen; (ii) carbon (IV) oxide; (iii) oxygen.
(c)(i) State the composition of water gas.
(ii) List two uses of water gas.
(d) Describe briefly a simple experiment to determine the type of hardness in a sample of water.
(a)(i) Industrial preparation of ammonia (Haber process): nitrogen (from air) and hydrogen (from natural gas) are mixed in the ratio 1:3 and passed over a finely divided iron catalyst at about 450 °C and about 200 atmospheres pressure.
(ii) \[N_2 + 3H_2 \rightleftharpoons 2NH_3\]
(iii) Increase the yield by increasing the pressure (or by lowering the temperature, or removing ammonia as it forms).
(iv) Uses of ammonia: manufacture of fertilizers (ammonium salts) and manufacture of trioxonitrate(V) acid.
(b) Chemical tests
(c)(i) Water gas is a mixture of carbon(II) oxide and hydrogen (CO + H2).
(ii) Uses of water gas: as a fuel; as a source of hydrogen in industry (for example in the manufacture of methanol/ammonia).
(d) Type of hardness: boil a sample of the water and then add soap solution. If the water now lathers readily (hardness removed by boiling), the hardness is temporary. If it still does not lather easily after boiling, the hardness is permanent. Comparing lathering before and after boiling distinguishes the two.
Bayanin Amsa
(a)(i) Industrial preparation of ammonia (Haber process): nitrogen (from air) and hydrogen (from natural gas) are mixed in the ratio 1:3 and passed over a finely divided iron catalyst at about 450 °C and about 200 atmospheres pressure.
(ii) \[N_2 + 3H_2 \rightleftharpoons 2NH_3\]
(iii) Increase the yield by increasing the pressure (or by lowering the temperature, or removing ammonia as it forms).
(iv) Uses of ammonia: manufacture of fertilizers (ammonium salts) and manufacture of trioxonitrate(V) acid.
(b) Chemical tests
(c)(i) Water gas is a mixture of carbon(II) oxide and hydrogen (CO + H2).
(ii) Uses of water gas: as a fuel; as a source of hydrogen in industry (for example in the manufacture of methanol/ammonia).
(d) Type of hardness: boil a sample of the water and then add soap solution. If the water now lathers readily (hardness removed by boiling), the hardness is temporary. If it still does not lather easily after boiling, the hardness is permanent. Comparing lathering before and after boiling distinguishes the two.
Tambaya 4 Rahoto
(a) Write the molecular formula of X.
(i) What type of reaction is represented by the equation?
(ii) Consider the following reaction equation: \( \mathrm{C_{12}H_2 \to X + C_8H_{18}} \)
(iii) Draw the structure of two isomers of X.
(iv) Name the isomers drawn in (a)(iii).
(v) Write a balanced equation for the reaction between X and hydrogen.
(b) Describe one test for fats.
(c) Sulphur (IV) oxide is converted to tetraoxosulphate (VI) acid according to the following equation: \( \mathrm{2SO_{2(g)} + O_{2(g)} + 2H_2O_{(l)} \to 2H_2OSO_{4(aq)}} \). If 1.5 moles of oxgen reacts with sulphur (IV) oxide, calculate the mass of tetraoxosulphate (VI) acid produced. [H = 1.0; O = 16.0; S = 32.0].
(d) Consider the following neutralization reaction:
\( \mathrm{CH_3COOH + NaOH \to CH_3COONa + H_2O;} \ \bigtriangleup H_1 \)
\( \mathrm{CH_3COOH + NH_4OH \to CH_3COONH_4 + H_2O;} \ \bigtriangleup H_2 \)
\( \mathrm{NaOH + HCl \to NaCl + H_2O} \ \bigtriangleup H_3 \)
(i) Arrange the enthalphy changes for the reactions in order of increasing magnitude.
(ii) Explain briefly your order in (d)(i).
