INSTRUCTIONS TO CANDIDATES
- Answer all the questions in the spaces provided.
- All working must be clearly shown where necessary.
- Scientific calculators may be used.
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- In an experiment to determine the percentage of oxygen in air, the apparatus below were set up. Study the set up and the information provided to answer thequestions that follow.
A 500cm3 measuring cylinder K was filled with water and assembled for gas collection. Copper turnings were heated red hot and water was slowly passed into 500cm3 flask H until it reached the 500cm3 mark. A colourless gas was collected in K.- What was the purpose of passing water into flask H? (1 mark)
- What observations were made in the tube I? (1 mark)
- Name one of the gases that is likely to be found in J. (1 mark)
- What was the volume of the gas collected in the measuring cylinder at the end of the experiment? (1 mark)
- Calculate the percentage of oxygen in air using the above results. (2 marks)
- Study the diagram below and answer the questions that follow.
- Give one observation made in the combustion tube after some time. (1 mark)
- Write an equation for the formation of the colourless liquid Y. (1 mark)
- What was the aim of the above experiment as demonstrated in the combustion tube? Explain. (2 marks)
- In an experiment to determine the percentage of oxygen in air, the apparatus below were set up. Study the set up and the information provided to answer thequestions that follow.
- Use the information below to answer the questions that follow. The letters are not the actual symbols of the elements.
Element Atmoic No. M.P°C B.P°C Ionic radius (nm) P 11 98 890 0.095 Q 12 650 1110 0.065 R 13 660 2470 0.050 S 14 1410 2360 0.041 T 15 44.2&590 280 0.034 U 16 113&119 445 0.184 V 17 −101 −35 0.181 W 18 −189 −186 - -
- Write the electronic configuration of the atoms represented by letters T and W. (1 mark)
- State the nature of the oxides of the elements represented by Q and U. (2 marks)
- Why does the elements represented by the letters T and U have two values of melting points? (1 mark)
- Explain the following observations in terms of structure and bonding.
- There is an increase in boiling point from P to R. (2 marks)
- Element S has a high boiling point. (2 marks)
- There is a decrease in boiling points from U to W. (2 marks)
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- Compare the atomic radius of U and V. (1 mark)
- Why is there no ionic radius for W reported in the table? (1 mark)
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- The solubilities of potassium nitrate and potassium bromide at different temperatures was determined. The following data was obtained.
Temperature °C 0 10 20 30 40 50 60 70 80 Solubility g/100g H2O KNO3 5 15 26 43 61 83 105 135 165 KBr 50 55 60 65 70 77 85 90 95 - Draw solubility curves for both salts on the same axis. (3 marks)
- What was the solubility of each salt at 65°C? (1 mark)
- 100g of a saturated solution of potassium nitrate at 70°C was cooled to 20°C. What mass of the crystals will be crystallized? (2 marks)
- Study the flow chart below and answer the questions that follow.
- Write an equation for the formation of solid A and gas B. (1 mark)
- Name;
Solution C - ………………………………………………….. (1 mark)
Solid D - ………………………………………………….. (1 mark)
- Write the formula of the complex ion in solution E. (1 mark)
- The solubilities of potassium nitrate and potassium bromide at different temperatures was determined. The following data was obtained.
- Study the flow chart below and answer the questions that follow.
- Name substance. (3 marks)
X - ………………………………………………………………….
Q - ………………………………………………………………….
R - …………………………………………………………………. - Write down an equation for the reaction represented by step III. (1 mark)
- What are the conditions and reagent required for steps?
- I (2 marks)
Reagent - ………………………………………………………………………………….
Condition - ………………………………………………………………………………….. - IV (2 marks)
Reagent - …………………………………………………………………………………..
Condition - …………………………………………………………………………………..
- I (2 marks)
- Name the process represented by: (4 marks)
- I - ……………………………………………………………………….
- II - ……………………………………………………………………….
- IV - ……………………………………………………………………….
- V - ……………………………………………………………………….
- Name substance. (3 marks)
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- Study the scheme below and answer the questions that follow.
- Identify substances. (3 marks)
- A - …………………………………………………………………..
- B - …………………………………………………………………..
- D - …………………………………………………………………..
