Chemistry Paper 1 Questions and Answers - Nginda Girls Mock Examination 2023

Instructions 

• Answer all the questions 
• KNEC Mathematical tables and silent electronic calculator may be used.
• All the working must be shown clearly where necessary
• Candidates should answer questions in English.

QUESTIONS

1.  
   1. Bauxite is the chief ore found in the extraction of Aluminium. Name two impurities found in bauxite (2mks)
   2. Name the chief ores of both zinc and copper (1mk)
      zinc
      copper
2.  
   1. Identify the products formed when dinitrogen tetra oxide is dissolved in water (2mks)
   2. Write the balanced equation for the reaction above (1mk)
3. State one use of the following substances (3mks)
   AgBr
   CaSO₄.XH₂O
   Tincture of iodine
4. The grid below represents part of the periodic table .Study it and answer the questions that follow .The letters given do not represent the actual symbols of the elements.
   
   
   1. Select the element that can form a divalent anion (½mk).
   2. Name type of structure would the oxide of C have? (½mk).
   3. How does the melting point of A compare with that of E? (½mk).
   4. 2.6 g of B reacts completely when heated with 2.42 litres of chlorine gas (Cl₂) at s.t.p, calculate the relative atomic mass of B.(1 mole of gas occupies 22.4 litres at s.t.p.) (11/2mk).
5. Explain the differences in bleaching properties of chlorine and sulphur (use equations where necessary) (3mks)
6. 6. Metals K and N were connected to form a cell as shown in the diagram below. Their reduction potentials are as shown below:
   
   K+_(aq) / K(s) ≡- 0.17V
   N_+(aq) / N(s) = + 1.1 6V
   1. P is made by dipping a filter paper in a solution of sodium nitrate, on the salt bridge show the direction of flow of ions (1mk)
   2. On the diagram, show the flow of electrons (1mk)
   3. Write the equation for the half-cell reaction that occurs at (1mk)
      Metal K electrode.
      Metal N electrode
7. Write equations for the reactions between the following metals and steam. (3mks)
   Iron
   Zinc
   Copper
8. Study the diagram below and answer the questions that follow.
   
   
   1. Name (1mk)
      Solid V
      Gas W
   2. Describe a chemical test for chloride ions (2mks)
9. Starting with ethanol, describe how a sample of tetrachloroethane can be prepared (3mks)
10. A solution of bromine in water is a chemical reaction in equilibrium. The reaction involved is represented by the equation below;
    Br_2(aq) + H₂O_(l)     ↔   2H^+(aq) + Br_-(aq) + OBr_-(aq)
              Yellow                       Colourless
    1. State and explain the observation made when dilute sulphuric (VI) acid is added to the mixture at equilibrium. (2mks)
    2. Define the term dynamic equilibrium (1mk)
11.  
    1. Apart from downward delivery name another method that can be used to collect the following gases (2mks)
       Nitrogen (IV) oxide
       Sulphur(VI) oxide
    2. Name one gas that can be dried using anhydrous calcium oxide (1mk)
12. Starting with magnesium metal describe how a sample of magnesium carbonate can be prepared. (3mks)
13. With aid of well labelled diagrams show how a sample of sodium chloride, iodine and sand can be separated (3mks)
14. Explain the following (3mks)
    1. Why number of protons and electrons are equal in an atom
    2. The role of neutrons in the nucleus of an atom
    3. Cations are positively charged
15.  
    1. In an experiment 10.6g of a mixture of a anhydrous Sodium Carbonate and Sodium chloride were dissolved in water to make 100cm3 of solution .25cm³ of this solution required 20cm³ of 1M Hydrochloric acid solution for complete neutralization.
       1. Calculate the number of moles of Hydrochloric acid used (1mk)
       2. Write a balanced equation for the above reaction. (1mk)
       3. Calculate the mass of Sodium Carbonate in 25 cm³ of this mixture. (1mk)
16. Briefly describe how caffeine can be extracted from tea leaves. (3mks)
17. State the two roles of platinised-platinum in a standard hydrogen electrode (2mks)
18. Explain the following (3mks)
    1. Yellow phosphorus is stored under water
    2. Sodium is stored under paraffin oil
    3. Lime water and not potassium hydroxide is used to test for carbon(iv) oxide
19. Study the information below and use it to answer the questions that follow
    
