Chemistry Paper 2 Questions and Answers - Bondo Mocks 2021 Exams

QUESTIONS

1.      
   1. The table below shows the ions of elements W, X, Y, Z, and their electron arrangement.
      The letters do not represent the actual symbols of the element.
      

      Ion	Electron configuration
      W-	2.8.8
      X2+	2.8.8
      Y3+	2.8
      Z2-	2.8

      1. Which two elements belong to the same period? Give a reason. (2 marks)
      2. In which group of the periodic table does Y belong? (1 mark)
      3. Write the formula of the compound formed between W and X (1 mark)
      4. What type of bond is formed between W and X. Explain. (2 marks)
   2.        
      1. What is a coordinate bond? (1 mark)
      2. Draw a dot (•) cross (×) diagram to show bonding in the Ammonium ion (NH4+)
         (N = 7, H = 1) (2 marks)
   3. Aluminum chloride and sodium chloride are both chlorides of period 3 elements.
      Use this information to explain the following observations.
      1. A solution of A1CI₃ in water turns blue litmus paper red while that of sodium chloride does not (1 mark)
      2. The melting point of sodium chloride (801°C) is higher than that of AlC1₃ (180°C). (1 mark)
2.        
   1. Give the names of the following compounds:
      1. CH₃COOCH₂CH₃ (1 mark)
      2. CH₃CHCHCH₂CH₃ (1 mark)
   2. Study the information in the table below ad answer the questions that follow.
      

      No. of carbon atoms per molecule	Relative molecular mass of hydrogen
      2	28
      3	42
      4	56

      1. Write the general formula of the hydrocarbons in the table. (1 mark)
      2. Predict the relative molecular mass of the hydrocarbon with 5 carbon atoms. (1 mark)
      3. Determine the molecular formula of the hydrocarbon in ii) above and draw its structural formula. (2 marks)
   3. Study the scheme given below and answer questions that follow.
      
      1. Name the reagent used in
         Step I (1 mark)
         Step II (1 mark)
         Step III (1 mark)
      2. Write an equation for complete combustion of CH CH (1 mark)
      3. Explain one disadvantage of the continued use of items in step III. (1 mark)
3.      
   1. The solubilities of potassium nitrate and potassium bromide at different temperatures was determined. The following data was obtained.
      

      Temperature ºC		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

      1. Plot a graph of solubility against temperature for both salts on the same axis (3 marks)
         
      2. What was the solubility of each salt at 65ºC (1 mark)
      3. 100g of a saturated solution of potassium nitrate at 70ºC was cooled to 20ºC. What mass of the salt will be crystallized? (2 marks)
   2. Study the flow chart below and answer the questions that follow.
      
      1. Write an equation for the formation of solid A and gas B. (1 mark)
      2. Name:
         Solution C …………………………………………………………...…… (1 mark)
         Solid D ………………………………………………………….………… (1 mark)
   3. Write the formula of the complex ion in solution E. (1 mark)
4.        
   1. Study the flow chart below and answer the questions that follow.
      Residue V was yellow when hot and white when cold. Identify:
      1. White precipitate I. (1 mark)
      2. Solution II. (1 mark)
      3. Residue V. (1 mark)
      4. Write an ionic equation for the reaction of solution II with Pb(NO3)2 (aq) (1 mark)
      5. Write observations that would be made when ammonia solution is added drop-wise till in excess to the colourless solution II (l mark)
   2. The diagram below represents a set-up for large scale manufacture hydrochloric acid. Study it and answer the questions that follow:
      
      1. Name substance X. (1 mark)
      2. What is the purpose of glass beads? (1 mark)
      3. Give one source of substance X used in the above process. (1 mark)
      4. Give two uses of hydrochloric acid. (2 marks)
   4. The table below shows the ammeter readings obtained when two different electrolytes the same concentration was tested.
      

      Electrolyte	Ammeter reading (Amps)
      Hydrochloric acid	4.0
      Ethanoic acid	1.2

      Why does Ethanoic acid give a lower ammeter reading? Explain your answer (2 marks)
5. The figure below shows parts of Le’Clanche cell (dry cell).
   
