Chemistry Paper 1 Questions and Answers - 2021 KCSE Eldoret Diocese Mock Exams

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Questions

  1. Element K has atomic number 20 while element M has atomic number 8.
    1. Write the electron configuration of K and M
      K ______________________ (1mk)
      M ______________________ (1mk)
    2. Write the symbol of the most stable ion of K and M
      K ____________________________ (1/2 mk)
      M ___________________________ (1/2mk)
  2.        
    1. Molten lead (ii) iodide is electrolyzed using inert electrodes. Write the half equation of the reactions that occur at the anode and cathode.
      1. Anode _______________________________________ (1mk)
      2. Cathode ______________________________________ (1mk)
    2. Explain why the conductivity of metals decrease with increase in temperature
      ________________________________________________________________________
      ________________________________________________________________________
  3. Some sodium chloride was found to be contaminated with copper (ii) oxide. Describe how a sample of dry sodium chloride can be obtained from the mixline
    ________________________________________________________________________
    ________________________________________________________________________
    ________________________________________________________________________
  4. Hot platinum wire was lowered into a flask containing concentrated ammonia solution as shown below
    Eld21Chemp1q4
    State and explain the observations made (3mks)
    ________________________________________________________________________
    ________________________________________________________________________
    ________________________________________________________________________
  5.          
    1. What is a dative boud? (1mk)
      ________________________________________________________________________
    2. Draw a dot (.) and cross (x) diagram to show bouding in carbon (ii) oxide (2mks)
  6. Air was passed through several reagents as shown in the flow chart diagram
    Eld21Chemp1q6
    1. What is the purpose of concentrated potassium hydroxide solution? (1mk)
      ________________________________________________________________________
    2. Write an equation for the reaction which takes place in the chamber with magnesium powder (1mk)
      ________________________________________________________________________
    3. Name one gas which escapes from the chamber containing magnesium powder (1mk)
      ________________________________________________________________________
  7. Name the following substances
    1. CH2CH CH2CH3 ______________________________________ (1mk)
    2. CH3CHCHCH2CH3 _______________________________________ (1mk)
    3. State the observation made when compound in (a) above was passed through acidified potassium (vii) manganite (1mk)
      ________________________________________________________________________
      ________________________________________________________________________
      ________________________________________________________________________
  8. The diagram below shows a wooden splint that was placed horizontally across the middle part of a non-luminous flame.
    Eld21Chemp1q8
    1. Explain the observation made (2mks)
      _____________________________________________________________________
      ________________________________________________________________________
    2. Explain why non-luminous flame is preferred for heating than luminous flame (1mk)
      _____________________________________________________________________
      ________________________________________________________________________
  9. Explain giving reasons why?
    1. Sulphuric(vi) acide is not used with marble in the preparation of carbon(iv) oxide (2mks)
      _____________________________________________________________________
      ________________________________________________________________________
      ________________________________________________________________________
    2. Water cannot be used to extinguish oil fire
      ________________________________________________________________________
      ________________________________________________________________________
      ________________________________________________________________________
  10. 15cm3 of a solution containg 2.88g/dm3 of an alkali XOH completely reacts with 20.0cm3 of 0.045m sulphuric(vi) acid. Calculate the molarity and relative atomic mass of x present in the alkali
    ________________________________________________________________________
    ________________________________________________________________________
    ________________________________________________________________________
    ________________________________________________________________________
    ________________________________________________________________________
  11. An hydrocarbon Q was found to decolourise potassium manganate(vii)solution. When two moles of Q were burnt completely six moles of carbon(iv)oxide and six moles of water were formed.
    1. Write the structural formula of Q (2mks)
      ________________________________________________________________________
      ________________________________________________________________________
    2. Name the homologous series to which Q belongs
      ________________________________________________________________________
      ________________________________________________________________________
  12. The diagram below represents an electrochemical cell
    Eld21Chemp1q12
    1. On the diagram label the salt bridge (1mk)
    2. State two observations made in cell B (1mk)
      ________________________________________________________________________
      ________________________________________________________________________
    3. Write the overall ionic equation of the cell (1mk)
      ________________________________________________________________________
      ________________________________________________________________________
  13. During the extraction of copper and zinc from their ores, some of the processes include
    1.           
      1. Crushing
      2. Mixing of the crushed ore with oil and water and bubbling air through it.
    2.      
      1. Name the process (ii) above (1mk)
        ________________________________________________________________________
      2. What is the purpose of (ii) above
        ________________________________________________________________________
        ________________________________________________________________________
  14. Dry chlorine gas was passed through two pieces of coloured cotton cloth as shown
    Eld21Chemp1q14
    1. State what is observed in each experiment (1mk)
      Experiment I
      ______________________________________________________________________
      Experiment II
      ______________________________________________________________________
    2. Explain your observation using an equation (1mk)
      ______________________________________________________________________
