Chemistry Paper 2 Questions and Answers - Cekana Mock Exams 2023

INSTRUCTIONS TO CANDIDATES

1. Write your name and index number in the spaces provided above
2. Sign and write date of examination in the space provided.
3. All working must be clearly shown where necessary.
4. Mathematical tables and silent electronic calculations may be used
5. Answer all questions in English.

Questions

1. The grid below represents part of the periodic table. Study it and answer the questions that follow. The letters do not represent the actual symbol of elements.
   
   
   1.  
      1. Select elements which belong to the same chemical family (1mark)
      2. Write the formulae of ions for two elements in the same period (1mark)
   2. The first ionization energies of two elements K and M at random are 577kJ/mol and 494kJ/mol.
      1. Write equations for the 1st ionisation energies for elements K and M and indicate their energies (2marks)
      2. Explain the answer in b (i) (1mark)
      3. Write the formula of the compound formed when I and L react (1mark)
      4. Give one use of element L (1mark)
   3.    
      1. How do the reactivity of elements K and L compare? Explain (2marks)
      2. Element L and M form chlorides. Complete the table by writing the formulae of each chloride and state the nature of the solutions (2marks)
         

         Element	Formula of chloride	Nature of chloride solution
         L
         M

      3. The chloride of element M vaporizes easily while its oxide has a high melting point. Explain (2marks)
      4. Which elements forms a trivalent:
         1. Cation (½mark)
         2. Anion (½mark)
2.  
   1. The following is a structure of an organic compound.
      
      1. Which organic series does the compound belong? (1mark)
      2. Give the structures and names of the reactants that form the above compound (2marks)
   2. The table shows structural formula of some organic compounds
      Compound                                                                      Structural formula
      A                                                                                      CH₃CH₂CH₂CH₃
      B                                                                                     CH₃CH₂COOH
      C                                                                                     CH₃CHCH₂
      D                                                                                    CHCCH₃
      E                                                                                    CH₃CH₂CH₂CH₂OH
      1. Give the chemical test that can be used to identify compound C. (1mark)
      2. Compare the boiling points of compound E and A (2marks)
      3. State and explain the observation made when Sodium carbonate is added to compound G. (2marks)
      4. Write an equation to show the reaction between compound E and magnesium metal and give the name of the product formed. (2marks)
      5. The following is a structure of a section of a polymer
         
         1. Draw the structure of the monomer (1mark)
         2. Give the name of the polymer (1mark)
         3. State one use of the polymer. (1mark)
3.  
   1. Dry chlorine gas was passed over heated iron resulting in P. P was dissolved in water resulting in the formation of a solution of P. To a little of the solution P a few drops of Sodium hydroxide were added and solid Q was obtained.
      1. Name substance (2marks)
         1. P –
         2. Q –
      2. Write equations to show how substances P and Q were formed. (2marks)
      3. Name a suitable drying agent for chlorine gas (1mark)
   2. Chlorine burns in dry ammonia gas as shown in the diagram below
      
      1. Identify solid N (1mark)
      2. A colourless and odourless gas is produced. Identify the gas (1mark)
      3. Write the equation for the burning of chlorine in dry ammonia gas (1mark)
      4. 3g of divalent metal X (atomic mass=24) react with dilute hydrochloric acid.
         Calculate the volume of hydrogen gas produced at STP. (X=12, H=1 molar gas volume at STP=22.4dm3 (3marks)
      5. When excess chlorine was bubbled into hot concentrated sodium hydroxide, the following reaction occurred.
         3Cl_2(g)+6NaOH_(aq)→NaCLO_3(aq)+5NaCL_(aq)+3H₂O_(g)
         In which product did chlorine under oxidation. Explain (2marks)
4.  
   1. Aqueous potassium sulphate was electrolysed using platinum electrodes in a cell.
      1. Shows the product formed at the anode and cathode with the help of an equation (2marks)
         Anode
         Cathode
      2. Why would it not be advisable to electrolyse aqueous potassium sulphate using potassium metal electrodes? (1mark)
   2. Use the standard electrode potential for elements A, B, C, D and F given below to answer that follow;
      
