Chemistry P1 Questions and Answers - Momaliche 4 cycle Post Mock Exams 2021/2022

Instructions to Candidates

1. Write your name and index number in the spaces provided above.
2. Answer all the questions in the spaces provided.
3. All working must be clearly shown.
4. Non-programmable silent electronic calculators and KNEC mathematical tables may be used.

For Examiner’s Use only

QUESTIONS

1. 1. 120 cm³ of oxygen gas diffused through a porous partition in 50 seconds. How long would it take 80cm³ of Sulphur (IV) oxide to diffuse through the same partition under the same conditions? (S=32.0, 0=16.0) (3mks)
      
2. The flow chart represents a series of reactions . Study it and answer the questions that follow.
   
   
   1. Identify substances G and J (2mks)
      G.........................................................
      J.............................................................
   2. Write a chemical equation for the formation of J. (1mk)
3. At 20ºC, NO₂ and N₂O₄ gases exist in equilibrium as shown in the equation below.
   
   State and explain the observation that would be made when.
   1. The syringe containing the mixture is immersed in ice-cold water. (2mks)
   2. The volume in the gaseous mixture in the syringe is reduced. (2mks)
4. A student suspected a given sample of water contains sulphate ions. Describe how he can show the presence of the sulphate ions in the water sample. (2mks)
5. In the industrial manufacture of nitric (v) acid the first step is catalytic oxidation of ammonia gas.
   1. What is the name of the catalyst used. (1mk)
   2. Write the equation for the catalytic oxidation of ammonia gas. (1mk)
   3. State one use nitric acid. (1mk)
6. Explain why boiling point of ethanol is higher than that of dimethylether. (Relative molecular mass of both of them is 46). (2mks)
7. When 94.5g of hydrated barium hydroxide Ba(OH)₂.n H₂O were heated to a constant mass, 51.3g of anhydrous barium hydroxide were obtained. Determine the value of n.
   (Ba=137, O=16,H=1) (3mks)
8. Study the diagram below and answer the questions that follow.
   
   
   1. What do Δ H1 and Δ H2 represent (2mks)
      1. Δ H₁
      2. Δ H₂
   2. Give an expression for heat of solution in terms ofΔ H1, ΔH2 and Δ H3. (1mk)
9. 6.84g of aluminium sulphate were dissolved in 300cm3 of water. Calculate the molar concentration of sulphate ions in the solution. (R.M.F=342) (3mks)
10. Study the information given in the table below and answer the questions that follow.
    

    Bond	Bond energy (KJ mol)
    C-H	413
    Br-Br	193
    C-Br	280
    H-Br	365

    1. Calculate the Enthalpy changes for the reaction below (2mks)
       CH₄ (g) + Br₂ (g) → CH₃Br (g) + HBr (g)
    2. State whether the reaction is exothermic or endothermic. Explain (1mk)
11. A certain mass of a metal E reacted with excess dilute hydrochloric acid at 250C. The volume of hydrogen gas liberated was measured after every 30 seconds. The results were represented as shown in the graph below. (1mk)
    