      ______________________________________________________________________
  15.      
    1. what is meant by solubility? (1mk)
      ________________________________________________________________________
      ________________________________________________________________________
    2. In an experiment to determine the solubility of solid Y in water at 30oC the following results were obtained.
      Mass of evaporating dish = 26.2g
      Mass of evaporating dish + saturated solution = 42.4g
      Mass of evaporating dish + dry solid y = 30.4g
      Using the information, determine the solubility of solid Y at 30oc in grams per 100g of water (2mks)
      ________________________________________________________________________
      ________________________________________________________________________
      ________________________________________________________________________
  16. the molar heat of formation of carbon(ii) oxide is -105kjmol-1, molar heat of combustion of carbon is -393 kjmol-1 by using an energy cycle diagram, determine the molar heat of combustion of carbon(ii)oxide (3mks)
    ________________________________________________________________________
    ________________________________________________________________________
    ________________________________________________________________________
  17. The diagram below was used to study the effect of heat on copper(ii)sulphate crystals
    Eld21Chemp1q17
    1. Name liquid M (1mk)
      _____________________________________________________________________
    2. State and explain the precaution that should be made before stopping heating (2mks)
      _____________________________________________________________________
      _____________________________________________________________________
      _____________________________________________________________________
  18. Deuterium 21D and tritium 31T are two isotopers of hydrogen. They react to form element Y and neutron particles according to the equation below.
    21D + 31T  → abY + 10n
    1. Find the value of a and b (2mks)
      ________________________________________________________________________
      ________________________________________________________________________
      ________________________________________________________________________
    2. What name is given to the type of reaction undergone by the isotope of hydrogen (1mk)
      ________________________________________________________________________
  19. A gas occupies 4dm3 at -230c and 152mmHg. At what pressure will its volume be halved, if the temperature then is 2270c? (2mks)
    ________________________________________________________________________
    ________________________________________________________________________
    ________________________________________________________________________
  20. Ammonium nitrate was gently heated and the products collected as shown in the diagram
    1. Identify
      1. Colourless liquid H (1mk)
        ____________________________________________________
      2. Gas G (1mk)
    2. Describe one chemical test that can be used to identify gas G
      _____________________________________________________________________
      _____________________________________________________________________
  21. The diagram below shows the acidic and basic oxides fit into the general family of oxide
    Eld21Chemp1q21
    1. State the type of oxide that would be placed in the shaded area (1mk)
      _____________________________________________________________________
    2. Name an oxide that would be placed in the shaded area (1mk)
      _____________________________________________________________________
  22. A dynamic equilibrium between dichromate and chromate ions is established as shown in the equation below.
    Cr2O72-(aq) + ZOH-(aq) â‡Œ  2Cro2-4 + H2O (l)
       Orange                             Yellow
    1. What is meant by dynamic equilibrium? (1mk)
      _____________________________________________________________________
      _____________________________________________________________________
    2. State and explain the observation made if a dilute hydrochloric acid is added to the equilibrium mixture (2mks)
      _____________________________________________________________________
      _____________________________________________________________________
  23. An experiment showed that the composition of a compound to be 5838% Barium, 13.72% Sulphur and 27.47% oxygen. Calculate the empirical formula of the compound (Ba = 137; S=32, O=16) (3mks)
    ________________________________________________________________________
    ________________________________________________________________________
    ________________________________________________________________________
  24. In an experiment to study diffusion of gases, the following set up was used
    Eld21Chemp1q24
    1. State and explain observations made in the experiment (2mks)
      ________________________________________________________________________
      ________________________________________________________________________
      ________________________________________________________________________
    2. Write an equation for the reaction that occurs in the experiment (1mks)
      __________________________________________________________________
      __________________________________________________________________
  25. The figure below is an energy level diagram for the reaction 2Z (g) + 2B(g) = 2AB(g)
    Eld21Chemp1q25
    Explain the effect of yield AB by
    1. Increase in pressure (1 ½ mk)
      _____________________________________________________________________
      _____________________________________________________________________
    2. Decrease in temperaline (1 ½ mk)
      _____________________________________________________________________
      _____________________________________________________________________
  26. Study the following changes that took place when the following substances are exposed to air.
    1.                 I
      NaOH(s) â†’ NaOH(aq)
    2.                                II          
      Na2CO3.IOH2O(s)  →  Na2CO3(s) + IOH2O(l)
    3.                                   III
      CuSO4(s) + 5H2O(l) â†’ CuSO4.5H2O(s)
      Name the process (3mks)
      I _______________________________
      II ______________________________
      III _____________________________
  27. A white solid K was heated. It produced a brown gas A and another gas B which relights a glowing splint. The residue left was yellow when hot and white when cold.
    1. Identify gases A and B (2mks)
      A ______________________________
      B ______________________________
    2. Write an equation for the decomposition of solid K (1mk)
      _____________________________________________________________________
      _____________________________________________________________________
    3. Bronze is an alloy of copper and another metal. Identify the other metal.
      _______________________________________________________________________
      _______________________________________________________________________

