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

QUESTIONS

1. The element Y is represented by ²⁷₁₃Y.
   
   1. What does letter Y represent? (1 mark)
   2. What name and symbol is given to the superscript and what does it represent? (1 mark)
2. Element W (not the actual symbol) belongs to period 3 and group VI of the periodic table. Write the formula of its most stable ion. (1 mark)
3. An alkanol has the following composition by mass: Hydrogen 13.5%, Oxygen 21.6% and Carbon 64.9%)
   
   1. Determine the empirical formula of the alkanol. (C=12, H=1, O=16) (2 marks)
   2. Given that the empirical formula and the molecular formula of the alkanol are the same, draw the structure of the alkanol. (1 mark)
4. With the help of an equation, show how chlorine water bleaches (1 mark)
5. The table below gives the ionization energies of group I elements.
   

   Element	I	II	III	IV
   Ionization energy (kJ/mole)	94	418	519	576

   Arrange the elements in order of reactivity starting with the most reactive ( 1 mark )
6. Oxygen and Sulphur belong to group VI of the periodic table. Explain why there is a big difference in their melting points (melting point of Oxygen is -216ºC while that of Sulphur is 114ºC) (2 marks)
7. Heated iron can react with both Chlorine gas and hydrogen chloride gas. Write an equation for each reaction (2 marks)
8. Distinguish between a covalent bond and a co-ordinate bond (2 marks)
9. Draw a dot (.) and cross (X) diagram of an Oxygen molecule (O₂) given that oxygen has an atomic number of 8. (2 marks)
10.      
    1. Differentiate between a strong acid and a concentrated acid ( 2 marks)
    2. Identify the acid in the forward reaction given by the equation below. Explain ( 2 marks)
       HSO₄-(aq) + H₂O(i) ⇌ H₂SO₄(aq) + OH-(aq)
       Acid
       Reason
11. Describe how a sample of Lead (II) chloride can be prepared in the laboratory starting with Lead metal. ( 3 marks )
12. The table below gives information on four elements represented by the letters K, L, M and N. Study it and answer the questions that follow. The letters do not represent the actual symbol of the elements.
    

    Element	Electron Arrangement	Atomic Radius (nm)	Ionic Radius
    K	2.8.2	0.136	0.065
    L	2.8.7	0.099	0.181
    M	2.8.8.1	0.203	0.133
    N	2.8.8.2	0.174	0.199

    1. Which two elements have similar chemical properties? Explain (2 marks)
    2. What is the most likely formula of the oxide of L? (1 mark)
    3. Which element is a non-metal? (1 mark)
13.      
    1. Define a binary electrolyte. (1 mark)
    2. Solid Lead (II) Iodide does not conduct electricity, but fused Lead (II) Iodide does. Explain. (2 marks)
14. Write a half equation for what is formed at the cathode in the reaction above. (1 mark)
15. The diagram below shows a setup that can be used to obtain nitrogen gas in an experiment.
    
    
    1. Name liquid L (1 mark)
    2. What observation would be made in tube K after heating for some time?(1 mark)
    3. Write an equation for the reaction that took place in tube K(1 mark)
16. 60cm³ of Oxygen gas diffused through a porous partition in 50 seconds. How long would it take 60cm³ of Sulphur (IV) Oxide gas to diffuse through the same partition under the same conditions?
    (S=32, O=16)(2 marks)
17. 30cm³ of 0.06M Sodium Hydroxide reacted with 25cm³ of a dibasic acid HOOC(CH₂)xCOOH containing 4g/litre. Calculate the value of X .
    ( C=12, H=1 O=16, Na=23). (3 marks)
18. Water from a town in Kenya is suspected to contain sulphate. Describe how the presence of sulphate ions in the water can be tested. (2 marks)
19. The figure below was set up by a student to investigate the reaction between chlorine gas and hydrogen sulphide gas.
    
    
    1. Write an equation for the reaction that took place in the flask. (1mark)
    2. What observation was made in the flask? (1 mark)
    3. What precaution should be taken when carrying out the experiment? ( 1 mark)
20. Describe how Sulphur is extracted by the frasch process (2 marks)
21.      
    1. State Gay Lussac’s law (1 mark)
    2. 250cm³ of Ammonia reacted with 350cm³ of Oxygen gas to form 200cm³ of Nitrogen (II) Oxide and 300cm³ of steam. 50cm³ of Oxygen remained unreacted. Determine the equation for the reaction. (2 marks)
22. Wooden splints F and G were placed in different zones of a Bunsen burner flame. The diagram below gives the observations that were made.
    
