Chemistry Questions and Answers - Form 2 Term 1 Mid Term Exams

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CHEMISTRY
FORM 2
MID TERM
TERM 1

INSTRUCTIONS

  • Answer all the questions
  1. Define the following:
    1. Element (1mk)
    2. Ion (1mk)
  2.    
    1. Identify the following apparatus and give a use for each (3mks)
      ChemF2midt1q2
      1.    
      2.    
      3.    
    2. Name another apparatus that can be used in place of (b) (1mk)
  3. Give four reasons why most apparatus are made of glass (4mks)
  4. Define the following terms
    1. Isotope (1mk)
    2. Ionization energy (1mk)
    3. Electron affinity (1mk)
  5. Hydrogen gas was prepared in the lab. Using the following set up
    ChemF2midt1q5
    1. Write an equation for the reaction taking place and balance it (2mks)
    2. Name the method used to collect the gas and give a property of hydrogen that enables it to be collected through the method. (2mks)
    3. Name liquid R and state its function in the set up (2mks)
      Liquid R:
      Function:
    4. Explain why it is not advisable to use sodium metal in place of zinc metal (2mks)
    5. State two uses of hydrogen gas (2mks)
    6. What will happen to the pH of the solution in the beaker after one day? Give an explanation.(2mks)
  6. Samples of urine from three participants F, G and H at an international sports meeting were spotted onto a chromatography paper alongside two from illegal drugs A1 and A2. A chromatogram was run using methanol. The figure below shows the chromatogram.
    ChemF2midt1q6
    1. Identify the athlete who had used an illegal drug (1mk)
    2. Which drug is more soluble in methanol? (1mk)
  7. The curve below represents the variation of temperature with time when pure and impure samples of a solid were heated separately.
    ChemF2midt1q7
    Which curve shows the variation in temperature for the pure solid? Explain. (2mks)
  8. In an experiment, a test-tube full of chlorine water was inverted in chlorine water as shown in the diagram below and the set up left in sunlight for one day.
    ChemF2midt1q8
    After one day, a gas was found to have collected in the test-tube
    1. Identify the gas (1mks)
    2. How can the above gas be tested? (2mks)
  9. The table below shows some properties and electronic arrangements of common ions of elements represented by letters P to X. Study the information in the table and answer the questions that follow
    Element  Ion Electron arrangement Atomic radius Ionic radius 
     P P2+  2,8,8  0.197  0.099
     Q Q-  2,8  0.072  0.136
    R R+  2,8,8  0.231  0.133
     S S3+   2,8  0.143  0.050
     T  T2+  2,8,8  0.133  0.074
     U  U2+  2,8  0.160  0.065
    V V+ 2,8 0.186 0.095
    W W+ 2 0.152 0.060
     X  X-  2,8,8  0.099  0.181
    1. Give the atomic numbers of the elements P and Q (2mks)
      P -
      Q –
    2. Select the most reactive metallic element (1mk)
    3. Select 3 elements that belong to the same group of periodic table (2mks)
    4. Select 3 elements that would react with cold water to evolve hydrogen gas (1mk)
    5. Why is the ionic radius of element X larger than its atomic radius? (1mk)
    6. Write an equation of the reaction between element S and Oxygen (2mks)
  10. Moist iron wool was inverted over water. The set up was left to stand for 2 days
    ChemF2midt1q10
    1. Explain whether rusting is a physical or chemical reaction (2mks)
    2. Write an expression using X and Y to show the percentage of Oxygen (2mks)
    3. What would be the effect of using a larger piece of iron wool? Explain. (2mks)
    4. State two similarities between rusting and combustion (2mks)
  11. Observe the equation below
    Fe2O3(s) + CO(g)  Fe(s) + CO2(g)
    1. Balance the equation (1mk)
    2. Select the following from the above equation
      Oxidizing agent (1mk)
      Reducing agent (1mk)
    3. State two situations where redox reactions are applied in industry (2mks)
  12. Carbon (IV) sublimes at -78ºC. It is called dry ice
    1. Why is it called dry ice? (1mk)
    2. It is used for keeping ice cream cold. Why is it preferred to ordinary ice? (2mks)
    3. Name two other substances that behave as dry ice (2mks)
    4. Give an industrial application of sublimation (1mk)
  13.    
    1. Element X has two isotopes. Two thirds of 3316X and one-third 3016X. What is the relative mass of element X? 
    2. An element, A, has 30 protons and 35 neutrons. What is (2mks)
      1. The mass number of element A?
      2. The charge on the most stable ion of element A?
    3. An element B consists of three isotopes of mass, 28, 29 and 30 and percentage abundances of 92.2, 4.7 and 3.1 respectively. Show that the relative atomic mass of element is 28.11 (4mks)
    4. Elements X and Y have atomic numbers 11 and 17 respectively. Which one of the elements is a metal? Give a reason for your answer. (2mks)
    5. The table below shows the atomic numbers of four elements W,X,Y and Z
      Element  W X Y Z
      Atomic number  20 17 19 9
      Which two elements belong to the same group? (2mks
    6. Two elements M and N have atomic numbers 17 and 20 respectively. Write the formula of the compound formed when M and N react. (1mk)
  14. The following diagram represents a non-luminous flame of the Bunsen burner
    ChemF2midt1q14
    1. Name the parts of the flame labeled A, B and C (3mks)
    2. Which of the parts in (a) above is the hottest? (1mk)
    3. A non-luminous flame is preferred for heating. Explain (2mks)
    4.    
      1. Name the other type of flame produced by a Bunsen burner (1mk)
      2. Under what conditions does the Bunsen burner produce the flame in d(i)? (1mk)
    5. Define the following terms as used in medicine
      1. Drug (1mk)
      2. Prescription (1mk)
      3. Dosage (1mk)
      4. Drug abuse (1mk)
  15. Balance the following chemical equations
    1. Mg + O2 → MgO (1mk)
    2. Mg + N→ Mg3N2 (1mk)
    3. Al + HCl → AlCl3 + H2 (1mk)
    4. C3H8 + O2 → CO2 + H20 (1mk)
  16. Hydrated Copper (II) Sulphate is heated in a boiling tube as shown.
    ChemF2midt1q16
    1. State the colour of Copper (II) Sulphate before and after heating? (1mk)
    2. Explain why the boiling tube was slanted (1mk)
    3. How can the purity of the colourless liquid be confirmed? (1mk)
    4. Name another substance that can undergo the same change as hydrated Copper (II) Sulphate (1mk)
  17. A Magnesium ribbon was cleaned with steel wool and used in the following set up. Wet sand was heated before Magnesium ribbon.
    ChemF2midt1q17
    1. Explain the following:
      1. Sand was heated first before heating Magnesium ribbon (1mk)
      2. Magnesium ribbon was cleaned with steel wool (1mk)
    2. Name gas R (1mk)
    3. Write an equation for the reaction taking place in the combustion tube (1mk)
    4. Name the method used to collect gas R (1mk)

