Chemistry Paper 1 Questions and Answers - Form 3 End Term 1 Exams 2022

Answer all the questions in the spaces provided.

1. Dyes W,X, Y and Z were analysed using P as the purest sample of the dye required by a chemist .the result obtained were as shown on the chromatogram below.
   
   
   1. What names are given to the lines marked?
      
      1. A 1mk
      2. B 1mk
   2. State with a reason the most unsuitable dye for the chemist to use . 2mks
2.    
   1. Distinguish between allotropes and isotopes. 2mks
   2. Name the two allotropes of sulphur . 2mks
3. The table below shows the atomic numbers of elements F G and H.
   

   Element	F	G	H
   Atomic number	4	12	20

   Which of the elements is the least reactive? Explain 2mks
4. Classify the changes below as physical or chemical changes.
   

   	Type of change
   Magnetization of iron
   Heating iron until it softens
   Souring of milk

5. A student prepared ammonia gas and wanted to make it solution in water. Complete the diagram to show how he made the solution.
   
6. Element J belong to period 3 and group V.
   
   1. Write the electron arrangement of J. 1mk
   2. The equation of the reaction when J reacts with oxygen gas. 2mks
7. A fixed mass of a gas has a volume of 200cm3 at a temperature of 47oC and 750mmHg .calculate the volume the gas would occupy at 7oC and 750mmHg pressure. 3mks
8. The diagram below represents a luminous flame.
   
   Mark and label on the diagram the hottest and coolest parts 2mks
9. Burning magnesium was lowered in a gas jar full of dry sulphur IV oxide.
   
   1. State the observation that was made. 2mks
   2. Write the equation for the reaction occurring. 1mk
   3. State the reducing agent in the above reaction. 1mk
10. Draw a dot (.) and cross (X) diagram to show the bonding in the molecules of :
    (Atomic number of carbon is 6, Oxygen is 8 and hydrogen is 1)
    1. Carbon II oxide.
    2. Water.
11. Explain the following observations
    
    1. Magnesium is a better electrical conductor than sodium. 1mk
    2. A solution of aluminum chloride has PH of 3.0. 1mk
12. A compound W consist of 26.7%carbon, 2.2%hydroen and the rest oxygen. It has a relative formula Mass of 90(C=12, H=1, O=16,)
    1. Determine it empirical formula. 2mks
    2. Workout its molecular formula 2mks
13. Hydrogen was passed over copper II oxide in a combustion tube.
    
    1. Write an equation for the reaction that took place. 1mk
    2. What observation was made in the combustion tube? 2mks
    3. Name two other gases which could be used to reduce copper II oxide. 2mks
14.    
    1. State grahams law of diffusion. 1mk
    2. 20cm³ of oxygen diffused through a porous partition in 70s .how long would it take 20cm³. Of sulphur VI oxide to diffuse through the same portion under the same condition. 3mks
15. He set up below was used to collect gas Z produced by the reaction between water and calcium metal.
    
    
    1. Give a chemical test for gas Z. 2mks
    2. Write the equation of the reaction between the calcium metal and water. 2mks
16. The diagram below shoes the bonding between aluminium chloride and ammonia
    
    
    1. Name the type of bond labeled
       
       1. X. 1mk
       2. Y 1mk
    2. How many electrons are used for bonding in the molecule? 1mk
17. Graphite is a non metal, yet it conduct an electric current .explain this observation. 1mk
18. A sample of air contaminated with carbon monoxide and sulphur dioxide was passed through the apparatus shown in the diagram below.
    
    Which contaminant was removed by passing the contaminated air through the apparatus?
    Explain. (2mks)
19. Explain how you would show chemically that a given gas is ammonia. 2mks
20. Chlorine water was exposed to sunlight for a few hours .Colourless gas F was collected in the boiling tube as shown.
    
    
    1. Name gas F. 1mk
    2. Write an equation for the formation of gas F.2mks
21. The equation below shows the action of heat on three metal nitrates.
    2S(NO₃)₂ → 2SO + 4NO₂ +O₂
    2TNO₃ → 2TNO₂ + O₂
    2UNO₃ → 2U +2NO₂ + O₂
    
    1. Arrange the metals S,T and U in the order of reactivity from least to the most reactive. 3mks
    2. Give one element that could be used. 1mk
22.      
    1. Define the term transition temperature concerning the allotropes of sulphur. 1mk
    2. Draw the structure of a sulphur molecule. 1mk
23. Dilute hydrochloric acid was added to a compound Z of sodium. The solid reacted with the acid to form a colorless solution H and a colourless gas K which formed a white precipitate when bubbled through lime water.
    Write the formula of:
    1. 1. Compound Z 1mk
       2. Colorless gas K 1mk
       3. Write an equation for the reaction that took place. 2mks
24. The diagram below represents the extraction of sulphur by Frasch process
    
    
    1. Name the substance that passes through tube;
       1. ½ mk
       2. ½ mk
    2. What is the purpose of hot compressed air in this process? (1mk)
25. A student used the setup below to prepare oxygen gas in the laboratory. Study it and answer the questions that follow.
    