    
    1. Explain the difference between F and G. (2 marks)
    2. Name the type of flame that was used in the above experiment. (1 mark)
23. 1g of potassium carbonate was placed in two different tubes. 2M sulphuric (VI) acid was added into one test of the tubes and in the other test tube 2M ethanoic acid was added. Explain the observations that were made. ( 3 marks).
24. Draw a set up of apparatus to show how dry sulphur (IV) oxide can be prepared in the laboratory starting with dilute hydrochloric acid. ( 3 marks)
25. Give the formula of the polymer formed from the following monomers.
    
    1. H₂N – R – NH₂ and HOOC – R – COOH (1 mark)
    2. Name the type of polymerization shown in (i) above (1 mark)
    3. What substance is lost during the polymerization named above? (1 mark)
       
26. Study the diagram below and answer the questions that follow.
    
    1. Why is it necessary to pass hydrogen through the tube before lighting the hydrogen gas?(1 mark)
    2. After reduction is complete, the apparatus is allowed to cool while hydrogen is still passed over the reduced oxide. Explain (1 mark)
    3. Name another gas that can be used to reduce the metal oxide other than hydrogen. (1 mark)
27. The table below shows solubility of two salts A and B at different temperatures.
    

    Temp (ºC)	Salt	0	10	20	30	40	50
    Solubility (g/100g H2O)	A	3.0	5.0	7.4	10.0	14.0	19.0
    	B	15.0	17.0	20.7	28.7	29.9	33.3

    1. If both A and B were present in 100 cm³ of a saturated solution at 50ºC. What would be the total mass of crystals formed if the solution is cooled to 20ºC. (2 marks)
    2. Solubility of gases decreases as the temperature increases. Explain. (1 mark)
    3. A certain salt C dissolves with absorption of heat from the surroundings. How would its solubility change with an increase in temperature? Explain.(2 marks)
28. The scheme below was used to prepare a cleansing agent. Study it and answer the questions that follow:
    
    
    1. Name the category of cleansing agent prepared by the method above.(1 mark)
    2. Name one chemical substance added in step 2.(1 mark)
    3. What is the purpose of adding the chemical substance named in ii) above (1 mark)
    4. Name another suitable substance to be used in step 1. (1 mark)
29. Melting and boiling points of Hexanoic acid is higher than hexan-1-ol. Explain. (1 mark)
30. Classify the following processes as chemical changes or physical changes.
    
    1. Neutralization
    2. Sublimation
    3. Fractional distillation
    4. Displacement(2 marks)
31. Study the heating curve below and answer the questions that follow:
    
    
    1. What physical changes occur at H and W? ( 1 mark )
    2. Explain what happens to the melting point if sodium chloride is added to this substance.( 1 mark)
    3. Give the names of the intermolecular forces of attraction in the segments: (1 mark)
       
       1. AB
       2. CD

MARKING SCHEME

1.      
   1. Chemical Symbol of the element
   2. Mass number , A ½ mk
      Represents sum of protons and neutrons ½ mk
2. W2-
3.      
   1. 
                           C                   H                  O
      %               64.9.             13.5.              21.6
      moles      64.9/12          13.5/1            21.6/16
                      5.40833        .  13.5              1.35
                  5.40833/1.35.   13.5/1.35.      1.35/1.35
      ratio              4.                  10.                  1
      C₄H₁₀O
   2. H H H H
      H-C-C-C-C-O-H
      H H H H
4. HOCl(aq) + dye → HCl (aq) + (dye +O)
5. I II III IV
6. Oxygen is a diatomic molecule while Sulphur exists as S₈ rings. 1mk
   S₈ rings has a higher molecular mass ½ mk, hence stronger Van Der Waals forces ½ mk compared to oxygen molecule.
7. 2Fe(s) + 3Cl_2(g) → 2FeCl_3(s)
   Fe(s) + 2HCl → FeCl_2(s) + H_2(g)
8. Covalent bond – the sharing of a pair of electrons where each atom forming the bond contributes one electron. 1mk
   Coordinate bond- the sharing of a pair of electrons which are contributed by only one of the atoms forming the bond. 1mk
9.    
   