MARKING SCHEME

  1. Define the following:
    1. Element (1mk)
      • Pure substance which cannot be split into simpler substance by chemical means

    2. Ion (1mk)
      • Charged atom(s)
  2.    
    1. Identify the following apparatus and give a use for each (3mks)
      ChemF2midt1q2
      1.  - round bottomed flask – heating substances (½mk)  
      2.  - Measuring cylinder/Measuring volume of liquids (½mk)  
      3.  - Spatula/Scooping solids/chemicals from containers (½mk)
         
    2. Name another apparatus that can be used in place of (b) (1mk)
      • Burette/syringe/beaker (1mk any one correct)
        (Reject apparatus that can’t measure accurate volumes)

  3. Give four reasons why most apparatus are made of glass (4mks)
    • Easy to clean
    • Transport
    • Unreactive
    • Modelled into many shapes
    • Recyclable (Any 4 correct 1mk each)

  4. Define the following terms
    1. Isotope (1mk) - Atoms of same element having different number of neutrons hence different mass number (1mk)

    2. Ionization energy (1mk) - Energy required to remove an electron from an atom to form an ion in gaseous state (1mk)

    3. Electron affinity (1mk) - Energy required to capture/gain an electron by an atom to form an ion in gaseous state

  5. Hydrogen gas was prepared in the lab. Using the following set up
    ChemF2midt1q5
    1. Write an equation for the reaction taking place and balance it (2mks)
      Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)
      Wrong formula = no mark
      Symbols ½
      Balance ½

    2. Name the method used to collect the gas and give a property of hydrogen that enables it to be collected through the method. (2mks)
      • Upward delivery/downward displacement of air (1mk)
      • It is less denser than air (1mk)

    3. Name liquid R and state its function in the set up (2mks)
      Liquid R: - Conc. Sulphuric (VI) acid (1mk)
      Function: - For drying hydrogen (1mk)

    4. Explain why it is not advisable to use sodium metal in place of zinc metal (2mks)
      • Reaction would be explosive/dangerous because sodium is very reactive (1mk)

    5. State two uses of hydrogen gas (2mks)
      • Manufacture of hydrochloric acid
      • Manufacture of ammonia
      • Hydrogenation of oils to form fats
      • Weather balloons (rej. Air balloon)
      • In oxy-hydrogen flame for welding
      • As rocket fuel
      • As fuel cells (Any 2 correct, a mark each)

    6. What will happen to the pH of the solution in the beaker after one day? Give an explanation.(2mks)
      • It goes down.
      • The solution becomes more acidic.

