Chemistry Paper 1 Questions and Answers - Kangundo Subcounty Pre Mock Exams 2021/2022

INSTRUCTIONS TO CANDIDATES

1. Answer all the questions in the spaces provided.
2. Mathematical tables and electronic calculators may be used.
3. All working must be clearly shown where necessary.

1. An oxide of element G has the formula as G2O3.
   
   1. State the valency of element G. (1 mark)
      ………………………………………………………………………………………………………
   2. In which group of the periodic table is element G? (1 mark)
      ……………………………………………………………………………………………………
2. The set-up below was used to separate a mixture.
   
   
   1. Name the apparatus missing in the set-up. (1 mark)
      ……………………………………………………………………………………………………...
   2. Give one example of mixture T. (1 mark)
      ……………………………………………………………………………………………………...
   3. What is the name of this method of separation? (1 mark)
      ………………………………………………………………………………………………………
3. Name the process which takes place when:
   
   1. Solid Carbon (IV) oxide (dry ice) changes directly into gas. (1 mark)
      ……………………………………………………………………………………………………...
   2. A red litmus paper turns white when dropped into chlorine water. (1 mark)
      ………………………………………………………………………………………………………
   3. Propene gas molecules are converted into a giant molecule. (1 mark)
      ………………………………………………………………………………………………………
4. The information below gives pH values of solutions V, W, X, Y Z.
   

   Solution	pH values
   V W X Y Z	2 6.5 11 14 4.5

   1. Which solution is likely to be?
      
      1. Calcium hydroxide? (1 mark)
         ………………………………………………………………………………………………………
      2. Rain water? (1 mark)
         ……………………………………………………………………………………………………...
   2. Which solution would react most vigorously with Zinc carbonate? (1 mark)
      ………………………………………………………………………………………………………
5. Explain why very little Carbon (IV) oxide gas is evolved when dilute sulphuric (VI) acid is added to lead (II) carbonate. (1 mark)
   ………………………………………………………………………………………………………
6. Air was passed through several reagents as shown below:
   
   
   1. Write an equation for the reaction which takes place in the chamber containing magnesium powder. (1 mark)
      ………………………………………………………………………………………………………
   2. Name one gas which escapes from the chamber containing magnesium powder.
      Give a reason for your answer. (2 marks)
      …………………………………………………………………………………………………………
7. The set-up below was used to study some properties of air.
   
   State and explain two observations that would be made at the end of the experiment. (2 marks)
8. Below is a list of oxides.
   MgO, N₂O, K₂O, CaO and Al₂O₃
   Select:-
   
   1. A neutral oxide. (1 mark)
   2. A highly water soluble basic oxide. (1 mark)
   3. An oxide which can react with both sodium hydroxide solution and dilute hydrochloric acid. (1 mark)
9.    
   1. Hydrogen can reduce copper (II) Oxide but not aluminium oxide. Explain. (1 mark)
   2. When water reacts with potassium metal, the hydrogen produced ignites explosively on the surface of water.
      
      1. What causes this ignition? (1 mark)
      2. Write an equation to show how this ignition occurs. (1 mark)
10. In an experiment an unknown mass of anhydrous sodium carbonate was dissolved in water and the solution made up to 250 cm³. 25cm³ of this solution neutralized 20 cm³ of 0.25 M nitric acid. Calculate the mass of unknown sodium carbonate used. (3 marks)
    (Na = 23.0, C = 12.0, O = 16.0)
11. An element M has two naturally occurring isotopes, 63M and 65M. Calculate the percentage of each isotope if the relative atomic mass of M is 63.55. (2 marks)
12. Carbon and silicon belong to the same group of the periodic table, yet Carbon (IV) oxide is a gas while silicon (IV) oxide is a solid with a high melting point. Explain this difference (2 marks)
13. The table below gives information about the ions T+ and Z2-.
    

    Ion	T+	Z2
    Electron arrangement	2.8	2.8.8
    Number of neutrons	12	16

    1. Determine the relative formula mass of the compound formed between T and Z. (2 marks)
    2. State two conditions under which the compound in (a) above would conduct electricity. (1 mark)
14. An ion of oxygen is larger than oxygen atom. Explain. (2 marks)
15. A solution of hydrogen chloride gas in methylbenzene has no effect on calcium carbonate while a solution of hydrogen chloride gas in water reacts with calcium carbonate to produce a gas. Explain. (2 marks)
16. Starting with Lead (II) carbonate explain how you would prepare a pure sample of Lead (II) sulphate. (3 marks)
17. Draw a dot (•) and cross (x) diagram to show bonding in:-
    
    1. Ammonium ion, NH + (N = 7.0, H = 1.0) (1 mark)
    2. Silane, SiH4 (Si = 14.0, H = 1.0) (1 mark)
18. Sodium carbonate decahydrate crystals, Na2CO₃.10H₂O, were left exposed in the atmosphere on a watch glass for two days.
    
