Chemistry Paper 1 Questions and Answers - Catholic Diocese of Kakamega Mock Exams 2023

INSTRUCTIONS TO CANDIDATES

• Answer all the questions in the spaces provided.
• Scientific calculators may be used.
• Answer all questions in English

Questions

1.  
   1. Draw a simple diagram of a wooden splint after being passed through the inner region of a non- luminous flame of the Bunsen burner flame      (2 mks)
   2. Explain why butane is not commonly used as domestic fuel in gas cylinders. (1 mk)
2. Element T whose atomic number is 16 and mass number 32,combines with Oxygen whose atomic number is 8.
   
   1. Determine the number of protons and neutrons in element T.    (1mark)
   2. Name the type of bond formed between T and Oxygen.     (1mark)
   3. State the nature of solution formed when Oxide of T is bubbled through water. (1mark)
3. Study the flow chart below and answer the questions that follow
   
   
   1. Name 
      1.  A    (1⁄2 mk)
      2. X      (1⁄2 mk)
   2. Give a reason why potassium metal cannot be used as metal B     (1 mk)
   3. State any two uses of hydrogen chloride gas       (1 mk)
4.  A monomer has the following structure
   CH = CH₂
      I
   C₆H₅
   
   1. Give the name of the monomer    (1 mk)
   2. A sample of a polymer formed by the monomer above has a molecular mass of 4992.
      Determine the number of monomers that formed the polymer     (C=12, H=1.0)         (2 mks)
5. Below is a nuclear equation. Study it and answer the questions that follow.
   
   
   1. Find the values of x and n in the nuclear equation below     (2mks)
   2. State two uses of radioisotopes in health    (1mk)
6. 100 cm³ of sulphur (IV) oxide diffuses through a porous pot in 72 seconds. What is the molecular mass of a gas P if 50 cm³ of the gas diffuses through the same porous pot in 37.92 seconds under the same conditions (S=32, O=16)       (3mks)
7. The table below shows the pH values of solutions of compounds J, K, L and M
   

   Compound	J	K	L	M
   pH Value	1	6.5	7	10

   
   
   1. State which one of the compounds is likely to be
      
      1. Water obtained from an ion exchange resin   (1mk)
      2. anti-acid tablet      (1mk)
   2. A certain soil sample was found to be acidic. State two activities that would have led to decrease in the soil pH     (1mk)
8. Starting with copper metal and dilute sulphuric (VI) acid, describe how you would prepare pure crystals of copper (II) sulphate.       (3marks)
9. The figure below shows an energy level diagram for decomposition of hydrogen peroxide using a
   catalyst.
   
   
   1. Using the energy values A,B and C,write an expression for:
      
      1. Η for the reaction    (1mk)
      2. activation energy    (1mk)
   2. On the same axis sketch a curve that would be obtained if the reaction was carried out without a catalyst      (1mk)
10. The table below is part of the periodic table. The letters do not represent the actual symbols of the elements. Study it and answer the questions that follow
    
    
    1. Select an element stored under water in the laboratory    (1mk)
    2. How do the ionic radii of C and E compare? Explain       (2 mks)
11. The set-up shown below was used to separate a mixture T.
    
    
    1. Name the apparatus missing in the set-up.   (1 mark)
    2. Give one example of mixture T   (1 mark)
    3. What is the name of this method of separation?    (1 mark)
12. Below is a representation of an electrochemical cell Pb_(s)/Pb²⁺_(aq)// Ag⁺_(aq)/Ag_(s)
    
    1. What does // represent?   (1mk)
    2. Explain why it is not advisable to use aqueous sodium carbonate as the salt bridge in this electrochemical cell.    (2mks)
13. The set up can be used to prepare oxygen gas. Use it to answer the questions that follow
    
    
    1. Name substance A   (1 mk)
    2. Name the method used to obtain oxygen on large scale   (1 mk)
    3. Write an equation for the reaction which occurred in the flask.    (1 mk)
14. An oxide of nitrogen was bubbled through a solution of sodium hydroxide in which methyl orange indicator had been added. The solution changed to orange after sometime.
    1. Identify the oxide.    (1mk)
    2. Write the equation for the reaction to explain the observation.     (1mk)
15. When 87.1g of hydrated barium hydroxide [Ba(OH)₂.nH₂0] were heated to constant mass, 61.3g of anhydrous barium hydroxide were obtained. Determine the value of n in hydrated barium hydroxide. (Ba = 137,0=16, H = 1)       (3marks)
16. In an experiment to study properties of carbon, a small amount of charcoal is placed in a boiling tube. 5.0cm³ of concentrated nitric acid is added. The mixture is then heated.
    1. State one observation made. (1mark)
    2. Write an equation for the reaction that took place in the boiling tube. (1mark)
    3. What property of carbon is shown in this reaction? (1mark)
17.  
    1. State the Le-Chatelier's principle.
       (1mark)
    2. The equation for dissolution of bismuth (III) chloride in water is
       
