Chemistry Questions and Answers - Form 1 End Term 3 Exams 2021

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QUESTIONS

  1. The following diagram represents a non-luminous flame of the Bunsen burner
                Bunsen burner non luminous
    1. Name the parts of the flame labeled A,B andC(3 marks)
    2. Which of the parts in (a) above is the hottest and why?          (2marks)
    3. Under what conditions does the Bunsen burner produce the flame drawn above(1mark)
  2. Complete the following word equations.                    (3marks)
    1. Magnesium Hydrogen Carbonate+ dilute Nitric acid→
    2. Carbon + Oxygen→
    3. Zinc oxide + dilute Sulphuric acid→ 
  3. The curve below is a heating curve of naphthalene. Use it to the questions that follow. 
             Heating curve of Naphthalene
    1. Explain what happens in the following regions. (6 mks)  
      1. AB
      2. BC
      3. CD 
    2. Give the effect of impurities on both melting and boiling points of a pure substance. (2mrks)  
  4.  
    1. Give any two examples of mineral acids       (2marks)
    2. Give two effects of acids on substances. (2marks) 
    3. Acids and bases are of importance in our daily life. State 3 uses of bases   (3 marks)
  5.  
    1. Air is a mixture of gases. Give the various components of air. (2marks) 
    2. The apparatus below were used to determine the volume of oxygen in air. About 200 cubic centimeters of air were passed repeatedly from syringe A to syringe B over heated copper turnings are shown in the diagram below. After some time, the volume of air in syringe A was 160 cubic centimeters and in syringe B 0 cubic centimetres. 
       Aparatus of volume of oxygen in air
      Calculate the percentage of oxygen in the initial sample of air. (3marks)              (1mark)
    3. Write down a word equation for the reaction that took place in the combustion tube. (1mark)
    4. Give one possible source of error in the experiment. (1mark)
  6.  
    1. Define the following terms (2marks)
      1. Rust 
      2. Saturated solution
    2. Give two conditions necessary for rusting to occur. (2marks) 
    3. State two ways of preventing rusting to occur.        (2marks) 
    4. Cars in Mombasa rust faster than those in Nyeri .Explain (2mrks) 
  7. Classify each of the following change as either temporary or permanent.    (3marks)
    1. Striking a match to burn.
    2. Burning a piece of paper.
    3. Zinc oxide Equation Zinc oxide                
      (White)                (Yellow)
  8. Identify the elements present in the following compounds.
    1. Calcium oxide(1mark)       
    2. Magnesium nitrate (11/2 marks)
    3. LeadSulphate(11/2 marks)
  9. The diagram below shows a set-up of apparatus used to separate miscible liquids.
             diagram of separation of miscible liquids
    1. Name the parts labelled A and B.                                  (2marks)
      A
      B
    2. State the function of the part labeled A . (1mark)
    3. State the property of the mixture that makes it suitable to be separated by the method above.                                                                                                                           (1 mark)
  10. Samples of urine from three participants F, G and H at an international sports meeting were spotted onto a chromatography paper alongside two illegal drugs A1 and A2. A chromatograph was run using Ethanol. The figure below shows the chromatograph.
            Diagram of chromatography
    1. Identify the athlete who used an illegal drug                                                           (1mk)
    2. Which drug is soluble in Ethanol(1 mk)
    3. Which two properties of the component of the mixture facilitate separation? (2 marks)
    4. Normally line A is drawn using a pencil and not ink.  Explain why the pencil is preferred to ink.(2marks) 
  11.  
    1. Describe how coconut oil can be obtained from coconut in the laboratory.    (3 marks)
    2. State one practical application of the process in a) above (1mk)
  12. Study the table below which shows the pH values of solutions A, B, C, D and E.
    Use it to answer the questions that follow.
    Solution  A       B        C      D      E      
     pH 13.0  7.0  9.0 6.5  2.0 