   1. Name:
      1. Substance D (1 mark)
      2. Mixture B (1 mark)
      3. Electrolyte C (1 mark)
   2. In the cell, the electrolyte is a paste. Explain. (1 mark)
   3. The following reaction occurs when the cell is in use.
      Zn(s) + 2NH₄+_(aq) →MnO₂ → Zn²⁺_(aq) + 2NH_3(aq)+ H₂O_(l)
      Given that:
      Zn²⁺_(aq) + 2e- → Zn(s)       E^Ф = -0.76V
      2NH+_(aq) + 2e- →MnO₂→ 2NH3(g) + _H2O(l)    E^Ф = +0.74V
      Calculate the e.m.f. of the cell. (2 marks)
   4. Use the standard reduction electrode potentials given below to answer the questions that follow.
      Zn²⁺_(aq) + 2e- → Zn(s) E^Ф = -0.76V
      Pb²⁺_(aq) + 2e- → Pb(s) E^Ф = -0.13V
      Cu²⁺_(aq) + 2e- → Cu(s) E^Ф = +0.34V
      Ag²⁺_(aq) + 2e- → Ag(s) EФE^Ф = +0.80V
      The metal copper, zinc, silver and lead were placed in different solutions as shown:
      

      Metal	Metal ion	Reaction / No reaction
      Cu	Ag2+(aq)
      Zn	Cu2+(aq)
      Ag	Pb2+(aq)
      Pb	Zn2+(aq)

      1. Indicate in the table with a tick (√) where a reaction occurs and a cross (×) where no reaction occurs. (2 marks)
      2. Identify the strongest reducing agent. (1 mark)
   5.        
      1. Draw a well labeled diagram of the electrochemical cell when copper and magnesium half cells are connected. (3 marks)
      2. On the diagram you have drawn in e i) above, label the anode and the cathode and show the direction of flow of electrons. (2 marks)
6.          
   1. The set up below is used to prepare nitric acid
      
      1. 1. Name the reagents in mixture X (1 mark)
         2. Write an equation for the reaction which takes place in the glass retort (1 mark)
         3. Explain the reason why the apparatus used is all glass and why heating should be gentle as possible. (2 marks)
   2. Study the flow chart below and answer the questions that follow.
      
      1. Name element M. (l mark)
      2. Why is it necessary to use excess air in step 4? (1 mark)
      3. Identify gas Q (l mark)
      4. Write an equation for the reaction in step 7 (l mark)
      5. Give one use of ammonium nitrate. (l mark)
   3. Ammonia can be formed by the reaction shown below
      N_2(g) + 3H_2(g) ⇌  2NH_3(g) ; ∆H = - 92kJ/mol
      State and explain what happens if:
      1. The volume of the system is increased (1 mark)
      2. Cold water is poured over the system (1 mark)
7. In an experiment to determine the heat of combustion of compound X, a pupil used heat from the burning compound of X to heat 100cm³ of water in a beaker. He obtained the following results:
   Volume of water in the beaker = 100cm³
   Initial temperature of water = 17ºC
   Final temperature of water = 42ºC
   Initial mass of burner + compound X = 10.5g
   Final mass of burner + compound X = 10.2g.
   1. Determine the mass of the compound burnt? (1 mark)
   2. Calculate the rise in temperature? (1 mark)
   3. Determine the amount of heat produced by the compound (2 marks)
      (specific heat capacity 4200Jg-1K-1, density of H₂O = 1g/cm³)
   4. Calculate the molar heat of combustions of compound X (2 marks)
      (R.M.M. of X = 256)
   5. Use the following thermochemical equations below to answer the questions that follow.
      C₂H₆(g) + ⁷/₂O_2(g) → 2CO_2(g)+ 3H₂O (s) ∆H1, = -1560kJmol-1
      C (graphite) + O_2(g) → CO_2(g) ∆H₂ = - 394 kJ mol-1
      H_2(g) + ½ O_2(g) → H₂O(l)   ∆H3 = - 286 kJ mol-1
      1. Calculate the molar enthalpy of combustion of C₂H₆. (2 marks)
      2. Draw an energy level diagram for the reaction represented by the first equation above (3 marks)

MARKING SCHEME

1.      
   1.      
      1. W and Y
         Have three energy levels;
      2. Group III
      3. XW₂ 
      4. Ionic bond;
         There is complete transfer of 2 electrons from X to W
   2.      
      1. Type of bond in which the shared pair of electrons forming the bond is contibuted by only one of the atoms forming the bond
      2.        
         