  6. Samples of urine from three participants F, G and H at an international sports meeting were spotted onto a chromatography paper alongside two from illegal drugs A1 and A2. A chromatogram was run using methanol. The figure below shows the chromatogram.
    ChemF2midt1q6
    1. Identify the athlete who had used an illegal drug (1mk)
      • G(1mk)

    2. Which drug is more soluble in methanol? (1mk)
      • From A1 (1mk)

  7. The curve below represents the variation of temperature with time when pure and impure samples of a solid were heated separately.
    ChemF2midt1q7
    Which curve shows the variation in temperature for the pure solid? Explain. (2mks)
    • I – does not have definite Mpt and Bpt (1mk)

  8. In an experiment, a test-tube full of chlorine water was inverted in chlorine water as shown in the diagram below and the set up left in sunlight for one day.
    ChemF2midt1q8
    After one day, a gas was found to have collected in the test-tube
    1. Identify the gas (1mks)
      • Oxygen (1mk)

    2. How can the above gas be tested? (2mks)
      • Introduce a glowing splint into the gas (1mk)
      • It will relight (1mk)

  9. The table below shows some properties and electronic arrangements of common ions of elements represented by letters P to X. Study the information in the table and answer the questions that follow
    Element  Ion Electron arrangement Atomic radius Ionic radius 
     P P2+  2,8,8  0.197  0.099
     Q Q-  2,8  0.072  0.136
    R R+  2,8,8  0.231  0.133
     S S3+   2,8  0.143  0.050
     T  T2+  2,8,8  0.133  0.074
     U  U2+  2,8  0.160  0.065
    V V+ 2,8 0.186 0.095
    W W+ 2 0.152 0.060
     X  X-  2,8,8  0.099  0.181
    1. Give the atomic numbers of the elements P and Q (2mks)
      P - 20 (1mk)
      Q –9 (1mk)

    2. Select the most reactive metallic element (1mk)
      R

    3. Select 3 elements that belong to the same group of periodic table (2mks)
      • P,T,U  All 3 = 2mk/2 = 1mk/Otherwise no mark

    4. Select 3 elements that would react with cold water to evolve hydrogen gas (1mk)
      • P, R, T, U, V  (Any 3 = 1mk)

    5. Why is the ionic radius of element X larger than its atomic radius? (1mk)
      • Form ions by gaining electrons ½mk/ Since it is a non-metal/resulting in electron-electron ½mk  repulsion

    6. Write an equation of the reaction between element S and Oxygen (2mks)
      • 4S + 3O→ 2S2O3

  10. Moist iron wool was inverted over water. The set up was left to stand for 2 days
    ChemF2midt1q10
    1. Explain whether rusting is a physical or chemical reaction (2mks)
      • Chemical change 1mk/new substance formed

    2. Write an expression using X and Y to show the percentage of Oxygen (2mks)
      Oxygen = Y – X x 100
                         Y
      1mk for x – y
      1mk for %age

    3. What would be the effect of using a larger piece of iron wool? Explain. (2mks)
      • No change 1mk/ since % of oxygen is the same OR Vol. of O2 is fixed 1mk

    4. State two similarities between rusting and combustion (2mks)
      • New substance formed
      • Mass increases
      • Heat change involved (Any 2 correct = 1mk each)

  11. Observe the equation below
    Fe2O3(s) + CO(g) → Fe(s) + CO2(g)
    1. Balance the equation (1mk)
      Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2       (1mk)

    2. Select the following from the above equation
      Oxidizing agent (1mk)- Fe2O3
      Reducing agent (1mk)- CO
    3. State two situations where redox reactions are applied in industry (2mks)
      • Extraction of metals e.g. Iron 1mk each
      • Purification of metals e.g. Iron
        (Any other correct)

  12. Carbon (IV) sublimes at -78oC. It is called dry ice
    1. Why is it called dry ice? (1mk)
      • Sublimes without leaving a liquid

    2. It is used for keeping ice cream cold. Why is it preferred to ordinary ice? (2mks)
      • Leaves no liquid to spoil cream
      • Takes longer to sublime
      • Has a wider sublimation temp.
      •  
    3. Name two other substances that behave as dry ice (2mks)
      • Iodine Iron III chloride naphthalene (1mk)

    4. Give an industrial application of sublimation (1mk)
      • Extraction of Zinc metal (any correct = 1mk)
  13.        
    1. Element X has two isotopes. Two thirds of 3316X and one-third 3016X. What is the relative mass of element X?
      2 x 33 + 1 x 30 Total 4mks
        3              3
    2. An element, A, has 30 protons and 35 neutrons. What is (2mks)
      1. The mass number of element A? 
        30 + 35 = 65 (1mk)