    
    1. Name one piece of apparatus that may be used to measure the volume of gas liberated. (1mk)
    2.                      
       1. On the same axis , sketch the curve that would be obtained if the experiment was repeated at 35ºC. (1mk)
       2. Explain the shape of your curve in b( i) above. (2mks)
12.                          
    1. Why is hydrogen not readily used as a fuel? (1mk)
    2. State one uses of hydrogen gas. (1mk)
13.                    
    1. State Charles’ Law. (1mk)
    2. A certain mass of a gas occupies 150cm³ at 281K and 109.41kPa. What will be its temperature if its volume is reduced by 16 cm³ at 101.325kPa. (2mks)
14. 3g of iron reacted with hydrogen chloride gas at S.T.P. Calculate the volume of the hydrogen chloride gas used. (Fe=56, Molar gas volume at s.t.p=22.4dm³) (2mks)
15. Under certain conditions , chlorine gas reacts with sodium hydroxide to form sodium hypochlorite.
    1. Name the conditions under which sodium hydroxide reacts with chlorine to form sodium hypochlorite. (1mk)
    2. State one use of sodium hypochlorite . (1mk)
16.                      
    1. Distinguish between isotopes and allotropes (2mks)
    2. An element X has RAM of 69.39. Given that the element has two isotopes of masses 60.15 and 70.15. Calculate the relative abundance of each isotope (3mks)
17. A student has a mixture of anhydrous aluminium chloride and zinc sulphate. Which is the simplest method of separation? (1mk)
18. A student prepared ammonia and bubbled it into a solution of Magnesium sulphate as shown in the diagram below.
    1. Name any two reactants required for the production of ammonia. (1mk)
    2. State the observation in the beaker (1mk)
    3. Write ionic equation for the reaction in the beaker (1mk)
19. The compound HCLO decomposes according to the following equation .
    5HClO(aq) → 2Cl₂(g) + H⁺ (g) + ClO₃^- (aq)+ 2H₂O(l)
    Deduce the oxidation states of chlorine in the following species.
    1. HClO (1mk)
    2. ClO₃^- (1mk)
20. The set-up below was used to prepare dry sample of Oxygen gas
    1.                      
       1. Complete the diagram to show how the gas was collected (1mk)
       2. Identify the following
          1. Solid H....................................................................................................(1mk)
          2. Solid J...................................................................................................... (1mk)
    2. Write an equation for the reaction that occurred in the flask between solid H and water. .............. (1mk)
21. The table below gives the solubility of salt L and K at 100C and 800C. Solubility in g/100g water
          Salt             At 10ºC          At 80ºC
           L                 60                   75
           K                 20                   32
    When an aqueous mixture containing 80g of L and 10g of K in 100g water at 80ºC was cooled to 10ºC,crystallization occurred.
    1. What is crystallization (1mk)
    2. Determine the mass of the crystals formed (1mk)
    3. Name the method of separation (1mk)
22. The table below gives elements represented by letters T,U,V,W,X,Y and their atomic numbers . (Letters are not the actual symbols.
    

    Element	T	U	V	W	X	V
    Atomic number	12	13	14	15	16	17

    1.                           
       1. How does the atomic radius of V compare with that of X? Explain. (2mks)
       2. Give the formula of the compound that could be formed between U and X. (1mk)
    2.                          
       1. Arrange the species T,T^- and T⁺ in increasing order of size. (1mk)
       2. Which of the ions X²⁺ and X^2- is the most stable ? Explain. (2mks)
23.                                
    1. What would be observed in sulphur IV Oxide is bubbled through acidified potassium. chromate VI (1mk)
    2. In an experiment, sulphur (IV) Oxide was dissolved in water to form solution M.
       1. State the observation made if a few drops of barium chloride solution immediately added to solution M (1mk)
       2. Identify the spectator ions from the reaction b(i) above (1mk)
24. Copper-64 has a half life of 12.8days.
    1. What is meant by the term half life (1mk)
    2. What mass of a copper-64 will be left after 51.2 days starting with 20 g of the isotopes (2mks)
    3. Give one use of radioactive isotopes in medicine (1mk)
25.                              
    1. Zeolites (Na₂X) is a complex compound used to soften hard water in the ion-exchange methods according to the equation below.
       Ca ²⁺ (aq) +Na₂X (aq) → CaX(s) + 2Na⁺ (aq)
       After sometimes the Zeolites get exhausted and ceases to soften water. Write a reaction to show how Zeolite is regenarated. (1mk)
26. Name the particle responsible for electrical conductivity on;
    1. Molten magnesium metal (1mk)
    2. Molten magnesium chloride (1mk)
27. Carbon is one of the elements that exhibit allotropy
    1. Define the term allotrophy (1mk)
    2. Name two allotropes of carbon (1mk)
    3. Which allotrope of carbon is a good conductor of electricity. Explain. (2mks)

