Chemistry Paper 1 Questions and Answers - Momaliche Joint Pre Mock Exams 2022

QUESTIONS

1.      
   1. When the air hole is fully opened, the Bunsen burner produces a non-luminous flame. Explain (1mks)
   2. Draw a labeled diagram of a non-luminous flame  (2mks)
2. Describe an experimental procedure that can be used to extract oil from nuts seeds (2mks)
3. Study the diagram below and use it to answer the questions that follow
   
   
   1. Write the equations for the reactions taking place at the;
      1. Anode  (1mks)
      2. Cathode(1mks)
   2. Name one application of electrolysis  (1mks)
4. In a titration experiment, 25cm³ of a solution of sodium hydroxide containing 8 g per litre was required for complete neutralization of 0.245 g of a dibasic acid. Calculate the relative molecular mass of the acid ( Na = 23.0, O = 16.0, H = 1) (3mks)
5. The flow chart below shows processes involved in the industrial extraction of Zinc metal
   
   
   1. Name one ore from which zinc is extracted (1mks)
   2. Write the equation of the reaction taking place in unit II (1mks)
   3. Name two uses of zinc metal  (1mks)
6. The table below shows the pH values of solutions P, R, Q and S
   

   Solution	P	R	Q	S
   pH	2	7	6.5	13.5

   1. Which solution represents:
      1. Strong base (1mks)
      2. Weak acid (1mks)
   2. Give an example of solution S  (1mks)
7. The electron arrangement of ions of a certain elements represented by letters P, Q, R and S are:
   P^2- -2.8.8
   Q²⁺ -2.8
   R+ - 2.8
   S -2.8.8
   1. Explain why S is not represented as an ion (1mks)
   2. Which element has the largest atomic radius? Explain.(2mks)
8. Sulphur is extracted from underground deposits by a process in which three concentric pipes are sunk down to the deposits as shown
   
   
   1. Name the process represented above (1mks)
   2. What is passed down through pipe J? (1mk)
   3. Name the two allotropes of sulphur (1mk)
9. Element A has atomic mass 23 and element B has atomic mass 7 and also have 12 neutrons and 4 neutrons respectively.
   1. Write the electronic arrangement of A and B. (1mk)
   2. Which element has higher ionization energy? Explain (2mks)
10. W grammes of a radioactive isotope decayed to 5 grammes in 100 days. The half life of the isotope is 25 days.
    1. What is meant by half life?  (1mk)
    2. Calculate the initial mass W of the radioactive isotope (3mks)
11. Haber process ( the manufacture of ammonia gas) is given by the following equation
    N_2(g) + 3H_2(g)  2NH_3(g) ⇌ ∆H = -92kJ/mole
    State and explain the effect of
    1. Introducing some drops of water to the equilibrium (1mk)
    2. Pumping nitrogen gas to the equilibrium mixture (1mk)
    3. Lowering the temperature of the reaction (1mk)
12. The scheme below shows some reactions starting with ethyne. Study it and answer the questions that follow.
       
    1. Name substance 
       1. X(½mk)
       2. N (½mk)
    2. Name the reagent M (½mk)
    3. Ethene undergoes polymerization to form a polymer. Write an equation for the reaction and name the product(1½mks)
13.      
    1. State Graham’s law of diffusion (1mk
    2. 30cm³ of hydrogen chloride gas diffuses through a porous in 20 seconds. How long would it take 42cm³ of sulphur (IV) gas to diffuse through the same pot under the same conditions? ( H = 1, Cl = 35.5, S = 32, O = 16) (2mks)
14. In the laboratory experiment, hydrogen gas was passed over heated copper (II) oxide as shown in the diagram below
    
    
    1. Write equation for the reaction taking place in the combustion tube  (1mk)
    2. Describe a chemical test that can be used to identify the product D  (2mks)
15. The scheme below represents the manufacture of a cleaning agent X
    
    
    1. Draw the structure of X and state the type of clearing agent to which X belong  (1mk)
    2. State one disadvantage of using X as a cleaning agent  (1mk)
16. Diamond and graphite are allotrope of carbon.
    1. What are allotropes? (1mk)
    2. Explain why graphite can be used as a lubricant while diamond cannot? (1mk)
    3. Give another element which exhibit allotropy  (1mk)
17. Given sodium carbonate solid, lead II nitrate solid and water, Explain how you can obtain a solid sample of lead II carbonate (3mks)
18. Given the following bond energies:
    C - C                                          347kJ/mol
    C - H                                          413kJ/mol
    C = C                                           612 kJ/mol
    H - H                                          435.9kJ/mol
    Calculate the enthalpy change of hydrogenation of ethane  (3mks)
19. Excess magnesium ribbon sample was heated in equal volumes of:
    1. Pure oxygen gas
    2. Air 
       1. Why was the mass of the resulting product in (ii) more than in (i)? (1mk)
       2. Write the equations for the reactions in part (ii)  (2mks)
20. Excess carbon (II) oxude was passed over heated sample of an oxide of ironas shown in the diagram below. Study it and answer the questions that follow.
    
