Chemistry Questions and Answers - Form 1 End Term 1 Exams 2023

Instructions    

• Answer all the questions in the spaces provided.

1. Name the elements present in the following compounds.
   1. Sodium bromide (2mks)
   2. Lead oxide (2mks)
2. The curves below represent the variation of temperature wit time when pure and impure sample of a solid were heated separately   
   
               
   
   1. Which curve shows the variation in temperature for the pure solid?Explain? (2mks)
   2. State the effect of an impurity on the melting and boiling points of a pure substance. (2mks)
3.  
   1. State any three differences between luminous and non-luminous flames.(3mks)
   2. Explain how the hotness of a Bunsen burner flame can be increased.(1mk)
4. Give three reasons as to why laboratory apparatus are made of glass.(3mks)
5. Write a word equation for the reaction between;
   1. Carbon and oxygen (1mk)
   2. Sodium and sulphur (1mk)
   3. Copper and chlorine (1mk)
6. Define the following;
   1. Drug abuse (1mk)
   2. Prescription (1mk)
   3. Name two commonly abused drugs. (2mks)
7. State three difference between compounds and mixtures. (3mks)
8. The diagram below shows a set up that was used by a student to separate a mixture of water and ethanoic acid. Study it and answer the questions that follow. (Boiling point water = 100°C, ethanoic acid = 118°C
          
   
   1. State one mistake in the set up. (1mk)
   2. Which component of the mixture will be collected first and why?(2mks)
   3. State two chemical test that you can carry out to identify the component you stated in (b) above. (2mks)
   4. What are the roles of the following; (3mks)
      1. Thermometer
      2. Liebig condernser
      3. Pieces of broken porcelain
   5. Why is it preferable for the distillation flask to be round- bottomed rather than flat bottomed rather than flat bottomed. (1mk)
   6. At what point does one know that all of the first fraction has been removed from the distillation flask. Explain. (2mk)
9.  
   1. State a simple method that you can use to separate a mixture of iron fillings and sulphur powder. (1mk)
   2. A mixture of iron and sulphur was heated strongly until it glowed red throughout and then left to cool. Explain why you cannot obtain iron and sulphur from the product. Using the method you stated in (a). (2mks)
10.  
    1. Explain why a candle flame is not suitable for heating in the laboratory.(1mk)
    2. Besides a Bunsen burner, name one other apparatus that can be used conveniently for heating in the laboratory. (1mk)
11. State four characteristics of permanent chemical changes. (4mks)
12. Explain the differences between solid, liquid and gaseous state using the thermostatically mode of mater in terms of the kinetic theory. (6mks)
13. The diagram below shows the heating curve of a pure substance. Study it and answer the questions that follow.
    a. What physical changes are taking place at point: (2mks)
    1. 1. X
       2. Z
    2. What is the physical status of the substance at points? (2mks)
       1. W
       2. Y
    3. What happens to the temperature between point: (1mk)
       • AB
       • BC
       • CD
14.  
    1. What is sublimation? (1mk)
    2. State four substances that undergoes sublimation. (4mks)
15. Study the table below and complete it. (3mks)
    
    

    Element	Latin name	Symbol
    Potassum	Kelium
    	Natrium	Na
    Gold
    Iron	Ferrum
    	Plumbum	Pb
    		Cu

16.  What is a flame? (1mk)
17. Name three apparatus for measuring volume. (3mks)

MARKING SCHEME

1.  Name the elements present in the following compounds.
   1. Sodium bromide (2mks)
      • Sodium and bromine
   2.  Lead oxide (2mks)
      • Lead and oxygen
2. The curves below represent the variation of temperature wit time when pure and impure sample of a solid were heated separately. 
   
                         
   1. Which curve shows the variation in temperature for the pure solid? Explain? (2mks)
      • Curve B. it has a sharp melting point and boiling point.
   2. State the effect of an impurity on the melting and boiling points of a pure substance. (2mks)
      • Impurity lowers the melting point of a pure substance while impurity raises the boiling point of a pure substance.
3.  
   1. State any three differences between luminous and non-luminous flames.(3mks)
      
      

      Luminous	Non -luminous
      Has 4 reagion	Has 3 regions
      It is sooty	Its not sooty
      Large and unsteady	Small and steady
      Bright yellow in colour	Blue in colour

