Chemistry Form 2 Questions and Answers - End Term 2 Exams 2021

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Chemistry Form 2 End Term 2 Exams 2021 with Marking Schemes

  1. Complete the table below for the characteristics of the sub atomic particles. ( 2marks)

    sub atomic particle Relative mass Electrical charge
    Proton 1  
    Neutral 1  
  2. A sample of air contaminated with carbon monoxide and sulphur dioxide was passed through the apparatus shown in the diagram below.
    chem2
    Which contaminant was removed by passing the contaminated air through the apparatus? Explain. (2mks)

  3. Explain how you would obtain solid lead carbonate from a mixture of lead carbonate and sodium carbonate powders. (3mks)
  4. Describe how the following reagents can be used to prepare copper (II) hydroxide, solid copper (II) sulphate, solid sodium hydroxide and distilled water. (3mks)
  5. Aluminium metal is a good conductor and is used for overhead cables. State any other two properties that make aluminium suitable for this use. (2mks)
  6. State with reasons whether the changes below are physical or chemical. (3mks)

    CHANGE TYPE OF CHANGE REASON
    I. Heating iodine crystals gently.    
    II. Formation of brown coating on iron when exposed to moist air.    
    III. Heating Zinc oxide    
  7. The table below shows the relative molecular masses and the boiling points of methane and water.

      Relative molecular mass Boiling point(oC)
    Methane 16 -161
    Water 18 100

    Explain why the boiling point of water is higher than that of methane. (2mks)

  8.  
    1. Two solutions J and K were tested with blue litmus papers and methyl orange indicator.

      Blue litmus remained blue in both solutions. Methyl orange remained orange in K but turned yellow in J.
    2. What is the nature of substance J? Explain. (2 marks)
    3. Give an example of a substance that K is likely to be. (1mark)
  9. Air was passed through several reagents as shown in the flow chart below.
    chem9
    1. Write an equation for the reaction which takes place in chamber with magnesium powder.(1mk)
    2. Name one gas, which escapes from the chamber containing magnesium powder. Give a reason for your answer. (2mks)
  10. A student setup the apparatus below in order to determine the percentage by volume of oxygen in air.
    chem10
    1. Why did water rise when the reaction had stopped? (1mk)
    2. The student wrote the expression for the percentage by volume of oxygen in air as 

      (y -x) /y x 100%

      Why was the volume of oxygen calculated using the above expression incorrect? (1mk)
    3. What should have been done after the reaction had stopped in order to get a correct volume. (1mk)
  11. Study the table below.

    Ion Electron Configuration
    L 2.8.8
    M2+ 2.8
    N3+ 2.8.8

    1. Which elements belong to the same period of the periodic table? (1 mark)
    2. What is the formula of the compound formed by L and N.? (1 mark)
    3. Compare the atomic and ionic radii of element L. (1 mark)
  12. In temperate countries, salt is sprayed on roads to defrost and clear roads but the long term effect on this practice is costly to motorist.
    1. Explain the role of salt in defrosting the ice. (1mk)
    2. Explain why the long term effect is costing to motorist. (1mk)
  13. The grid below shows part of a periodic table. The letters do not represent the actual symbols of the elements
    chem13
    1. Select the:
      1. Element which has the largest atomic radius. (1mk)
      2. Most reactive nonmetal. (1mk)
    2. Show on the grid the position of the element J which forms J2 ions with electronic configuration 2, 8, 8. (1mk)
  14. Oxygen is obtained on large scale by the fractional distillation of air as shown on the flow chart below.
    chem14
    1. Explain why air is considered as a mixture (1mk)
    2. Identify the substance that is removed at the filtration stage (1mk)
    3. Explain why Carbon (IV) oxide and water are removed before liquefaction of air. (1mk)
    4. Identify the component that is collected at -186°C (1mk)
  15. Study the table below and answer the questions that follow:

    Substance A B C D E F
    Melting Point (oC ) 801 113 OR 119 -39 5 -101 1356
     Boiling point (oC) 1410 445 457 54 -36 2860
     Electrical
    Conductivity
    Solid Poor Poor Good Poor Poor Poor
    Liquid Good Poor Good Poor Poor Poor