- State the catalyst necessary for; (2 marks)
- Step I - …………………………………………………………………………………………
- Step II - …………………………………………………………………………………………
- Write an equation for the reaction taking place in step II. (1 mark)
- Write two balanced chemical equations for the reaction between chlorine gas and;
- Hot and concentrated sodium hydroxide. (1 mark)
- Dilute and cold sodium hydroxide. (1 mark)
- Identify substances. (3 marks)
- The diagram below shows an experiment in which the Lead (II) nitrate crystals are heated.
- Name; (2 marks)
- Liquid P - ………………………………………………………………………..
- Gas Y - ………………………………………………………………………..
- Write a balanced chemical equation for the decomposition of Lead (II) nitrate. (1 mark)
- Explain how you can distinguish between nitrogen (II) oxide and nitrogen (I) oxide. (2 marks)
- Name; (2 marks)
- Study the scheme below and answer the questions that follow.
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- Study the standard electrode potentials given below and answer the questions that follow.
D2+ (aq) + 2e−D(S) Eθ = −2.92V
G2+ (aq) + 2e−G(S) Eθ= −2.36V
½J2+ (g) + e−J(S) Eθ = 0.00V
M2+ (aq) + 2e−M(S) Eθ = +0.34V
½R2+ (aq) + e−R(S) Eθ = 2.87V
- Identify the strongest:
- Reducing agent ……………………….. (1 mark)
- Oxidizing agent ……………………….. (1 mark)
- Calculate the e.m.f of a cell made of G and M. (2 marks)
- Write the cell representation for the above cell in (b). (1 mark)
- Draw a cell diagram for the cell in (b) above. (2 marks)
- Write the cell reaction for the drawn cell diagram in (d) above. (1 mark)
- Identify the strongest:
- Electrolysis of aqueous solution of metal M resulted in the deposition of 1.07g of metal upon passage of a current of 1.32 amperes for 75 minutes.(M = 52, 1F = 96500C)
- Calculate the quantity of electricity passed through the cell. (1 mark)
- Calculate the charge on the metal ion. (3 marks)
- Study the standard electrode potentials given below and answer the questions that follow.
- Extraction of iron involves two main processes, smelting and refining. Below is the blast furnace which is used to smelt iron from its ore.
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- What does the word smelt mean? (1 mark)
- Name the reducing agent in the process. (1 mark)
- What is the role of the hot air blast in the process? (2 marks)
- Write equations for the reactions that take place at the region marked A, B and C. (3 marks)
A - ……………………………………………………………………………………………………….
B - ……………………………………………………………………………………………………….
C - ………………………………………………………………………………………………………. - What is the purpose of limestone in the extraction process? (1 mark)
- Write equations to show how impurities are removed from the ore. (3 marks)
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MARKING SCHEME
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- In an experiment to determine the percentage of oxygen in air, the apparatus below were set up. Study the set up and the information provided to answer the questions that follow.
A 500cm3 measuring cylinder K was filled with water and assembled for gas collection. Copper turnings were heated red hot and water was slowly passed into 500cm3 flask H until it reached the 500cm3 mark. A colourless gas was collected in K.- What was the purpose of passing water into flask H? (1 mark)
To displace air in flask H over the hot copper turnings. - What observations were made in the tube I? (1 mark)
The brown solid changes to black - Name one of the gases that is likely to be found in J. (1 mark)
Nitrogen, carbon (IV) oxide, argon, (Xeron, neon) (Any one - What was the volume of the gas collected in the measuring cylinder at the end of the experiment? (1 mark)
410cm3 - Calculate the percentage of oxygen in air using the above results. (2 marks)
(500 × 410) × 100 = 90 × 100 = 18%
500 500
- What was the purpose of passing water into flask H? (1 mark)
- Study the diagram below and answer the questions that follow.
- Give one observation made in the combustion tube after some time. (1 mark)
Black CuO turns to red-brown Cu. - Write an equation for the formation of the colourless liquid Y. (1 mark)
2H2(g) + O2(g) → 2H2O(l) - What was the aim of the above experiment as demonstrated in the combustion tube? Explain. (2 marks)
- To determine the reducing property of hydrogen. ✓1 Hydrogen is above Cu ✓1 in the reactivity series, thus it reduces the oxygen from CuO.
- Give one observation made in the combustion tube after some time. (1 mark)
- In an experiment to determine the percentage of oxygen in air, the apparatus below were set up. Study the set up and the information provided to answer the questions that follow.
