Chemistry Paper 2 Questions and Answers - Chogoria Murugi Zone Pre Mock Exams 2023

INSTRUCTIONS TO CANDIDATES. 

• Answer ALL the questions in the spaces provided in the question paper.
• KNEC Mathematical tables and electronic calculators may be used for calculations.
• All working MUST be clearly shown where necessary.
• Candidates should answer the questions in English.

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 symbols of the elements.
        
   
   1. State the elements that can form ions with a charge of -1. Give a reason for your answer.  (2 marks)
   2. What type of structure exists in the oxide of A. Give a reason for your answer? (1 mark)
   3. How does the reactivity of I compare with that of H. Explain. (1 mark)
   4. The oxide of D has a low melting point than the oxide of element C. Explain. (1 mark)
   5. With a reason choose the most;
      1. Electropositive element (2 marks)
      2. Electronegative element (2 marks)
   6. Compare the atomic radius of;
      1. B and H (1 mark)
      2. D and E (1 mark)
   7. State and explain the observations made when concentrated Nitric (V) acid is added to turnings of copper. (2 marks)
2. The flow chart below shows how nitric (v) acid is produced on a large scale. Study it and answer the questions that follow.
          
   
   1. State the functions of:
      1. Purifier (1mark)
      2. Heat exchanger (1mark)
   2. Identify
      1. Gas A (½ mark)
      2. Gas B (½ mark)
      3. Catalyst C (½mark)
   3. Write equations for the reaction that take place;
      1. in catalytic chamber. (1mark)
      2. in absorption tower. (1mark)
   4. Calculate the molarity of the commercial nitric (v) acid, given that it is 68% pure and has a density of 1.42g/cm³ . (N=14, H=1,)=16) (3mark)
   5.  
      1. State the observation made when concentrated nitric (v) acid is added to acidified sulphur powder and warmed. (1mark)
      2. Give a reason for the answer given in c (i) above. (1mark)
3. Study the flow chart below starting from iron metal.
          
   
   1. Name gases (1½mk )
      1. D……….……………………………………………………………………………………
      2. L……….…………………………………………………………………………………....
      3. V……….…………………………………………………………………………….............
   2. Identify the following substances. (2 ½mk)
      1. Compound B……….……………………………………………………………………….
      2. Compound T……….……………………………………………………………………….
      3. Solid A……….……………………………………………………………………………..
      4. Solid V……….……………………………………………………………………………..
      5. Solid X……….…………………………………………………………………...................
   3. What name is given to the reaction in step 2? (½mk )
   4. State the colour of solid X (½mk)
   5. Write balanced equations for the reactions that occurred in:- (2mks)
      1. Step 1……….…………………………………………………………………………………...
      2. Step 5……….…………………………………………………………………………………...
   6. What property of hydrogen peroxide (H₂O₂ ) is indicated in step 7 of the flow chart? (1mk)
4. The set up below was used to prepare hydrogen chloride gas and salt T.
   