    ∆Hθlattice =MgCl₂ - 2477kjmol^-1
    ∆Hθ hydration Cl^-1 (aq) -363kjmol^-1
    ∆Hθ hydration Mg⁺² (aq) -1891jmo^l-1 
    1. Differentiate between hydration energy and lattice energy? (1mks)
    2. Calculate the heat of solution of Magnesium Chloride (2mks)
20. Nylon 6,6 is formed from two monomers, hexan-1,6-dioic acid(adipic acid) and hexan-1,6-diamine (hexamethylene diamine ) through condensation polymerisation as shown in the diagrams below .
    1. Define condensation polymerisation (1mk)
    2. Write the equation for the formation of Nylon 6,6 (2mks)
21. According to Bronsteäd-Lowry theory, define an acid (1mk)
    NH_3(aq) + H₂O_(l) NH_4+(aq)+ OH_-(aq)
    Identify the species that acts as;
    1. A base
       Explain (1mks)
    2. An acid.
       Explain(1mk)
22.  
    1. Explain how painting prevents iron from rusting (1mk)
    2. Apart from protection from rusting state another reason for electroplating (1mk)
    3. What is sacrificial protection , use an example to explain your answer. (2mks)
23. The structure of RCOO^-Na⁺ below represents a type of cleansing agent. Describe how the cleansing agent removes grease from a piece of cloth. (3mks)
    
24. The diagram below represents a ‘jiko’ when in use .Study it and answer the questions that follow.
    1. Write equations for the reactions that occur in region
       1. B (1 mk)
       2. C (1 mk)
    2. Explain what happens in region A. (1 mks)
25. A compound contains 82.75% carbon and the rest is Hydrogen. (C=12, H=1)
    1. Determine its empirical formula. (2 Mrks)
    2. Determine the molecular formula if its molecular mass is 58. (1 Mks)
26. Determine the oxidation state of manganese in the following; (3mks)
    KMnO₄
    Mn₂O₃
27. Explain why the melting point of magnesium oxide is 3080°C while that of carbon IV oxide is -79°C. (2mks)

MARKING SCHEME

1.  
   1. Name two impurities found in bauxite(2mks)
      silica
      iron (ii) oxide
   2. Name the chief ores of both zinc and copper(1mk)
      zinc-zinc blende
      copper- copper pyrites
2.  
   1. Name the products formed when dinitrogen tetraoxide is dissolved in water(2mks)
      Nitric (V) acid
      Nitric (III) Acid
   2. Write the balanced equation for the reaction above (1mk)
      N₂O_4(l) + H₂O_(l) →HNO_3(aq) + HNO_2(aq)
3. State one use of the following substances (3mks)
   AgBr- light sensitive photographic plates
   CaSO₄.XH₂O-plaster of Paris in reinforcing fractured bones
   Tincture of iodine- as an antiseptic
4. The grid below represents part of the periodic table .Study it and answer the questions that follow .The letters given do not represent the actual symbols of the elements.
   
   1. Select the element that can form a divalent anion (1/2mk).
      A
   2. Name type of structure would the oxide of C have? (1/2mk).
      Giant ionic structure
   3. How does the melting point of A compare with that of E? (1/2mk).
      E has higher melting point than A
   4. 2.6 g of B reacts completely when heated with 2.42 litres of chlorine gas (Cl₂) at s.t.p, calculate the relative atomic mass of B.(1 mole of gas occupies 22.4 litres at s.t.p.) (11/2mk).
      22.4----------------1mole
      2.42-------------- 0.11mole
      Raio B : Cl2
      1 : 1
      0.11: 0:11
      2.6/0.11 = 23.6
5. Explain the differences in bleaching properties of chlorine and sulphur (use equations where necessary) (3mks)
   Chlorine bleaches by oxidation
   -HClO _(aq) + Dye →HCl _(aq) + Dye +O
     Coloured                     colourless
   Sulphur (IV) oxide by reduction
   -H₂SO_3(aq) + Dye H₂SO₄ + Dye-O
6. Metals K and N were connected to form a cell as shown in the diagram below. Their reduction potentials are as shown below:
   K⁺_(aq) / K_(s) ≡ - 0.17V
   N⁺_(aq) / N_(s) = + 1.1 6V
   1. P is made by dipping a filter paper in a solution of sodium nitrate, on the salt bridge show the direction of flow of ions (1mk)
   2. On the diagram, show the flow of electrons (1mk)
   3. Write the equation for the half-cell reaction that occurs at (1mk)
      Metal K electrode- K_(s)→ K²⁺(aq) +2e-
      Metal N electrode- N²⁺ _(aq) + 2e- → N(s)
7. Write equations for the reactions between the following metals and steam. (3mks)
   Iron-3 Fe_(s) + 4 H₂O_(g) →Fe₃O_4(s) + 4H_2(g)
   Zinc- Zn_(s) + H2O_(g)→ ZnO_(s) + H_2(g)
   Copper- no reaction
8. Study the diagram below and answer the questions that follow.
   