       Explain the effect on the position of equilibrium if sodium hydroxide solution is added to the mixture at equilibrium.   (2marks)
18. The following table gives the melting points of oxides of elements in period 3. Study it and
    answer the questions that follow:-
    

    Formula of oxide	Na2O	MgO	Al2O3	SiO2	P4O10	SO3
    Melting point (°C)	1190	3080	2050	1730	560	−73

    1. Explain the difference in melting points of MgO and P₄0₁₀ (2marks)
    2. Name the compound in the above table that will react with both dilute hydrochloric acid and dilute sodium hydroxide. (1mark)
19. The formula of the complex ion formed when aqueous copper (II)sulphate reacts with excess
    aqueous ammonia solution is given as [Cu (NH₃)₄]²⁺
    
    1. Name the complex ion above    (1mk)
    2. State one use of the complex ion in (a) above     (1mk)
    3. Explain how the +2 charge is obtained    (1mk)
20. The scheme below was used to prepare a cleaning agent. Study and answer the questions that follow.
    
    
    1. What name is given to the type of cleaning agent prepared by the method shown in the scheme?  (1⁄2mk)
    2. Name one chemical substance added in step II   (1mk)
    3. Explain how the cleaning agent removes dirt from clothes   (1/2mk)
21. Blue petals were dropped into a gas jar containing sulphur (IV) oxide as shown below.
    
    
    1. Which observation was made?  (1 mark)
    2. Which property of sulphur (IV) oxide is exhibited above?  (1 mark)
    3. Write the equation for the reaction above.  (1 mark)
22. A substance contains 40.32g of substance XOH per litre. 25cm³ of this solution required 30.0 cm³ of  0.3 M Sulphuric (VI)acid for complete neutralization
    
    1. Calculate the number of moles of XOH that reacted   (1mk)
    2. Determine the relative atomic mass of X   (2mks)
23. During the extraction of aluminium from its ores, the ore is first purified to obtain alumina
    
    
    1. Name
       
       
       1. Substance C₁     (1mk)
       2. Process D₁    (1mk)
    2. Give a reason why copper is a better conductor of heat and electricity than aluminium       (1mk)
24. Study the scheme below and use it to answer the questions that follow.
    
    
    1. Write down the formulae of two possible anions present in salt solution P.    (2marks)
    2. Write an ionic equation for the formation of white precipitate.     (1mark)
25. Hydrogen gas exhibits reduction properties. Use the set up below to answer the questions that follow.
    
    State and explain two observations made in the combustion tube    (3mks)
26. The diagram below represents an in complete set up for preparation of a dry sample of gas R.
    
    
    1. Complete the set up to show how a dry sample of gas R is collected.    (2 marks)
    2. Write a chemical equation for the reaction that produces gas R.      (1 mark)
27. Below is a diagram of set-up of apparatus that is used to investigate the effect of electric current on a binary electrolyte, lead (II) bromide.
    
    
    1.  Explain what is meant by a binary electrolyte.    (1 mark)
    2. State the importance of heating in the above experiment.     (1 mark)
    3. Write the ionic equation for the reaction taking place at the anode.       (1 mark)
       
       

MARKING SHEME

1.  
   1. 
      
   2. Burns with a yellow sooty flame which would dirtify the apparatus 
2.  
   1. 32=16 +N
      N=16 
      P=16
   2. Covalent
   3. acidic
3.  
   1. A- concentrated sulphuric (VI) acid// anhyd. Calcium chloride
      X- Hydrochloric acid / spirit of salt
   2.  
      1. Reacts explosively with dilute hydrochloric acid
      2. Production of chlorine and chlorides
   3. 
      
      • In tanning industry
      • Dyeing calico printing
      • In several medicines
      • Production of glucose
4. 1. polyphenylethene/polystyrene
   2. n=     4992          =    4992    =  48
            8(12)+8(1)           104
      104(1mk)
      48(1mk)
5.  
   1. n=3(1), x= 88(1)
   2.  
      • Cobalt-60 and caesium -137 are used to destroy cancerous tissues
      • Gamma rays are used to sterilize surgical instruments
      • Iodine-131 is used to treat patients with defective thyroid
      • Flouride-18 is used to detect fractures in bones etc
        
        
6. Tp = 100 x 37.92
                   50
         = 75.84cm³
   
   =   72       =   64 
      75.84          x
     
    = 71 sec
7.  
   1.  
      1.  K
      2. M
   2.  
      • Excessive use of nitrogeneous fertilisers such as NH₄NO₃, (NH₄)₂SO₄ which are slightly acidic 1
      • Acid rain due to release of acidic gases in the region such as SO₂ 
8.  
   • Burn copper // heat in air/oxygen obtain copper (II) oxide
   • Add excess copper (II) oxide with dilute sulphuric (VI) acid.
   • Filter the unreacted copper (II) oxide as residue and get copper (II) sulphate solution as the filtrate
   • Heat the solution to saturation and then cover it with perforated filter paper & then leave crystals to form
   • Dry the crystals between filter papers.
9.  
   1. shown on graph
      
      1. ΔH=C - A
      2. ΔH_Ea=C - B
   2.  
      
