Chemistry Paper 1 Questions and Answers - Mokasa II Mock Exams 2022

Questions

Instructions to Candidates

• Answer all the questions in the spaces provided
• Scientific calculators may be used
• All working must be clearly shown where necessary

1.      
   1. Explain the term 'strike back' as applied to a Bunsen burner (1mk)
   2. Give the name and state the function of the apparatus labeled N in the diagram shown below (2mks)
      
      Name
      Function
2. 1.6g of Ammonium nitrate were dissolved in 100cm3 of water at room temeprature 21°C and the mixture was stirred wiht a thermometer. The molar heat of solution obtained in the experiment was +126Kj/mol, calculate the final temperature of solution (3 mks)
   (C = 4.2kJ/Kg/K, Density of solution 1g/cm3, N=14, H=1, O= 16)
3. Describe how constant mass of copper can be determined in copper II carbonate (3 mks)
4.       
   1. Define the term Homologous series (1mk)
   2. Hydrocarbon A with 3 carbon atoms decolorizes bromine water in the presence of light but does not decolorize acidified Potassium Manganate VII
      1. Name the homologous series to which hydrocarbon A belongs (1 mk)
      2. Write the chemical equation to show how the Hydrocarbon A s prepared in the laboratory. (1mk)
5.        
   1. The diagram below shows allotropes of Carbon. Study them and asnwer questions that follows
      
      State
      1. One use of allotrope X
      2. Why allotrope Y is very hard
   2. Set up below is used to prepare gas W
      
      
      1. Identify gas W and liquid J (1 mk)
         Gas W
         Liquid J
      2. State the observation made when gas W is bubbled in lead (II) nitrate solution (1 mk)
6. A form two student in an attempt to stop rusting placed copper and zinc metals in contact with iron separately as shown below.
   
   
   1. State the observation made set up I and II (1 mk)
      Set I
      Set II
   2. Explain your answer in (a) above (1mk)
   3. Name the method of preventing rusting illustrated above (1 mk)
7.      
   1. State Graham's law of diffusion
   2. 100cm³ of Carbon (IV) oxide gas diffused through a porous partition in 30 seconds, How long would it take 150cm3 of Nitrogen (IV) oxed to diffuse through the same partition under similar condiitons. C= 12, N= 14, O= 16 
8. An element M has 19 neutrons and a mass number of 39
   1. Write the electron arrangement of its stabel ion (1mk)
   2. Which period does M belong to (1 mk)
   3. Draw the structure of its ion (1mk)
9. The flow chart below shows stages in extraction of copper , use it to answer questions that follow
   
   
   1. Write the eqaution for the reaction that occurs in the roaster (1 mk)
   2. Name Gas A (1 mk)
   3. What is the importance of assing silica in roaster 1(1 mk)
10.     
    1. Using dots (.) and crosses (x) to represent electrons draw the structure of aluminium chloride dimer
    2. Explain why aluminium carbonate does not exist.
    3. Melting point of lithium chloride  is higher than sodium chloride.
11. The diagram below is a cross section o the dry cell. Study it and answer questions that follow.
    
    
    1. Write the overall equation to represent the reaction that takes place in the cell.
    2. The carbon rod is surrounded with a mixture of powdered carbon and manganese IV oxide.
       What is the function of Manganese IV oxide (1mk)
    3. Explain why a-brass CAp is suitable over copper cap in the above cell. (1 mk)
12. The diagram below shows preparations of Hydrgen gas. Study it and answer questions that follow.
     
    1. Explain why no hydrogen was produced.
    2. When the mistake is corrected, hydrogen gas is produced name the method used to collect the gas and give reason why it was used.
       Method
       Reason
    3. Describe a test that can be done to identify Hydrogen gas in the laboratory
13. The equation and the curves below shows decomposition of dinitrogentetraoxide.
         N₂O₄     ⇌   2NO_2(g) ΔH = +17kJ/mol
    pale yellow          brown
    
    
    1. Which curve represents change in concentration of NItrogen (IV) oxide. Explain. (1½mks)
    2. State and explain the observation made when the beaker containing the mixture is placed in hot water.
14. A student bubbled chloride gas through a solution of Magnesium bromide in a corked conical flask.
    1. State and explain the observation made.(2mks)
    2. Write the ionic equation for the reaction which occurered at the conical flask. (1mk)
15.    
    1. It is not appropriate to refer to group VIII elements as 'Inert gases'. Explain giving an example. (2mks)
    2. Give one use of them (1mk)
16. The diagram below shows burning of Magnesium in air and collecting the products
    
    
    1. Name the observation made during the reaction (1mk)
    2. Water was added to the product formed, a colourless gass with a pungent irritating smell was produced.
       1. State the chemical test for the colourless gas (1mk)
       2. Write the equation leading to fomation of colourless gas (1 mk)
17.          
    1. Name the compound below (1mk)
       
    2. Compound M reacts with ethanol in the presence of few drops concentrated of sulphuric (VI) acid to form a fruity smelling compound below.
       
