Chemistry Paper 1 Form 3 Questions and Answers - Term 3 Opener Exams 2021

INSTRUCTIONS TO CANDIDATES

• Answer all the questions
• Mathematical table and silent electronic calculators may be used.
• All working must be clearly shown where necessary.

QUESTIONS

1. Three pure pigments were prepared and their spots placed on a filter paper as shown below. The three pigments are A, B and C. A mixture F was also placed on the filter paper at the same time with the pure pigments. The filter paper was then dipped in ethanol solvent and left for some half an hour. The results were obtained as follows.
   
   1. Which of the three pure pigments is most sticky? Give a reason for your answer.   (1mk)
   2. Which pure pigment is not present in the mixture F? (1mk)
   3. Show on the diagram the baseline. (1mk)
2. Describe how a pure sample of lead (II) carbonate can be prepared in the laboratory starting with lead II oxide.(3mks)
3. The set-up below was used to prepare nitric (v) acid in the laboratory
         
   1. Name the mixture W (1 mk)
   2. Write an equation for the reaction that takes plac ein Flask A (1 mk)
   3. Explain why conc. nitric (v) acid produced appears yellow when exposed to sunlight. (1mk)
4. A mixture contains ammonium chloride, aluminium oxide and sodium chloride. Describe how each solid substance can be obtained from the mixture. (3mks)
5. State the difference between the following salts;
   Deliquescent and hygroscopic salts.  (2mks)
6. Below is a set-up of apparatus used to investigate the effect of electric current on molten lead (II) bromide.
   
   1. Name electrode. (1mk)
      K
      L
   2. State the observation made at electrode K.  (1mk)
   3. Write an equation for the reaction taking place at electrode L.  (1mk)
7. A sample of a polyethene polymer has the following structure.
      
   1. Draw the structural formula of the monomer that makes the above polymer
   2. The polymer is found to have a molecular mass of 2268g. Determine the number of monomers in the polymer.
      (H = 1, C = 12). (2mks)
8. The isotopes hydrogen are ¹₁H and _²1H_. Determine the molecular masses of the molecules formed when each of these isotopes react with chlorine. (Cl = 37, H=1)  (1mk)
9. The table below gives the atomic numbers of elements W,X,Y and Z. The letters do not represent the actual symbol of the elements
   

   Element	A	B	C	D
   Atomic Number	9	10	11	12

   
   
   1. Which one of the elements is unreactive? Explain (1mk)
   2.  
      1. Which two elements would react most vigorously with each other?  (1mk)
      2. Give the formula of the compound formed when the elements in b (i) above react       (1mk)
10.    
    1. Distinguish between a hydrogen bond and covalent bond     (2mks)
    2. Explain why the boiling point of water is higher than that of hydrogen Sulphide
       (Relative molecular mass of water is 18 while that hydrogen sulphide is 34) (2mks)
11. The set-up below was used to investigate the products of burning methane gas. Study it and answer the questions that follow:
     
    1. What product will be formed in the test tube Y?  (1mk)
    2. State and explain the observations made in tube Z. (2mks)
12. Below are PH values of some solutions.
    

    Solution	Z	Y	X	W
    pH	6.5	13.5	2.2	7.2

    1. Which solution is likely to be:
       1. Acidic rain.  (½mk)
       2. Potassium hydroxide (½mk)
    2. A basic substance V reacted with both solutions Y and X. What is the nature of V. (1mk)
13. In cold countries, salt is sprayed on the road to melt ice but in the long run it costs the motorists.
    1. How does the salt help in melting ice?  (1mk)
    2. How does the salt affect the motorists?  (1mk)
14. Using dots (. ) and crosses (x) to represent electrons, show bonding in the compounds formed when the following elements react: (Si=14, Na=11, Cl=17):
    
    1. Sodium and chlorine.  (2 Mks)
    2. Silicon and chlorine. (2 Mks)
15.  
    1. State Graham’s law of diffusion. (1mk)
    2. 20cm³ of an unknown gas Q takes 12.6 seconds to pass through a small orifice, 10cm³ of oxygen gas takes 11.2 seconds to diffuse through the same orifice under the same conditions of temperatures and pressure. Calculate the molecular mass of unknown gas Q (O = 16). (3mks)
16. The peaks below show the mass spectrum of element X.
       
