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Chemistry Paper 1 Questions and Answers- Mokasa 1 Joint Pre Mock Exams 2023

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INSTRUCTIONS TO CANDIDATES
  • Answer all the questions in the spaces provided
  • All working MUST BE clearly shown where necessary
  • Scientific calculators may be used
  • Candidates should answer the questions in English 
  1.  
    1. Give the systematic names of the following hydrocarbons
      1. CH3(CH2)4CH3     (1Mark)
      2. CH3 − C = CH2    (1Mark)
                    l
                 CH3
    2. The molecular formula of a hydrocarbon is C6H14
      The hydrocarbon can be converted into two other hydrocarbons as shown by the equation below.
      C6H14 → X + C3H8
      1. What is the name of above process?       (1/2Mark)
      2. Write the molecular formula of X        (1/2Mark)
  2. Mr. Rudisha went to a doctor who sent him to a pharmacy to pick some drugs.  The pharmacist wrote on the medicine packaging 2 x 3 
    1. Clearly state what 2 x 3 meant?       (1Mark)
    2. State one reason why it is important to adhere to the doctor’s prescription.        (1Mark)
  3. The apparatus below were used by a student to study to effect of heat on hydrated copper (II) Sulphate. 
    F4ChemMokMP12023Q3
    1. What is the role of the ice-cold water? (1Mark)
    2. Name liquid P. (1/2 Mark)
    3. What is the observation made in the boiling tube. (1Mark)
    4. Name type of change illustrated above (1/2Mark)
  4. The diagram below shows a paper chromatogram of substances A, B and C which are coloured.
    F4ChemMokMP12023Q4
    1. Indicate baseline on the chromatogram. (1Mark)
    2. Which substance is pure? Explain (1Mark)
    3. Substance D is a mixture of B and C.  Indicate it chromatogram on the diagram  (1Mark)
  5.  
    1. A beekeeper found that when stung by a bee, application of a little solution of sodium hydrogen carbonate helped to relieve the irritation on the affected.  Explain. (2Marks)
    2. Flower extracts can be used to Acid-bade indicators.  Give two limitations of such indicators. (1Mark)
  6. The apparatus below was a set up to show catalytic oxidation of ammonia.
    F4ChemMokMP12023Q6
    1. Write an equation for the reaction that takes place in the gas jar. (1Mark)
    2. What is the role of the hot nichrome wire (1Mark)
    3. Apart from nichrome wire what else can be used? (1Mark)
  7. The set-u is used to investigate the properties of hydrogen. 
    F4ChemMokMP12023Q7
    1. On the diagram, indicate what should be done for the reaction to occur. (1Mark)
    2. Write an equation for the reaction that occur in the combustion tube. (1Mark)
    3. What property of hydrogen gas is being investigated? (1Mark)
  8. When hydrogen is burnt and the product cooled, the following results are obtained as shown in the diagram below. 
    F4ChemMokMP12023Q8
    1. Write the equation for the formation of liquid Y. (1Mark)
    2. Give a chemical test of liquid Y. (1Mark)
    3. Give two uses of hydrogen gas. (1Mark)
  9. The diagram below shows a frasch process used for extraction of sulphur.
    F4ChemMokMP12023Q9
    1. Identify X (1Mark)
    2. What is superheated water? (1Mark)
    3. State two physical properties of sulphur that makes it possible for it to be extracted by this method. (1Mark)
  10. Study the information in the table below and answer question that follow. 
     Ions  Electron arrangement   Ionic radius
     Na+
     K2−
     Mg2+    		  2.8
     2.8.8
     2.8    		  0.95
     0.133
     0.065
    Explain why:-
    1. Ionic radius of K+ is greater than that of Na+ (1Mark)
    2. Ionic radius of Mg2+ is smaller than that of Na+ (2Marks)
  11. The table below gives properties of four substances 
     Substance  Melting points   Boiling points   Eletrical conductivity 
           Solid  Liquid 
     A  1083  2567  Good  Good
     B  −182  − 164  Poor  Poor
     C  1723  2230  Poor  Poor
     D  993  1695  Poor  Good
    State with a reason which of the above is :-
    1. An ionic compound (1Mark)
    2. A metallic structure (1Mark)
    3. Giant atomic structure (1Mark)
  12. Study the flow charts below and answer questions that follow. 
    F4ChemMokMP12023Q12
    1. Identify
      1. Cation present in solution  K (1Mark)
      2. White precipitate L. (1Mark)
    2. Write down the formula of the complex ion present in the colourless solution M (1Mark)
  13. Describe how a dry sample of Barium Sulphate can be prepared starting with Barium Carbonate (2Marks)
  14. Diamond and graphite are allotropes of carbon.
    1. What are allotropes? (1Mark)
    2. In terms of structure and bonding explain why diamond is used in drilling through hard rock while graphite is a lubricant. (2Marks)
  15.  
