Chemistry Paper 1 Questions and Answers - Form 4 Term 1 Opener Exams 2021

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CHEMISTRY
PAPER 1
(THEORY)

FORM 4 TERM 1 OPENER EXAMS
TIME: 2 HOURS

INSTRUCTIONS TO CANDIDATES

  • Answer ALL the questions in the paper
  • Mathematical tables and silent electronic calculators may be used.
  • All questions should be answered in English.
  1.      
    1. What role do the following parts play during fractional distillation of water and ethanol?
      1. The fractionating column. (1mark)
      2. The glass beads (1mark)
    2. State one application of fractional distillation. (1mark)
  2. Study the table below and answer the questions that follow:-
    Ion Electron Arrangement
    R2+ 2.8.8 
    S2- 2.8
    1. Write the electron arrangement of each atom.
      R _______ (½ mark)
      S _______ (½ mark)
    2. Write the formula of the oxide of R and Chloride of S
      Oxide of R (1mark)
      Chloride of S (1mark)
  3. When 5.35g of Sodium Nitrate were heated in an open crucible, the mass of oxygen produced was 0.83g. given that the equation for the reaction is:-
    2NaNO3(s) → 2NaNO2(s) + O2(g)
    Calculate the percentage of Sodium Nitrate that was converted to sodium nitrite. (3marks)
    (Na=23, O=16, N = 14)
  4. Equal volumes of water put in 100cm3 glass beaker and heated for 5 minutes using Bunsen flames. It was observed that water in beaker A registered higher temperature than beaker B.
    ChemForm4Term1OpPP1Q4
    1. Name the kind of flame used in beaker; A (1mark)
    2. State the condition under which flame that heated B was produced. (1mark)
  5. Silver chloride can be prepared in the laboratory by the reaction between potassium chloride and silver nitrate.
    1. What name is given to this method of reaction? (1mark)
    2. Write an ionic equation for the reaction that occurs. (1mark)
  6. During heating of hydrated copper (II) sulphate crystals, the following readings were obtained:-
    Mass of evaporating dish = 300g
    Mass of evaporating dish + hydrated salt = 305g
    Mass of evaporating dish + dehydrated salt = 303.2g
    Calculate the empirical formula of hydrated copper (II) sulphate.
    (Cu = 64.5, S = 32.0, O= 16.0, H = 1) (3marks)
  7. A seed catalogue that the preferred soil pH range for the growth of different varieties of a crop are as shown in the table.
    Type of plant Preferred pH
    4.5 – 6.0 
    5.0 – 7.5 
    5.5 – 6.5 
    D 6.0 – 6.5 
    1. Which seed variety will grow over the largest pH range. (1mark)
    2. What soil pH range will a gardener be able to grow all these crops (1mark)
    3. The soil in a garden has a pH of 4.5, which substance can be added to the soil in order to grow plant type D? explain (2marks)
  8. Using dot (.) and cross (x) diagram, show bonding in the compound Ammonium ion (NH+4).(N= 14, H = 1) (2marks)
  9.    
    1. State Graham’s Law of diffusion. (1mark)
    2. 200cm3 of oxygen gas take 250seconds to diffuse through a porous plug. Under similar conditions, an equal volume of an unknown gas take 277 seconds to diffuse through the same porous plug. Calculate the relative molecular mass of the unknown gas. (3marks)
    3. Give two products formed when a candle burns. (1mark)
    4. From the above products; which elements make up a candle? (1mark)
  10. Explain how the following substances conduct an electric current.
    1. Magnesium metal. (1mark)
    2. Molten magnesium chloride (1mark)
  11. The molar mass of a gaseous compound XO2 is 64 gmol-1. A sample of this gas occupied 11.2dm3 at s.t.p.molar gas volume =22.4dm3.find
    1. The number of moles of this gas. (2marks)
    2. The amount in grams that occupied the above volume. (2marks)
  12. Classify the following processes as either chemical or physical. (3marks)
    Heating copper (II) sulphate crystals .  
    Obtaining kerosene from crude oil  .  