    Calculate the relative atomic mass of X.   (2mks)
17. Name the following compounds using the IUPAC rules.
    1. CH₃CH₂CHCH₂CH₂CH₃
                   |
                   CH₂CH₃          (1mk)
    2. CH₃CHCHCH₃              (1mk)
    3. Draw TWO structural formulae of isomers of compound with the molecular formula CH₃CH₂CH₂CH₃ (2mks)
18.  
    1. What is meant by allotropy?   (1 mk)
    2. The diagram below shows the structure of one allotropes of carbon.
       
       1. Identify the allotrope              ( 1 mk)
       2. State one property of the above allotrope and explain how it is related to its structure (2mk)
19. 24cm³ of a solution of 0.1 M potassium hydroxide were exactly neutralized by 30cm³ of a solution of sulphuric acid. Find the molarity of the acid.  (3 mks)
20.    
    1. Give one use of hygroscopic substances in the laboratory. (1 mk)
    2. What is meant by the terms: (2 mks)
       1. Isotopes
       2. Mass number
    3. The formulae for a chloride of phosphorus is PCl₃. What is the formula of its sulphide? (1 mk)
21. The diagram below shows the Frasch process used for extraction of sulphur. Use it to answer the questions that follow.
    
    1. Identify X.   (1mk)
    2. Why is it necessary to use super heated water in this process? (1mk)
    3. State two physical properties of sulphur that makes it possible for it to be extracted by this method (1mk)
22. A certain carbonate XCO₃ , reacts with dilute hydrochloric acid according to the equation given below:
    XCO_3(s) +2HCl _(aq)   →  XCl_{2 (aq)} + CO_{2 (g)} + H₂O _(l)
    If 4g of the carbonate reacts completely with 40cm³ of 2M hydrochloric acid, calculate the relative atomic mass of X.
    (C=12.0 ,O=16.0, Cl=35.5).  (3 Mks)
23. The table below gives some properties of three substances I, J and K. Study it and answer the questions that follow.
    

    Substance	Mpt (ºC)	Solubility in water	electrical conductivity
    			solid	molten
    I	1063	Insoluble	conduct	conduct
    J	113	Insoluble	Doesn't	Doesn't
    K	402	Sparingly soluble	Doesn't	conduct and is decomposed

    1. Suggest the type of structure in:
       1. I    (1mk)
       2. K   (1mk)
          Explain why the molten K is decomposed by electric current but I is not decomposed.(2mks)
24. Concentrated sulphuric acid is slowly added to a mixture of freshly prepared solution of iron (II) sulphate and potassium nitrate as below.
    
    
    
    1. State the observation (1mk)
25. Study the inforation given in the table below and answer the questions that follow.
    
    
    1. predict the cation and anion present, in solid H
       • Cation (1mk)
       • Anion  (1mk)
    2. Identify:
       • solution K (1mk)
       • solution B (1mk)
       • White precipitate (1mk)

Marking scheme                                                

1.    
   1.  A – moves shortest distance
   2. B
   3.   
      
2.    
   • Measure a fixed volume of nitric V acid  in a beaker
   • Add lead II oxide to the acid until in excess
   • Filter the mixture and collect the filtrate lead II nitrate
   • To the filtrate add a solution of sodium carbonate solution to precipitate lead carbonate
   • Filter the mixture and collect the residue lead II carbonate wash the residue  and dry it under low temperature or btw filter papers
3.  
   1. Conc. sulphuric (VI) acid + potassium nitrate
   2. H₂SO_4(l) + KNO_3(S) → KHSO_4(aq) + HNO_3(aq)
   3. Nitric (V) acid decomposes on exposure to light to form nitrogen (IV) oxide.
4.  
   • Heat the mixture ammonium chloride sublimes and is collected on the cooler  part of boiling tube./accept a diagram
   • Add water to dissolve NaCl.
   • Filter to obtain Al₂O₃ as a residue.
   • Evaporate the filtrate to obtain NaCl 
5.  
   • Deliquescent – Absorbs water from atmosphere to form a solution.
   • Hygroscopic – Absorbs water from the atmosphere and do not form solution.
6.  
   1.  
      • K Anode
      • L Cathode
   2. Red-brown vapour
   3. Pb²⁺_(l) + 2ë → Pb_(s) 
7.  
   1.    
      