       
       1. Write the molecular fromula of compound M (1 mk)
       2. Give one use of the fruity smelling compound (1 mk)
18. 100g of ²³¹₉₁Th with a half life of 12 days decayed to a mass of 6.25g on the grid below, plot the graph of ²³¹₉₁Th against time (3mks)
19.   
    1. The following data gives pH values of solution M, N and P
       

       Solution	pH value
       M N P	13.6 7.0 1.3

       1. Which solution will produce carbon iv oxide when reacted with copper (ii) carbonate (1mk)
       2. What would be the colour of solution M after adding a few drops of phenophtalein (1 mk)
    2. The graph below shows how the pH value of soil in a farm over a period of time.
       State one factor that may have been responsible for the change in soil pH in the interval AB(1mk)
20. When 80cm3 of Hydrogen gas were mixed with 60cm3 of chlorine and mixture exploded in a bright sunlight. Reaction took place according to the equation below.
    H2(g) + Cl2(g) → 2Hcl(g)
    1. Determine the volume of resulting gas mixture (1mk)
    2. When the resulting gas mixture was shaken well with water, the volume the gas was found to be less than the original mixture
       1. Why was the volume reduced (1mk)
       2. Determine the volume the residue gas after the reduction (1mk)
21. The diagram below represents the mercury cell used in the industrial manufacture od sodium hydroxide. Study it and answer questions that follow.
    
    
    1. Name the substance B (1mk)
    2. Write the equation for the reaction that takes places at electrode Z(1 mk)
    3. Give one reason why electrode J is made up of mercury (1mk)
22. Student was required to prepared crystals of Magnesium chloride, starting with 100cm3 of 2M Magnesium Hydroxide. Describe how the student prepared pure dry crystals of magnesium chloride. (3mks)
23. In an experiment to separatea mixture xanthophyll and Chlorophyll in plant leaf.
    1. Describe a procedure that was carried out first before separating the two pigments (2mks)
    2. After sometime it was discovered that Xanthophyll is more soluble than chlorophyll in the solvent. Draw a well-labelled diagram to show the results of this experiment (1 mk)
24. The table below shows the tests carried out on a sample of solution and the results obtained as shown on the table below:
    

    	Tests	Results
    I	Addition of excess sodium hydroxide	White precipitate soluble in excess
    II	Addition of excess aqueous ammonia solution	White precipitate soluble in excess
    III	Addition of acidified Barium Nitrate	White precipitate.

    1. Identify the Anion in the solution (1mk)
    2. Write the ionic equation for the reaction in step III (1 mk)
    3. Write the formula of the complex ion formed in step II (1mk)
25. In the laboratory, Nitric V acid can be prepared using the set up below
    1. Name (1mk)
       1. Apparatus N
       2. Reagent R 
    2. Give a reason why sodium nitrate is preferred over other nitrates in above experiment (1mk)
    3. State one property that makes reagent R suitable for use in this experiment (1mk)
26. Potassium carbonate cannot be manufactured by the solvay process. Explain. (1mk)
27. The setup below was used to collect dry sample of a gas.
    Give two reasons wy the set up above is suitable for collecting Carbon IV oxide(2mks)

Marking Scheme

1.     
   1. Phenomenon where the flame goes down the chimney ans goes off. It happens when thegas is being burnt faster than can be supplied.
   2. Name -  Fractionating column
      Function - Condenses vapour of a liquid with higher boiling point back to flask before attaining its boiling point.
2. Moles of NH₄NO₃ used 
   1.6 - 0.02 moles
   ΔH = 1 mole → 126 = 2.52Kg
   2.52 = 100/1000 x 4.2 x ΔT
   ΔT = 6°C 
   Final temp = 21 - 6
   = 15°C
3.     
   • Weigh the mass of the crucible and CuCO3
   • Heat CuCO3 in a crucible strongly to form CuO as residue
   • Pass dry hydrogen over heated CuO to from Cu metal.
   • Determine(weight) the mass of the residue.
   • Subtract the mass of the crucible from the mass of the residue and crucible.
4.           
   1. Sequence of compounds with the same chemical properties, chemical fomula and functional group and they exhibit gradual change in physical properties.
   2.       
      1. Alkane
      2. C3: H₇COONa_(s) + NaOH_(s) → C₃H_8(g) + Na₂CO_3(s)
         (ignore state symbols off ommitted otherwise penalize wrong states)
5.         
   1.       
      1. Dry lubricant, positive terminal in dry cell, pencils
      2.   
         • Strong covalent bonds between carbon atoms that are uniformly distributed
         • Close packaging of the carbon atoms
   2.        
      1.   
         • Gas W - hydrogen sulphide/ H₂S
           Liquid J - warm water
      2. Black precipitate.
6.         
   1. Set I - Iron remains grey
      Set II - A brown coating is formed on iron
   2. In setup I, iron did not rust since zinc offers sacrificial portection
      In setup II, itron ruysted since copper is less reactive and offered no protection.
   3. Sacrificial protection.
7.      
   1. Under similar conditions of temperature and pressure , the arte of diffusion of a gas is inversely proportional to the square root of its density.
   2. 100cm3 of CO2 → 30 
      150 → ?
      150 x 30 = 45
      100
        TCO₂ =   √MCO₄  
       TNO₂        √MNO₂
         45    =    √44   
       TNO₂      √46
       TNO₂  = 46.011 seconds
8.        
   1. 2.8.8
   2. Period 4
   3.   
      
