Chemistry Paper 1 Questions and Answers - Kapsabet Pre Mock Exams 2021/2022

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CHEMISTRY
PAPER 1 :THEORY

INSTRUCTIONS TO CANDIDATES

  • Write your name and index number in the spaces provided above
  • Sign and write the date of examination in the spaces provided.
  • Answer all the questions in the spaces provided.
  • Mathematical table and silent electronic calculators may be used.
  • All working must be clearly shown where necessary.
  • Candidates should answer the questions in English

  1. The set shown below is used to prepare nitrogen (IV) oxide.
    KapPreM Chem p1q1
    1. Complete the diagram to show the collection of the gas. (1 mark)
    2. Identify substance X. (1 mark)
    3. Write the equation for the reaction that occurs in the conical flask. (1 mark)
  2. The flow chart below shows stages involved in obtaining nitrogen gas from air
    KapPreM Chem p1q2
    State the use of the,
    1. Filters (1mark)
    2. Sodium hydroxide solution (1mark)
    3. Cooling to -200ºCelsius. (1mark)
  3. The electron arrangement of ions X3+ and Y2- are 2. 8 and 2. 8. 8 respectively.
    1. To which groups do X and Y belong to? (1 mark)
    2. State the atomic numbers of X and Y. (1 mark)
    3. Write a formula of compound formed when Y and X reacts. (1 mark)
  4. In the extraction of iron in the blast furnace, state the uses of the following in the furnace.
    1. Molten slag. (1 mark)
    2. Waste gases leaving the furnace. (1 mark)
  5.       
    1. Water from Nairobi dam is suspected to be hard water with a little presence of chloride ions from the industrial effluents. Give the formulae of two ions that cause hardness of water and describe a chemical test to detect the presence of chloride ions . (3 mark)
    2. Given that the structure of soap is C17H35COONa, use ionic equations to show the reaction that occurs when the above ions react with soap. (2 marks)
  6. The diagram below shows some parts of a Bunsen burner
    KapPreM Chem p1q6
    Explain how the parts labelled T and U are suited to their functions (2marks)
  7. Ethyne reacts with hydrogen as shown below
    Use the bond energies below to calculate the enthalpy changes for the above reaction (3marks)
    BOND  ENERGY(kJ/Mole)
     H-H  435
     C-H  413
     C≡C  835
     C=C  611
  8.           
    1. What is meant by the term isomerism? (1mark)
    2. Draw structural formulae of two positional isomers of pentene. (2marks)
  9. 18.7cm3 of a dibasic acid (H2A) required 25cm3 of 0.1M Sodium hydroxide for complete neutralization.
    1. How many moles of sodium hydroxide are contained in 25cm3? (1mark)
    2. Calculate the molarity of the acid. (2marks)
  10. The figure below shows a paper chromatography for a pure substance X
    KapPreM Chem p1q10
    1. What do the letters A and B represent? (1 mark)
    2. Given that X contains blue and green dyes, show the chromatography of X on the diagram. (1 mark)
    3. Give the reason why the spot for red moves further than that of blue and green. (1 mark)
  11. Draw the dimer structure of aluminium chloride and name the bonds. (2 marks)
    (Atomic number Al = 13, Cl =17)
  12. One of the applications of electrolysis is electroplating of iron.
    1. Give two reasons why iron is electroplated. (1 mark)
    2. An iron spoon was to be electroplated with silver. Draw the labelled set-up that can be used. (2 marks)
  13.            
    1. Distinguish between isotopes and allotropes. (2marks)
    2. Other than sulphur, name two elements that are allotropic. (1mark)
  14. Study the diagram below and answer the questions that follow.
    KapPreM Chem p1q14
    1. Between N and M which part should be heated first? Explain (2marks)
    2. Write the equation for the reaction occurring in the combustion tube. (1mark)
  15. Describe how you would prepare crystals of sodium nitrate starting with 200 cm3 of 2M sodium hydroxide. (3 marks) 
  16. Two reagents that can be used to prepare chlorine gas are potassium manganate (VII) and hydrochloric acid.
    1. What is the role of potassium manganate (VII) in this reaction? (1 mark)
    2. Give the formula of another reagent that can be used instead of potassium manganate (VII). (1 mark)
    3. Using an equation, illustrate how chlorine bleach coloured substances. (1 mark)
  17. A certain hydrocarbon on complete combustion gave 9.9g of carbon (IV) oxide and 4.86g of water. Calculate the empirical formula of the hydrocarbon (3marks) 
  18. Magnesium hydroxide is used as a medication to relieve stomach acidity.
    1. Write the equation for the reaction that occurs in the stomach when one takes in the medicine. (1 mark)
    2. What type of reaction takes place in the stomach after taking the medicine? (1 mark)
    3. Sodium hydroxide cannot be used for the same purpose. Explain. (1 mark)
  19. The table below shows atomic numbers of elements represented by the letter R to Y. The letters are not the actual chemical symbols of the elements.
    Elements R S T U V W Z Y
    Atomic number 3 7 8 9 10 11 12 13