Marking Scheme

  1.              
    1. K 2. 8.8.2 √1mk
      M 2.6 √1mk

    2. K 2+
      M 2-
  2.   
    1.  Anode: I-(l) I2(g) + 2e- √1mk
      Cathode: Pb2+ + 2e- Pb (s) √1mk

    2. Increase in temperature increases the kinetic energy (1/2 mrk) of positive centres and electrons making them to vibrate more. These increase collisions of positive centres and electrons hence increased resistance (1/2mrk)

  3. Add water to the mixture and stir sodium chloride dissolve leaving copper (ii) oxide which is insoluble. (√1mk )
    Filter (1/2) to remove copper (ii) oxide and sodium chloride as the filtrate
    Evaporate the filtrate to saturation and cool to obtain sodium crystals (√1mk )
    Dry them between filter papers/leave them in the open to dry (√1mk )

  4. Hot platinum wire glows red. (√1mk )
    Brown fumes are observed (√1mk )
    Reaction between oxygen gas and ammonia gas over platinum wire is exothermic. (1/2mrk)
    Ammonia is oxidized to nitrogen (ii) oxide which reacts with excess oxygen to form nitrogen (iv) oxide,(1/2 mrk)

  5.          
    1. A bond formed by two atoms/elements by share of electrons from one of the atoms/element(√1mk)
  6.                 
    1. Remove / absorb carbon (iV) oxide (√1mk )
    2. 3Mg (s) + N2(g)   â†’ Mg3N2(s) (√1mk )
    3. Neon/ Argon (√1mk )
  7.     
    1. But – 1 – ene (√1mk )
    2. Pent – 2 –ene (√1mk )
    3. Potassium manganate (VII) is decolourised/ Potassium manganate (VII) changes colour from purple to colourless (√1mk )
  8.       
    1. The outer zone has complete combustion and hence hotter tha the middle zone forming the charred black part (1mrk) Middle zone has incomplete combustion and hence less hot forming unburnt part (√1mk )
    2. - Non – luminous flame is hotter than luminous flame (1mrk)
      Non – luminous flame does not produce soot (1mrk) Any one (√1mk )
  9.    
    1. Sulphuric (VI) acid react with marble (Calcium carbonate) forming insoluble calcium sulphate(1mrk) which form a coat over marble stopping any further reaction (√1mk )
    2. Oil is less dense (1/2) than water making oil float(1/2) on top hence continues to burn.

  10. 2XOH(aq) + H2SO4(aq) → X2SO4 (aq) + 2 H2O(l)
       XOH     =   2         15 X M           
    H2SO4         1        20 X 0.045 (√1mk)

    M = 2 X 20 X 0.045
                 1 X 15
    = 0,12 moles/l (1/2)
    1mole = 2.88    = 24 (1/2)
                   0.12
    RFM of XOH = X + 16 + 1 (1/2)
         X = 7 1/2)

  11.          
    1. 2CxHy               X CO2 + y/2 H2O
      X = 6/2   = 3 (1/2)
      Y = 12/ 3 = 6 (1/2)
      MF = C3H6 (1/2)
      Structural fprmula = CH3 CH = CH2 (1/2)