9.            
   1. 2CuFeS2(s) + 4O2(g) → Cu2S(s) + 2FeO(s) + 3SO2(g)
   2. Sulphur (iv) oxide
   3. Reacts with iron (ii) oxied to form iron (iii) silicate (slag)
10.         
    1.   
       
    2. Aluminium salts hydrolyzes in water to form hydrogen ions which reacts with carbonates to form CO₂ gas
    3. LiCl has stronger ionic bond than NaCl since Li forms small ionic radius than Na.
11.              
    1. ZnC_(s) + 2NH⁴⁺_(aq) → Zn²⁺_(aq) + 2NH_3(g) + H_2(g)
    2. Deplarizes/ oxidizes hydrogen gas to water preventing accumulation of bubble at the positive terminal. 
    3. Brass is resistant to corassion than copper/ it is highly conductive and perfect for electrical parts.
12.       
    1. Copper is lower than hydrogen in the reactivityy series hence cannot displace hydrogen nfrom the dilute acid.
    2. Method - Upward delivery/ downward displacement of air
       Reason - hydrogen is less dense than air/ lighter than air.
    3. Introduce a burning splint into a gas jar containing hydrigen gas. It extinguishes the burning splint wiht a 'pop' sound.
13.           
    1. Curve I - Increase concentration of NO₂
    2. Brown colour intesnifies - Equilibrium shifts forward since endothermic reaction is favoured by increase in temperature.
14.           
    1. Solution changes to brown - Cl2 displaces Br from the solution.
    2. 2Br ^-_(aq) + Cl_2(g) → 2Cl ^-_(aq) + Br_2(l)
15.           
    1. Some group VIII elements are chemically reactive because of larger atomic radius hence can lose electrons eg xenon.
    2. Research baloons/ Arch welding
16.            
    1. Brilliant white flame
    2.     
       1. Introduce glass rod dipped in concentrated HCl, white fumes are formed.
       2. Mg₃N_2(s) + 6H₂O_(l) → 3Mg(OH)_2(aq) + 2NH_3(g)
17.      
    1. 2-Methylhexan-1-ol
    2.        
       
       1. C₃H₇COOH/C₄H₈O₂
       2. Fresheners
          Cosmetics
          Perfumes
18. 100g → 50 → 25 → 12.5 → 6.25
        0        12      24        36      48
    
19.      
    1.  
       1. P
       2. pink
    2. Acidic rain/ leaching/ water logging
20.           
    1. H2 : Cl2: 2HCl
          1:      1:   2
         60:    60 : 120
       Volume of H2 used 80 - 60 = 20cm
       Total volume = 20cm³ + 120 = 140cm³
    2.       
       1. HCl(g) dissolved in H2O
       2. 140cm³ - 120cm³ = 20cm³ of H_2(g)
21.        
    1. Hydrogen gas
    2. 2Cl -(aq) → Cl2(g) + 2e-
    3. Hg prevents / blocks discharge of H+(aq) at chatode
22. Mg(OH)_2(aq) + 2HCl_(aq) → MgCl_2(aq) + 2H₂O(l)
                     1 :      2
             100     :   200
    
    • Add 200cm³ of 2MHCl to 1000cm³ of 2MMg(OH)
    • Evaporate the resulting solution to saturation.
    • Cool the solution
    • Dry crsytals betwen filter paper.
23.          
    1.    
       • Crush the leaves in mortar using pestle
       • Add propanone and continue crushing
       • Decant the solution formed into a beaker.
    2.      
       
24.      
    1. SO^2-₄/ sulphate ion
    2. Ba²⁺_(aq)  + SO^2-_4(aq) → BaSO_4(s)
    3. (Zn(NH₃)₄)²⁺_(aq)
25.    
    1.      
       1. Retort flask
       2. Concentrated sulphuric (VI) acid
    2. Lacks water of crystalization
    3. Less volatile
26. KHCO₃ is more soluble than NaHCO₃ hence does not crsyatllize
27. CO₂ does not react with H₂SO₄
    CO₂ is denser than air