MARKING SCHEME

1. 120 cm³ of oxygen gas diffused through a porous partition in 50 seconds. How long would it take 80cm³ of Sulphur (IV) oxide to diffuse through the same partition under the same conditions? (S=32.0, 0=16.0) (3mks)
   RO₂ = 120 = 24 cm³/sec
               50
   O₂ = 32
   SO₂ = 64
      2.4    = √64
   RSO₂       32
   RSO₂ = 1.697cm³/sec
   1.697 = 80cm³
                 t
   t = 47.14 sec
2. The flow chart represents a series of reactions . Study it and answer the questions that follow.
   
   
   1. Identify substances G and J (2mks)
      G.......sodium hydroxide
      J........methane
   2. Write a chemical equation for the formation of J. (1mk)
      CH₃COONa(s) + NaOH(aq) → CH₄ (g) + Na₂CO₃(s)
3. At 20ºC, NO₂ and N₂O₄ gases exist in equilibrium as shown in the equation below.
   
   State and explain the observation that would be made when.
   1. The syringe containing the mixture is immersed in ice-cold water. (2mks)
      forward reaction is favoured because it is pale yellow colour intensifies as the brown color fades
   2. The volume in the gaseous mixture in the syringe is reduced. (2mks)
      foward reaction is favoured  because pale yellow colour intensifies as brown color fades
4. A student suspected a given sample of water contains sulphate ions. Describe how he can show the presence of the sulphate ions in the water sample. (2mks)
   to the sample add 2/3 drops of acidified Ba(NO₃)₂ / BaCl₂ solution
   a white ppt is formed
5. In the industrial manufacture of nitric (v) acid the first step is catalytic oxidation of ammonia gas.
   1. What is the name of the catalyst used. (1mk)
      platinum / platinum - rhodium
   2. Write the equation for the catalytic oxidation of ammonia gas. (1mk)
      4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(l)
   3. State one use nitric acid. (1mk)
      manufacture of nitrogenous fertilizer / explosives / dyes purification of metals / etching designs on metals
6. Explain why boiling point of ethanol is higher than that of dimethylether. (Relative molecular mass of both of them is 46). (2mks)
   molecules of ethanol are held by hydrogen bonds that are stronger than van der waals that hold molecules of dimethyether
7. When 94.5g of hydrated barium hydroxide Ba(OH)₂.n H₂O were heated to a constant mass, 51.3g of anhydrous barium hydroxide were obtained. Determine the value of n.
   (Ba=137, O=16,H=1) (3mks)
   

   compound	Ba(OH)2	H2O
   mass	51.3	43.2
   R.F.M	171	18
   no.of .moles	0.3	2.4
   mole ratio	1	8

   n = 8
8. Study the diagram below and answer the questions that follow.
   
   
   1. What do Δ H1 and Δ H2 represent (2mks)
      1. Δ H₁ lattice energy
      2. Δ H₂ hydration energy
   2. Give an expression for heat of solution in terms ofΔ H1, ΔH2 and Δ H3. (1mk)
      Δ H₃ = Δ H₁ + Δ H₂
9. 6.84g of aluminium sulphate were dissolved in 300cm3 of water. Calculate the molar concentration of sulphate ions in the solution. (R.M.F=342) (3mks)
   Al₂(SO₄)₃ → 2AL³⁺(aq) + 3SO₄^2-(aq)
   6.84 = 0.02
   342
   Al₂(SO₄)₃ : SO₄^2-
                 1:3
           0.02 : 0.06
   1000 × 0.06
    300
   = 0.2M
10. Study the information given in the table below and answer the questions that follow.
    

