Chemistry Paper 1 Form 3 Questions and Answers - End Term 2 Exams 2021

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Chemistry Paper 1 Form 3 End Term 2 Exams 2021 with Marking Schemes

Questions

  1. The diagram below shows Chromatograms for five different dyes.
    chemp1endterm2q1
    1. Name one condition required to separate the chromatograms present in a dye. (1 mk)
    2. What is meant by the solvent front? . (1 mk)
    3. Which chromatograms are present in dye E. (1 mk)
    4. Name two industrial applications of chromatography. (2 mks)
  2. An element Y has the electronic configuration 2.8.5
    1. Identify its period __________ (1mk)
    2. Write a formula of the most stable anion formed when U ionizes. (1mk)
    3. Explain the differences between the atomic radius of element Y and its ionic radius. (2mks)
  3.  
    1. What is meant by allotropy? (1 mark)
    2. The diagram below shows the structure of one of the allotropes of carbon
      chemp1endterm2q3b
      1. Identify the allotrope (½mk)
      2. State one property of the above allotrope and explain how it is related to its structure. (1½mk)
  4. Study the flow chart below and answer the questions that follow.
    chemp1endterm2q4
    1. Identify the metal oxide. (1mk)
    2. Write an ionic equation leading to the formation of the white precipitate X. (1mk)
    3. Give the formula of the ions responsible for the colourless solution Y. (1mk)
  5.  
    1. Apart from their location, state any two differences between a proton and an electron.(2 mks)
    2. Protons and neutrons are found in the nucleus of an atom. State two important roles played by of neutrons in the nucleus of an atom. (2 mks)
  6. Give equations to show the reactions that take place when;
    1. Iron reacts with steam. (1 mark)
    2. Name and give one industrial use of the gas produced in the reactions in (i) above. (2mks)

      Name: 

      Use:

  7. 20cm3 of an unknown gas Q takes 12.6 seconds to pass through small orifice.10cm3 of oxygen gas takes 11.2 seconds to diffuse through the same orifice under the same conditions of temperature and pressure. Calculate the molecular mass of unknown gas Q (O=16). (3mks)
  8. A compound of carbon, hydrogen and oxygen contains 71.12g by mass of oxygen, 2.2g hydrogen and the rest is carbon. It has relative molecular mass of 90.
    1. Determine the empirical formula of the compound. (3mks)
    2. Determine the molecular formula of the compound. (2mks)
  9. Study the information in the table and answer questions that follow:
    chemp1endterm2q9
    1. Determine the number of neutrons of R1 (1mk)
    2. Calculate the relative atomic mass of element R. (2mks)
  10.  
    1. Identify the type of bond formed in (i) and (ii). (1mks)
      chemp1endterm2q10
      (I)…………………………………………………..
      (II)…………………………………………………..
    2. Use dot (.) and cross (x) diagram to draw the structure of Sulphur (IV) oxide. ( 2marks)
  11. Complete the table below. (3 mks)
  12.  
    1. State Gay Lussac’s law. (1mk)
    2. What volume of oxygen will be required for complete combustion of 100cm3 of carbon (II) oxide. What is the volume of the product formed (All volumes at same temperature and pressure). (2mks)
  13. If 25.0cm3 of 0.1 M H2SO4 solution neutralized a solution containing 1.06g of sodium carbonate in 250cm3 of solution, calculate the molarity and volume of the sodium carbonate solution used. (3mks)
  14.  
    1. State Charles’ law. (1mk)
    2. The capacity of a balloon to hold a gas at 5oC is 1dm3 before it bursts due to expansions show whether it will burst or not at 35oC at constant pressure. (2mks)
  15. What is the colour of the following?
     Metal oxide  Colour when hot  Colour when cold
     Zinc oxide  (i)  (ii)
     Lead (II) oxide  (iii)  (iv)
    (4mks)
  16. Form two students from Anestar Premier High School reacted three elements as shown in the table below
     Element  Reaction with oxygen  Reaction with water
     X  Formed acidic oxide  No reaction
     Y  Formed basic oxide  Formed soluble hydroxide 
     Gave off hydrogen gas
     Z  Formed acidic oxide  Dissolved to form an acidic solution

