Chemistry Paper 1 Questions and Answers - Maranda Mocks 2021/2022 Exams

CHEMISTRY
Paper 1 

Instructions to candidates

•  All working MUST be clearly shown.
• KNEC mathematical tables and silent non programmable electronic calculators may be used. 

Questions

1.          
   1. Give two reasons why luminous flame is not used for heating purposes in the laboratory. (2marks)
   2. Explain how the hotness of a Bunsen burner flame can be increased. (1mark)
2. The scheme below shows the energy changes that are involved between ice, water and steam. Study it and answer the questions that follow
   
   
   1. What name is given to the process represented by energy change ∆H₄? (1 mark)
   2. What is the sign of ∆H₃? Give a reason (2 marks)
3. Samples of urine from three participants U, V and W at an international sport meeting were spotted onto chromatography paper alongside two from illegal drugs T1 and T2. A chromatogramwas run using methanol. The figure below shows the chromatogram.
   
   
   1. Identify the athlete who had used an illegal drug. (1mark)
   2. Which drug is more soluble in methanol? (1mark)
   3. Identify a mistake made on the chromatogram. (1mark)
4. The grid below is part of the periodic table. Study it and answer the questions that follow. Theletters are not actual symbols of elements.
   
   
   1. What is the name given to the chemical family of element C? (1mark)
   2. Would element B reacts with J? Explain. (1mark)
   3. Compare the melting points of B and M. (1mark)
5. The following diagrams show the structure of two allotropes of carbon. Study them and answerthe questions that follow.
   
   
   1. Name the allotropes. A and B (1 mark) A:
   2. Give one use of A. (½ mark)
   3. Which allotrope conducts electricity? Explain. (1½ marks)
6.       
   1. A few drops of freshly prepared Iron (II) Sulphate solution were added to Potassium nitrate solution in a test-tube. Concentrated sulphuric (VI) acid was then carefully added to the mixture. State the observations that were made. (1mark)
   2. Write an equation for the reaction that occurs when solid potassium nitrate is strongly heated. (1mark)
   3. What is the role of the test shown in (a) above. (1mark)
7.         
   1. Using electrons in the outermost energy level, draw the dot (•) and cross (X) diagrams torepresent bonding in:
      1. C2H6 (1mark)
      2. Magnesium nitride (1mark)
   2. The formula of a complex ion is [Cu(NH 3 )4 ]2+ . Name the type of bond that is likely to exist between copper and ammonia in the complex. (1 mark)
8. The set-up below can be used to study the reaction of magnesium and steam
   
   
   1. Name gas P. (1 mark) 
   2. Explain the observation made when copper is used instead of magnesium in the set up above? (1 mark)
   3. Write the equation for the reaction between magnesium and steam. (1mark)
9. 280cm³ of nitrogen gas diffuse through a porous plug in 70 seconds. How long will it take 400cm³ of carbon (IV) oxide gas to diffuse through the same porous plug? (C = 12, O = 16, N = 7).(3mks)
10. State two factors that accelerate rusting. (2 marks)
11.         
    1. Define the term ionization energy. (1mark)
    2. State and explain a factor that determine the value of ionization energy of a given element. (2marks)
12. Study the flow chart below and answer the questions that follow
    
    
    1. Identify
       1. Solid X (½ mark) 
       2. Process W (½ mark) 
    2. Write an equation for the reaction in step II. (1mark)
    3. Explain why Copper is suitable in making soldering equipment. (1mark)
13. The table below shows the solubility of a salt at various temperatures.
    

    Temperature °C	Solubility (g/100g water)
    0	36
    40	30
    80	25
    100	22
    120	20

    
    
    1. Define the term Fractional Crystallization. (1 mark)
    2. Calculate the mass of salt formed when 20g of a saturated solution of the salt at 0°C is place in a water bath maintained at 100°C. (2 marks) 
14. The table below shows properties of some elements A,B,C and D which belong to the same period of the periodic table. The letters do not represent the actual symbols of the elements.
    

    Element	A	B	C	D
    M.P.°C	1410	98	-101	660
    Atomic radii(nm)	0.117	0.186	0.099	0.143
    Electrical conductivity	Poor	Good	Non conductor	Good

    
    
    1. Arrange the elements in the order they would appear in the period. Give a reason. (2 marks)
    2. Select the metallic element which is better conductor of electricity. Give a reason. (1 mark)
15. Study the diagrams below.
    