   
   1.  
      1. Name the following
         1. Liquid M (½ mark)
         2. Gas V (½ mark)
      2. Write the formula of Salt T (1mark)
   2. Write balanced chemical equations for reactions that occur at
      1. Flask I (1mark)
      2. Combustion tube. (1mark)
   3. Name the process that formed salt T as shown in the diagram. (1mark)
   4. Sulphuric (VI) acid is used as a drying agent in this experiment. Explain why calcium oxide is unsuitable for the same purpose in this reaction (2marks)
   5. The water in the trough was found to have a pH of 2.0 at the end of the experiment. Explain. (1mark)
   6. Calculate the mass of salt T formed if 480cm³ of hydrogen chloride gas measured at r.t.p was reacted with aluminium powder. (Al=27, Cl = 35.5, MGV=24dm³ ) (2marks)
   7. In the space provided below, draw a well labelled diagram showing how you would dissolve hydrogen chloride gas in water. (1mark)
   8. A solution of hydrogen chloride in methylbenzene does not react with carbonates. However, on adding water and then shaking the resulting mixture, there is vigorous effervescence. Explain the above observation. (2marks)
   9. Using equation, state the observation made when a gas jar containing hydrogen chloride gas is opened near an open bottle of liquid ammonia. (1mark)
5.  
   1. Name each of the processes described below which takes place when salts are exposed to air for sometime.
      1. Anhydrous copper (II) sulphate becomes wet. (1 mark)
      2. Common table salt forms an aqueous solution (1 mark)
      3. Fresh crystals of sodium carbonate Na₂CO₃.10H₂O becomes covered with white powder of formula Na₂CO₃.H₂O.   (1mark)
   2. Write the formula of the complex ion formed in each of the reactions described below.
      1. Zinc metal dissolves in hot potassium hydroxide solution (1mark)
      2. Copper hydroxide dissolves in excess ammonia solution (1mark)
   3. A hydrated salt has the following composition by mass. Iron 20.2%, Oxygen 23%, Sulphur 11.5% and water 45.3%. Its relative formula mass is 278. Determine the formula of the hydrated salt. (Fe = 56, S = 32, O = 16, H = 1) (3marks)
   4. Describe how a solid sample of lead (II) chloride can be prepared using the following reagents:- dilute nitric acid, dilute hydrochloric acid and lead carbonate. (3marks)
6. A student set-up the apparatus shown below in order to determine the percentage by volume of oxygen in the air. Study it and answer the questions that follow.
        
   
   1.  
      1. State one observations made in the measuring cylinder at the start of the experiment. Explain. (2mks)
      2. The PH of the contents of the beaker at the end of the experiment was found to be 4.
         Explain the observation. (2marks)
      3. The volume of air in the measuring cylinder at the end f the experiment was measured. study the data given below and answer the questions that follow.
         • Volume of air at start of the experiment = 30.65 cm 3
         • Volume of air at the end of the experiment = 24.28 cm 3
           Determine the percentage volume of oxygen in the air. (2marks)
   2. State and explain the observation made when a mixture of zinc powder and copper (II) oxide is heated in a crucible. (2marks)
   3. State two air pollutants produced by motor vehicles. (1mark)
   4. A group of students burnt a piece of magnesium ribbon in air and its ash collected in a Petri dish. The ash was found to comprise of magnesium Oxide and Magnesium nitride
      1. Write an equation for the reaction leading to formation of the magnesium nitride. (1mk)
      2. A little water was added to the products in the Petri dish. State and explain the observation made. (2mks)
      3. A piece of blue litmus paper was dipped into the solution formed in (b) above. State the observation made. (1mk)
7.  
   1. A compound has an empirical formula C₃H₆O and a relative formula mass of 116.
      1. Determine its molecular formula. (H =1, C = 12, O =16) (2 marks)
      2. Calculate the percentage composition of carbon by mass in the compound. (1 mark)
   2. Study the scheme below and answer the questions that follow.
                   
      
      1. State the conditions for process in step V. (1 mark)
      2. Name the reaction represented by process.
         1. Z (1 mark)
         2. L (1mark)
         3. E 1 mark)
         4. N (1 mark)
      3. Draw and name the structure of the substance.
         1. V (1 mark)
         2. P (1 mark)
         3. U (1 mark)

