Chemistry Paper 1 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. An element Y has the electronic configuration 2.8.5
   1. Identify its period. (1mk)
   2. Write a formula of the most stable anion formed when Y ionizes.    (1mk)
   3. Explain the differences between the atomic radius of element Y and its ionic radius.   (2mks)
2. The table below shows tests carried out on a sample of water and the results obtained.

   	Test	Results
   I	Addition of sodium hydroxide solution	White precipitate which dissolves in excess
   II	Addition of excess aqueous ammonia	Colourless solution obtained
   III	Addition of dilute hydrochloric acid and barium chloride	White precipitate

   1. Identify the anion present in the water.  (1 mark)
   2. Write an ionic equation for the reaction in III.   (1 mark)
3. Solutions can be classified as acids bases or neutral. The table below shows solutions and their pH  values

   Solution	PH - VALUES
   K L M	1.5 7.0 14.0

   1. Select any pair that would react to form a solution of pH 7.      (1mark)
   2. Identify two solutions that would react with aluminum hydroxide. Explain.         (1mark)              
4.  
   1. State Graham’s Law of diffusion.                                                                                (1mk)
   2. 60cm³ of oxygen gas diffused through a porous partition in 50 seconds.  How long would it take for 60cm³ of sulphur (IV) oxide gas to diffuse through the same partition under the same  conditions?
      ( S = 32.0, O = 16.0)                               ( 3 marks )        
5. Study the flow chart below and answer the questions that follow.
   
   1. Identify the metal oxide.   (1mk)
   2. Write an ionic equation leading to the formation of the white precipitate X. (1mk)
   3. Give the formula of the ions responsible for the colourless solution Y.        (1mk
6. Two compounds of barium are barium sulfide and barium chloride. 
   1. The hazard symbol shown in Figure below is on bottles containing barium metal. 
      
      State the meaning of this hazard symbol.  ( 1mk)
   2. Give the names of the elements combined in barium sulfide.                         (1mk)
   3. Hydrogen sulphide gas is highly poisonous. Sate one safety precaution that should be taken when handling hydrogen sulphide.      (1mk) 
7. Study the information in the table and answer questions that follow:
   

   Isotope
   Relative abundance %	61.3	38.7

   1. Determine the number of neutrons of   R₁ (1mk)
   2. Calculate the relative atomic mass of element R. (2mks)
8.  
   1. Identify the type of bond formed compound below.  (1mk)
      
   2. Using dots (∙) and crosses (x) to represent electrons show bonding in magnesium oxide  (2mks)
9. Show the products formed when the following salts are heated by writing a balanced chemical equation.      (2 marks)               
   1. KNO_3(s)  
   2. (NH₄)₂ CO_3(s) 
10. Explain why when one is stung by a bee application of a little solution of sodium hydrogen carbonate helps to relieve the pain.   ( 2 marks )
11. The following table gives the melting point of oxides of the third period elements. 
    Study it and answer the questions that follow.

    Formula of oxides	Na2O	MgO	Al2O3	SiO2	P4O10	SO2
    Melting point (°O)	1190	3080	3050	1730	560	-73

    1. Explain the large difference in the melting points of Na₂O and P₄O₁₀.                    (2 mark)
    2. Write the equation for the reaction between Al₂O₃ with;
       1. NaOH    (1 mark)
       2. H₂SO₄ (1 mark)
12. A hydrocarbon slowly decolourlises bromine in presence of sunlight but does not decolourise acidified potassium permanganate. Name and draw the structural formula of the fourth member of the series to which the hydrocarbon belongs. (2 marks)
13. Distinguish between ionization energy and electron affinity.                                           (2mks)
14. The set-up below was used to prepare a carbon (IV) oxide gas.
    
    
    1. Give the name of substance A                                                                                      (1mk)
    2. Complete the diagram to show how the dry gas can be collected.                              (2mks)
    3. Write the equation for the reaction (1 mark)
15. Calculate the mass of sulphur which on complete combustion would yield 7dm³ of sulphur (IV) oxide measured at 182^oc and 722 mm Hg pressure. (0=16, S=32, molar gas volume = 24dm³  at r.t.p).   (3 mks)                                                                                                               
16. Form two students from Achiever’s secondary school reacted three elements as shown in the table below 

    Element	Reaction with Oxygen	Reaction with water
    X	Formed acidic oxide	No reaction
    Y	Formed basic oxide	Formed soluble hydroxide gave off hydrogen gas
    Z	Formed acidic oxide	Dissolved to form an acidic solution