    Souring of milk  .  
  13. The diagram below represents a charcoal burner. Study it and answer the questions that follow;
    ChemForm4Term1OpPP1Q13
    Write equations for the reactions taking place in part I and II.
    I (1mark)
    II (1mark)
  14. When a mixture of iron filings and sulphur are heated, a red glow spreads through the mixture and a dark grey solid was formed.
    1. Identify the dark grey solid formed. (1mark)
    2. Write a chemical equation in which the dark grey solid is formed. (1mark)
    3. What observation can be made when dark grey solid reacts with dilute hydrochloric acid. (1mark)
  15. The table below shows isotopes and their percentage abundances.
    Isotope 
    Isotope mass 54  56  57 
    Percentage abundances  6.0  92.0  2.0
    Calculate the relative atomic mass of the element with the above isotopes. (3marks)
  16. Metal R does not react with an oxide of metal S. Metal T reacts with an oxide of metal S. metal Q reacts with an oxide of T. Arrange the metals in increasing order of reactivity. (2marks)
  17. An experiment was set up as shown below.
    ChemForm4Term1OpPP1Q17
    1. A student passed dry ammonia gas into the glass tube and tried to ignite the gas before allowing oxygen gas. What observation was made? (1mark)
    2. Write the equation for the reaction above (1mark)
  18.    
    1. Complete the table below to show pairs of substances used to prepare oxygen. (2marks)
      Hydrogen peroxide  
        Sodium peroxide 
    2. State the importance of oxygen in cutting metals. (1mark)
  19. The diagram below illustrates an experiment set up to investigate the effect of heat on copper (II) carbonate. Study it and answer the questions that follow.
    ChemForm4Term1OpPP1Q19
    1. Give the expected observation in each test tube.
      X ______(1mark)
      Y ______(1mark)
    2. Write an equation for the change that occurs in tube X (1mark)
  20.    
    1. State one way in which the strength of a base or an acid can be determined in the laboratory. (1mark)
    2. Give the basicity of the following acids:-
      1. Sulphuric (VI) acid. (1mark)
      2. Phosphoric acid (1mark)
  21. An element X is represented as 1840X (X = is not the actual symbol of the element)
    1. What is the composition of the nucleus for this element? (2marks
    2. Give the electronic arrangement of the element. (1mark)
  22. Chlorine gas was bubbled through a solution of potassium iodide in boiling tube.
    1. State the observation made. (1mark)
    2. Name the oxidizing agent in this reaction. Explain. (2marks)
  23. Name the process which take place when:-
    1. Iodine changes directly from solid to gas (1mark)
    2. Fe2+ changes to Fe3+ (1mark)
    3. White sugar changes to black solid when mixed with excess concentrated sulphuric acid. (1mark)
  24. GSTRU and P belong to the same period in the periodic table. The ions formed by the atoms are as below:-
    Q2+, U-, T2-, R3+, P+, S3-
    1. Arrange the elements in order of decreasing atomic size. (1mark)
    2. Suggest a reason why elements P and Q cannot react with each to form a compound. (1mark)
  25. A piece of burning magnesium ribbon was plunged into a gas jar containing sulphur (IV) oxide.
    1. What observation was made? (1mark)
    2. Write an equation for the reaction taking place. (1mark)
    3. What property of sulphur (IV) oxide is investigated above. (1mark)
    1. What is paper chromatography? (1mark)
    2. Give two applications of chromatography? (2marks)
  26. The structure of two molecules of water can be represented as shown below.
    ChemForm4Term1OpPP1Q27
    Name the type of bonds X and Y (2marks)
    X __________
    Y __________
  27. In an experiment 3.36g of iron fillings were added to excess copper (II) sulphate. Calculate the mass of copper that was deposited. (CU= 63.5, Fe = 56) (3mks )

