Chemistry Paper 1 Questions and Answers - Kenya High Post Mock 2023 Exams

Instructions

• Answer ALL the questions
• Mathematical tables and silent electronic calculators may be used.
• All working MUST be clearly shown where necessary

QUESTIONS

1. Molten sodium chloride and graphite both conduct electricity. State their difference in electrical conductivity. (2mks)
2. Element R has atomic number 8 and a mass number 16.
   1. Draw the atomic structure of element R. (1mk)
   2. Explain why R forms a hydride with a low boiling point. (1mk)
3. Study the diagram below and answer the questions that follow
   .
   1. Name
      1. Solid X (1mk)
      2. Gas Y (1mk)
4. Compare the second ionization energy of magnesium with its first ionization energy. Explain your answer. (2mks)
5. The set-up represented below can be used to separate ethanol from its mixture with water.
   
   
   1. Identify an error in the set-up. (1 mk)
   2. Name this method of separation. (1 mk)
   3. What properties make it possible to separate ethanol from water by this method? (1 mk)
6. Element K has two isotopes ²⁰K and ²²K with relative abundance of 90% and 10% respectively.
   1. 1. What are isotopes? (1 mk)
      2. Determine the relative atomic mass of element K. (2 mks)
7. Xg of Potassium hydroxide were dissolved in water to make 100cm³ of solution.50cm³ of solution required 50cm³ of 2M Nitric acid for complete neutralization. Calculate the mass X of Potassium hydroxide. (3mks)
8. Sulphur burns in air to form a gaseous product.
   1. What is the colour of the flame of burning sulphur? (1 mk)
   2. Give an equation for the reaction that takes place when the gaseous product is bubbled through water. (1 mk)
   3. State one importance of the product formed in (ii) above. (1 mk)
9. The figure below shows a paper that was placed horizontally across the middle of a non-luminous flame and quickly withdrawn.
   
   
   1. Explain the observations. (1mk)
   2. Why is luminous flame not used for heating in the laboratory? (1mk)
10. Study the diagram below and answer the questions that follow.
    
    
    1. What is observed when the hot iron wool reacts with chlorine gas? (1mk)
    2. What is the purpose of:
       1. Tube B (1mk)
       2. Concentrated Sodium hydroxide solution. (1mk)
11. The table below shows results obtained from experiment carried out on a suspect salt solution M.
    

    Experiment	Results
    I.                    A few drops of Barium nitrate added to solution M	No ppt/ colourless solution
    II.                 A few drops of lead (II) nitrate added to solution M.	White ppt
    III.              Ammonia solution added dropwise until in excess	White precipitate Colourless solution

    
    
    1. Identify the cation and anion present in solution M. (1mk)
       Cation (½ mk)
       Anion (½ mk)
    2. Write an ionic equation for the formation of white precipitate in experiment II (1mk)
    3. Write the formula of the Ion responsible for formation of colourless solution in experiment III (1mrk)
12. The diagram below shows a set-up of apparatus used to prepare oxygen gas and pass it over burning candle. The experiment was allowed to run for several minutes.
    
    
    1. Identify liquid M. (1mk)
    2. The pH of the solution in flask II was found to be less than 7. Explain. (2mks)
    3. Write an equation for the reaction that forms oxygen gas in the set up. (1mk)
13. Briefly explain the following
    1. Alkaline earth metals are generally less reactive than alkali metals. (1mk)
    2. Melting point of alkali metals decrease down the group while melting point of halogens increases down the group. (2mks)
    3. Group VIII elements are gases at room temperature. (1mk)
14. How would you obtain a sample of pure iodine from a mixture of iodine and lead (II) sulphate. (2mks)
15. The table below indicates the PH values of solutions labelled A, B, C, D and E
    

    Solution	A	B	C	D	E
    pH value	5	13	2	10	7

    
    Identify the solution:
    1. Containing highest concentration of hydrogen ions. ( ½ mk)
    2. That is likely to be ethanoic acid. Give a reason. (1mk)
    3. That is likely to be common salt solution. ( ½ mk)
16. The table below shows physical properties of some substances. Use the information to answer the questions that follow.
    