    Which element (s) is likely to be:(3mks)
    1. Non-metal (s)
    2. Metal (s)
    3. Insoluble in water.
17. A polymer has the following structure
    
    A sample of this polymer is found to have a molecular mass of 5194.  Determine the number of monomers on the polymer. ( H = 1.0,  C = 12.0,   N = 14.0  )                                  ( 2 marks )
18.  
    1. State the likely products of the electrolysis of molten potassium chloride at the:-
       1. Cathode ……………………………………………………………………………….(½mk)
       2. Anode  ………………………………………………………………………………. (½mk)
    2. Write the equations that occur at the anode and cathode.                                  (2mks)
       1. Anode……………………………………………
       2. Cathode…………………………………………
19. Give two reasons why helium is used in weather balloons.                                                   (2mks)
20. A Bunsen burner produces a yellow flame when airhole is close. Explain.            (2mks)
21. In an experiment, a boiling tube full of chlorine gas was inverted into a trough of water as shown below.
        
    
    1. State and explain the observations.                                                                       (2mks)
    2. If the experiment is repeated with tetrachloromethane instead of water.
       1. State the observations made.                                                                           (1mk)
       2. Explain your observations in b(i) above.                                                       (1mk)
22. Study the flow chart below and answer the questions that follow. 
              
    1. Name substances
       1. W     ……………………………………………………………………………..….(½ mark)
       2. Y      …………………………………………………………………………….…..(½ mark)
    2. An organic compound K reacted with bromine to form 2,3 – dibromobutane. Draw the structural formula of K.        (1mks)
23. Starting with copper metal describe how a solid sample of copper (II) carbonate can be  prepared.   ( 3 marks )
24. Study the information in the table below and answer the questions that follow. The letters do not represent the actual symbols of the elements.
    

    Element	Electrical conductivity	Ductility	Action of water
    A	Good	Good	No reaction
    B	Good	Poor	No reaction
    C	Good	Good	Reacts

    Select the element which is
    1. Likely to be in group II of the periodic table.  ( ½ mark )
    2. Could be used to make electric cables.   ( ½mark )
    3. Likely to be graphite.   ( ½ mark )
25. In an investigation, sulphur (IV) oxide gas was bubbled through acidified bromine water. This was followed by drops of barium nitrate solution.
    
    1. State the property of sulphur (IV) oxide under investigation.                                     (½ mark)
    2.  
       1. State the observation that were made on addition on sulphur (IV) oxide into the bromine water. (1mk)
       2. Explain the observation.                                                                                              (1mk)
26. Study the flow chart below and answer the questions that follow
            
    
    1. Identify gas X (1mk)
    2. Write an equation for the reaction between ammonia and gas X     (1mk)
    3. Write an equation to show the formation of G and J. (1 mk)
27.  
    1. Define pollution.   ( 1 mark ) 
    2. Mention one pollutant that is
       1. A Particle   ( ½ mark )
       2. Gaseous   (½ mark)
28. Hydrogen gas was burnt in air to form a colourless liquid.
    1. Describe a chemical test to identify the colourless liquid.                                       (2mk)
    2. State how the purity of the colourless liquid can be determined.                               (1mk)

MARKING SCHEME

1.  
   1. Period 3
   2. Y^3-   
   3. Ionic radius is large because  incoming electrons are repelled  by the electrons already in energy levels.
2.  
   1. SO₄^2-√1mk
   2. Ba²⁺_(aq)  +  SO₄^2-_(aq)       BaSO_4(s)  ^√1mk
3.  
   1. K and M  ^√1mk    one stated no mark
   2. K^{√ ½ mk}  and M^{√  ½ mk}    Aluminium hydroxide  is amphoteric ^√1mk (i.e. reacts with both acids and bases)
4.  
   1. States that rate of diffusion of a gas is inversly proportional to the square root of its density at constant temperature and pressure
   2. ^ti/_t2 = √^m1/_m2 = ⁵⁰/_t2 = √³²/₆₄
      ⁵⁰/_t2 = 0.707  
          t2 =70.72
5.  
   1. Zinc oxide
   2. Zn²⁺_(aq)  +  2OH^-_(aq)        Zn(OH)_2(s)
   3. [Zn (NH₃)₄]²⁺
6.  
   1. flammable
   2. barium and sulfur
      both elements must be present for the mark. allow Ba and S
      reject sulfide/sulfate reject if any other elements included
   3. experiment involving handling H2S should be done in fume cupboard do not inhale the gas
7.  
   1. 69 − 31 = 38
   2. R.A.M of R = (61.3 x 69) + (38.7 x 71)
                                            100
                       = 69.774
8.  
   1. covalent bond              
   2.  
      