    
    1. State the observations made at I and II. (1mark)
    2. Write the equations to show the reaction in II if dry sulphur (IV) oxide was used in place of dry chlorine. (2marks)
16. A radioactive substance weighing M kg took 1900 years for the original mass to reduce to 15kg. Given that half-life of the radioactive substance is 380 years;
    1. Determine the original mass of the radioactive substance. (2 marks)
    2. State two uses of radioactivity in medicine. (1 mark)
17. 20cm³ of a dibasic acid required 25cm³ of 0.1M NaOH for complete neutralization.
    1. How many moles of sodium hydroxide reacted with the dibasic acid? (1mark)
    2. Calculate the concentration of the dibasic acid in moles per litre. (2mks)
18. The table below shows the standard reduction potentials for four half–cells. Study it and answer the questions that follow (letter are not the actual symbols for the elements)
    

    	Eθ (Volts)
    F2(aq) + 2 e  → 2F-(aq) G2+(aq) + 2e → G(s)  H2+(aq) + 2e → H(s) 2J+(aq) + 2e → J2(g)	+0.54 -0.44 +0.34  0.00

    
    
    1.  Identify the strongest reducing agent. Explain (1mark)
    2. Write the equation for the reaction which takes place when solid G is added to a solution containing H2+ ions. (1 mark)
    3. Calculate the E0 value for the reaction in (ii) above. (1mark)
19. Starting with solid lead (II) carbonate, briefly describe how a sample of lead (II) chloride can be prepared. (3marks)
20. Chlorine and iodine are elements in the same group in the periodic table.
    1. What observation would be made if chlorine gas is bubbled through aqueous sodium iodine? Explain using an ionic equation. (2 marks)
    2. Using the equation in (a) above, identify and explain the reducing agent. (1 mark)
21. Using energy cycle diagram, calculate the enthalpy of formation of ethane from the information given below.
    C_(s) + O_2(g)  → CO_2(g) ∆HC = -394kJmol^-1
    H_2(g) + O_2(g) → H₂O_(l) ∆HC = -286kJmol^-1
    C₂H_6(g) + 5O_2(g) → 2CO_2(g) + 3H₂O_(l) ∆Hc = -1300kJmol^-1 (3 marks)
22.              
    1. Identify the following cleansing agents. (2 mark)
       
    2. State one disadvantage of using the cleansing agent in (a) (ii) above. (1mark)
23. The empirical formula of a hydrocarbon is C2H3. The hydrocarbon has a relative molecular mass of 54. (H=1.0, C=12.0).
    1. Determine the molecular formula of the hydrocarbon. (1mark)
    2. Draw the structural formula of the hydrocarbon. (1mark)
    3. To which homologous series does the hydrocarbon drawn in (b) above belong? (1mark)
24.         
    1. State the Boyle’s law. (1mark)
    2. A gas occupies 300cm3 at 23oC and 100,000 Pa. What will be its volume at 00C and 101325Pa? (2marks)
25. In the laboratory, hydrogen sulphide gas is prepared by action of dilute hydrochloric acid on metal sulphides.
    1. Name the metal sulphide that can be used in preparing the gas. (1mark)
    2. Write down the equation for the reaction in (a) above. (1mark)
    3. Give one chemical test for hydrogen sulphide gas. (1mark)
26. Some crystals of sugar cane were placed in a test-tube and a few drops of concentrated sulphuric (VI) acid added to it.
    1. State what was observed. (1mark)
    2. What name is given to the property of concentrated sulphuric (VI) acid in (i) above? (1mark)
    3. Write an equation for the reaction between glucose, C6H12O6 and H2SO4 (l). (1mark)
27. The following equation shows a reversible reaction.
    H_2(g) + Br_2(g)     ⇌      2HBr_{(g )}           ∆H = − 74.4kJ
                brown        colourless
    1. State and explain the observation that can be made when:-
       1. Temperature is increased. (1½marks)
       2. Pressure is reduced (1½marks) 

Marking Scheme

1.        
   1. Soot it produces dirtifies the apparatus
      The flame is not very hot
      
      
   2. Opening the air hole fully
2.             
   1. Latent heat of fusion
      
      
   2. Negative(-)
      The process looses heat
3.           
   1. V
      
      
   2. T1
      
      
   3. Solvent front is labelled in place of baseline
      
      
4.             
   1. Alkaline earth metals
      
      
   2. No. J does not form compounds as it is chemically stable already
      
      
   3. M has a higher melting point than B as it has a strong metallic bond or it has more delocalised electrons
5.                
   1.   
      1. Diamond
      2. Graphite
         
         
   2. Jewellery/ Making drilling machines/ bits
      
      
   3. B. Existence of delocalised electrons which transfer electricity
      
      
6.                    
   1. A brown ring/ substance is formed between potassium nitrate and concentrated sulphuric (VI) acid
      
      
   2. 2KNO_3(s) → 2KNO_2(s) + O_2(g)
      
      
   3. Test for nitrates
7.               
   1.        
      1.    
         
      2.        
         