    Data collected as follows:
    Mass of empty crucible       10.98 g
    Mass of empty crucible + oxide of iron  13.30 g
    Mass of crucible + residue    12.66 g
    Determine;
    1. The mass of the iron   (½mk)
    2. The mass of oxygen   (½mk)
    3. The empirical formula of the oxide of iron    (2mks)
21. The table below gives some properties of three elements in groups (VII) of the periodic table. Study it and answer the questions that follow
    

    Element	Atomic No.	Melting point (ºC)	Boiling point(ºC)
    Chlorine Bromine Iodine	17 35 53	-101 -7 114	-34.7 58.8 185

    1. Which element is a gas at room temperature (25ºC)? Explain.  (1mk)
    2. Explain why the boiling point of bromine is higher than that of chlorine (1mk)
    3. Identify the element which has the highest electron affinity. Give a reason   (imk)
22. An element X has relative atomic mass of 88. When a current of 0.5 Ampheres was passed through the fused chloride of X for 32 minutes 10 seconds, 0.44 g of X was deposited at the cathode.  ( IF = 9650ºC) 
    1. Calculate the number of Faradays needed to liberate 1 mole of X   (2mks)
    2. Write the formula of the chloride of X  (1mk)
23. Aqueous ammonia was added to copper (II) sulphate solution dropwise until in excess. 
    1. What observations were made?  (1½ mks)
    2. Write down the ionic equations representing the observations mentioned in (a) above. ( 1½mks)
24. The diagram below shows the bonding between aluminium chloride and ammonia
    
    
    1. Name the type of bond labeled 
    2. How many electrons are used for bonding in the molecule? (1mk)
25. In an experiment, dry chlorine gas reacted with aluminium as shown in the diagram below.
    
    
    1. Name substance A  (1mk)
    2. Write an equation for the reaction that took place in the combustion tube  (1mk)
    3. State the function of the calcium chloride in the set up above    (1mk)
26.    
    1. State the Gay Lussaic’s law   (1mk)
    2. 10cm³ of gaseous hydrocarbon C2HX required 30cm³ of oxygen for combustion. If 1 mole of steam and 20cm³ of carbon (IV) oxide were produced, what is the value of X?  (2mks)
27. The set up below is an arrangement showing how metals react with nitrogen (IV) oxide. Study it and answer the questions that follow.
    
    
    1. Nitrogen (IV) oxide is passed through the combustion tube before copper is heated. Give a reason. (1mk)
    2. State the observations that would be made at the end of the experiment in the combustion tube(1mk)
    3. Name gas N (1mk)

MARKING SCHEME

1. The laboratory gas burns in excess oxygen 1 OR There is no unburnt carbon 1 
   
   NB: ½ for straight shape of flame
2. Crush the nuts using mortar and pestle 1
   Add appropriate solvent e.g Acetone and continue crushing 1
   Filter/decant the mixture to obtain a solution of oil in filtrate½
   Allow the filtrate/Acetone to evaporate in the sun½
3.      
   1. 2I-(aq) →I_2(g)  + 2e- 
      Pb²⁺(aq) + 2e- →Pb(s)       
   2. Extraction of reactive metals
      Purification of metals
      Electroplating
      Manufacture of pure chemicals e.g Cl₂, NaOH etc
      Any: one
4. Molarity/ conce. Of NaOH = 8/40 = 0.2
   Moles of NaOH in 25cm³ = 0.2 x 25  = 0.005mol
                                                 1000
   H⁺ + 2OH- →H₂O        ; M.R = 1:2
   Moles of acid = ½  x 0.005 = 0.0025 mol
   R.M.M = 0.245   = 98
                 0.0025 
5.      
   1. Zinc blende
   2. 2ZnO_(s) + C(s)→2Zn (s) + CO_2(g)  
   3. Manufacture of dry cell ½
      Galvanizing of iron ½
6.    
   1.    
      1. S   
      2. Q    
   2. Sodium hydroxide/ potassium hydroxide 
7.    
   1. Stable  
   2. R 
      As the number of electrons the same energy level, nuclear attraction increases leading to decrease in atomic radius  1
8.      
   1. Frasch process   
   2. Hot compressed air   
   3. Monoclinic/prismic  ½
      Rhombic/alpha   ½
9.      
   1. A  2.8.1   ½
      B   2.1  ½
   2. B 1: Strong attraction of outermost energy level electrons towards the nuclear  
10.      
    1. Time taken for a given mass of a radioactive isotope to reduce to half its original mass   
    2. No. of half-life = 100  = 4
                                   25
       5/W = (½)4 = W = 80 g
                      OR
       X → ½x → ¼x→ 1/8x → 1/16x
       1/16x = 5 g     x = 80 g
11.      
    1. Equilibrium shifts to the right ½ to replace ammonia gas absorbed by water molecule ½
    2. Equilibrium shifts to the right ½ to use up nitrogen gas added ½
    3. Forward reaction is exothermic ½ hence forward by low temperature: Equilibrium shifts to the right ½
12.      
    1. X- Bromoethene ½
       N- Ethylhydrogen sulphate ½
    2. M- Bromine gas ½
       