    1. State the observation made on the crystals after two days. (1 mark)
    2. Name the property of salts investigated in the above experiment. (1 mark)
19.    
    1. What is meant by the term solubility of salts? (1 mark)
    2. Calculate the solubility of a salt given that 15 g of the salt can saturate 25 cm³ of water. (1 mark)
20.    
    1. State the Graham’s law. (1 mark)
    2. A 100 cm³ of Carbon (IV) oxide gas diffused through a porous partition in 30 seconds.
       How long would it take 150 cm³ of Nitrogen (IV) oxide to diffuse through the same partition under the same conditions? (C = 12.0, N = 14.0, O = 16.0) (2 marks)
21. The diagram below represents an in complete set-up for preparation of a dry sample of gas R.
    
    
    1. Complete the set-up to show how a dry sample of gas R is collected. (2 marks)
    2. Write a chemical equation for the reaction that produces gas R. (1 mark)
22. When sulphur powder is heated to over 400ºC the following changes are observed:- At 113ºC it melts into light brown liquid. The liquid then darkens to become red- brown and very viscous at 160ºC. Above 160ºC the liquid becomes almost black. Near the boiling point (444ºC) the liquid becomes mobile. Explain these observations. (3 marks)
23. A gas cylinder contains about 1.12dm³ of butane measured at 0º and 1atm. Given that 25% of heat is lost, what is the maximum volume of water at room temperature which can be boiled to 100ºC in order to make some coffee?
    C4H_10(g) + 6 ½ O_2(g) → 4CO_2(g) + 5H2O_(l); ΔH^θ = -3,000 kJmol^-1 (3 marks)
    (Specific heat capacity of water = 4.2J g-1ºC^-1, density of water 1gcm^-3 Molar gas volume 22.4 at s.t.p)
24. Compound W reacted with chlorine to form compound X only. The structural formula of
    X is shown below:
    CH₃ ─ CH ─ CH ─ CH₃
                 │        │
                Cl       Cl
    1. Give the structural formula and name of compound W. (1 mark)
    2. Draw the structure of 1-chloro-2, 2-dimethylpropane. (1 mark)
25. A weighed sample of crystalline sodium carbonate (Na2CO₃.nH2O) was heated in a crucible until there was no further change. The mass of the sample reduced by 14.5%. Calculate the number of moles, n, of water of crystallization. (Na = 23, O = 16.0, C = 12, H = 1). (3 marks)
26. In an experiment, soap solution was added to three samples of water. The results below show the volume of soap solution required to lather with 500 cm³ of each water sample before and after boiling.
    1. Which water samples are likely to be soft? (1 mark)
       

       	Sample 1	Sample 2	Sample 3
       Volume of soap used before wate rboiled	26.0	14.0	4.0
       Volume of soap after water boiled	26.0	4.0	4.0

    2. Explain the change in volume of soap solution used in sample 2. (1 mark)
27. Study the flow diagram below and answer the questions that follow:
    
    
    1. Name salt M. (1 mark)
    2. Write a balanced chemical equation for the reaction between hydrochloric acid and manganese (IV) oxide. (1 mark)
    3. Identify another reagent that can be reacted with concentrated hydrochloric acid to produce gas L. (1mark)
28. The set-up below was used to prepare and collect hydrogen sulphide gas. Study it and answer the questions that follow.
    
    
    1. Name solid V. (1 mark)
    2. Write chemical equation of the reaction taking place in the flask. (1 mark)
    3. Give a reason why warm water is used in the set-up. (1 mark)
29. The table below gives information on four elements represented by letters K, L, M and N. Study it and answer the questions that follow:
    

    Element	Electron arrangement	Atomic radius (nm)	Ionic radius (nm)
    K L M N	2.8.2 2.8.7 2.8.8.1 2.8.8.2	0.136 0.099 0.203 0.174	0.065 0.181 0.133 0.099

    1. Select the elements with similar chemical properties. (1 mark)
    2. Explain why the ionic radius of L is greater than its atomic radius. (1 mark)
    3. Identify the most reactive metal. (1 mark)
30. The set up below was used to prepare a solution of hydrogen chloride.
    