    Identify with reasons the substances that:
    1. Have a metallic structure (2mks)
    2. Have a molecular structure (2mks)
    3. Substances A and C conduct electric current in the liquid state. State how the two substances differ as conductors of electric current (2mks)
  16. Atoms of element X exists as 146X and 126X
    1. What name is given to the two types of atoms. (1mk)
    2. Use dot (∙) and cross (x) diagrams to illustrate the atomic structure of 146X (2mks)
  17.   
    1. Give 2 reasons why most laboratory apparatus are made of glass. (1mk)
    2. The diagrams below are some common laboratory apparatus. Name each apparatus and state its use. (2mks)
      chem17bi chem17bii
  18. Soot is one of the environmental pollutants.
    1. Explain the term pollutant. (1mk)
    2. State how soot is formed from hydrocarbons. (1mk)
  19. Phosphorus element smoulders in air to form two oxides
    1. Name the two oxides. (2 mks)
    2. State the nature of the solution when the above mentioned oxides are dissolved in water. (1mk)
  20.   
    1. What is meant by the terms: ( 2 mark )
      1. Atom
      2. Mass number
    2. The formula of element T is TCl3. What is the formula of its sulphate? (1 mk)
  21. Crystals of sodium carbonate decahydrate (Na2CO3 . 10H2O ) were exposed to air for about four days.
    1. State what was observed. (1mk)
    2. Name the process that took place. (1mk)
    3. Write an equation for the reaction that occurred. (1mk)
  22. Explain why molten calcium chloride conducts electricity while silicon (IV) oxide does not. (2mks)
  23. The table below gives the first ionization energy of three elements

    Element A
    1st ionization energy(kJ/mol) 496 419 520

    1. Define the term first ionization energy. (1mk)
    2. Select the element that is the most reactive. Explain. (2mks) 
  24. State the colour of the indicators in the solutions given in the table below: (3mks)

      Colour in
    Indicator Acid Base
    Litmus Red  
    Methyl orange   Yellow
    Phenolphthalein Colourless  


 Marking Scheme

  1. Complete the table below for the characteristics of the sub atomic particles( 2marks)

    sub atomic particle Relative mass Electrical charge
    Proton  1  1 √1
    neutral  1  0 √1
  2.  A sample of air contaminated with carbon monoxide and sulphur (IV) oxide was passed through the apparatus shown in the diagram below.

    Which contaminant was removed by passing the contaminated air through the apparatus? Explain.

    Sulphur (IV) oxide√1, it reacts with limewater being an acidic gas √1

  3. Explain how you would obtain solid lead carbonate from a mixture of lead carbonate and sodium carbonate powders.

    Add water √1, filter to remove lead carbonate as a residue √1, wash and dry the residue √1

  4. Describe how the following reagents can be used to prepare copper (II) hydroxide, solid copper (II) sulphate, solid sodium hydroxide and distilled water.

    Add distilled water to solid copper (II) sulphate and solid sodium hydroxide in separate beakers to obtain their solutions. √1 mix the solutions to obtain copper (II) hydroxide precipitate √1 filter, wash and dry the residue √1

  5. Aluminium metal is a good conductor and is used for overhead cables. State any other two properties that make aluminium suitable for this use.

    Has low density// it is light √1
    Forms a protective oxide coating on its surface √1


  6. CHANGE TYPE OF CHANGE REASON
    I. Heating iodine crystals gently. Physical Change to gas then back to solid
    II. Formation of brown coating on iron when exposed to moist air. Chemical New substance formed
    III. Heating Zinc oxide Physical Color changes to yellow then back to white
  7. The table below shows the relative molecular masses and the boiling points of methane and water

      Relative molecular mass Boiling point(oC)
    Methane 16 -161
    Water 18 100

    Explain why the boiling point of water is higher than that of methane.

    The molecules of water interact through strong hydrogen bonding √1
    while molecules of methane have weak van der Waals forces√1 
  8.  
    1. J is basic
      Bases turn litmus blue and methyl orange yellow
    2. Water, NaCl (any neutral substance)

  9. Air was passed through several reagents as shown in the flow chart below.
    1. Write an equation for the reaction, which takes place in chamber with magnesium powder

      3Mg (s) + N2 (g) -> Mg3N2(s) √1

    2. Name one gas, which escapes from the chamber containing magnesium powder. Give a reason for your answer.

      Argon // Neon (name of a noble gas) √1
      Because they are inert and not likely to have reacted with any of the reagents. √1

  10.  
    1. To occupy space previously occupied by oxygen that was used by smouldering

      phosphorous. √01

    2. Because oxides of phosphorous formed still occupy space enviously occupied by oxygen.

      (P2O5, P2O3) √01

    3. Let all the fumes dissolve in water before final reading is taken √01

  11.  
    1. M & L
    2. NL3
    3. Ionic radii is bigger. It gains electrons to form ions
  12. In temperate countries, salt is sprayed on roads to defrost and clear roads but the long term effect on this practice is costly to motorist.