MARKING SCHEME

  1.      
    1. What role do the following parts play during fractional distillation of water and ethanol?
      1. The fractionating column. (1mark)
        • Fractionating column; allow water vapour to condense into liquid and flow back to the flask before boiling point of water is reached.  √1mk

      2. The glass beads (1mark)
        • Glass beads; - increase the surface area for condensation of water to take place. √1

    2. State one application of fractional distillation. (1mark)
      • Distillation of liquid Air in the manufacture of nitrogen and oxygen √1mk or
      • Distillation of crude oil.

  2. Study the table below and answer the questions that follow:-
    Ion Electron Arrangement
    R2+ 2.8.8 
    S2- 2.8
    1. Write the electron arrangement of each atom.
      R - 2.8.8.2 (½ mark)
      S - 2.6 (½ mark)

    2. Write the formula of the oxide of R and Chloride of S
      1. Oxide of R (1mark)
        • RO
      2. Chloride of S (1mark)
        • SCl2

  3. When 5.35g of Sodium Nitrate were heated in an open crucible, the mass of oxygen produced was 0.83g. given that the equation for the reaction is:-
    2NaNO3(s) → 2NaNO2(s) + O2(g)
    Calculate the percentage of Sodium Nitrate that was converted to sodium nitrite. (3marks)
    (Na=23, O=16, N = 14)
    • Moles of oxygen gas. = 0.83/32
      = 0.02594 √1mk
      Moles of 2NaNO3 : O2
                                2 : 1
      Moles of NaNO3 = 2 x 0.02594.
      = 0.05188 moles √ ½ mk
      Mass of NaNO3 = 85 x 0.05188
      = 4.4098g √ ½ mk
      Percentage of NaNO3 = 4.098/5.35 X 4.098/5.35  x 100 = 82.45%

  4. Equal volumes of water put in 100cm3 glass beaker and heated for 5 minutes using Bunsen flames. It was observed that water in beaker A registered higher temperature than beaker B.
    ChemForm4Term1OpPP1Q4
    1. Name the kind of flame used in beaker; A (1mark)
      • A = Non Luminous

    2. State the condition under which flame that heated B was produced. (1mark)
      • When the air hole is closed. √1mk

  5. Silver chloride can be prepared in the laboratory by the reaction between potassium chloride and silver nitrate.
    1. What name is given to this method of reaction? (1mark)
      • Double decomposition (precipitation )

    2. Write an ionic equation for the reaction that occurs. (1mark)
      • Ag+(aq)  +  Cl-(aq) → AgCl(s)

  6. During heating of hydrated copper (II) sulphate crystals, the following readings were obtained:-
    Mass of evaporating dish = 300g
    Mass of evaporating dish + hydrated salt = 305g
    Mass of evaporating dish + dehydrated salt = 303.2g
    Calculate the empirical formula of hydrated copper (II) sulphate.
    (Cu = 64.5, S = 32.0, O= 16.0, H = 1) (3marks)
    • Empirical formula
      Compounds present : CuSO4 : nH2O
      Mass present                 3.2  :   1.8
      R.F.M                          160.5 :  18√1mk
      No of moles          3.2/160.5    :   1.8/18√ ½ mk
                                          0.02 : 0.1
      Mole ratio              0.02/0.02 : 0.1/0.02√ ½ mk
                                               1 : 5
      E.F. CuSO4 .5H2O √1mk

  7. A seed catalogue that the preferred soil pH range for the growth of different varieties of a crop are as shown in the table.
    Type of plant Preferred pH
    4.5 – 6.0 
    5.0 – 7.5 
    5.5 – 6.5 
    D 6.0 – 6.5 
    1. Which seed variety will grow over the largest pH range. (1mark)
      • Variety B

    2. What soil pH range will a gardener be able to grow all these crops (1mark)
      • 5.5-6.5 Soil Ph or 5.0-7.5

    3. The soil in a garden has a pH of 4.5, which substance can be added to the soil in order to grow plant type D? explain (2marks)
      • Add lime water which is basic for the soil PH to be neutral√1mk

  8. Using dot (.) and cross (x) diagram, show bonding in the compound Ammonium ion (NH+4).(N= 14, H = 1) (2marks)
    ChemForm4Term1OpPP1a8

  9.    
    1. State Graham’s Law of diffusion. (1mark)
      • The volume of a fixed mass of a gas is inversely proportional to the square  root  of the density.