    2. Alkenes
  12. on the diagram
    1. √1mk
    2. arrow from zinc half-cell towards copper half cell √1mk
    3. Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) √1mk
  13.          
    1. Froath floatation √1mk
    2. Concetrating the mineral ore by making impurities to sink atb the bottom. √1mk
  14.      
    1. Exp. 1 – The colour of dry cloth did not turn to white/ cloth not bleached, because of the absence of hypochloric (I) acid which is responsible for bleaching
    2. Exp 2 – Wet cloth turned white due to bleaching as chlorine dissolves in water to form hypochloric(I) acid√1mk
    3. Cl2(g) + H2O(g) + Dye {Dye + [O]} + 2HCl(g) √1mk
  15.      
    1. Solubility is the maximum mass in grams of solute that will dissolve in 100g ofvwater at a given temperature/ is the mass in grams of solute required to make a saturated solution with 100g of water at given temperature. √1mk/

    2. Mass of solid Y = 30.4 – 26.2
      = 4.2g (1/2mrk)
      Mass of water in the solution = 42.4 – 30.4 = 12g (1/2 mrk)
      12 g of water dissolve 4.2g solid Y
      100g of ware will dissolve   
      100 x 4.2 (1/2mrk)
         12
      = 35g / 100g of water (1/2mrk)

  16. AH0f(CO) + AH0c(CO) = AH0c(C)
    -105 + AH0c(CO) = -393 √1mk
    AH0c(CO) = -393 + 105 √1mk
    = -188kJMol-1 √1mk

  17.        
    1. Water √1mk
    2. The delivery tube should first be removed √1mk to avoid sucking back of liquid M √1mk

  18.     
    1. Atomic mass of Y 2 + 3 = a + 1
      a = 4 √1mk
      Atomic number 1 + 1 = b + 0
      b = 2 √1mk
    2. Nuclear fusion √1mk)

  19. V1 = 4dm3 ; P1 = 152mmHg ; V2 = 2dm3 ; T1 = 250K ; T2 = 500K P2 = ?
    152 x 4 = P2 x 2
       250         500 √1mk
    P2 = 152 x4 x 500
                250 x 2 √1mk
    = 608mmHg √1mk

  20.        
    1.            
      1. Liquid H is Water √1mk
      2. Gas G is Nitrogen (i) oxide √1mk
    2. turn white anhydrous copper (II) sulphate to blue / Turns blue cobalt(II) chloride to pink √1mk
  21.      
    1. Amphoteric oxide √1mk
    2. Lead (II) oxide / Zinc oxide / Aluminium (III) oxide (Any one) √1mk
  22.      
    1. Rate of forward reaction equals to the rate of backward reaction. √1mk
    2. Orange colour of the solution intensifies √1mk
      Equilibrium shift to the left/ backward reaction is favoured to replace OH- that react with H+ √1mk

  23. Element                Ba             S                 O
    % composition    58.81        13.72         24.47
    RAM                      137         32                 16
    No. of moles           58.81    13.72            24.47 (1/2mrk)
                                     137       32                 16

                                 0.4293       0.4281         1.768
    Mole ratio                1                   1             4 (1/2mrk)
    E . F. BaSO4 (√1mk)

  24.                
    1. A white ring/ solid (1/2mrk) was formed inside the combustion tube closer to the cotton wool soaked in concentrated hydrochloric acid (1/2mrk). Ammonia is lighter/less dense than hydrochloric acid hence diffuse faster ( √1mk)
    2. NH3 (g) + HCl(g) → NH4Cl(s) (√1mk)
  25.     
    1. The yield of AB is increased. (√1mk)
      The forward reaction is accompanied by a decrease in volume(1/2mrk). Equilibrium shifts to the right following increase of the forward reaction (1/2mrk)
    2. The yield of AB is increased’ (√1mk)
      The forward reaction is exothermic.(1/2mrk) Decrease in temperature favours the forward reaction, equilibrium shifts to the right.(1/2mrk)
  26.     
    1. Deliquescence (√1mk)
    2. Efflorescence (√1mk)
    3. Hygroscopy (√1mk)
  27.  
    1. A – Nitrogen (IV) oxide/ NO2 (√1mk)
      B – Oxgygen/ O2 (√1mk)
    2. 2ZnNO3 (g) 2ZnO(s) + 4 NO2 (g) + O2(g) (√1mk)
  28. Tin (√1mk)

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