10.        
    1. A strong acid ionizes completely
       A concentrated acid contains many moles of acid per litre of solution
    2. Acid - H₂O
       Reason - It has donated a proton
11. Add excess lead to dilute nitric V acid to form lead II nitrate. 1 mk
    Filter off the excess lead ½ mk
    Add sodium chloride solution to the lead II nitrate solution ½ mk
    Filter the mixture, lead II chloride is obtained as the residue. ½ mk
    Wash the residue with distilled water and dry between filter papers. ½ mk
12.           
    1. K and N
       They have equal number of electrons in the outermost energy level
    2. L₂O , L₂O₇
    3. L
13.        
    1. An electrolyte that contains two ions, one cation and one anion 1mk
    2. In solid state the ions are in fixed positions hence cannot conduct electricity 1mk
       In molten state the ions are mobile therefore will conduct electricity 1mk
14. Pb2+(l) + 2e → Pb(s)
15.        
    1. Water
    2. Black solid changed to brown
    3. 2NH_3(g) + 3CuO(s) → Cu(s) + 3H₂O(l) + N_2(g)
16. Rate of O₂ = 60/50 = 1.2cm³/second
    Rate of SO₂ = 60/t
    1.2/rate of SO₂ = (64/32)^½ =1.41421
    Rate of SO₂ = 1.2/1.41421=0.84853
    60/t = 0.84853
    t = 70.71seconds
17. Moles of NaOH
    30/1000*0.06 = 0.0018
    Moles of acid = 0.0018 / 2= =0. 0009
    Molarity of acid = 1000 * 0.0009/25 = 0.036M
    RFM of acid = 4/0.036 = 111.11
    HOOC(CH₂)xCOOH = 111.11
    90 +( CH₂)x = 111.11
    14x =111.11 -90
    14x = 21.11
    X =21.11/14
    =1.5079
18. Transfer 2cm³ of the water to a test tube then add two drops of acidified barium chloride solution 1mk. A white precipitate is formed 1mk
19.        
    1. Cl_2(g) + H₂S(g)  S(s) + 2HCl(g)
    2. A yellow solid is formed
    3. The experiment should be carried out in a fume cupboard ½ mk both chlorine and hydrogen sulphide are poisonous gases ½ mk
20. Has three concentric pipes ½ mk
    Superheated water at 1700Cand 10atm is pumped through the outermost pipe ½ mk
    Hot compressed air at 15atm is passed through the innermost pipe ½ mk
    Molten Sulphur passes through the middle pipe to the surface ½ mk
21.          
    1. When gases react, they do so in volumes that bear a simple ratio to one another and to the volume of the products if gaseous, temperature and pressure remaining constant.
    2. NH₃ + O₂                       NO + H₂O
       200/50 250/50          200/50 300/50 1mk
         4            5                  4           6 ½ mk
       4NH_3(g) + 5O₂(g)   4NO(g) 6H₂O(g) ½ mk
22.              
    1. G. Not burnt uniformly. Burnt part was in contact with the blue part of the flame, the unburnt part was in Contact with the almost colourless region
       F. Burnt uniformly. Was placed at the top part (blue) region of the flame
    2. Non luminous flame
23. More bubbles/effervescence observed in the test tube with 2M Sulphuric VI compared to that containing 2M ethanoic acid. 1mk
    Sulphuric VI acid is a strong acid, it ionizes completely, producing many hydrogen ions which react with potassium carbonate liberating a lot of carbon IV oxide. 1mk
    Ethanoic acid is a weak acid is a weak acid, it ionizes partially giving few hydrogen ions which react with potassium carbonate producing little carbon IV oxide 1mk
24. Heat ½ mk
    Sodium sulphite ½ mk
    Drying ½ mk
    Collection ½ mk
    Workability 1mk
25.            
    1. -HN-R-NH-CO-R-CO-
    2. Condensation polymerisation
    3. Water
26.      
    1. To drive out air from the apparatus because a mixture of hydrogen and oxygen is explosive when ignited
    2. To prevent re oxidation of the hot copper metal
    3. Carbon II oxide
       Ammonia Any one
27.        
    1. A 19.0-7.4 =10.6g ½ mk
       B 33.3-20.7=12.6g ½ mk
       Total mass = 23.2g 1mk
    2. As the temperature rises, the kinetic energy of the gaseous solute increases, its molecules break from the attraction of solvent molecules and return to the gas phase
    3. The solubility will increase.
       Increase in temperature provides heat required to break the lattice hence dissolves faster
28.          
    1. Soapy detergent
    2. Sodium chloride
    3. Precipitates the soap
    4. Potassium hydroxide
29. Hexanoic acid forms more hydrogen bonds than hexan -1-ol therefore higher higher melting and boiling point.
    1. Chemical
    2. Physical
    3. Physical
    4. Chemical (2 marks)
30.      
    1. H. Melting
       W Evaporation
    2. The melting point will be lowered ½ mk and will melt over a range of temperatures ½ mk
    3. AB hydrogen bonds
       CD. Hydrogen bonds