    Bond	Bond energy (KJ mol)
    C-H	413
    Br-Br	193
    C-Br	280
    H-Br	365

    1. Calculate the Enthalpy changes for the reaction below (2mks)
       CH₄ (g) + Br₂ (g) → CH₃Br (g) + HBr (g)
       

       B.B	B.F
       (4 × 413) + 193	(3 × 413) + 280 + 365
       - + 1845	- - 1884

       (+ 1845) + (- 1884)
       = -39 kJmol^-
    2. State whether the reaction is exothermic or endothermic. Explain (1mk)
       exothermic - bond formation energy is higher than bond breakage energy
11. A certain mass of a metal E reacted with excess dilute hydrochloric acid at 250C. The volume of hydrogen gas liberated was measured after every 30 seconds. The results were represented as shown in the graph below. (1mk)
    
    
    1. Name one piece of apparatus that may be used to measure the volume of gas liberated. (1mk)
       graduated gas syringe
       graduated gas jar
    2.                      
       1. On the same axis , sketch the curve that would be obtained if the experiment was repeated at 35ºC. (1mk)
       2. Explain the shape of your curve in b( i) above. (2mks)
          increase in temp, increases the kinetic energy. This increases the number of effective collisions per given time, resulting in increase in rate of reaction
12.                          
    1. Why is hydrogen not readily used as a fuel? (1mk)
       it's explosive when mixed with air and ignited
    2. State one uses of hydrogen gas. (1mk)
       manufacture of NH₃/HCl
       hardening of oils
       rocket fuel
13.                    
    1. State Charles’ Law. (1mk)
       the volume of a given fixed mass of gas is directly proportional to its absoulute temperature at constant pressure
    2. A certain mass of a gas occupies 150cm³ at 281K and 109.41kPa. What will be its temperature if its volume is reduced by 16 cm³ at 101.325kPa. (2mks)
       281 × 134 × 101.325 k pa = 232.5 k
       150 × 109.41 k pa
14. 3g of iron reacted with hydrogen chloride gas at S.T.P. Calculate the volume of the hydrogen chloride gas used. (Fe=56, Molar gas volume at s.t.p=22.4dm³) (2mks)
    Fe(s) + 2HCl(g) → FeCl₂(s) + H₂(g)
    ³/₅₆ = 0.0534 moles
    fe:Hcl
    1:2
    0.0534:0.1068
    0.1068 × 22.4dm³
    =2.39dm³
15. Under certain conditions , chlorine gas reacts with sodium hydroxide to form sodium hypochlorite.
    1. Name the conditions under which sodium hydroxide reacts with chlorine to form sodium hypochlorite. (1mk)
       dilute NaOH
       cold NaOH
    2. State one use of sodium hypochlorite . (1mk)
       used for water purification
       bleaching agent
16.                      
    1. Distinguish between isotopes and allotropes (2mks)
       isotopes - atoms of some element with the same proton number but different neuron no.
       allotropes - different forms of an element in the same physical state
    2. An element X has RAM of 69.39. Given that the element has two isotopes of masses 60.15 and 70.15. Calculate the relative abundance of each isotope (3mks)
       69.39 = (x × 60.15) + ((100 - x) × 70.15)
                                100
       x = 7.6%
       100 - x = 92.4%
17. A student has a mixture of anhydrous aluminium chloride and zinc sulphate. Which is the simplest method of separation? (1mk)
    sublimation
18. A student prepared ammonia and bubbled it into a solution of Magnesium sulphate as shown in the diagram below.
    
    
    1. Name any two reactants required for the production of ammonia. (1mk)
       calcium hydroxide
       ammonium chloride
       any ammonium salt and alkali
    2. State the observation in the beaker (1mk)
       white ppt formed
    3. Write ionic equation for the reaction in the beaker (1mk)
       Mg²⁺(aq) + 2OH^-(aq) → Mg(OH)₂(s)
19. The compound HCLO decomposes according to the following equation .
    5HClO(aq) → 2Cl₂(g) + H⁺ (g) + ClO₃^- (aq)+ 2H₂O(l)
    Deduce the oxidation states of chlorine in the following species.
    1. HClO (1mk)
       (+1) + cl + (-2) = 0
       cl = +1
    2. ClO₃^- (1mk)
       cl + 3(-2) = -1
       cl = +5
20. The set-up below was used to prepare dry sample of Oxygen gas
    