    1. Two elements that belong to the same period of the periodic table. (1 mark)
    2. Two elements in the same group (1 mark)
    3. State one use of the element V. (1 mark)
  20. The curve below represent the changes in the concentrations of substance E and F with time in the reaction
    KapPreM Chem p1q20a
    KapPreM Chem p1q20b 
    1. Which curve represents the changes in the concentration of substance F? Give a reason. (2 marks)
    2. Give a reason for the shapes of the curves after time (t) seconds. (1 mark)
  21.            
    1. Define the term solubility. (1 mark) 
    2. The following were the results obtained in an experiment to determine solubility of potassium nitrate at room temperature.
      Mass of evaporating dish = 14.32 g
      Mass of evaporating dish + saturated solution = 35.70 g
      Mass of evaporating dish + salt (residue) = 18.60 g
      Calculate the solubility of potassium nitrate from the above results. (2 marks)
  22. Study the set-up below and answer the questions that follow;
    KapPreM Chem p1q22
    1. State and explain two observations made when the circuit is completed. (2marks)
    2. What precaution should be taken when performing this experiment? Give a reason (l mark)
  23. Dry carbon (II) oxide gas was passed over heated lead (II) oxide.
    1. Write the equation for the reaction. (1 mark)
    2. Give the industrial application of the above reaction. (1 mark)
    3. Name another gas that can be used in the above reaction. (1 mark)
  24.      
    1. Consider the reaction shown below.
      2H2S(g) + SO2(g) → 3S(s) + 2 H2O(l)
      Using oxidation numbers of sulphur in H2S and SO2, identify the reducing agent. Explain (2marks)
    2. What name is given to the process used to control pollution caused by sulphur (IV) oxide in a sulphuric (VI) acid plant?( 1mark)
  25. The following is a formula of an organic compound:CH3CH2COOCH2CH3
    1. Draw and name the organic acid and alkanol used in making the compound. (2 marks)
    2. Name the compound and the gas formed when the alkanol in (a) above is reacted with potassium. (1 mark)
  26.        
    1. State Graham’s law of diffusion. (1 mark)
    2. A certain volume of gas T takes 180 seconds to diffuse through a porous plug. An equal volume of gas Q takes 240 seconds to diffuse through the same plug. Calculate the molar mass of Q. (2marks)
      (Relative molecular mass of gas T =l8)
  27. Sulphur IV oxide gas dissolves in water to form sulphuric IV acid (H2SO3),
    1. Write the electronic arrangement of Suphur in the compound H2SO3 (2mks)

MARKING SCHEME

  1.          
    1.  
      KapPreM Chem p1qa1
    2.   X
      - Concentrated Nitric V Acid
    3. Reaction:
      Cu(s) + 4HNO3(l) â†’ Cu(NO3)2(aq) + 2H2O(l) + 2NO2(g)
  2.           
    1. Filters - Remove dust particles/ impurities
    2. Sodium hydroxide solution - Remove Carbon (IV) Oxide
    3. Cooling to -200º celsius - Condense gases into liquid
  3.           
    1. X - III
      Y - VI
    2. X - 13
      Y - 16
    3. X2Y3
  4.             
    1.       
    2.       
  5.           
    1. Mg2+ or Ca2+
      Test -  Add Silver NItrate ( AgNO3) to the sample and a white precipitate is formed.
    2. 2C17H15COO+ + Ca2+ â†’ (C17H15COO)2Ca8 
      or
      2C17H15COO+ + Mg2+ â†’ (C17H15COO)2Mg15
  6. T - Jet - Divert the gas to enter the chiney, forcing air to flow out
    U - Stand -  Wide base and heavy to support burner