    1. Define Graham’s Law of diffusion (1Mark)
    2. 60cm3 of oxygen diffused through a porous plate in 20 seconds.  How long will it take 120cm3 of carbon (IV) oxide to diffuse through same plate under same conditions? ( C = 12, O = 16)       (2Marks)
  16.  
    1. On the grid provided sketch a graph of pressure against volume for fixed mass of gas at constant temperature. (1Mark)
      F4ChemMokMP12023Q16
    2. 50dm3 of gas at one atmosphere was compress to four atmospheres at constant temperature.  Calculate the volume occupied by the gas. (2Marks)
  17. R – COO-Na+ and F4ChemMokMP12023Q17 are cleansing agents.  Identify (2Marks)
    1. R 
      1. – COO - NA+ _____
      2. F4ChemMokMP12023Q17___
    2. Which of the two cleansing agent is not affected by hard water.  Explain (1Mark)
  18. When a hydrated sample of calcium sulphate ( CaSO4.XH2O) was heated, the following data was recorded.
    Mass of crucible =  30.2969
    Mass of crucible + hydrated salt =  33.111g
    Mass of crucible + anhydrous salt = 32.781g
    Determine the value of X in the salt. (3Marks)
  19. Study the set-up and answer questions that follow. 
    F4ChemMokMP12023Q19
    1. What does the experiment demonstrate? (1Mark)
    2. When is the type of Bunsen burner flame produced? (1Mark)
    3. Name the type of flame above? (1Mark)
  20. The set up below was used to electrolyze molten lead (II) bromide.
    F4ChemMokMP12023Q20
    1. Explain why the bulb light brightly at the beginning of the experiment and become dim after sometimes. (2Marks)
    2. Write ionic equation for the reaction that took place at the cathode. (1Mark)
  21.  
    1. Aqueous sodium chloride and metals in liquid state conduct electricity.  Explain the difference in their conductivity. (2Marks)
    2. What is binary electrolysis? (1Mark)
  22. The set – up below was used to collected gas F produced by the reaction between sodium peroxide and water.
    F4ChemMokMP12023Q22
    1. Name gas F (1/2Mark)
    2. Write a balanced equation for formation of gas F (1Mark)
    3. At the end of the experiment, the solution in round bottomed flask was found to be strong base.  Explain. (1/2Mark)
  23. Study the information given below and answer questions that follows. 
     Bond  Bond energy KJ/Mol 
     C-Cl  325
     C-H  414
     Cl-Cl  244
     H-Cl  431
    CH4 + Cl2   → CH3Cl + HCl
    Calculate the enthalpy change for the reaction. (2Marks)
  24. A given element E has atomic number 14 and consist of isotopes as shown below
     Isotope  X  Y  Z
     Isotopic mass  28  29  30
    % abundance  92.2  4.7  3.1
    1. What are isotopes? (1Mark)
    2. Determine the relative atomic mass of E (2Marks)
  25.  
    1. Define the term half-life. (1Mark)
    2. X grammes of a radio isotope takes 100 days to decay to 20g.  If half – life of the same element is 25 days.  Calculate the initial mass X of the radio isotope. (2Marks)
  26. Name the process which takes 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 with excess concentrated sulphuric acid.   (1Mark)
  27.  
    1. Name a suitable drying agent to be used to dry chlorine gas.    (1Mark)
    2. Chlorine reacts with red hot powder to give Iron(II) Chloride but not Iron (II) Chloride. Explain.    (1Mark)
    3. Dilute Sodium hydroxide reacts with chlorine to form bleaching powder.  Write a      balanced chemical equation for the reaction.                (1Mark)
  28. 22.2cm3 of sodium hydroxide solution containing 4.0g per litre sodium hydroxide were required for completer neutralization of 0.1g of a dibasic acid.  Calculate the relative formula mass of dibasic acid. (Na = 23, O = 16, H = 1)    (3Marks) 

MARKING SCHEME

  1.  
    1. Give the systematic names of the following hydrocarbons
      1. CH3(CH2)4CH3     (1Mark)
        • Hexane
      2. CH3 − C = CH2    (1Mark)
                    l
                 CH3 
        • 2-methylpro-1-ene
    2. The molecular formula of a hydrocarbon is C6H14
      The hydrocarbon can be converted into two other hydrocarbons as shown by the equation below.