    
    1.                      
       1. Complete the diagram to show how the gas was collected (1mk)
       2. Identify the following
          1. Solid H..........sodium peroxide......(1mk)
          2. Solid J...........anhydrous CaCl₂........ (1mk)
    2. Write an equation for the reaction that occurred in the flask between solid H and water. .............. (1mk)
       2Na₂O₂(s) + 2H₂O(l) → 4NaOH(aq) + O₂(g)
21. The table below gives the solubility of salt L and K at 100C and 800C. Solubility in g/100g water
          Salt             At 10ºC          At 80ºC
           L                 60                   75
           K                 20                   32
    When an aqueous mixture containing 80g of L and 10g of K in 100g water at 80ºC was cooled to 10ºC,crystallization occurred.
    1. What is crystallization (1mk)
       process of allowing saturated solutions to cool for crystals to form
    2. Determine the mass of the crystals formed (1mk)
       75 - 60 = 15 + 5 = 20g
       80 - 60 = 20g
    3. Name the method of separation (1mk)
       fractional crystalisation
22. The table below gives elements represented by letters T,U,V,W,X,Y and their atomic numbers . (Letters are not the actual symbols.
    

    Element	T	U	V	W	X	V
    Atomic number	12	13	14	15	16	17

    1.                           
       1. How does the atomic radius of V compare with that of X? Explain. (2mks)
          v is larger than x
          v has a lower nuclear charge than x due to less number of prorons/ due to less effective nuclear charge
       2. Give the formula of the compound that could be formed between U and X. (1mk)
          U₂X₃
    2.                          
       1. Arrange the species T,T^- and T⁺ in increasing order of size. (1mk)
          T⁺, T, T^-
       2. Which of the ions X²⁺ and X^2- is the most stable ? Explain. (2mks)
          X^2-, gains electrons to attain an actet state
23.                                
    1. What would be observed in sulphur IV Oxide is bubbled through acidified potassium. chromate VI (1mk)
       the orange acidified potassium chromate (VI) turns to green
    2. In an experiment, sulphur (IV) Oxide was dissolved in water to form solution M.
       1. State the observation made if a few drops of barium chloride solution immediately added to solution M (1mk)
          white ppt is formed
       2. Identify the spectator ions from the reaction b(i) above (1mk)
          H⁺ and Cl^-
24. Copper-64 has a half life of 12.8days.
    1. What is meant by the term half life (1mk)
       time taken for a given mass of nuclide to decay to half of its original mass
    2. What mass of a copper-64 will be left after 51.2 days starting with 20 g of the isotopes (2mks)
       51.2 = 4
       12.8
       (1/2)⁴ × 20 = 1.25g
    3. Give one use of radioactive isotopes in medicine (1mk)
       destroy cancerous cee/ sterilization of surgical instruments/ monitor growth of bones (any other)
25.                              
    1. Zeolites (Na₂X) is a complex compound used to soften hard water in the ion-exchange methods according to the equation below.
       Ca ²⁺ (aq) +Na₂X (aq) → CaX(s) + 2Na⁺ (aq)
       After sometimes the Zeolites get exhausted and ceases to soften water. Write a reaction to show how Zeolite is regenarated. (1mk)
       CaX(s) + 2NaCl(aq) → CaCl₂ (aq) + Na₂X(s)
26. Name the particle responsible for electrical conductivity on;
    1. Molten magnesium metal (1mk)
    2. Molten magnesium chloride (1mk)
27. Carbon is one of the elements that exhibit allotropy
    1. Define the term allotrophy (1mk)
    2. Name two allotropes of carbon (1mk)
    3. Which allotrope of carbon is a good conductor of electricity. Explain. (2mks)