    2. 200cm3 of oxygen gas take 250seconds to diffuse through a porous plug. Under similar conditions, an equal volume of an unknown gas take 277 seconds to diffuse through the same porous plug. Calculate the relative molecular mass of the unknown gas. (3marks)
      • 250/279 = √(32/mx)
        250 x Jmx = 277 x √32
        √mx= (277 x 532)/250
        Mx = ((277 x √32)/250)
        Mx = 39.29

    3. Give two products formed when a candle burns. (1mark)
      • Carbon (iv) oxide √1mk    and water  √1mk

    4. From the above products; which elements make up a candle? (1mark)
      • Carbon √1mk    and hydrogen  √1mk

  10. Explain how the following substances conduct an electric current.
    1. Magnesium metal. (1mark)
      • delocalized electrons

    2. Molten magnesium chloride (1mark)
      • mobile ions

  11. The molar mass of a gaseous compound XO2 is 64 gmol-1. A sample of this gas occupied 11.2dm3 at s.t.p.molar gas volume =22.4dm3.find
    1. The number of moles of this gas. (2marks)
      • I mole of a gas occupy - 22.4dm3 at s.t.p
                                            ? - 11.2dm3√1mk
                                                 (11.2 x 1)/22.4 = 0.5mol √1mk

    2. The amount in grams that occupied the above volume. (2marks)
      • 22.4dm3 → 64g/l
        11.2dm3 → ?
        11.2 x 64/22.4=32g √1mk

  12. Classify the following processes as either chemical or physical. (3marks)
    Heating copper (II) sulphate crystals reversing chemical change √1mk  
    Obtaining kerosene from crude oil  Physical change √1mk 
    Souring of milk  Permanent chemical change √1mk 
  13. The diagram below represents a charcoal burner. Study it and answer the questions that follow;
    ChemForm4Term1OpPP1Q13
    Write equations for the reactions taking place in part I and II.
    I (1mark)  - CO2(s)  + C(s)  →    CO(g)
    II (1mark) - 2CO(g)  +  O2(g)  →  CO(g)

  14. When a mixture of iron filings and sulphur are heated, a red glow spreads through the mixture and a dark grey solid was formed.
    1. Identify the dark grey solid formed. (1mark)
      • Iron (II)  sulphide √1mk

    2. Write a chemical equation in which the dark grey solid is formed. (1mark)
      • Fe(s)  +  S(s)  →  FeS √1mk

    3. What observation can be made when dark grey solid reacts with dilute hydrochloric acid. (1mark)
      • A gas with rotten egg smell is produced √1mk
      • A pale green solution is formed

  15. The table below shows isotopes and their percentage abundances.
    Isotope 
    Isotope mass 54  56  57 
    Percentage abundances  6.0  92.0  2.0
    Calculate the relative atomic mass of the element with the above isotopes. (3marks)
    • R.A.M =  54 x 6+ 56 x 92 + 57 x 2
                              100                                  √1mk

      = 324 + 5152 + 114
                   100                 √1mk

      = 5590/100
      = 55.9√1mk

  16. Metal R does not react with an oxide of metal S. Metal T reacts with an oxide of metal S. metal Q reacts with an oxide of T. Arrange the metals in increasing order of reactivity. (2marks)
    • RSTQ  √1mk   increasing reactivity √1mk
        →

  17. An experiment was set up as shown below.
    ChemForm4Term1OpPP1Q17
    1. A student passed dry ammonia gas into the glass tube and tried to ignite the gas before allowing oxygen gas. What observation was made? (1mark)
      • Ammonia gas does not burn in air. Thus it did not ignite.  √1mk

    2. Write the equation for the reaction above (1mark)
      • The gas ignites with green – yellow flame  √1mk
      • 4NH3(g)  +  3O2(g)   →  2N2(g)  +  6H2O(g)  √1mk
  18.    
    1. Complete the table below to show pairs of substances used to prepare oxygen. (2marks)
      Hydrogen peroxide  Manganese (IV) oxide √1mk
       Water √1mk Sodium peroxide 
    2. State the importance of oxygen in cutting metals. (1mark)
      • Oxy – hydrogen √1mk very hot flames for cutting of metal
      • Oxy – acetylene