      1. Which element is likely to be hydrogen? Explain (1mark)
      2. What is the Eo value of the strongest reducing agent? (1mark)
      3. In the space provided draw a labelled diagram of the electrochemical cell that would be formed when the half cells of elements B and D are combined. (3marks)
      4. Calculate the Eo value of the electrochemical cell constructed in (III) above (1mark)
   3. During electrolysis of aqueous copper (ii) sulphate using copper electrodes, a current of 0.2 amperes was passed through the cell for 5 hours.
      1. Write an ionic equation for the reaction that took place at the anode (1mark)
      2. Determine the change in mass of the anode which occurred as a result of electrolysis (1mark)
5.      
   1. The diagram below represents the electrolytic cell used for extraction of aluminium.
      
      1. Write the formula of the main ore in which aluminium is extracted (1mark)
      2. Explain why the ore is first dissolved in hot concentrated sodium hydroxide. (2maks)
      3. Write equations for the reactions that takes place at
         1. The anode (1mark)
         2. The cathode (1mark)
      4. State why the graphite lining is used as the cathode (1mark)
      5. Give two reasons for mixing aluminium oxide with cryolite in the electrolyte cell (2marks)
   2. Aluminium is resistant to corrosion while iron corrodes very fast.
      1. Why is aluminium not used to make window frames? (1mark)
      2. State one reason why galvanised iron is resistant to corrosion even when the protective surface of zinc is broken? (1mark)
      3. Write an equation to show the reaction between aluminium and concentrated sodium hydroxide solution (1mark)
      4. Explain how one word obtain aluminium oxide given the following; aluminium chloride solid, sodium hydroxide solid and distilled water. (3marks)
6.  
   1. What are isotopes (1mark)
   2. The table below shows the isotopic composition of naturally occurring neon
      

      particle	2210Ne	2110Ne	2010Ne
      %abundance	9.2	0.3	90.5

      
      
      1. Which is the most stable isotope of Neon? Explain (2marks)
      2. Calculate the relative mass of Neon (2marks)
      3. Balance the nuclear equation below
         ¹⁴₆C→¹⁴₇N+__________________________ (1mark)
      4. Distinguish between nuclear fission and nuclear fusion. (1mark)
   3. Bismuth undergoes radioactive decay. The table below shows the mass of Bismuth remaining at different times.
      

      Time (min)	0	6	12	22	38	62	100
      mass of Bismuth remaining (g)	50	41.5	32.5	23	14.5	6	1.5

      
      
      
      1. Plot a graph of mass of bismuth remaining (vertical axis) against time. (3marks)
      2. From the graph determine
         1. Mass of Bismuth remaining after 30 minutes (1mark)
         2. The half life of bismuth (1mark)
         3. What would happen to the rate of disintegration of bismuth if the temperature is increased? Explain (2marks)
   4. State one application of radio isotopes in agriculture (1mark)