   
   1. Name(1mk)
      1. Solid V –Barium sulphite
      2. Gas W –Sulphur(iv) oxide
   2. Describe a chemical test for chloride ions (2mks)
      to the solution of chloride ions add lead (ii) nitrate and warm,
      a white precipitate if formed that dissolves on warming
9. Starting with ethene gas, describe how a sample of tetrachloroethane can be prepared (3mks)
   Add excess hydrogen gas to ethene gas in presence of nickel catalyst and 200oC to form ethane gas
   Add four moles of chlorine gas to ethane gas in presence of uV-light to form tetrachloroethane and hydrogen chloride gas
   Fractionate to obtain tetrachloroethane
10.  
    1. A solution of bromine in water is a chemical reaction in equilibrium. The reaction involved is represented by the equation below;
       Br_2(aq) + H₂O_(l)↔ 2H^+(aq) + Br_-(aq) + OBr_-(aq)
       Yellow                             Colourless
       State and explain the observation made when dilute sulphuric (IV) acid is added to the mixture at equilibrium. (2mks)
       The solution turns to yellow,
       Increase in hydrogen ions cause the equilibrium to shift to the left and more of bromine and water are formed
    2. Define the term dynamic equilibrium (1mk)
       State at which the rate of forward reaction equals the rate of backward reaction
11.  
    1. Apart from downward delivery name another method that can be used to collect the following gases (2mks)
       Nitrogen (IV) oxide -Liquifaction/liquidification
       Sulphur(VI) oxide –solidification/crystallisation
    2. Name a gas can be dried using calcium oxide (1mk)
       Ammonia gas
12. Starting with magnesium metal describe how a sample of magnesium carbonate can be prepared (3mks)
    Add magnesium into dilute hydrochloric acid to form magnesium nitrate
    To magnesium sulphates solution add sodium carbonate solution to form magnesium carbonate and sodium nitrate.
    Filter to obtain magnesium carbonate as the residue and sodium nitrate as the filtrate.
    Wash the residue with distilled water and dry between filter papers.
13. With an aid of well labled diagram show how a sample of sodium chloride, iodine and sand can be separated (3mks)
     