   2. Dative covalent bond
8.              
   1. Hydrogen
      
      
   2. Copper would not react with steam copper is below hydrogen in the reactivity series and hence cannot displace it in a reaction
      
      
   3. Mg_(s) + H₂O_(q)  → MgO_(s) + H_2(g)
      
      
9. RN2 = 280/70 = 4cm3/sec 
   RCO2 = 400/t 
   Hence 4/400/t = √44/28
   t= √44/28 x 100
   = 125.36 sec
   
   
10. Low pH/ acidic conditions
    High temperature
    Salty conditions
    
    
11.         
    1. The minimum amount of energy needed to remove an electron from an atom in its gaseous state.
       
       
    2. Atomic radius/ size of the atom
       The distance between the outermost electron and the nucleus affects nuclear attraction
       
       
12.                   
    1.         
       1. Iron (II) oxide/ FeO
          
          
       2. Electrolysis/ Purification
          
          
    2. 2CuFeS_2(s) + 4O_2(g) → Cu₂S_(s) + 2FeO_(s) + 3SO_2(g)
       
       
    3. This is due to its high thermal conductivity
13.             
    1. A process by which solutes are separated from each other according to their solubilities/ separation of salts by making use of the differences in their solubility.
       
       
    2. From the table, 100g of saturated solution will give= 36g - 22g = 14g
       Hence , if 100g of saturated solution = 14g of salt
       Therefore 20g of saturated solution
       = 20 x 14
            100
       = 2.8g of salt
14.                   
    1. BDAC
       Because the atomic radius decreases across a period/ decrease with increase in nuclear charge or number of proton
       
       
    2. D
       Becauseit has more delocalised electrons than B
15.           
    1. In I - There is no bleaching
       In II - There is bleaching
       
       
    2. SO_2(g) + H₂O_(l) → 2H⁺_(aq) + SO^2-_3(aq)
       SO^2-_3(aq) + Dye → SO^2-_4(aq) + (Dye - [O])
       
       
16.                 
    1. Number of half-life = 1900/380 = 5
       480kg ← 240kg ← 120kg ← 15kg
       Hence M= 480kg
       
       
    2. Used to destroy cancerous cells
       Used to sterilise surgical instruments
       
       
17.                  
    1. Moles of NaOH = 25/1000
       = 0.0025 moles
       
       
    2. H₂X_(aq) + NaOH_(aq) → Na₂X_(aq) + 2H₂O_(l)
       Mole ratio Acid:NaOH= 1:2 (either from equation or just stated)
       Moles of H₂X= ¹/₂ x 0.0025 = 0.00125
       Concentration in moles per litre
       = 0.00125 x 1000
                   20
       = 0.0625 moles per litre
       
       
18.                      
    1.      
       1. G_(s) This is because it has the highest negative electrode potential
          
          
       2. G_(s) + H²⁺_(aq) → G²⁺_(aq) + H_(s) 
          
          
       3. +0.34 + 0.44 = +0.78v
          
          
19.                      
    • To excess lead(II) carbonate, add nitric (V) acid
    • Filter to obtain lead(II) nitrate filtrate
    • Add dilute hydrochloric acid/ any soluble chloride tot he filtrate
    • Filtrate to obtain lead (II) chloride residue
      
      
20.                      
    1.         
       • Colourless solution would turn brown
       • This is because chlorine displaces iodine from iodine solution
         Cl_2(g) + 2I^-_(aq) → 2Cl^-_(aq) + I_2(aq)
         
         
    2. I^-_(aq)
       The oxidation number of iodine increases from in -1 in I-(aq) to 0 in I₂
       
       
21.         
    
22.          
    1.          
       1. Soapy detrgent
       2. Soapless detergent
          
          
    2. Non biodegradable hence pollutes the environment
       It is expensive 
       
       
23.                    
    1. (C₂H₃)_n = 54
       27n = 54
       n=2
       Molecular formula is C₄H₆
       
       
    2.        
       
                  
    3. Alkyne
       
       
24.                      
    1. The volume of a fixed mass of a gas is inversely proportional to its pressure at constant temperature
       
       
    2.  v1 = 300cm³ 
       T1= 23 + 273 = 296K
       P1= 100,000Pa
       V2 = x
       T2 = 0 + 273 = 273K
       P2= 101, 325Pa
       V2 = 100,000 x 300 x 273
                 296 x 101,325
       = 273.07cm3
25.                       
    1. Iron(II) sulphide
       (accept metal chloride that do not form insoulble chlorides)
       
       
    2. FeS_(s) + 2HCl_(aq) → FeCl_2(aq) + H₂S_(g)
       
       
    3. Use lead acetate paper or lead(II) ethanoate ppaer or soak a paper in lead (II) nitrate solution. The paper turns from white to black.
26.                    
    1. The white crystals of sugar can changes into a black mass
       
       
    2. Dehydration property
       
       
    3. C₆H₁₂O_6(g) + H₂SO_4(l) → 6C_(s) + 6H₂O_(l) 
       
27.                    
    1.                 
       1. Intensity of the brown colour will increase. More recatants will be formed as the forward reaction is exothermic
          
          
       2. No effect. The volume of the reactants and products are equal.