10.  
    1.  J
    2. C^3- has a larger ionic radius than E^- effective nuclear pull on outer electrons in C^3- is stronger than
       1. in E^- // ion of E more protons/stronger nuclear charge than ion of C
11.  
    1. Wire gauze
    2. Sodium chloride solution
    3. Evaporation.
12. 1. Salt bridge will
    2. Reacts with electrolytes(1) forming insoluble salts/ppt(1)// PbCO; insoluble will be formed (1) no flow of ions. (1)
13.  
    1. Sodium peroxide
    2. Fractional distillation
    3. 2Na₂O_2(s) + 2H2O_(l) → 4NaOH_(aq) + O2_(g)
14.  
    1. nitrogen(IV) oxide
    2. 2NaOH_(aq) + 2 NO2_(g) → NaNO3_(aq) + NaNO2_(aq) + H2O_(l)
15. Mass of water of crystallization= 87.1 - 61.3 = 25.8
    Mass of Ba(OH)₂ = 61.3
    Compound                                       Ba(OH)₂                                      2H₂O
    Mass                                                  61.3                                            25.8
    No. Of moles                                     ^61.3/₁₇₁                                        ^25.8/₁₈
    Mole ratio                                        ^0.3585/_{0.3585                                           ^1.4333}/_0.3585
    3.9981 = 4
    n = 4 
16.  
    1. A brown gas was formed at the boiling tube.
    2. C_(s) + 4HNO_3(aq)-4NO_2(aq) + CO_2(g) + 2 H₂O_(l)
    3. Reducing property.
17.  
    1. When a system at equilibrium is put under stress, it tries to readjust itself to possibly overcome the stress.// when a change in condition is applied to a system in equilibrium, it moves so as to oppose the change
    2. Sodium hydroxide removes the hydrogen ions in the mixture thereby causing instability in the system.
       The equilibrium position shifts to the right to try and replace the lost hydrogen ions.(1)
       - white colour intensifies
18.  
    1.  
       • MgO- it is an ionic compound with giant ionic structure which requires a lot of heat energy to separate
         the ions.
       • P₄O₁₀ -it is a molecular substance where discrete molecules are joined by weak vanderwaal's forces of attraction that require little heat energy to separate.
    2. Al₂O₃ -Aluminium oxide
19.  
    1.  Tetraaminecopper(II)ion
    2.  
       • Imparting blue, green or red tints in glasses and enamels
       • Production of cellulose fibres in production of rayon
    3. Cu has a charge of +2 while NH₃ has zero hence
                                           charge of ion = +2 +4 (0)
                                                                 = + 2
20.  
    1. soapy detergent
    2. Sodium chloride
    3. Has polar end (-COO^–Na⁺) which dissolves in water and non-polar which dissolves in dirt, when rinsed the dirt is washed away.
21.  
    1. Blue petals turned white // colourless
    2. The bleaching property of S0₂.
    3. Dye + H₂S0₃ (aq)   →   (dye - Oxygen) + H2SO4
                (Blue)                                 (White)
       SO₂ gas has reducing agent ability thus takes oxygen from the dye hence bleaching it
22. 1. 2XOH_(aq)+ H₂SO_4(aq)        →        X₂SO_4(aq) + H₂O(1)
       mole ratio XOH: H₂SO₄
                              2:1
       moles of H₂SO₄  =   30x3    =  0.009 
                                       1000
       moles of XOH = 2×0.009
                               = 0.018 
    2. 0.018 x 1000   =   0.72
              25
         40.32   =   56
         0.72
       
       X + 16 + 1 = 56
       X+17 = 56
       X = 56 - 17
       =39 
23.  
    1.  
       1. C₁ - Sodium hydroxide
       2. D₁- Electrolysis
    2. Has high density than Al hence higher density of free electrons in Cu than A1
24.  
    1. CO₃^2-  (1mk)  or   SO₃^2-   (1mk)
    2. Ba²⁺_(aq) + CO₃^2- _(aq)     →     or  BaCO_3 (s)
       Ba²⁺_(aq)   +  SO₃^2-_(aq)      →     BaSO_{3 (s)}
25. Black copper(II)oxide changed to brown(1/2) and white anhydrous copper(II)sulphate crystals formed a blue substance(1/2), hydrogen gas reduces copper(II) oxide to copper metal(1) and itself is oxidized to steam which condenses on the cooler parts of the and combines with anhydrous copper(II)sulphate to form hydrated copper(II)sulphate solution.(1)
26. 
    
    
27.  
    1. Electrolyte that contain only one type of cation and anion.
    2. To melt lead(II)bromide for the ions to be free and mobile.
    3. 2Br ‾ _(l)        →      Br _{2 (g)} + 2e¯