  7.  (2(H-C)+(C≡C) + (H-H) - 2(-C-H) + (C=C)
    (2(473) + 835 + 435) - 2(413) + 611
    826 + 835 + 435 
    2096 - 1222
    = -874KJ/No
  8.         
    1. Compound with the same chemical formula but different in their structural formula

    2. Chem qa18
  9.              
    1. If 0.1 moles NaOH - 1000
      25 x 0.1 = 0.0025 moles
        1000
    2. 2NaOH: 1H2A â†’ Na2A + H2
      0.0025 moles of H2A - 1/2 x 0.0025
      =0.00125
      if 0.00125 moles - 18.7cm3
                         ?      -  1000cm3
      1000 x 0.00125 = 0.066845
             18.7
  10.             
    1.      
      1. Base line
      2. Solvent front
    2.          
    3.      
      • Red is the most soluble dye
      • Red is the least absorbent dye
  11.      
    KapPreM Chem p1qa12b       
  12.          
    1.      
    2.           
  13.            
    1. Isotope - as atoms of the same element will the same atomic number but different mass number 
      Allotropes - different forms of an element but the same physical state.
    2.    Carbon, phosphorus
  14.            
    1. N -  water is heated to produce steam to expel thin air in combustion heating iron to avoid the formation of reaction of iron with oxygen.
    2. 2Fe(s) + 3H2O(l) â†’ Fe2O3(s) + 3H2(g)
  15. prepare 200cm3 of 2m nitric(V) acid in a beaker. Add all the 200cm3 of 2m sodium hydroxide. To the result of solutionheat boil and evaporate the obtain the crystals.
  16.           
    1. oxidising agent
    2. Lead (iv) oxide
      Manganese (iv) oxide
    3. Cl2(g) + H2O(l) â†’ HOCl(aq) + HCl(aq)
      HOCl(aq) + dye coloured flower â†’ HCl + [dye + O](white)
  17.  12/44 x 9.9 = 2.699997
    2/18 x 4.86 = 0.539999
    C H
    2.7g 

    12
     0.54

    1
     2.7/12  0.54
     0.225/0.225  0.54/0.225
     1  2.4
    1 x 5 2.4 x 5
    5 12
    C5H12
  18.             
    1. Mg(OH)2(aq) + 2HCl(aq) â†’ MgCl2(aq) + H2O(l)
    2. Neutralisation
    3. Sodium hydroxide is a drug base. It affects the stomach linings/walls
  19.             
    1. RSTUV   or
      WZY
    2. R and W
    3. Street/ advertisement lights
      Provide inert environemnt for bulbs
  20.          
    1. Curve I - concentration increases with time until equilibrium
    2. The rate of forward/ backward reaction is attained (Dynamic equilibrium is attained)
  21.             
    1. The maximum amount of a solid that can saturate 100g of water at a given temperature
    2. Mass of saturated solution = 35.70 - 14.32 â†’ 21.38g
      Mass of dry salt = 18.60 - 14.32 â†’ 4.28
      Mass of water â†’ 21.38 - 4.28
      = 17.1g
      If 17.1g H2O - 4.28 Salt
      100g H2O - ?
      100 x 4.28 = 25.029g/100gH2O
           17.1
  22.           
    1.     
      1. Bulb lights
      2. Grey beads of lead metal are deposited at the cathode
      3. Red-brown vapour of bromine are formed at the anode
    2.          
      1. Use a gas mask/ do the experiment in the fume chamber to avoid inhaling bromine gas. It is corrosive to humn tissue, irritates eyes.
  23.             
    1. 2PbO(s) + 2CO(g) â†’ 2Pb (s) + 2CO2(g)
    2. In extraction of lead metal/metals
    3. Hydrogen
      ammonia
  24.          
    1. Hydrogen sulphide.
    2. Scrubbing
  25.           
    1.      
      KapPreM Chem p1qa25    
    2. Potassium ethoxide
      Hydrogen gas
  26.           
    1. Rate of difussion of a gas is inversely proportional to the square root of the density provided temperature and pressure remain constant.
    2. RA/RB = âˆšMB/MA = âˆšDB/DA = Tm A/TmB
      T/Q = âˆšMT/MQ = 180/240 = âˆš18/Q

  27. H2SO3 =0
    (+2) + S +(-6)=0
    S=(+6 -2)
    S=+4

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