(e) Consider the following substances. \( \mathrm{Cu_{(s)}} \), \( \mathrm{BeCl_2} \), \( \mathrm{NaH_{(s)}} \), \( \mathrm{HF_{(s)}} \)and \( \mathrm{CCl_{4(l)}} \). State the substance(s) which;
(i) can conduct electricity;
(ii) is/are soluble in water.
From \(C_{12}H_{26} \rightarrow X + C_8H_{18}\), balancing gives X = C4H8 (an alkene, butene).
(a) Molecular formula of X: C4H8.
(i) The reaction is cracking (thermal/catalytic decomposition of a large alkane into a smaller alkane and an alkene).
(iii) Two isomers of C4H8
But-1-ene: CH2=CH-CH2-CH3
But-2-ene: CH3-CH=CH-CH3(iv) The isomers are but-1-ene and but-2-ene.
(v) Reaction of X with hydrogen (nickel catalyst):
\[C_4H_8 + H_2 \rightarrow C_4H_{10}\]
(b) Test for fats: rub the substance on a piece of paper; a fat leaves a translucent (greasy) spot that does not disappear on gentle warming.
(c) \(2SO_2 + O_2 + 2H_2O \rightarrow 2H_2SO_4\). Molar mass of H2SO4 = \(2 + 32 + 64 = 98\).
1 mol O2 gives 2 mol H2SO4, so 1.5 mol O2 gives \(1.5 \times 2 = 3\ \text{mol}\) H2SO4.
Mass \(= 3 \times 98 = 294\ \text{g}\).
(d)(i) Increasing magnitude: \(\Delta H_2 < \Delta H_1 < \Delta H_3\).
(ii) \(\Delta H_3\) (strong acid + strong base) is the most exothermic because both are fully ionized, so the full heat of neutralization is released. \(\Delta H_1\) (weak acid + strong base) is smaller because some energy is used to complete the ionization of the weak acid. \(\Delta H_2\) (weak acid + weak base) is the smallest because energy is absorbed to ionize both the weak acid and the weak base.
(e)(i) Can conduct electricity: Cu(s) (a metal with mobile electrons).
(ii) Soluble in water: BeCl2 and HF.
Bayanin Amsa
From \(C_{12}H_{26} \rightarrow X + C_8H_{18}\), balancing gives X = C4H8 (an alkene, butene).
(a) Molecular formula of X: C4H8.
(i) The reaction is cracking (thermal/catalytic decomposition of a large alkane into a smaller alkane and an alkene).
(iii) Two isomers of C4H8
But-1-ene: CH2=CH-CH2-CH3
But-2-ene: CH3-CH=CH-CH3(iv) The isomers are but-1-ene and but-2-ene.
(v) Reaction of X with hydrogen (nickel catalyst):
\[C_4H_8 + H_2 \rightarrow C_4H_{10}\]
(b) Test for fats: rub the substance on a piece of paper; a fat leaves a translucent (greasy) spot that does not disappear on gentle warming.
(c) \(2SO_2 + O_2 + 2H_2O \rightarrow 2H_2SO_4\). Molar mass of H2SO4 = \(2 + 32 + 64 = 98\).
1 mol O2 gives 2 mol H2SO4, so 1.5 mol O2 gives \(1.5 \times 2 = 3\ \text{mol}\) H2SO4.
Mass \(= 3 \times 98 = 294\ \text{g}\).
(d)(i) Increasing magnitude: \(\Delta H_2 < \Delta H_1 < \Delta H_3\).
(ii) \(\Delta H_3\) (strong acid + strong base) is the most exothermic because both are fully ionized, so the full heat of neutralization is released. \(\Delta H_1\) (weak acid + strong base) is smaller because some energy is used to complete the ionization of the weak acid. \(\Delta H_2\) (weak acid + weak base) is the smallest because energy is absorbed to ionize both the weak acid and the weak base.
(e)(i) Can conduct electricity: Cu(s) (a metal with mobile electrons).
(ii) Soluble in water: BeCl2 and HF.
Tambaya 5 Rahoto
(a)(i) Describe briefly how trioxonitrate (V) ions could be tested for in the laboratory.