      2. The charge on the most stable ion of element A?
        A2+ or +2 (1mk)

    3. An element B consists of three isotopes of mass, 28, 29 and 30 and percentage abundances of 92.2, 4.7 and 3.1 respectively. Show that the relative atomic mass of element is 28.11 (4mks)
      • 92.2 x 28 + 4.7 x 29 + 3.1 x 30 = R.A.M
               100          100          100
        25.816 + 1.363 + 0.93 = 28.11
        Show percentages = 2mks
        Work outs = 1mk
        Ans. = 1mk

    4. Elements X and Y have atomic numbers 11 and 17 respectively. Which one of the elements is a metal? Give a reason for your answer. (2mks)
      • Y / has 7 outermost electrons showing it is in group 7/a halogen (1mk)

    5. The table below shows the atomic numbers of four elements W,X,Y and Z
      Element  W X Y Z
      Atomic number  20 17 19 9
      Which two elements belong to the same group? (2mks)
      • X and Z (1mk)

    6. Two elements M and N have atomic numbers 17 and 20 respectively. Write the formula of the compound formed when M and N react. (1mk)
      • NM2     (1mk)

  14. The following diagram represents a non-luminous flame of the Bunsen burner
    ChemF2midt1q14
    1. Name the parts of the flame labeled A, B and C (3mks)
      1. Pale blue zone (1mk)
      2. Green blue zone (1mk)
      3. Almost colourless zone (1mk)

    2. Which of the parts in (a) above is the hottest? (1mk)
      • A 1mk

    3. A non-luminous flame is preferred for heating. Explain (2mks)
      • It is very hot/hotter than luminous does not produce soot (Any correct 1mk each)

    4.    
      1. Name the other type of flame produced by a Bunsen burner (1mk)
        • Luminous flame

      2. Under what conditions does the Bunsen burner produce the flame in d(i)? (1mk)
        • When air hole is closed

    5. Define the following terms as used in medicine
      1. Drug (1mk)
        • Any substance, natural or manufactured which when used alters body functions (1mk)

      2. Prescription (1mk)
        • giving written instructions by a qualified medical officer giving details on type
          of drugs and how they should be used (1mk)

      3. Dosage (1mk)
        • amount of drug/medicine to be taken at a time or regularly on a period of time

      4. Drug abuse (1mk)
        • Use of a drug for a use other than what it is meant for/under prescription or over prescription (1mk)

  15. Balance the following chemical equations
    1. Mg + O2 → MgO (1mk)
      2Mg(s) + O2(g)→2MgO(s)      (1mk)

    2. Mg + N2 → Mg3N2 (1mk)
      3Mg(s)+ N2(g) →Mg3N2(s) (1mk)

    3. Al + HCl → AlCl3 + H2 (1mk)
      2Al  + 6HCl(aq)→2AlCl3(aq) + 3H2(aq)    (1mk)

    4. C3H8 + O2 → CO2 + H20 (1mk)
      C3H8(g) + O2(g)→3CO2(g) + 4H20(l)    (1mk)

  16. Hydrated Copper (II) Sulphate is heated in a boiling tube as shown.
    ChemF2midt1q16
    1. State the colour of Copper (II) Sulphate before and after heating? (1mk)
      • Before – blue ½ mk/ after – white ½ mk

    2. Explain why the boiling tube was slanted (1mk)
      • Avoid boiling tube cracking due to condensed water flowing back (1mk)

    3. How can the purity of the colourless liquid be confirmed? (1mk)
      • Test its Bpt/Mpt/density (any 1 correct = 1mk)

    4. Name another substance that can undergo the same change as hydrated Copper (II) Sulphate (1mk)
      • Any hydrated slat (1mk)

  17. A Magnesium ribbon was cleaned with steel wool and used in the following set up. Wet sand was heated before Magnesium ribbon.
    ChemF2midt1q17
    1. Explain the following:
      1. Sand was heated first before heating Magnesium ribbon (1mk)
        • to generate steam for – driving air ½ mk from apparatus; react with Magnesium ½ mk

      2. Magnesium ribbon was cleaned with steel wool (1mk)
        • Remove layer of Magnesium oxide to allow Magnesium to combine with steam (1mk)

    2. Name gas R (1mk)
      • Hydrogen (1mk)

    3. Write an equation for the reaction taking place in the combustion tube (1mk)
      • Mg(s) + H2O(g)→MgO(s) + H2(g)       (1mk)

    4. Name the method used to collect gas R (1mk)
      • Over water method (1mk) 

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