    Which element (s) is likely to be: (3mks)
    1. Non-metal (s)
    2. Metal (s)
    3. Insoluble in water
  17. State the function of the following parts of a Bunsen burner (3mks)
    1. Air hole
    2. Collar
    3. Base
  18. Study the flow chart below and answer the questions that follow
    chemp1p1endterm2q18
    1. Identify gas X (1mk)
    2. Write an equation for the reaction between ammonia and gas X (1mk)
    3. Write an equation to show the formation of G and J (1mk)
  19. The diagram below shows the effect of sunlight on chlorine water
    chemp1endterm2q19
    1. Identify gas W (1mk)
    2. Write an equation to show the formation of gas W (1mk)
    3. What compounds are present in chlorine water? (1mk)
    4. Which compound is left in the beaker after complete formation of gas W? (1mk)
  20. Study the table below and answer the questions that follow
     Element  Atomic number  Atomic radius  Ionization energy
     K  3  0.089  1800
     V  11  0.136   1450
     T  19  0.174  1150
    1. Define the term ‘ionization energy’ (1mk)
    2. Explain the trend in the ionization energy from element K to T (2mks)
    3. Compare the trend in the melting and boiling points of elements K and T. (2mks)
  21. Explain using chemical means how you would differentiate between carbon (II) oxide and carbon (IV) oxide. (2mks)
  22. The following diagram shows the effect of electric current on lead (II) Chloride.
    chemp1p1endterm2q22
    1. When the circuit was completed no current flowed. Explain why. (1mk)
    2. When lead (II) Chloride was heated to about 3000C, it melted and there was light on the bulb. State and explain the observation made at the anode. (2mks)
  23. The set-up below shows the products formed when solid lead (ii) nitrate is heated.
    chemp1p1endterm2q23
    1. Identify:
      1. Liquid X …………………………………………………………… (1 mark)
      2. Gas Y…………………………………………………………… ( 1 mark)
    2. When lead (ii) Nitrate crystals are heated, they decrepitate and decompose, what is meant by the term decrepitating? (1 mark)
  24. Calculate the number of Al3+ ions released when 30cm3 of 0.1M of Aluminium Sulphate is dissolved in water. (L = 6.024 x 1023). (3mks)

Marking Scheme

  1.  
    1. – The chromatogram must have different solubility rate. (1 mk)
      - The dyes must have different adsorption on the filter paper. (1 mk)
    2. – It is the furthest distance reached by the solvent on the adsorbent material (or filter paper). (1 mk)
      - It is indicated as H on the diagram. (1 mk)
    3. Red, blue and green. (1 mk) (if only two are correct)
    4. D and A
    5. – Detecting and identifying poisonous substances present in food substances. (1 mk)
      - Separation of dyes into pure colours. (1 mk)
  2.  
    1. Period 3 
    2. Y3- 
    3. Ionic radius is large because incoming electrons repelled by energy levels.
  3.  
    1. Existence of a substance in two or more forms without a change of state (1 mk)
    2.  
      1. Graphite(½ mk)
      2. Conducts electricity, (1 mk) contains delocalised electrons. (½ mk) OR soft and slippery (1 mk) Hexagonal layer are held together by weak van der waals forces(½mk)(total 3 marks)
  4.  
    1. Zinc oxide 
    2. Zn2+(aq) + 2OH-(aq) → Zn(OH)2(s)
    3. Zn(NH3)42+
  5.  
    1. Apart from their location, state any two differences between a proton and an electron. (2 marks)
      • A proton is positively charged whereas an electron is negatively charged.
        The mass of a proton is/atomic mass units whereas that of an electron is a.m.u
    2. Protons and neutrons are found in the nucleus of an atom. State two important roles played by of neutrons in the nucleus of an atom. (2 mks)
      • Prevent repulsion between the positively charged protons.
      • Provide weight hence stability of the atom
  6. Give equations to show the reactions that take place when;
    1. iron reacts with steam. (1 mark)
      3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
    2. Name and give one industrial use of the gas produced in the reactions in (i) above. (1mk
      • Hydrogen.
        Uses: (Any one )
      • Industrial manufacture of hydrochloric acid
      • Industrial manufacture of Ammonia
      • Used in weather balloons
  7.  
  8.  