       NB;carbon atom MUST have 4 covalent bonds
13.      
    1. Rate of diffusion of fixed mass of a gas is inversely proportional to the square root of its density  
    2. RHCl  = 30/20    = 1.5cm³/s
       1.5/RB =√64/36.5    RB = 1.1333cm³/s
       If 1sec = 1.1333cm³
       ? =  42cm³   = 37 sec
14.      
    1. CuO(s) + H_{2 (g)} → Cu (s)  +  H₂O (l)
    2. Add anhydrous copper II sulphate 1 to D, if changes to form white to blue  1 OR dip cobalt (II) chloride paper into substance D; if changes from blue to pink 1
15.      
    1. Soapless detergent½
       
    2. Non-biodegrable
       Accept K+ in the reagent X
16.      
    1. Different forms of pure substance/Element existing in the same physical state
    2. Has layers bonded with weak vander waal forces which slide on slight heating      
    3. Sulphur    
17. Place the sodium carbonate in a test tube containing water and stir to make a solution 1
    Place the lead (II) nitrate in another test tube containing water to make a solution 1
    React an equal portions of the two solution in a boiling tube to precipitate lead (II) carbonate ½
    Filter off the precipitate as a residue and wash with distilled water. ½
18. Bond breaking =  (C=C) + (H-H) + 4(C-H) 
    =   612 + 435.9 + 4(413) ½ 
    =   +2699.9kJ½
    Bond formation  =   (C-C) + 6(C-H)
    = 347  + 6(413) ½
    =  -2825kJ½
     Enthalpy change  =   (+2699.9- 2825) ½
    = -125.1kJ½
19.    
    1. Reacts with  both oxygen ½ and nitrogen ½ in air
    2. 3Mg (s) + N₂  → Mg₃N₂ (s)          
       2Mg (s)  + O₂(g) → 2MgO (s)    
20.      
    1. Mass of iron = (12.66 – 10.98) 
                            = 1.68 g½
    2. Mass of oxygen   = (13.30 – 12.66)  = 0.64 g½
    3. Empirical formula
       Element                  Fe                         O
       Mass                      1.68                       0.64
       R.A.M                    56                          16
       Mole                      0.03                        0.04         ½
       M .R                       1x3                       1.33x3 ½
                                      3                            4  ½
       Formula  Fe₃O₄ ½      
21.      
    1. Chlorine → melts and boils below room temperature (25ºC)
    2. Bromine has large molecular/atomic mass√ 1 hence experience stronger  √1 intermolecular force of attraction than chlorine
    3. Chlorine has smallest atomic radius hence easily attract electrons /low shielding effect
22.      
    1. Q = It
       = 0.5 x (32 x 60 + 10) =   9650√½
       No. of faradays = 9650   √½      
                                  96500
       = 0.01 F√½
       No. of Faraday liberating 1 mole = (0.01 x 88)√½
                                                                   0.44
       =  2 F½
    2. XCl₂        ½
23.      
    1. Light blue precipitate√ formed that dissolves√ in excess ammonia forming a deep blue√ solution
    2. Cu2+(aq) + 2OH- (aq) → Cu(OH)_2(s)√
                                                 Light blue
       Cu(OH)_2(s) + 4NH_3(aq) → Cu(NH3)4²⁺(aq)√
                                                    Deep blue
24.      
    1. a→Dative bond OR coordinate bond
       b→Covalent bond          
    2. 7 x 2 = 14e-            
25.      
    1. ACl₃    
    2. 2Al(s)  + 3Cl_2(g) → 2 AlCl₃ (s)  
    3. Prevents moisture from entering the apparatus   
26.      
    1. When gases react, they do so in volumes that bear simple ratio to one another and to the products formed
    2. C₂Hx + 3O₂ → CO₂ + H₂O 
       10         30           20    20
        1           3            2      2   
        X = 4
27.      
    1. Expel air from the combustion tube to avoid pre-oxidation of copper metal (hot) 
    2. Brown copper metal turns black  
    3. Nitrogen gas  

TOTAL MARKS 80