    
    1. Identify solid K. 1mk
    2. Name the apparatus labeled L. 1mk
    3. Write an equation for the reaction in the conical flask. 2mk
26. Nitrogen gas is used as an inert atmosphere in electric lamps.
    1. Explain in terms of structure and bonding why nitrogen gas is so stable .2mks
    2. Give a reason why despite this stability nitrogen reacts with burning magnesium metal. 1mk

MARKING SCHEME

1.    
   1. A - Solvent front
      B- Baseline
   2. Z - Z is the most impure with 3 substances not in the pure dye
2.        
   1. Allotropes are two or more forms of an element in the same physical state
      Isotopes are atoms of the same element having the same atomic number but different mass numbers
   2. Rhombic sulphur
      Monoclinic sulphur
3. F - F has the smallest atomic radius/size and has the least tendency to lose electrons
4.      
   1. Physical change
   2. Physical change
   3. Chemical change
5. .
   
6.      
   1. 2.8.5
   2. 4J + 3O_2(g) → 2J₂O_3(g) 
      4J_(s) + 5O_2(g) → 2J₂O_5(g)  
      Award 2 marks if correct state symbols are there
7. V₁ = 200cm³
   T₁ = 47ºC = 47 + 273 - 320K
   P_{1 =} 750mmHg
   V₂ = ?
   T₂ = 7ºC = 7 + 273 = 280K
   P₂ = 750mmHg
   V₁  = V₂ 
   T₁     T₂
   V2 =  V₁T₂   = 200 x 280 = 175cm³ 
              T₁             320
8.    
   
9.      
   1. White ash and yellow specs formed
   2. 2Mg_(s) + SO_2(g) → 2MgO_(s) + S_(s) 
   3. Magnesium
10.   
    
11.      
    1. Magnesium has 2 delocalised electrons compared to sodium which has 1
    2. Aluminium chloride hydrolyses in solution to form an acidic solution
12.        
    1. %oxygen = 100-(26.7 + 2.2) = 71.1%
       
    2. (CHO₂)_n = 90 
       12n + n + 32n = 90
       45n = 90
       n = 2
       M.F is C₂H₂O₄
13.      
    1. H_2(g) + CuO_(s) → H₂O(l) + Cu_(s)
    2. Black copper (II) oxide turned brown
    3. Ammonia gas and carbon (II) oxide gas
14.      
    1. Graham's law of diffusion states that under the same conditions of temperature and pressure the rate of diffusion of a gas is inversely proportional to the square root of its density
    2. MO₂ = 2 x 16 = 32 
       TO₂ = 70 secs
       MSO₃ = (32 + 16 x 3) = 80
       TSO₃=?
       TSO₃ = √MSO₃
       TSO₂       MO₂
       TSO₃ = √80
       70 32
       TSO₃ = 70√80 = 70 x 8.944 = 110secs
                       √32        5.657
15.    
    1. It burns with a pop sound
    2. Ca(s) + 2H₂O(l) → Ca(OH)₂(al) + H₂(g)
16.      
    1. X - Co-ordinate /Dative bond
       Y - Covalent bond
    2. 14 electrons
17. Graphite has delocalised electrons in its structure
18. Sulphur (iv) oxide
    Carbon (II) oxide gas/does not react with lime water nor conc H2SO4 but SO2 being acidic is absorbed by the lime water
19. Dip in a glass rod in concentrated hydrochloric acid and introduce it near the unknown gas. If dense white fumes are formed, then the gas is ammonia
    OR
    If it turns damp red litmus paper blue it is ammonia
20.      
    1. Gas F - oxygen gas
    2. 2HOCl(aq) → 2HCl(aq) + O_2(g)
21.      
    1. UST - U(least reactive) T(most reactive)
    2. Silver or mercury
22.      
    1. Transition temperature - is the temperature at which one allotrope of sulphur changes to another
    2.    
       
23.      
    1.      
       1. NaCO₃
       2. CO₂
    2. Na₂CO_3(s) + 2HCl(aq) → CaCl_2(aq) + H₂O(l) + CO_2(g)
    3. Effervescence occurs/production of bubbles of a colorless gas
24.      
    1.      
       1. Molten sulphur
       2. Superheated water
    2. To force out molten sulphur from underground
25.      
    1. Solid K - Solid peroxide
    2. Beehive stand
    3. 2Na₂O₂(s) + 2H₂O_(l) → 4NaOH(aq) + O_2(g)
26.      
    1. The atoms of nitrogen are bonded by three strong covalent bonds which need a lof of energy to breathe
    2. Burning magnesium releases a lot of heat energy which gets absorbed by the nitrogen molecule breaking the triple covalent bond