   2. Explain how the hotness of a Bunsen burner flame can be increased.(1mk)
      • by keeping the air holes fully open
4. Give three reasons as to why laboratory apparatus are made of glass.(3mks)
   • Does not react with most chemicals
   • Are relatively cheap
   • Easy to clean
   • Are transparent
5. Write a word equation for the reaction between;
   1. Carbon and oxygen (1mk)
      • Carbon + Oxygen carbon (IV) oxide
   2. Sodium and sulphur (1mk)
      • Sodium + surlphur sodium sulphide
   3. Copper and chlorine (1mk)
      • Copper + chloride copper chloride
6. Define the following;
   1. Drug abuse (1mk)
      • Use of a drug for a purpose other than what it is meant for, or use of overdose or underdose of prescribed drugs.
   2. Prescription (1mk)
      • Written instructions by a qualified medical officer, giving details on the type of drugs and how the drugs should be used.
   3. Name two commonly abused drugs. (2mks)
      • Tobacco
      • Alcohol
      • Bhang
      • Miraa
7. State three difference between compounds and mixtures. (3mks)
   
   

   Compound	Mixture
   Heat produced absorbed	No heat change during formation
   They are sing substance	Contains atleast two substances
   Cannot be separated into constituent element  by physical means	Can be saparated into constituent substance  by physical means

8.  The diagram below shows a set up that was used by a student to separate a mixture of water and ethanoic acid. Study it and answer the questions that follow. (Boiling point water = 100 O C, ethanoic acid = 118 O C)
   
   
   1. State one mistake in the set up. (1mk)
      • Water intake and water outlet have been reversed.
   2. Which component of the mixture will be collected first and why?(2mks)
      • Water. Because its boiling point is lower.
   3. State two chemical test that you can carry out to identify the component you stated in (b) above. (2mks)
      • It will turn blue cobalt (II) chloride paper pink
      • It will turn white copper (II) sulphate blue
   4. What are the roles of the following; (3mks)
      1. Thermometer
         • Shows the temperature of the vapour.
      2. Liebig condernser
         • To cool and condense the vapour of the fraction that is distilling out.
      3. Pieces of broken porcelain
         • To prevent bumping of the boiling mixture.
   5. Why is it preferable for the distillation flask to be round- bottomed rather than flat bottomed rather than flat bottomed. (1mk)
      • Ensures even distribution of heat.
   6. At what point does one know that all of the first fraction has been removed from the distillation flask. Explain. (2mk)
      • When the thermometer reads 118.1°C. because all the vapour coming out of the flask will be of ethanoic acid which has a boiling point of 118.1°C
9.  
   1. State a simple method that you can use to separate a mixture of iron fillings and sulphur powder. (1mk)
      • Magnetic separation/adding water to the mixture followed by decanting.
   2. A mixture of iron and sulphur was heated strongly until it glowed red throughout and then left to cool. Explain why you cannot obtain iron and sulphur from the product. Using the method you stated in (a). (2mks)
      • A new substance is formed which has properties very different from those of iron and sulphur.
10.  
    1. Explain why a candle flame is not suitable for heating in the laboratory.(1mk)
       • It is not hot enough and it is sooty. 
    2. Besides a Bunsen burner, name one other apparatus that can be used conveniently for heating in the laboratory. (1mk)
       • Spirit lamp
11. State four characteristics of permanent chemical changes. (4mks)
    • New substance are formed
    • The change is irreversible
    • The change is accompanied by change in mass
    • Heat energy is released or absorbed.
12. Explain the differences between solid, liquid and gaseous state using thethermostatically mode of mater in terms of the kinetic theory. (6mks)
     
    

    Solid	Liquid	Gas
    Particles closely packed	Particles  not closely  packed as in solid	Particles widely separated
    Particles hold in fixed positions	Particles move within the liquid in a container	Particles move independently

13. The diagram below shows the heating curve of a pure substance. Study it and answer the questions that follow.       
    1.  What physical changes are taking place at point: (2mk)
       • X- Melting
       • Z- Boiling
    2. What is the physical status of the substance at points? (2mks)
       • W – Solid
       • Y - Liquid
    3. What happens to the temperature between point: (1mk)
       1. AB – temperature increases steadily
       2. BC – The temperature remain constant until all the substances melts.
       3. CD – Temperature rises steadily as the liquid absorbs heat energy.
14. What is sublimation? (1mk)
    1. • The process where a substance changes from solid to vapour directly.
    2. State four substances that undergoes sublimation. (4mks)
       • Benzoic acid
       • Aluminum chloride
       • Carbon (IV) oxide
       • Iodine
       • Anhydrous iron (III) chloride
15. Study the table below and complete it. (3mks)
    
    

    Element	Latin name	Symbol
    Potassium	Kelium	k
    Sodium	Natrium	Na
    Gold	Aurum	Au
    Iron	Ferrum	Fe
    Lead	Plumbum	Pb
    Copper	Cuprum	Cu

16. What is a flame? (1mk)
    1. • A flame is a mass of burning gases.
17. Name three apparatus for measuring volume. (3mks)
    1. • Volumetric flask
       • Syringe
       • Beaker
       • Conical flask
       • Measuring cylinder