MARKING SCHEME

1.  
   1. H✓½  I✓½  group VII✓½ gains one electron✓½     to form ion
   2. Giant ionic structure✓½ - A is a metal, oxygen is a non-metal hence form ionically, bounded compound✓½
   3. H ✓ is more reactive than I . H is more ✓½ electronegative element
   4. The oxide of D is covalently bounded hence has simple molecular structure ✓½and weak van der waals forces while that of C has ionic bond, hence giant ionic structure ✓½
   5.  
      1. A ✓½ the most electropositive element the only element in group I✓½ i.e. metallic element          in group I has the highest ability to ✓½ loose      valence electron from ion. Due to weakest          electrostatic ✓½ forces
      2. H ✓½is the most electronegative element. the only element in group VII✓½ which has the       shortest/shorter✓½ atomic radius, has the highest✓½ ability to gain electron to form iron✓½
   6.  
      1. B has larger✓½ atomic radius than H, B belong  to group II. B has less charge nuclear charge✓½            than H:
      2. E has large✓½ atomic radius than D for E has 3 energy levels i.e. belongs in third period while     D has✓½ two energy levels, in 2^nd period.          
   7. The brown ✓½ solid of copper changes to   blue½ solution of copper (II) nitrate solution brown gas ✓½ of nitrogen (IV) oxide gas formed. The copper metal is oxidized by conc HNO₃ to Cu²⁺ while the acid is reduced to NO₂ gas and water
2.  
   1.  
      1. Purifies – removes dust particles and other impurities that would otherwise poison  the catalyst. √ (½)
      2. Heat exchanger – Heats the ammonia – air mixture reactions from the compressor while it cools the hot gaseous products from the catalytic chamber√ (½)
   2.  
      1. Gas A – Ammonia /NH₃ √( ½)
      2. Gas B – Nitrogen (II) Oxide /NO √ (½)
      3. Catalyst C– Platinum – rhodium √ (½)
   3.  
      1. 4NH_3(g) + 5O_2(g) → 4NO_(g) + 6H₂O_{(g)    ✓} 1
      2. 2NO₂ (g) + H₂O (l) → HNO_{3 (aq)} + HNO_{2 (aq)  ✓}1
   4. RFM HNO₃  = 1 + 14 + 48  = 63 √( ½)
      1cm³         (1.42 x 68/100) √ (½) g of HNO₃ = 0.9656g
       1cm³   →           (1.42 x 68 ) √ (½) moles of HNO₃ = 0.015326 moles  √ (½)
                                    63    100
      ∴  1000     1000   x 1.42 x  68  √ (½)
                           1          63     100
                            = 15.33 M (½) total 3 mk
   5.  
      1. Effervescence of red / brown gas / fumes are produced(√ 1)      
      2. Hot conc. HNO₃ oxidizes sulphur to sulphuric (VI) acid and itself is reduced to nitrogen (IV) oxide (√ 1). Or      
         S(s)   + 6HNO_{3 (aq)} → H₂SO_{4 (aq)}   + 6NO_{2 (g)}    + 2H₂O _(l)            
3.  
   1.  
      1. Gas D – Sulphur (IV) Oxide // Sulphure dioxide ✓ ½
      2. Gas L – Hydrogen Sulphide  ✓ ½                                                
      3. Gas V – Hydrogen gas✓½                                 Accept – name only 1½mk
   2.  
      1. Compound B – Iron (III) Chloride // FeCl₃ ✓½
      2. Compound T – Iron (II) Sulphide // FeS  ✓  ½        
      3. Solid A – Iron (III) oxide // Fe₂O₃   ✓½
      4. Solid V – Iron (III) hydroxide //  Fe(OH)₃ ✓½                                          
      5. Solid X – Iron (II) hydroxide // Fe(OH)₂ ✓   ½
         Accept – name  or formula. Rej if name and formula do not tally 2½mk
   3. Rusting  ✓ 1                                                                                                   1mk
   4. Dirty green/green  ✓1
   5.  
      1. Step 1 2Fe_(s)  +  3Cl_2(g)     2FeCl₃ ✓1 1mk
      2. Step 5 FeS_(s)    +    2HCl_2(ag)  2FeCl_2(s)    + H₂ S_(g)✓ 1                      
         Deny ½ if state symbols are wrong or missing.
   6. An oxidizing agent ✓1                                                                         1mk
4.  
   1.  
      1.  
         1. Conc. Sulphuric (VI) acid ✓ ½ / sulphuric acid                                      Acc. formula
         2. Hydrogen gas // H₂✓ ½
      2. AlCl₃ ✓ 1                                                                
   2.  
      1. NaCl_(s)    +  H₂SO_4(l)    NaHSO_4(aq)  + HCl_(g)  ✓1                    1 mk or                                                                                     Deny ½ if state symbols wrong or missing
         H₂SO_4(l)  +   Cl^-_(aq)       H₂SO_4(aq)  +  HCl_(g)
      2.  2Al_(s) +  6HCl _(g)       2AlCl_3(s)     +  3H_2(g)   ✓1                                             1 mk
   3. Sublimation ✓ ½
   4. Gas is acidic ✓1 therefore reacts ✓ ½  with the basic ✓½ calcium oxide      2mk         
   5. Unreacted HCl ✓½  gas dissolves forming a strong acidic ✓½   solution     
      acc- correct equation 1mk
   6. moles of HCL =   480    = 0.02 mols ✓½
                                 24000
      Moles ratio  HCl : AlCl₃ is 3:1
      Moles of AlCl₃ =   0.02  x 1/3
                               = 0.0066 moles         ✓ ½                                                     2mk
      RFM ✓ ½   = 133.5
      Mass of T = 0.0066 x 133.5 = 0.8811 g ✓ ½  
   7.   
       1mk
   8. Hydrogen Chloride does not dissociate into ions in methylbenzene (it exists in molecular form). ✓ On addition of water, HCl dissociates ✓ and H⁺_(aq)  reacts with carbonates evolving Carbon (IV) Oxide gas (CO_{2 (g)})  
   9. HCl_{(g )}   + NH_3(g)  NH₄Cl _(s)   ✓ ½                                                       1mk
                                                 White Fumes ✓ ½                                                                       
      The observation must be mentioned / indicated
5.  
   1.  
      1. Hygroscopy
      2. Deliquescence
      3. efflorescence
   2.  
      1. [(Zn(OH)₄)]  ^2+ ✓1mk                  
      2. [CU(OH)4]²⁺          √1
   3.  
      