    1. Which solution is the most acidic? (1 mark)
    2. Which solution is a neutral? (1 mark)
    3. Identify the solution that is most likely to be:
      1. Rain water 
      2. Antacids tablet 
      3. Sodium hydroxide (3 marks)
  13. State any two differences between luminous and non-luminous flames      (2 marks)
  14. State three uses of Oxygen gas(3marks)

 

 

 

 

 

 MARKING SCHEME

  1.  
    1. A-Pale blue zone
      B-Green blue zone
      C-Almost colorless zone
    2. A,it has plenty of air hence the gases burn completely
    3. When the air hole is open
  2.  
    1. Magnesium nitrate + carbon IV oxide + water
    2. Carbon+ oxygen →Carbon (IV) oxide
    3. Zinc sulphate + water
  3.  
    1.  
      1. AB
        Temperature increases steadily as the naphthalene absorbs heat energy. Kinetic energy is increased and the particles vibrate more vigorously
      2. BC
        Temperature remains constant until all the naphthalene melts. The heat energy absorbed weakens the forces of attraction holding the particles of naphthalene together. The particles move far apart and naphthalene changes from solid to liquid
      3. CD
        Temperature rises steadily as the liquid naphthalene absorbs heat energy. Kinetic energy of the particles is increased causing the particles to move faster.
    2. B.P raises M.P lowered
  4.  
    1.  
      • Sulphuric acid
      • Nitric acid
      • Hydrochloric acid
    2.  
      • Causes corrosion
      • Causes burning
    3.  
      • manufacture of antiacid tablets
      • nuetralizing soil acidity
      • manufacture of soaps and detergents
      • making of cement
  5.  
    1. Air is a mixture of gases. Give the various components of air. ( 2 mks)
      • Water vapor carbon (iv) oxide oxygen nitrogen gas
    2. calculate the percentage of oxygen in the initial sample of air. ( 2 mks)
      200 -160 ×100
         200
       40  × 100 =20%
      200
    3. write down a word equation for the reaction that took place in the combustion tube. ( 2 mks)
      • copper + oxygen =copper (ii) oxide
    4. give one possible source of error in the experiment. ( 1 mk)
      • Inaccuracy in measuring the volume
  6.  
    1.  
      1. rust hydrated iron (iii) oxide
      2. A solution that cannot dissolve any more solute
    2. Give two conditions necessary for rusting to occur. ( 2 mks)
      • Water and oxygen
    3. State two ways of preventing rusting to occur. ( 2 mks)
      • Oiling, galvanizing , electroplating
    4. Cars in Mombasa rust faster than those in Nyeri .Explain ( 2 mks)
      • Presence of salt in Mombasa
  7.  
    1. permanent
    2. Permanent
    3. Temporary
  8.  
    1. calcium and oxygen
    2. Magnesium, nitrogen and oxygen
    3. Lead, sulpur and oxygen
  9.  
    1. A-Fractionating column
      B-Liebig’s Condeser
    2. To condense vapour of liquid which has not reached its boiling point.
    3. The fractions have different boiling points
  10.  
    1. G
    2. A1
    3.  
      • Adsorption ability
      • Solubility of the drugs in ethanol
    4. Ink contains different dyes thus will also separate
  11.  
    1. Put the coconut in a mortar. Crush the coconut using a pestle.
      Add an appropriate solvent e.g Ethanol/Propanone to dissolve the seeds and leave the coconut oil to settle at the top. Decant and evaporate the solution to obtain oil.
    2.  
      • Extraction of oil from nuts
      • Removal of stains from clothes
  12.  
    1. E
    2. B
    3.  
      1. D
      2. C
      3. A
  13.  
    • Luminous flame produces soot while non-luminous does not
    • Luminous is large and wavy while non-luminous is short and steady
  14. Give two commercial applications of oxygen. ( 2mks)
    • Produces oxy- acetylene flame used in welding.
    • Used in hospitals to patients with breathing difficults
    • Used by mountain climbers, deep see divers
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