MARKING SCHEME

1.  
   1.  
      1. GKJ
      2. 
   2.  
      1. K_(g) → K⁺_(g) + e^-                  494kJ/mol
      2. K_(s) → M³⁺_(g) + 3e^-              577kJ/mol
      3. L²I³
         L³L² 
      4. Used in the manufacture of calcium oxide which is added to soil to raise pH.
         Used to manufacture calcium carbonate used in extraction of iron
         Used to manufacture calcium carbonate which is mixed with oil to make putty
   3.  
      1. K is more reactive than L . K has only the first ionization energy while L has two ionization energies
      2. LCl2
         MCl3 
      3. Chloride of M has a simple molecular structure with weak vandawaal forces that require little energy to break while oxide of M has strong ionic bond with giant ionic structure
2.  
   1.  
      1. Esters
      2. 
   2.  
      1.  
         • decolorizes red brown bromine water
         • decolorizes purple acidic KMnO₄
      2. E has a high boiling point than A. E contains hydrogen bond that requires high energy to break than A with weak van dar wall forces attraction between molecules
      3. Effervescence because of production of carbon IV oxide
      4. Magnesium ethoxide
      5.  
         1. 
         2. methyl-2-methylpropenoate/perspex
         3. substitute for glass in aircraft and vehicle parts
3.  
   1.  
      1.  
         1. I P- iron(iii) chloride
         2. Q- iron (iii) hydroxide
      2. 2Fe(s) + 3Cl₂(g) → 2FeCl₃(s)
         FeCl_3(aq) + 3NaOH_(aq) → Fe(OH)₃(s) + NaCl_(aq) 
      3. conc H₂SO₄/Anhydrous CaCl₂
   2.  
      1. Ammonium chloride
         Accept NH4Cl
      2. Nitrogen
      3. 8NH_3(g)
      4. X_(s) + 2HCl_(aq) → XCl_(aq) + H2_(g) 
         24g of X = 1mole
         3g = ?
         1 x 3  = 0.125 mole
          24
         mole ratio 1:1
         1mole of H₂ = 0.125 
         1mole of H₂ = 24dm³ 
         0.125 mole - ?
         (^{0.125 x 24} / ₁ ) = 2.8dm³
      5. NaClO₃
         Oxidation number of chlorine increases from 0 to +5
         Accept calculation
      6. L_A = 55cm           M_A (M_HCL) = 36.5
         L_B = 44cm           M_B (M_x) = ?
         ^LHCL/_Lx =  √(^Mx/_MHCl)
         (⁵⁵/₄₄)² =  Mx²
                        36.5
         √(mx²) = √ (55²/44² x 36.5)
         Mx = 57.03
         = 57
4.  
   1.  
      1. Anode
         4OH_(aq) → 2H₂ + O_(l)O2_(g) + 4e^-
         Cathode
         4H⁺ _(aq) + 4e^-
      2. The anode would dissolve in to solution and may cause a serious explosion
   2.  
      1. C-It has E^θof 0.00v
      2. +2.87V
      3. 
      4. + 238 + 0.34 = + 2.72v
   3.  
      1. Cu_(s) → Cu²⁺_(aq) + 2e^-
      2. 
         c = 0.2 x 60 x 5
         = 3600C
         1mol = IF = 96500 = 63.5
         3600C = ?
            3600       x  63.5
         96500 x 2
         = 1.184
         = 1.18g
5.  
   1.  
      1. Al₂O₃ • 2H₂O
      2. • To remove impurities (iron and titanium)
         • To concentrate the ore
      3.  
         1. Anode
            2O²_(l) → O_2(g) + 4e^-
         2. Cathode
            Al³⁺_(l) + 3e^- → Al_(l)
      4. Graphite is an inert electron and prevents the formation of an alloy
      5. • To lower the M.P of the electrolyte
         • To improve the electrical conductivity of the electrolyte
   2.  
      1. Aluminum is more expensive than iron.
      2. Zinc is more reactive than iron. It loses electrons more easily than iton, thus zinc corrodes forming Zn(OH)2 which blocks the scratch preventing further corrosion.
      3. 2Al_(s) + 2NaOH_(aq) + 2H₂O → 2NaAl_2(aq) + 3H_2(g)
      4.  
         • Add distilled water to aluminum chloride and stir to dissolve
         • In an separate beaker add distilled water to sodium hydroxide and stir to dissolve.
         • Mix the two solutions
         • Filter to obtain aluminium oxide as the residue.
         • Wash the residue with distilled water and dry between filter paper.
6.  
   1. Isotopes are atoms of the same element with the same atomic number but different mass number.
   2.  
      1. ²⁰₁₀Ne
         It has the highest percentage abundance
      2. RAM =
         22 x 9.2  +  21 x 0.3  +  20 x 90.5  =  20.187 
           100             100             100
      3. ¹⁴₆ C  →  ¹⁴₇ N+ ⁰_-1 e^-
      4. Nuclear fusion id the splitting of an atomic nuclear into two fragment about half the size of the original nucleus together with smaller particles wherels nuclear fusion is a process of joining two light nuclear to form a heavy one
   3.  
      1. 
         I: 18.5g✔1 ±0.2
         II: 20min✔1 ±0.2
         III No heat  - radioactive decay is not affected by changing in temperature
   4.  
      • Monitoring photosynthesis
      • Absorption or phosphate fertilizer
      • Used to trace the route of photosynthesis through the animals body plant and its fine deposition.
        Any one application