      element	Fe	S	O	H2O
      mass	20.2	11.5	23.0	45.3
      Ram	56	32	16	18
      mols	0.36	0.36	1.44	2.52✓1mk
      Mole ratio	1	1	4	7

      Empirical formula is FeSO₄.7H₂O
      n(FeSO₄.7H₂O)=278
      278n=278
      n=1✓1mk
      Formula FeSO₄.7H₂O✓1mk
   4.  
      • Add excess lead carbonate to dilute HNO₃  acid ✓ 1mk    
      • Filter ✓¹/₂mk
      • Add excess dilute HCl to the filtrate ✓¹/₂mk
      • Filter the residue is lead(ii) chloride ✓¹/₂mk
      • Rinse residue with distilled water and dry between filter paper to obtain solid PbCl₂✓¹/₂mk
6.  
   1.  
      1. phosphorous smolders ✓1
         Its reaction with air is exothermic ✓1
      2. phosphorous (iii)oxide formed is an acidic oxide which dissolves in water to form phosphoric oxide.  phosphoric(iii) acid ✓1
      3. volume of air used = 30.65 – 24. 28 = 6.37 cm³
         percentage volume = 6.37/30.65 x 100 = 20.78%✓1
   2.  
      • black powder changes to red brown bead and White ash formed ✓1
      • Zn reduces CuO to copper metal and Zn is oxidized to MgO✓1
   3.  
      • carbon (II) oxide  ✓1
      • Sulphuric (IV) oxide ✓1
      • Nitrogen (IV) oxide
      • Carbon (iv) oxide
   4.  
      1. 3Mg(s) + N₂(g)       Mg₃N₂(s)
      2. a colourless gas with a characteristic pungent smell is produced. Magnesium nitride is hydrolyzed by water producing ammonia gas.
      3. blue litmus paper remained blue
7.  
   1.  
      1. R.F.M of E.M.F = 58
         R.F.M    = 116
         n =      RFM       = 116 ✓½ = 1.7 =  2✓½
               RFM of EMp    58
         Molecular formula = (Emp formula) x n
         =  (C₃H₆O)x ✓½ = C₆H₁₂O₂ ✓½
      2. % of C = mass of c × 100%
                            RFM
         = 3 × 12 × 100 = 36  × 100 ✓½ = 31.03%✓½
               116               116
   2.  
      1. few drops of conc.sulphuric acid✓1
      2.  
         1. Z  -self-addition polymerisation.             Reject polymerisation
         2. L  -   Hydrolysis✓1
         3. E  -Oxidation of ethanol✓1 by acidified KMnO₄
         4. N  - Esterification✓1      
      3.  
         1.  
             ✓½                                                  
            1, 2 – difluoroethane✓½         
         2.  
            ✓½
             Ethanoic acid ✓½
         3.  
            ✓½
            Ethylethanoate ✓½