      C6H14 → X + C3H8
      1. What is the name of above process?       (1/2Mark)
        • Cracking
      2. Write the molecular formula of X        (1/2Mark)
        C3H6
  2. Mr. Rudisha went to a doctor who sent him to a pharmacy to pick some drugs.  The pharmacist wrote on the medicine packaging 2 x 3 
    1. Clearly state what 2 x 3 meant?       (1Mark)
      • Two tablets 3 times a day at interval of 8 hours.
    2. State one reason why it is important to adhere to the doctor’s prescription.        (1Mark)
      • To avoid overdose or underdose  (any other correct)
  3. The apparatus below were used by a student to study to effect of heat on hydrated copper (II) Sulphate. 
    F4ChemMokMP12023Q3
    1. What is the role of the ice-cold water? (1Mark)
      • To condense water vapour to liquid water
    2. Name liquid P. (1/2 Mark)
      • Water
    3. What is the observation made in the boiling tube. (1Mark)
      • Blue hydrated CuSO4 changes to white CuSO4 powder
    4. Name type of change illustrated above (1/2Mark)
      • Temporary Chemical change
  4. The diagram below shows a paper chromatogram of substances A, B and C which are coloured.
    F4ChemMokMP12023Q4
    1. Indicate baseline on the chromatogram. (1Mark)
      F4ChemMokMP12023Ans4
    2. Which substance is pure? Explain (1Mark)
      • B: only one spot
    3. Substance D is a mixture of B and C.  Indicate it chromatogram on the diagram  (1Mark)
  5.  
    1. A beekeeper found that when stung by a bee, application of a little solution of sodium hydrogen carbonate helped to relieve the irritation on the affected.  Explain. (2Marks)
      • Bees produces an acid on the skin which is neutralized by basic solution NaHCO3
    2. Flower extracts can be used to Acid-bade indicators.  Give two limitations of such indicators. (1Mark)
      • Composition of the extract changes over time.
      • Give inconsistent results
  6. The apparatus below was a set up to show catalytic oxidation of ammonia.
    F4ChemMokMP12023Q6
    1. Write an equation for the reaction that takes place in the gas jar. (1Mark)
      4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(l)
    2. What is the role of the hot nichrome wire (1Mark)
      • Catalyst
    3. Apart from nichrome wire what else can be used? (1Mark)
      • Copper wire
      • Platinum
  7. The set-u is used to investigate the properties of hydrogen. 
    F4ChemMokMP12023Q7
    1. On the diagram, indicate what should be done for the reaction to occur. (1Mark)
      F4ChemMokMP12023Ans7
    2. Write an equation for the reaction that occur in the combustion tube. (1Mark)
      CuO(s) + H2(g) →Cu(s) + H2O(l)
    3. What property of hydrogen gas is being investigated? (1Mark)
      • Reducing property
  8. When hydrogen is burnt and the product cooled, the following results are obtained as shown in the diagram below. 
    F4ChemMokMP12023Q8
    1. Write the equation for the formation of liquid Y. (1Mark)
      2H2(g) + O2(g) → 2H2O(l)
    2. Give a chemical test of liquid Y. (1Mark)
      • Turns white anhydrous CuSO4 to blue
      • Turns blue anhydrous CoCl2 to pink
    3. Give two uses of hydrogen gas. (1Mark)
      • Hardening of oils to fats (hydrogenation)
      • Large scale manufacture of ammonia (Haber)
      • Large scale manufacture of HCl
        (any other correct)
  9. The diagram below shows a frasch process used for extraction of sulphur.
    F4ChemMokMP12023Q9
    1. Identify X (1Mark)
      • Hot compressed air at 15 atms.
    2. What is superheated water? (1Mark)
      • Water at 170°C under pressure at about 10atms
    3. State two physical properties of sulphur that makes it possible for it to be extracted by this method. (1Mark)
      • Low melting points of Sulphur
      • Sulphur is insoluble in water.