  19. The diagram below illustrates an experiment set up to investigate the effect of heat on copper (II) carbonate. Study it and answer the questions that follow.
    ChemForm4Term1OpPP1Q19
    1. Give the expected observation in each test tube.
      X - green copper (II) carbonate changes to black copper (ii) oxide.(1mark)
      Y - The colorless solution of limewater turns to a white ppt. √1mk(1mark)

    2. Write an equation for the change that occurs in tube X (1mark)
      • CuCO3(s)      → CuO(s)  +  CO2(g) √1mk

  20.    
    1. State one way in which the strength of a base or an acid can be determined in the laboratory. (1mark)
      • By use of universal indicator solution √1mk    and compairing the colour obtained with the PH scale.

    2. Give the basicity of the following acids:-
      1. Sulphuric (VI) acid. (1mark)- 2
      2. Phosphoric acid (1mark) - 3

  21. An element X is represented as 1840X (X = is not the actual symbol of the element)
    1. What is the composition of the nucleus for this element? (2marks)
      • Protons 18 √1mk
        neutrons 22√1mk


    2. Give the electronic arrangement of the element. (1mark)
      • X : 2,8,8 √1mk

  22. Chlorine gas was bubbled through a solution of potassium iodide in boiling tube.
    1. State the observation made. (1mark)
      • Yellow colour of chlorine turns to colourless√1mk  and a black solid is formed at the  bottom of the    solution.

    2. Name the oxidizing agent in this reaction. Explain. (2marks)
      • 2KI (aq)  +  Cl2(g)  →  2KCl(aq) +  I2(g)
      • Chlorine is the oxidizing agent √1mk    because its oxidation number changes form 0 to -1

  23. Name the process which take place when:-
    1. Iodine changes directly from solid to gas (1mark)
      • Sublimation √1mk

    2. Fe2+ changes to Fe3+ (1mark)
      • Oxidation √1mk

    3. White sugar changes to black solid when mixed with excess concentrated sulphuric acid. (1mark)
      • Dehydration √1mk

  24. GSTRU and P belong to the same period in the periodic table. The ions formed by the atoms are as below:-
    Q2+, U-, T2-, R3+, P+, S3-
    1. Arrange the elements in order of decreasing atomic size. (1mark)
      • U ,T ,S ,R ,Q ,P √1mk
                      →
        Decreasing atomic size

    2. Suggest a reason why elements P and Q cannot react with each to form a compound. (1mark)
      • Both P and Q need to loose √1mk   electrons to become stable, therefore they cannot react to form a compound.

  25. A piece of burning magnesium ribbon was plunged into a gas jar containing sulphur (IV) oxide.
    1. What observation was made? (1mark)
      • A yellow deposit of sulphur is observed and a white powder of MgO formed.

    2. Write an equation for the reaction taking place. (1mark)
      • 2Mg(s)  +  SO2(g)  → 2MgO(s) + S(s) √1mk

    3. What property of sulphur (IV) oxide is investigated above. (1mark)
      • Oxidising agent/property

  26.         
    1. What is paper chromatography? (1mark)
      • A method used to separate coloured pigments.  √1mk

    2. Give two applications of chromatography? (2marks
      • In food industry to identify contaminants in food and drinks. √1mk
      • In sports to identify illegal substances e.g steroids in urine or blood samples. √1mk

  27. The structure of two molecules of water can be represented as shown below.
    ChemForm4Term1OpPP1Q27
    Name the type of bonds X and Y (2marks)
    X - Covalent bond √1mk
    Y - Hydrogen bond √1mk

  28. In an experiment 3.36g of iron fillings were added to excess copper (II) sulphate. Calculate the mass of copper that was deposited. (CU= 63.5, Fe = 56) (3mks )
    • Fe(s) + CuSO4(aq) → FeSO4(aq + Cu(s)
      1mol         1mol
      Moles of iron used = 3.36/56
                                 = 0.06moles √1mk

      Mole ratio of reaction
      Fe : Cu
      1 : 1√1
      Moles of Cu produced is 0.06.
      Thus mass of copper deposited
      = 0.06 x 63.5
      = 3.81g√1

 


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