14. Explain the following (3mks)
    1. .Why protons and electrons are equal
       To make an atom electrically neutral
    2. The role of neutrons in the nucleus
       To reduce the repulsion between the protons in the nucleus
    3. Cations are positively charged
       They have more protons than electrons
15.  
    1. In an experiment 10.6g of a mixture of a anhydrous Sodium Carbonate and Sodium chloride were dissolved in water to make 100cm³ of solution .25cm³ of this solution required 20cm³ of 1M Hydrochloric acid solution for complete neutralization.
       1. Calculate the number of moles of Hydrochloric acid used(1mk)
          1mole---------------------1000cm3
          .---------------------20cm3
          =0.02moles
       2. Which substance reacts with the Hydrochloric acid in this mixture? (1mk)
          Sodium carbonate
       3. Calculate the mass of Sodium Carbonate in 25cm³  of this mixture. (1mk)
          Ratio: Na₂CO₃ : HCl
                       1          :   2
                  0.01                0.02
          0.01--------------25cm³
                                 100cm³
          =0.04moles
          0.04 X 10.6 = 4.24g
16. Briefly describe how caffeine can be extracted from tea leaves.(3mks)
    Grind a handful of tea leaves in a mortar using a pestle. Add a little propanone at a while as you continue crushing.
    Decant the extract into an evaporating dish
    Leave the extract in a sunny place to evaporate the solvent leaving behind caffeine
17. State the three roles of platinised-platinum in a standard hydrogen electrode (3mks)
    1. Act as inert metal connection to H/H+ system
    2. Provide a surface area for dissociation of H₂
    3. Serves as an electrical conductr to the external circuit
18. Study the information below and use it to answer the questions that follow
    ∆H^θlattice =MgCl₂ - 2477kjmol^-1
    ∆H^θ hydration Cl^-1 (aq) -363kjmol^-1
    ∆H^θ hydration Mg⁺² (aq) -1891jmol^-1 
    1. Differentiate between hydration energy and lattice energy? (1mark)
       Hydration: energy when one mole of gaseous ions becomes hydrated
       Lattice : energy change when 1 mole of an ionic compound is formed from its constituent ions in gaseous state
    2. Calculate the heat of solution of Magnesium Chloride (2 marks)
       Heat of solution= lattice + hydration energies
       =-1891-(-363X2)+2477
       =-140Kj/mol
19. Explain the following (2mks)
    1. yellow phosphorus is stored under water
       To prevent smouldering in the air
    2. Sodium is stored under paraffin oil
       To prevent reaction with both air and water
    3. Lime water and not potassium hydroxide is used to test for carbon(iv) oxide
       Lime water forms a white precipitate while potassium hydroxide does not
20.  
    1. Nylon 6,6 is formed from two monomers, Hexan -1,6-dioc acid and Hexan-1,6-diamine monomers through condensation polymerization.
       1. Define condensation polymerisation (1mk)
          Identical or different monomers combine to form a long chain molecule with the loss of small molecules
       2. Write the equation for the formation of Nylon 6,6 (1mk)
          
21. According to Bronsteäd-Lowry theory, define an acid (1mk)
    An acid is a proton donor
    NH_3(aq) + H₂O_(l) →NH₄⁺_(aq)+ OH_-(aq)
    Identify the species that acts as;
    1. A base. (1mk)…NH₃
       Explain … acts a proton acceptor
    2. An acid. (1mk) …H₂O
       Explain……act as proton donor
22.  
    1. Explain how painting prevents iron from rusting(1mk)
       It prevents contact between iron and water and oxygen
    2. Apart from protection from rusting state another reason electroplating(1mk)
       Beauty/aesthetics
    3. What is sacrificial protection , use an example to explain your answer. (2mks)
       A corrosion protection where a more reactive element (metal is electrically attached to a less reactive metal eg zinc bar attached to a ship body or magnesium attached oil pipeline to prevent rusting
23. The structure below represents a type of cleansing agent.
    RCOO-Na+
    Describe how the cleansing agent removes grease from a piece of cloth. (3mks)
    The hydrophilic end dissolves in the water while hydrophobic end dissolve in the grease spot. Upon agitation of the garment the greasy spot is dislodged in form of small droplets micelles which are washed away by water upon rinsing
24. The diagram below represents a ‘jiko’ when in use .Study it and answer the questions that follow.
    1. Write equations for the reactions that occur in region
       1. B (1 mk)
          C_(s) + O_2(g)→ CO_2(g)
       2. C (1 mk)
          C_(s) + CO_2(g)→ CO_(g)
    2. Explain what happens in region A. (1 mk)
       Carbon(ii) oxide burns in a blue flame in excess supply of air
25. A compound contains 82.75% carbon and the rest is Hydrogen.
    1. Determine its empirical formula. (2 Marks)
       

       Element	Carbon	Hydrogen
       Percentage	82.75%	17.25%
       Atomic masses	82.75/12	17.25/1
       mole	6.89	17.25
       Mole ratio	6.895/6.895	17.25/6.895
       	1      1x2	2.5      2.5x2

       
       = C2H5
    2. Determine the molecular formula if its molecular mass is 58. (1 Mark)
       Efm =29
       Mfm=58
       58/29=2
       C₄H₁₀
26. Determine the oxidation state of manganese in the following; (3mks)
    1. MnO₂
       X + (-2 x 2)=0
       X=+4
    2. KMnO4
       1+ x +(-2 x 4)= 0
       X=+7
    3. Mn₂O₃
       2x + (-2 x 3)=0
       X= +3
27. Explain why the melting point of magnesium oxide is 3080°C. (1mks)
    Have a giant ionic structure and strong ionic bonds hence high melting and boiling points