    1. Explain the role of salt in defrosting the ice. (1mk)
      It acts as an impurity in the ice hence lowering its melting point. √ ½
    2. Explain why the long term effect is costing to motorists. (1mk)
      Salt accelerates the rate of rusting of the iron parts of the motor vehicles. √ ½

  13. The grid below shows part of a periodic table. The letters do not represent the actual symbols of the elements

    1. Select the:
      1. Element which has the largest atomic radius.
        F √1

      2. Most reactive non-metal.
        I √1

    2. Show on the grid the position of the element J which forms J2- ions with electronic configuration 2, 8, 8. (1mk)
  14. Oxygen is obtained on large scale by the fractional distillation of air as shown on the flow chart below.
    1. Explain why air is considered as a mixture (1mk)
      - Various components can be separated using a physical means / method.
      - Components in air are not in fixed proportions. Any 1 x 1 = 1 mk
    2. Identify the substance that is removed at the filtration stage (1mk)
      - dust particles √1
    3.  Explain why Carbon (IV) oxide and water are removed before liquefaction of air (1mk)
      -They would readily solidify √ ½ and block the pipes √ ½
    4.  Identify the component that is collected at -186°C (1mk)
      Argon √1

  15. Study the table below and answer the questions that follow:-

    Identify with reasons the substances that:
    1. Have a metallic structure (2mks)

      C √1 Good conductor of electricity √1 in both solid and liquid state due to delocalised

    2. Have a molecular structure (2mks)

      D or E √1 Are poor conducts in both solid / liquid state.
      Have relatively low M.P and B.P due to molecular structure.

    3. Suggest a reason why substance B has two melting points (1mk)
      Exists as allotropes √1

    4. Substances A and C conduct electric current in the liquid state. State how the two substances differ as conductors of electric current (2mks)

      A – mobile / free ions
      B – Delocalized electrons

  16. Atoms of element X exists as and 
    1. What name is given to the two types of atoms.
      Isotope √1
    2. Use dot (∙) and cross (x) diagrams to illustrate the atomic structure of 
  17.  
    1. Give 2 reasons why most laboratory apparatus are made of glass. (1mk)
      • Glass does not react with most chemicals √ ½
      • It is transparent one can see when reaction is taking place. √ ½ 
      • It is easy to clean. √ ½ any 2

    2. The diagrams below are some common laboratory apparatus. Name each apparatus and state its use. (2mks)
      Name: Desiccator
      Use Drying or keeping substances from moisture

      Name Evaporating dish
      Use Evaporating liquids to obtain crystals
  18. Soot is one of the environmental pollutants .
    1. Explain the term pollutant.
      Harmful substance released into the environment √1
    2. State how soot is formed from hydrocarbons.
      Soot is formed when hydrocarbons burns in a limited supply of oxygen √1 // incomplete combustion
  19.  
    1.  
      1. Phosphorus (III) oxide
      2. Phosphorus (V) oxide 
    2. Acidic
  20.  
      1. Smallest particle of an element that can take part in a chemical reaction.
      2. Number of protons and neutrons in the nucleus of an atom.
    1. T2(SO4)3
  21. Crystals of sodium carbonate decahydrate (Na2CO3.10H2O) were exposed to air for about four days.
    1. State what was observed.
      A white powder was formed √1 
    2. Name the process that took place.
      Efflorescence √1 
    3. Write an equation for the reaction that occurred.
      Na2CO3.10H2O(s ) Na2CO3.H2O(s ) + 9H2O(l) √1
  22. Explain why molten calcium chloride conducts electricity while silicon (IV) oxide does not.

    Molten calcium chloride contains delocalized ions which carry charge√1 but silicon (IV) oxide does not √1

  23. The table below gives the first ionization energy of three elements.
    1. Define the term first ionization energy. 

      First ionization energy is the minimum amount of energy required to remove the first electron From a gaseous atom √1

    2. select the element that is the most reactive. Explain.

      B √1 it has the least ionization energy therefore loses electrons most readily √1

  24. State the colour of the indicators in the solutions given in the table below:

      Colour in
    Indicator Acid Base
    Litmus Red Blue √1
    Methyl orange Orange √1 Yellow
    Phenolphthalein Colourless Pink √1
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