    Elements

    C

    H

    O

    % mass

    No. of moles

    Ratio of moles

    No. of atoms

    26.7    

    26.7/12 = 2.225

    2.225/2.2 =1

    1

    2.2

    2.2/1 = 2.2

    2.2/2.2 = 1

    1

    71.1  

    71.1/16 = 4.44375

    4.44375/2.2 = 2

    2    


    Empirical formula CHO2
    Molecular formula = (CHO2) n = 90
    = (12+1+32) n =90
    = (45) n = 90
        45        45
    = n=2
    = C2H2O4
  9.  
    1. 69 -31 = 38
    2. R.A.M of R = (61.3 x 69) + (38.7 x 71)
                                         100
      = 69.774
  10.  
    1.  
      1. Dative covalent bond
      2. Covalent bond
  11. – Lead; Pb;
    - Cuprum; 
    - Kalium;
    - Sternum
  12.  
    1. State Gay Lussac’s law. (1mk)
      • When gases combine they do so in volumes that bears simple ratio to one another and to the product if it is gaseous.
    2. What volume of oxygen will be required for complete combustion of 100cm3 of carbon (II) oxide. What is the volume of the product formed ( All volumes at same temperature and pressure) (2mks) 
      2CO(g) + O2(g) → 2CO2(g) (1 mk)
      100        50         100 volume of product = 100 cm3 (1 mk)
  13. Moles of acid = 25 x 0.1
    1000 = 0.0025.
    Moles of Na2CO3 = 0.0025 mol since mole ratio = 1:1
    Moles of Na2CO3 in 1000 cm3 = 1.06 x 1000 = 4.24g
                                                         250 
    Molarity = 4.24 = 0.04
                    106 
    Ma x va = mol of a
    Mb x Vb    mol of b
    Vb = 0.1 x 25
              0.04
    62.5cm
  14.  
    1. the volume of a given mass of gas is directly proportional to its absolute temperature at constant pressure.
    2. V1= V2
      T1   T2
      V2 = 1 x 308 = 1.108dm3
                 278
      The balloon will burst; at 35oC since volume is more than 1 dm3.; 
  15.  
    1. Yellow;
    2. White; 
    3. Red-brown;
    4. Yellow;
  16.  
    1. Z or X
    2. Y
    3. X
  17.  
    1. To allow air to pass through;
    2. To regulate the amount of water entering through the air hole;
    3. To support the Bunsen burner;
  18.  
    1. Oxygen;
    2. 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)
    3. 2NO2(g) + H2O(l) → HNO2(aq) + HNO3(aq)
  19.  
    1. Oxygen
    2. 2HOCl(l) → 2HCl(aq) + O2(g)
    3. Chloric (I) acid and hydrochloric acid
    4. hydrochloric acid
  20.  
    1. Ionization energy is the minimum amount of energy required to remove an electron from the last energy level of an isolated neutral atom form a positively charged ion in gaseous state. 
    2. The ionization energy decreases from K to T; this is because of the addition of an extra energy level from K to T which decreases the nuclear attraction hence easy to remove an electron from the outermost energy level; 
    3. Group I; they all have one electron in their outermost energy level;
    4. Both K and T have giant metallic structures. K has smaller atomic/ionic size with strong metallic bonds that require higher amount of energy to break hence high melting and boiling point compared to T. 
  21. Pass both gases through lime water; carbon (IV) oxide forms a white precipitate while carbon (II) oxide does not;
  22. The following diagram shows the effect of electric current on lead (II) Chloride.
    1. When the circuit was completed no current flowed. Explain why. (1mk) 
      • Solid lead (ii) chloride does not conduct electricity for there are no mobile ions 
    2. When lead (II) Chloride was heated to about 3000C, it melted and there was light on the bulb. State and explain the observation made. (2mks) 
      • Bubbles (1 mk) of yellow green –chloride ions(1 mk) migrate to the anode and are discharged to form chlorine gas.
    3. On the diagram, indicate the anode and the cathode. (1mk)
  23. The set-up below shows the products formed when solid lead (ii) nitrate is heated.
    1. Identify:
      1. Liquid X
        • Dinitrogen tetra – oxide (1 mark)
      2. Gas Y
        • Oxygen … ( 1 mark)
    2. When lead (ii) Nitrate crystals are heated, they decrepitate and decompose, what is meant by the term decrepitating? (1 mark
      • Production of cracking noise when heated
  24. Calculate the number of Al3+ ions released when 30cm3 of 0.1M of Aluminium Sulphate is dissolved in water. (L = 6.024 x 1023). (3mks)
    Al2(SO4)3(aq) → 2Al3+(aq) + 3SO42-(aq)
    Moles of Al2(SO4)3
    0.1 moles → 1000 cm3
     ? = 30 cm3
    0.1 × 30 = 0.003 moles
      1000
    From mole ratio
    Moles of Al3+ = 0.003 x 2
    = 0.006 moles ✓ ½
    No. of ions = 0.006 x 6.024 x 1023
    = 3.6144 x 1021 ✓ ions
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