  10. Study the information in the table below and answer question that follow. 
     Ions  Electron arrangement   Ionic radius
     Na+
     K2−
     Mg2+    		  2.8
     2.8.8
     2.8    		  0.95
     0.133
     0.065
    Explain why:-
    1. Ionic radius of K+ is greater than that of Na+ (1Mark)
      • K+ has more number of occupied energy level than Na+
    2. Ionic radius of Mg2+ is smaller than that of Na+ (2Marks)
      • Mg2+ has more number of protons than Na+, therefore Mg2+ has stronger nuclear charge than Na+
  11. The table below gives properties of four substances 
     Substance  Melting points   Boiling points   Eletrical conductivity 
           Solid  Liquid 
     A  1083  2567  Good  Good
     B  −182  − 164  Poor  Poor
     C  1723  2230  Poor  Poor
     D  993  1695  Poor  Good
    State with a reason which of the above is :-
    1. An ionic compound (1Mark)
      • D
    2. A metallic structure (1Mark)
      • A
    3. Giant atomic structure (1Mark)
      • C
  12. Study the flow charts below and answer questions that follow. 
    F4ChemMokMP12023Q12
    1. Identify
      1. Cation present in solution  K (1Mark)
        • Pb2+ or Lead II ions
      2. White precipitate L. (1Mark)
        Pb(OH)2/ Lead(II)hydroxide
    2. Write down the formula of the complex ion present in the colourless solution M (1Mark)
      [Pb(OH)4]2−
  13. Describe how a dry sample of Barium Sulphate can be prepared starting with Barium Carbonate (2Marks)
    • Add excess BaCO3 to HNO3 acid to obtain Ba(NO3)2 Solution
    • Filter to remove unreacted BaCO3 as resedive & Ba(NO3)2 as filter
    • React Ba(NO3)2 with NaSO4 solution to precipitate BaSO4
    • Filter and dry between the filter papers to obtain BaSO4 crystals
  14. Diamond and graphite are allotropes of carbon.
    1. What are allotropes? (1Mark)
      • Different forms of an element in the same physical state
    2. In terms of structure and bonding explain why diamond is used in drilling through hard rock while graphite is a lubricant. (2Marks)
      • Diamond has compactly packed particles with strong covalent bond while graphite has hexagonal layers held by weak Vander Waals therefore can slide over each other.
  15.  
    1. Define Graham’s Law of diffusion (1Mark)
      • Under same conditions of temperature and pressure, rate of diffusion of gas is inversely proprotional to the square root of its density.
    2. 60cm3 of oxygen diffused through a porous plate in 20 seconds.  How long will it take 120cm3 of carbon (IV) oxide to diffuse through same plate under same conditions? ( C = 12, O = 16)       (2Marks)
      60cm3 → 20sec
      120cm3 → ?
      120×20 = 40sec
          60
        40   = √32/44
      TCO2 
      40 = 0.8528
       x          1
      x =     40    
            0.8528
      x = 46.9 sec
  16.  
    1. On the grid provided sketch a graph of pressure against volume for fixed mass of gas at constant temperature. (1Mark)
      F4ChemMokMP12023Ans16
    2. 50dm3 of gas at one atmosphere was compress to four atmospheres at constant temperature.  Calculate the volume occupied by the gas. (2Marks)
      P1V1 = P2V2
      50×1  = 4 ×V2
          4       4
  17. R – COO-Na+ and F4ChemMokMP12023Q17 are cleansing agents.  Identify (2Marks)
    1.  
      1. R – COO - NA+ _____ Soapy detergent
      2. F4ChemMokMP12023Q17___ Soapless detergent
    2. Which of the two cleansing agent is not affected by hard water.  Explain (1Mark)
  18. When a hydrated sample of calcium sulphate ( CaSO4.XH2O) was heated, the following data was recorded.  (Ca=40, S=32, O=16,H=1)
    Mass of crucible =  30.2969
    Mass of crucible + hydrated salt =  33.111g
    Mass of crucible + anhydrous salt = 32.781g
    Determine the value of X in the salt. (3Marks)
    Mass of anhydrous CaSO4 =    32.781
                                                   − 30.2969
                                                        2.4841
    Mass of water = 33.11 − 32.781
                            = 0.33
    Compound        CaSO4             H2O
    Mass                 2.4841              0.33
    RFM                   136                   18
    No. of moles     0.018265        0.01833
    Mole ratio            1              :          1
    x = 1
  19. Study the set-up and answer questions that follow. 
    F4ChemMokMP12023Q19
    1. What does the experiment demonstrate? (1Mark)
      • Almost colourless zone contains unburnt gases.
    2. When is the type of Bunsen burner flame produced? (1Mark)
      • Air-hole open
    3. Name the type of flame above? (1Mark)
      • Non-luminous flame
  20. The set up below was used to electrolyze molten lead (II) bromide.
    F4ChemMokMP12023Q20
    1. Explain why the bulb light brightly at the beginning of the experiment and become dim after sometimes. (2Marks)
      • At the beginning ions are still many in the molten liquid but after sometimes it decreases due to discharge of ions
    2. Write ionic equation for the reaction that took place at the cathode. (1Mark)
      Pb2+(aq) + 2e− → Pb(s)
  21.  