- Use the information below to answer the questions that follow. The letters are not the actual symbols of the elements.
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- Write the electronic configuration of the atoms represented by letters T and W. (1 mark)
T - 2.8.5 ✓½
W - 2.8.8 ✓½ - State the nature of the oxides of the elements represented by Q and U. (2 marks)
Q - Basic Oxide ✓1
U - Acidic oxide ✓1
- Write the electronic configuration of the atoms represented by letters T and W. (1 mark)
- Why does the elements represented by the letters T and U have two values of melting points? (1 mark)
The two elements exhibit allotropy. - Explain the following observations in terms of structure and bonding.
- There is an increase in boiling point from P to R. (2 marks)
There is gradual increase in the strength of the metallic bonds ✓1 due to the increase in the number of delocalized (valence) electrons in the element ✓1 - Element S has a high boiling point. (2 marks)
The atomic radius of V is smaller than that of U. ✓1 V has more protons therefore has a stronger nuclear attraction hence the smaller atomic radius. ✓1 - There is a decrease in boiling points from U to W. (2 marks)
Elements U, V and W have simple molecular structures ✓1 in which the molecules are held by weak Van der waals forces. The Van der waals ✓1 forces weaken from U to W.
- There is an increase in boiling point from P to R. (2 marks)
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- Compare the atomic radius of U and V. (1 mark)
The atomic radius of V is smaller than that of U. ✓1 - Why is there no ionic for W reported in the table? (1 mark)
It has a stable electron configuration hence does not ionize.
- Compare the atomic radius of U and V. (1 mark)
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- The solubilities of potassium nitrate and potassium bromide at different temperatures was determined. The following data was obtained.
- Draw solubility curves for both salts on the same axis. (3 marks)
- What was the solubility of each salt at 650C? of water (1 mark)
- KBr 87g/100g of water ±1✓½
- KNO3 − 120g/100g of water ±1 ✓½
- 100g of a saturated solution of potassium nitrate at 70°C was cooled to 20°C. What mass of the crystals will be crystallized? (2 marks)
At 70°C solubility = 135g/100g of water
If 235g contain 135g of salt
100g contain 135g
100×135 = 57.4468g ✓½
235
At 20°C solubility = 26g/100g of water
If 126g contain 26g of salt
100g contain ?
100×26 = 20.6349g ✓½
235
Mass which will crystallized
57.4468 – 20.6349
= 36.8119g
- Draw solubility curves for both salts on the same axis. (3 marks)
- Study the flow chart below and answer the questions that follow.
- Write an equation for the formation of solid A and gas B. (1 mark)
CuCO3(s)CuO(s) + CO2(g)
- Name;
Solution C - Copper (II) chloride (1 mark)
Solid D - Copper (II) hydroxide (1 mark)
- Write an equation for the formation of solid A and gas B. (1 mark)
- Write the formula of the complex ion in solution E. (1 mark)
(Cu(NH3)42+
- The solubilities of potassium nitrate and potassium bromide at different temperatures was determined. The following data was obtained.
- Study the flow chart below and answer the questions that follow.
- Name substance. (3 marks)
X - Sodium ethonoate ✓1
Q - Sodium ethoxide ✓1
R - Iodoethane ✓1 - Write down an equation for the reaction represented by step III. (1 mark)
CH3COOONa(s) + NaOH(aq) → CH4(g) + Na2CO3(s) - What are the conditions and reagent required for steps?
- I (2 marks)
Reagent - Propan-l-ol ✓1
Condition - Conc. H2SO4 ✓1 - IV (2 marks)
Reagent - Conc. H2SO4 ✓1
Condition - Temp 160 – 180° ✓1
- I (2 marks)
- Name the process represented by: (4 marks)
- I - Esterification
- II - Substitution
- IV - Oxidation
- V - Dehydration
- Name substance. (3 marks)
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- Study the scheme below and answer the questions that follow.