9.  
   1. KNO_3(s)      KNO_2(s)  +  O_{2(g)  ✓}1
   2. (NH₄)₂ CO_3(s)   NH_3(g)  + CO_2(g)  + H₂O_(l)   ✓1  
10. A bee sting produces an acidic ✓1 substance application of sodium hydrogen ✓1 carbonate, a base neutralizes the acid from the bee sting ✓1.
11.  
    1. Na₂O has a giant ionic structure with strong ionic or electrovalent bonds which need large amounts of heat to break hence high melting points. P₄O₁₀ has covalent bond with simple molecular structure1
    2.  
       1. Alkali
          Al₂O_3(s)  +  2NaOH_(aq)  +  3H₂O_(l)      2Na Al(OH)_{4 ✓}1
       2. Acid
          Al₂O_3(s)  +  3H₂SO_4(aq)        Al₂(SO₄)_3(aq)  +  3H₂O_(l)   ✓1
12. Butane    
    
13.  
    • ionization energy-minimum energy required to remove an electron form the outermost energy level in the gaseous state
    • Electron affinity-energy released when an atom gains an electron in the gaseous state.
      Na₂CO_3(aq)  + MgSO_4(aq)                      MgCO_3(s)  +  Na₂SO_4(aq)
      CO₃^2-_(aq)  + Mg ²⁺_(aq)              MgCO_3(s)                     ✓1
       ( MgSO₄ / CaSO₄)
14.  
    1. HCl acid
15. 760 x V     =    722 X 7
      298                 455
    = 4.4dm³
    24dm³   - Mol
    4.4dm³
    4.4   = 0.18mol
     24
    Mass = 0.18 x 64 = 11.52g
16.  
    1. Z
    2. Y
    3. X
17. Monomer      
    ✓ ½
    RMM of monomer      =          36 + 3 + 14 = 53 ✓½
    No of monomers         =          5194  ✓ ½        = 98 ✓ ½ 
                                                      53
18.  
    1.  
       1. Potassium
       2. chlorine gas
    2.  
       1. cathode 2K⁺(l) +2e¯       2K(s)
       2. Anode 2Cl¯ (l)         Cl₂(g) + 2e¯
19.  
    • its less dense than air
    • Its unreactive
20.  
    • closure of air hole leads to insufficient supply of air hence incomplete combustion of gas.
    • incomplete combustion of gas produces tiny carbon particles which glow yellow when heated
21.  
    1. level of water in boiling tube reduces/Gas is collected in boiling tube
       Chloric (I) acid present in chorine water decomposes in sunlight producing oxygen gas and HCl acid.
    2.  
       1. No gas wil be collected in the boiling tube.
       2. Chlorine dissolves in tetrachloromethane but remains in molecular form thus no chloric (I) acid is formed.
22.  
    1.  
       1. W – Sodalime  / NaOH
       2. Y  -  Sodium carbonate Na₂CO₃  ^√1mk 
    2.   
       
23. Add excess Cu to HNO₃ ✓1, filter the mixture, add excess soluble carbonate filter ✓ rinse residue with  water  and dry residue between filter papers
    //
    Heat copper metal in excess air. Add excess CuO to H₂SO₄ and warm ✓, filter ✓ ½ then add soluble  carbonate ✓1, filter ✓ ½ . rinse residue with  water  and dry residue between filter papers
24.  
    1. C ✓1
    2. A ✓1
    3. B ✓1
25.  
    1. reducing property/reduction
    2.  
       1. Yellow/red-brown colour of bromine water is decolourised
       2. SO₂ reduces bromine water to colourless hydrobromic acid while itself is oxidized to sulphuric (VI) acid.
26.  
    1. Oxygen;
    2. 4NH_3(g) + 5O_2(g)      4NO_(g) + 6H₂O_(g)
    3. 2NO_2(g) + H₂O_(l)     HNO_2(aq) + HNO_3(aq)
27.  
    1. Pollution is the presence of harmful substances in the atmosphere ✓1
    2.  
       1. Particles – particulate carbon✓ ½ / lead ✓ ½ / dust
       2. SO₂ ✓ ½ , H₂S ✓ ½ , NO₂, CO
28.  
    1.  
       • add the liquid to anhydrous copper (ii) sulphate.
       • Anhydrous copper (ii) sulphate changes from white to blue hydrated copper (ii) sulphate
    2.  
       • freeze the liquid. Freezes at 0°C  
       • boil the liquid. Boils at 100°C at sea level