   2. 2268/28 = 81 monomers
8.  
   Molecule:    HCl
   MM. of  ¹₁ HCl = 38
   Of  ²₁ HCl = 39
9.   
   1. B. Has completly filled outer energy level
   2.  
      1. A and C
      2. CA   //NaF                reject AC
10.    
    1. hydrogen bond is formed between a hydrogen atom of one molecule with a more electronegative/an oxygen of another element of another molecule.
       accept illustration e.g
       
       Covalent bond is formed when two electronegative elements bond by each donating an electron to be shared in the bond.
    2. (Relative molecular mass of water is 18 while that hydrogen sulphide is 34)
       Water has hydrogen bonding in addition to vanderwaals forces which makes the intermolecular force strong requiring more energy, while hydrogen sulphide has only weak vander waals forces which requires less energy to break.
11.    
    1. Water/H₂O
    2. A white precipitate. ✔½ Burning methane produces carbon (IV) oxide ✔½
       Which reacts with calcium hydroxide to form the insoluble ✔½ calcium carbonate ✔½
12.  
    1.    
       1. Z
       2. Y
    2. Amphoteric
13.  
    1. Salt acts as an impurity.  Lowers Mpt of ice hence ice melts at low Mpt.
    2. Salt increases rate of rusting of the metallic parts of the vehicles.
14.   
    1. Sodium and chlorine.
        
    2. Silicon and chlorine.
        
15.    
    1. Graham's law of diffusion: Under the same conditions of temperature and pressure, the rate of diffusion of a gas is inversely proportion to the square root of its density.
    2.    
       ^TO₁/ _TO2 = √^MO₁/_MO2
       Where TO₁ = 12.6 sec.
                  TO₂ = 22.4 sec.
       MO₂ = 2 × 16 = 32
       ^12.6/_22.4 ^= √MO₁/₃₂
       RQ₁ = RMM of Q₂
       RQ₂ = RMM of Q1
       MO~ = (^12.6/_22.4)² × 32
       = 10.13 M
16. Atomic mass of X
    (24 × 82.8) + (25 × 81) + (26 × 9.1)
                               100
    = 1987.2 + 202.5 + 236
                  100
    =2426.3
        100
    =24.263
17.  
    1. 3-ethyl hexane
    2. But-2-ene
    3.    
       
        
18.  
    1. Allotropy is the existence of an element in more than one form without change in physical state
    2.  
       1. graphite.
       2.    
          • It is a lubricant because layers slide over each other
          • a good conductor of both heat and electricity because it has delocalised/mobile electrons
19.  2KOH_(aq) + H₂SO_4(aq) →  K₂SO_4(aq) + 2H₂O  ✔½
                0.0024        0.0012
    Moles of KOH_(aq)      =24 × 0.1 = 0.0024      ✔½
                                       1000
    Moles of H₂SO_4(aq) = ½ × (0.0024) = 0.0012     ✔½
    Molarity of H₂SO₄     = 0.0012 × 1000
                                              30
    = 0.04M                          ✔½
20.  
    1. used as drying agents for wet gases/test presence of water
    2.  
       1. Isotopes are atoms with same number of protons/atomic numbers but different number of neutrons/mass numbers
       2. Mass number is the total number of number  of protons and neutrons in an atom.
    3. P₂S₃
21.  
    1. Hot compressed air.
    2. To melt sulphur
    3.    
       • Low melting point
       • Does not dissolve in water
22. No. Of moles of HCl in 40cm³ of 2M HCl
    = 40cm³ × 2M
              1000
    =0.08moles
    Mass of HCl in 0.08moles = 36.5 × 0.08
    = 2.92g
    4g of the XCO₃ reacts with 2.92g 0f HCl.
    X + 60g of XCO₃ reacts 2 x 36.5g of HCl
    2.92 ( X + 60 )g = 4 × 2 × 36.5g
    2.92X + 175.2 = 292
    2.92X = 292 - 175.2
    =116.8
    X= ^116.8/_2.92
    =40
23.    
    1.    
       1. I             Giant metallic ✔½ Reject metallic
       2. K            Giant ionic ✔½          Reject ionic
    2. K is an ionic compound while I is a a metallic element with mobile electrons
24.    
    1. A brown ring
25.  
    1.  
       • Cation Zn²⁺ 
       • Anion  No^-3 
    2.  
       • solution K -ZnO
       • solution B ZnSO⁴
       • White precipitate Zn(OH)_2(s)