    
    1. Explain why an inverted funnel is used. (2 marks)
    2. Name another gas whose aqueous solution can be prepared in the same way. (1 mark)
31. Heated iron can react with both chlorine gas and hydrogen chloride gas.
    
    1. Write equations for the two reactions. (2 marks)
    2. Chlorine gas has no effect on dry blue litmus paper. Explain. (1 mark)

MARKING SCHEME

1.    
   1. Valency 3 
   2. Group 3 
2.    
   1. Wiregauze 
   2. Sodium chloride solution (or any named slat solution)
   3. Evaporation
3.      
   1. Sublimation.
   2. Bleaching 
   3. Polymerisation 
4.      
   1.    
      1. X
      2. W 
   2. V
5. InsolubleLead(II) sulphate is formed preventing any further reaction.
6.    
   1. 3Mg_(s)+N_2(g) → Mg₃N_2(s) 
   2. Argon
      • It is inert 
7.    
   • Water rose up the test-tube to occupy the space of active air or oxygen√½ which has been used in rusting.√½
   • Iron wool turned red–brown√½ due formation of hydrated iron(III) oxide√½.
8.      
   1. N₂O orNitrogen(I)oxide
   2. K₂O (Potassium oxide)
   3. Al₂O₃ (Aluminium oxide)
9.      
   1. Hydrogen is above Cu√½ and below Al in the reactivity series√½ of elements.
   2.      
      1. The reaction is too exothermic that alot of heat is produced causing ignition of hydrogen in presence of oxygen.
      2. H_2(g)+O_2(g)→ H₂O(g)
10. Na₂CO_3(aq)+2HNO_3(aq) → 2NaNO_3(aq)+CO_2(g)+H₂O_(l)
    Mole ratio Na₂CO₃:HNO₃=1:2√½
    Moles of HNO₃ in 20cm³=20/1000 x 0.25=0.005 moles√½
    Moles of Na₂CO₃ in 25cm³=½ of 0.005=0.0025 moles√½
    If 25cm³=0.0025moles
    in 250cm³=?
    250 x 0.0025=0.025moles√½
           25
    RFM of Na2CO₃ = 106 ½
    I mole of Na2CO₃=106g
    0.025 moles=?
    0.025 x 106 =2.65g of Na2CO₃  ½
              1
11. 63x + 65(100–x) = 63.55√½
            100
    63x + 6500 – 65x = 6355
    2x = 6355 – 6500 =145
    x=72.5 ½
    % abundance of ⁶³M =72.5%   ½
    ⁶⁵M =100–72.5=27.5%   ½
12. Silicon(IV) Oxide has giant atomic structure  with strong covalent bond holding the atom together. These require alot of energy to break, hence it has high melting point.
    Carbon (IV) Oxide has simple molecular structure with weak Van Der Waals forces holding the molecules together which require little energy to break, hence is a gas at room temperature and pressure.
13.      
    1. Number of protons
       T=11protons
       Z=16protons
       Formula of compound =T2Z
       Mass number of T=11+12=23
       Mass number of Z = 16+16=32
       Formula Mass of T₂Z=(23 x 2)+32=78
    2.      
       • When molten
       • When in aqueous solution
14. The oxide ions has 2 extra electrons that causes greater electron repulsion than in oxygen atom
15. HCl_(g) is polar.It ionizes/dissociates in water which is a polar solvent to produce H+(aq) that gives the solution acidic properties.HCl_(g) doesnotionize/dissociate in methyl benzene which is a non-polar solvent.It remains as molecules hence no H+
    ions.1mk
16.      
    • Add dilute nitric acid to lead(II) carbonate.
      PbCO₃(s)+2HNO₃(aq) → Pb(NO₃)₂(aq)+CO₂(g)+H₂O(l)
    • React the resulting solution with solution of sodium sulphate or dilute sulphuric acid.
      Na₂SO_4(aq)+Pb(NO₃)2(aq) → PbSO₄(s)+2NaNO₃(aq)
    • Filter to obtain lead(II) sulphate as residue. Dry the salt of lead(II) sulphate in between the filter papers or in sunshine.
17.    
    1.  
          