    1. Aqueous sodium chloride and metals in liquid state conduct electricity.  Explain the difference in their conductivity. (2Marks)
      • NaCl solution has mobile ions while metals in liquid state has delocalised electrons.
    2. What is binary electrolysis? (1Mark)
      • Electrolysis that involves one type of cation and one type of anion.
  22. The set – up below was used to collected gas F produced by the reaction between sodium peroxide and water.
    F4ChemMokMP12023Q22
    1. Name gas F (1/2Mark)
      • Oxygen gas.
    2. Write a balanced equation for formation of gas F (1Mark)
      2Na2O2(s) + 2H2O(l) → 4NaOH(aq) + O2(g)
    3. At the end of the experiment, the solution in round bottomed flask was found to be strong base.  Explain. (1/2Mark)
      • NaOH solution is formed which is a strong base.
  23. Study the information given below and answer questions that follows. 
     Bond  Bond energy KJ/Mol 
     C-Cl  325
     C-H  414
     Cl-Cl  244
     H-Cl  431
    CH4 + Cl2   → CH3Cl + HCl
    Calculate the enthalpy change for the reaction. (2Marks)
    ΔH = B.B.E + B.F.E
    B.B.E
    C−H → 414 × 4 = 1656
    Cl−Cl → 244 ×1 = 244   
                              + 1900  
    C−H → 414 × 3 = 1242
    C−Cl → 325 × 1 = 325
    H−Cl → 431 × 1 =  431   
                                − 1998  
    ΔH = 1900 −1998
    = −98KJ/mol
  24. A given element E has atomic number 14 and consist of isotopes as shown below
     Isotope  X  Y  Z
     Isotopic mass  28  29  30
    % abundance  92.2  4.7  3.1
    1. What are isotopes? (1Mark)
      • Atoms of same element with same atomic number but different mass number due to different in number of neutrons.
    2. Determine the relative atomic mass of E (2Marks)
      (28 × 92.2) + (29 × 4.7) + (30 × 3.1)
            100               100             100 
      25.816 + 1.363 + 0.93 = 28.109
  25.  
    1. Define the term half-life. (1Mark)
      • Time taken by a radioactive substance to decay by half the original mass/number.
    2. X grammes of a radio isotope takes 100 days to decay to 20g.  If half – life of the same element is 25 days.  Calculate the initial mass X of the radio isotope. (2Marks)
      No. of half lifes = 100/25 = 4
      Remaining = (½)n × original
      20 = (½)4 × x
      20 = 1/16x
      x = 16 × 20
         = 320g
      F4ChemMokMP12023Ans25
  26. Name the process which takes place when:
    1. Iodine changes directly from solid to gas (1Mark)
      • Sublimation
    2. Fe2+  changes to Fe3+   (1Mark)
      • Oxidation
    3. White sugar changes to black solid when mixed with excess with excess concentrated sulphuric acid.   (1Mark)
      • Dehydration
  27.  
    1. Name a suitable drying agent to be used to dry chlorine gas.    (1Mark)
      • Concentrated H2SO4  
      • Anhydrous Calcium Chloride
    2. Chlorine reacts with red hot powder to give Iron(II) Chloride but not Iron (II) Chloride. Explain.    (1Mark)
      • Chlorine is an oxidising agent and it oxidises Fe2+ to stable Fe3+
    3. Dilute Sodium hydroxide reacts with chlorine to form bleaching powder. Write a balanced chemical equation for the reaction.                (1Mark)
      2NaOH(aq) + Cl2(g) → NaOCl(aq) + NaCl(aq) + H2O(l)
  28. 22.2cm3 of sodium hydroxide solution containing 4.0g per litre sodium hydroxide were required for completer neutralization of 0.1g of a dibasic acid.  Calculate the relative formula mass of dibasic acid. (Na = 23, O = 16, H = 1)    (3Marks) 
    2NaOH +bH2x → Na2x + 2H2O 
    Molarity of NaOH = 4.0 = 0.1M
                                     40
    Moles used = 0.1 × 22.2
                              1000
                       = 0.00222
    Moles of acid : NaOH : H2x
                                2      :    1
    = 0.00222 = 0.00111moles
             2
    RFM =     0.1     
                0.001    11
             = 90
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