   3.          
      1. AlCl₃ is hydrolised in water to form HCl and Al(OH)₃, while NaCl is not hydrated; HCl is acidic
      2. NaCl has a giant ionic structure with stronger ionic bonds while AlCl₃ has simple udecular structure with weaker intermolecular forces
2.        
   1.      
      1. Ethylethanoate
      2. Pent-2-ene
   2.      
      1. CnH₂n
      2. 70
      3. CH₃CH₂CH₂CHCH₂ 
         
   3.        
      1. Hydrogen
         Hydrogen Chloride
         Chloroethene
      2. 2C₂H₂(g) + 5O_2(g) 4CO_2(g) + 2H₂O_(I)
      3. Pollute the environment as they do not decompose easily (They are non-biodegradable) - cannot be digested by microorganisms
3.        
   1.      
      1.          
         
      2. KBr - 87g/100g of H₂O
         KNO3 - 120g/100g of H₂O
      3. 70ºC → 135g (135-26)g
         20ºC → 26g = 109g
   2.      
      1. CuCO_3(s) → CuO(s) + CO₂(g)
      2. Copper(II) Chloride
         Copper(II) hydroxide
   3.          
      
4.          
   1.           
      1.      
         1. Zinc hydroxide, Zn(OH)₂
         2. ZnCl₂
         3. ZnO
      2. Pb2+(aq) + 2Cl-(aq) → PbCl2(s)
      3. White precipitate that dissolves in excess NH_3(aq) to form a colourless solution
   2.      
      1. Dry Hydrogen gas
      2. Increase surface area over which HCl gas dissolves in water
      3. Cracking of long chain hydrocarbons;
         Reacting uethane gas with steam;
      4. Sewage treatment;
         Treatment of water
         Removing rust from metal;
         Making dyes, drugs & photographic materials
   3. Ethanoic acid is a weak acid;
      It dissociates partially to yield few ions hence low ammeter reading
5.      
   1.        
      1. Carbon(graphite) rod
      2. Powdered carbon and maganese(iv) oxide
      3. Ammonium chloride and zinc chloride paste
   2. Solid NH₄Cl is a poor electrolyte (no free ions)
   3. E^θ_cell = E_Red - E_oxi
      = {(0.76) - (-0.76)}
      0.74 + 0.76
      = +1.5V
   4.        
      1.        
         

         Metal	Metal ion	Reaction / No reaction
         Cu	Ag2+(aq)	√
         Zn	Cu2+(aq)	√
         Ag	Pb2+(aq)	X
         Pb	Zn2+(aq)	X

      2. Zn
   5.        
      
6.             
   1.                 
      1. Potassium nitrate
         Conc sulphuric(vi) acid
      2. KNO_3(s) + H₂SO_4(I) → KHSO_4(aq) + HNO_3(aq)
      3. HNO₃ attacks rubber and cork connections;
         Heating should be gentle to minimize thermal decomposition of HNO3
   2.      
      1. Hydrogen
      2. To ensure all ammonia is converted to nitrogen(II) oxide
      3. NO, nitrogen(II) oxide
      4. HNO₃(aq) + NH₃(aq) → NH4NO_3(aq)
      5. As a nitrogenous fertilizer
   3.        
      1. Pressure decreases and less ammonia yield i.e equilibrium shifts to the left hand side
      2. More yield of Ammonia which is favored by decrease in temperature
7.        
   1.        
      1. 10.5 - 10.2 = 0.3g
      2. (42 - 17)ºC
         = 25ºC
      3. ΔH = MCT
         = 100 x 4200 x 25
         = 1.05 x 10⁷J
      4. Moles = ^Mass/_RMM  
          = ^0.3/₂₅₆ = 0.001171moles
         0.001171 - 1.05 x 10⁷J
         1.07 x 10⁷ = -8.96 x 10⁹Jmol
         0.001171
   2.        
      1. 2C(s) + 3H2(g) C₂H6(g) 
         2CO_2(g) + 3H₂O
         Hf = 2(-394) + 3(-286) - (-1560)
         = -1646 + 1560
         = -86kJ/mol
      2.