       • award 1mk if one Hydrogen has two electrons donated by Nitrogen
       • 0mk if all hydrogen atoms
    2.  
       
       award full mark if Silicon and Hydrogen contributes shared electrons equally
18.      
    1. They became covered with a white powder
    2. Efflorescence
19.      
    1. This is the maximum mass of a salt that will dissolve in 100g of water at a given temperature
    2. 15g dissolve in 25cm³ water
       x g dissolve in (15 x 100) = 60g/100gwater
                                    25
20.      
    1. Grahams law states;
       Under the same conditions of pressure and temperature, the rate of diffusion of a gas is inversely proportional to the square root of its density.√
    2. TimeCO₂=MCO₂
       TimeNO₂  MNO₂
       Where 100cm³ of CO₂ takes 30 seconds
       150cm³ of CO₂ takes ³⁰/₁₀₀ x 150 = 45 seconds
         45  = 44 
       TNO₂  46
         45  = 0.975
       TNO₂
       TNO₂ =  45  = 46sec
                   0.97
       OR
       RCO₂=MNO₂
       RNO₂ MCO₂
       ButRCO₂ = 100cm³=3.33cm³per sec
                            30s
        3.33  = 46 =1.0225
       RNO₂    4
       RNO₂ =   3.33   
                    1.0225
       =3.26cm³ per second
       Time for No =   150cm ³
                               3.26cmsec^-1 = 46sec√½
21.      
    1. Drying agent which must be CaO
       Method of collection 1- upward delivery
       Workability
    2. 2NH₄Cl_(g)+Ca(OH)_2(s) → CaCl_2(g)+H₂O(l)+2NH_3(g)
22.      
    • At 113ºC consists of S8 rings that flow easily;
    • Darkens due to breaking of S8 rings and forming long chains consisting of thousands of atoms.The chains also entangle;
    • The long chains consisting of thousands of atoms.The chains also entangle;
    • The long chains break near b.p. to form shorter one;
23. Moles C₄H₁₀ = 1.12 = 0.05mol
                            22.4
    Heat produced 0.05 x 3000 = 150kJ√½
    Useful heat =75 x 150 =112.5kJ√½
                            100
    Let mass of water =m
    Room temperature =25ºC
    Boiling point =100ºC
    Change in temperature,ΔT =100-25=75
    ΔH=ΔT x m x C
    75 x m x 4.2 = 112.5
          1000
    315m =112500
    m = 35Kgm^-3
    Volume=357m³
24.    
    1. Formula:CH₃CH = CHCH₃√½
       Name:But-2-ene√½
    2.        H    CH₃
              │       │
       Cl─C─C─CH3
              │   │
             H   CH₃
25. % of H₂O lost =14.5%
    5 of anhydrous Na₂CO₃=85.5% ½
    R.F.M of Na₂CO₃=106 ½
    RMM of H₂O =18 ½mk
    

    NaCO3	H2O
    85.5 106 0.8066 = 1 0.8055	14.5   18 0.8055 = 1 0.8055

    n=1(Na2CO₃.H₂O) ½
26.    
    1. Sample 3 
    2. Sample 2 contained ions that caused temporary hardness ,therefore required large volume of soap solution before boiling, but after boiling the temporary hardness was removed thus required very little volume of soap solution to lather.
27.      
    1. Sodium chlorite(I)/Sodium hypochlorite
    2. 4HCl_(aq)+MnO₂  → MnCl_2(aq)+Cl_2(g)+2H₂O(l) 
       Penalize ½mk if state symbols are not correct;
       Penalize fully if the balancing is incorrect.
    3. Potassium manganate(VII)/KMnO₄ or lead(IV)oxide/PbO₂
28.      
    1. Any suitable metal sulphide e.g.FeS rej.PbS
    2. FeS(s)+H₂SO_4(aq) → FeSO_4(aq)+H₂S_(g)
    3. Hydrogen sulphide is less soluble in warm water compared to cold water
29.      
    1. Elements K and N
    2. Element L is a non-metal and reacts by gaining an electron
    3. Element M 
30.      
    1. HCl_(g) is extremely soluble in water 1mk. Inverted funnel provides a large surface area for the gas to dissolve in water and prevent suck-back.1mk
    2. Ammonia gas1mk
31.      
    1. 2Fe_(S) + 3Cl_2(g) → 2FeC_l3(g)
       Fe_(s)+2HCl_(g)→ FeCl_2(g)+H_2(g)√1mk
       N.B:Must be balanced
       State symbol must be correct
       Chemical symbols must be correct
    2. In the absence of moisture, chlorine cannot form HOCl, chloric(I) acid solution, responsible for its bleaching property.√1mk