- Identify substances. (3 marks)
- A - Hydrogen
- B - Nitrogen
- D - NO
- State the catalyst necessary for; (2 marks)
- Step I - Iron finely divided / iron
- Step II - Platinum – rhodium catalyst
- Write a balanced chemical equation for taking place in step II. (1 mark)
4NH(g) + SO2 → 2NO(g) + 6H2O - Write two balanced chemical equations for the reaction between chlorine Gas and;
- Hot and concentrated sodium hydroxide. (1 mark)
6NaOH(aq) + 3Cl2(g) → NaClO3(aq) + 5NaCl(aq) + H2O(l) - Dilute and cold sodium hydroxide. (1 mark)
2NaOH(aq) + Cl2 → NaOCl + NaCl + H2O
- Hot and concentrated sodium hydroxide. (1 mark)
- Identify substances. (3 marks)
- The diagram below shows an experiment in which the Lead (II) nitrate crystals are heated.
- Name; (2 marks)
- Liquid P - dinitrogen tetra oxide
- Gas Y - oxygen
- Write a balanced chemical equation for the decomposition of Lead (II) nitrate. (1 mark)
2Pb(NO3)2 → 2PbO(s) + 4NO2(s) + O2(g) - Explain how you can distinguish between nitrogen (II) oxide and nitrogen (I) oxide. (2 marks)
- Nitrogen (V) oxide relights a glowing splint while nitrogen (II) oxide does not.
- N2O has xtic sweet smell, while. NO2 is odourless.
- Name; (2 marks)
- Study the scheme below and answer the questions that follow.
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- Study the standard electrode potentials given below and answer the questions that follow.
D2+ (aq) + 2e−D(S) Eθ = −2.92V
G2+ (aq) + 2e−G(S) Eθ= −2.36V
½J2+ (g) + e−J(S) Eθ = 0.00V
M2+ (aq) + 2e−M(S) Eθ = +0.34V
½R2+ (aq) + e−R(S) Eθ = 2.87V
- Identify the strongest:
- Reducing agent D (1 mark)
- Oxidizing agent R2+ (1 mark)
- Calculate the e.m.f of a cell made of G and M. (2 marks)
e.m.f = EθR − EθO
=+0.34 − −2.36
= +2.70V - Write the cell representation for the above cell in (b). (1 mark)
G(s)/G2+(aq)//M2+(aq)/M(s) ; E = +2.70V
Penalize for lack of states and E value - Draw a cell diagram for the cell in (b) above. (2 marks)
- Write the cell reaction for the drawn cell diagram in (d) above. (1 mark)
G(s) + M2+(aq) → G2+(aq) + M(s) ; E = +2.70V
- Identify the strongest:
- Electrolysis of aqueous solution of metal M resulted in the deposition of 1.07g of metal upon passage of a current of 1.32 amperes for 75 minutes.
(M = 52, 1F = 96500C)- Calculate the quantity of electricity passed through the cell. (1 mark)
Q = 1t
= 1.32 × 75 × 60 ✓½
=5940C ✓½ - Calculate the charge on the metal ion. (3 marks)
If 1.07g is departed by 5940C
52g “ “
52 × 5940 = 2888672.8972C ✓1
1.07
If 1F is 96500C
? “ 288672.8972C
1 × 288672.8972 ✓1
96500
=2.994
=3
=+3 ✓1
- Calculate the quantity of electricity passed through the cell. (1 mark)
- Study the standard electrode potentials given below and answer the questions that follow.
- Extraction of iron involves two main processes, smelting and refining. Below is the blast furnace which is used to smelt iron from its ore.
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- What does the word smelt mean? (1 mark)
- Extraction of a metal from its ore using a reducing agent and heat.
- Name the reducing agent in the process. (1 mark)
- Carbon ( in form of coke)
- What is the role of the hot air blast in the process? (2 marks)
- Hot air reacts with coke to form carbon (IV) oxide producing a lot of heat which melts the iron formed in the blast furnace.
- What does the word smelt mean? (1 mark)
- Write equations for the reactions that take place at the region marked A, B and C. (3 marks)
- A
C(s) + O(2) → CO2(g) - B
CO2(g) + 3C(s) → 4Fe(s) + 3CO2(g) - C
2Fe2O3(s) + 3C(s) → 4Fe(s) + 3CO2(g)
- A
- What is the purpose of limestone in the extraction process? (1 mark)
- To remove silica impurities in the ore.
- Write equations to show how impurities are removed from the ore. (3 marks)
CaCO3(s)CaO(s) + CO2(g)
CaO(s) + SiO2(s) → CaSiO3(s)
Al2O3(s) + CaO(s) → CaAl2O4(s)
slag
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