(ii) State two uses of each of the following compounds: I. sodium chloride; II. sodium trioxocarbonate (IV).
(b) Write balanced equations for the reactions involved in the extraction of iron in the blast furnace.
(ii) State Faraday's first law of electrolysis.
(iii) State two applications of electrolysis.
(c) Concentrated tetraoxosulphate (VI) acid is added to sugar crystals in a beaker. State what would be observed. Explain briefly your answer.
(d) Write an equation for the reaction of zinc powder with:
(i) dilute tetraoxosulphate (VI) acid;
(ii) concentrated tetraoxosulphate (VI) acid.
(e) What property of concentrated tetraoxosulphate (VI) acid is shown in (d)(ii)
(a)(i) Test for trioxonitrate(V) (nitrate) ion - brown ring test: add freshly prepared iron(II) sulphate solution to the test solution, then carefully pour concentrated tetraoxosulphate(VI) acid down the side of the tube so it forms a layer below. A brown ring forms at the junction of the two liquids.
(ii)
(b)(i) Extraction of iron in the blast furnace
\[C + O_2 \rightarrow CO_2\]
\[CO_2 + C \rightarrow 2CO\]
\[Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2\]
\[CaCO_3 \rightarrow CaO + CO_2\]
\[CaO + SiO_2 \rightarrow CaSiO_3 \text{ (slag)}\]
(ii) Faraday's first law: the mass of a substance liberated or deposited at an electrode during electrolysis is directly proportional to the quantity of electricity (charge) passed through the electrolyte.
(iii) Applications: electroplating; purification (refining) of metals; extraction of reactive metals.
(c) The white sugar turns black (a spongy black mass of carbon rises up), with much heat and steam given off. Concentrated tetraoxosulphate(VI) acid is a powerful dehydrating agent: it removes hydrogen and oxygen from the sucrose as water, leaving carbon:
\[C_{12}H_{22}O_{11} \xrightarrow{conc.\ H_2SO_4} 12C + 11H_2O\]
(d)(i) \[Zn + H_2SO_4\ (dilute) \rightarrow ZnSO_4 + H_2\]
(ii) \[Zn + 2H_2SO_4\ (conc.,\ hot) \rightarrow ZnSO_4 + SO_2 + 2H_2O\]
(e) In (d)(ii) the concentrated acid acts as an oxidizing agent.
Bayanin Amsa
(a)(i) Test for trioxonitrate(V) (nitrate) ion - brown ring test: add freshly prepared iron(II) sulphate solution to the test solution, then carefully pour concentrated tetraoxosulphate(VI) acid down the side of the tube so it forms a layer below. A brown ring forms at the junction of the two liquids.
(ii)
(b)(i) Extraction of iron in the blast furnace
\[C + O_2 \rightarrow CO_2\]
\[CO_2 + C \rightarrow 2CO\]
\[Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2\]
\[CaCO_3 \rightarrow CaO + CO_2\]
\[CaO + SiO_2 \rightarrow CaSiO_3 \text{ (slag)}\]
(ii) Faraday's first law: the mass of a substance liberated or deposited at an electrode during electrolysis is directly proportional to the quantity of electricity (charge) passed through the electrolyte.
(iii) Applications: electroplating; purification (refining) of metals; extraction of reactive metals.
(c) The white sugar turns black (a spongy black mass of carbon rises up), with much heat and steam given off. Concentrated tetraoxosulphate(VI) acid is a powerful dehydrating agent: it removes hydrogen and oxygen from the sucrose as water, leaving carbon:
\[C_{12}H_{22}O_{11} \xrightarrow{conc.\ H_2SO_4} 12C + 11H_2O\]
(d)(i) \[Zn + H_2SO_4\ (dilute) \rightarrow ZnSO_4 + H_2\]
(ii) \[Zn + 2H_2SO_4\ (conc.,\ hot) \rightarrow ZnSO_4 + SO_2 + 2H_2O\]
(e) In (d)(ii) the concentrated acid acts as an oxidizing agent.
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