    Substance	Density (gm-3)	M-P (°c)	B.P (°c)	Electrical conductivity               Solid                 Liquid
    M O P Q R	3.5 0.8 3.8 21.4 1.53	801 -114 3550 -39 660	1413 -84.9 4827 357 2470	POOR POOR POOR GOOD GOOD	GOOD POOR POOR GOOD GOOD

    
    
    1. Which of the elements is a liquid at room temperature. Explain (1mk)
    2. Identify the type of structure in
       P…………………………………………………………………………
       R………………………………………………………………………… (1mk)
    3. Which element would be the most suitable for use in over-head electric wire transmission? (2 mks)
17. An element Y has relative atomic mass 6.939 and atomic number 3. it has two isotopes with atomic mass 6.015 and 7.016. Calculate the relative abudance of the isotopes. (3mks)
18.  
    1. Give the name of the organic compound formed when methanol and ethanoic acid reacts in the presence of concentrated sulphuric (VI) acid. (1mk)
    2. Write the structural formula of
       2 – methylpropane (1mk)
19. The diagram below shows how magnesium reacts with steam.
    
    
    1. Gas C would not be produced as in the set-up but when certain condition is introduced gas C is produced. On the diagram indicate the condition that was omitted. (1mk)
    2. Describe how gas C is produced after the mistake was corrected in the set-up. (1mk)
20. Study the information in the table below and answer the questions that follow. The letter do not represent the actual symbols of the elements.
    Element    Atomic number     Electronic arrangement
    X                     16
    Y                     19
    1. Complete the table by writing the electronic arrangement of the elements (1mk)
    2. Which type of bond is formed between X and Y. Explain (2mks)
21. Hydrogen chloride gas was passed into water as shown below.
    
    
    1. When a blue litimus paper was dropped into the resulting solution, it turned red. Give a reason for the observation. (1mk)
    2. What is the function of the funnel? (1mk)
22. The paper chromatogram below shows the identification of unknown metal ions in mixture M. The reference ions X, Y and Z are also shown. The experiment was done in an ascending method.
    
    X – Vanadium (IV) ion (V4+)
    Y – Chromium (III) ion (Cr3+)
    Z – Copper(II) ion (Cu2+)
    1. Name the ions present in the mixture M. (1mk)
    2. Indicate the solvent front on the diagram. (1mk)
    3. Mixture Q contains all the three ions. Show the chromatography of Q. (1 ½ mks)
23. The set-up below shows the preparation of carbon (II) oxide.
    
    
    1. Name gas N (1mk)
    2. What is the purpose of sodium hydroxide in flask K? (1mk)
    3. Why is it necessary to carry out this experiment in a fume cupboard? (1mk)
24. Determine the oxidation states of the underlined elements (2mks)
    1. Fe (CN)₆^3-
    2. K [Cr (CN)₆]⁴⁺
       Oxidation state of Fe Oxidation state of Cr
25. The diagram below shows a structure (i) of water molecules
    
    
    1. Name the bonds labelled ( 1 mk)
       1.  
       2.  
    2. Using dots (.) and cross(x) diagram show the bonding in the compound phosphonium ion
       PH₄⁺ (H = 1, P = 15) (1mks)
26. When dry hydrogen gas was passed over a heated lead (II) oxide sample in a combustion tube and the gaseous product cooled, a colourless liquid was obtained.
    1.  
       1. Name the colourless liquid. ( ½ mk)
       2. Describe a chemical test you would use to confirm the colourless liquid in a (i) above. (2mks)
    2. What observation can be made in the combustion tube at the end of the experiment? ( ½ mk)
    3. Write a chemical equation for the reaction between hydrogen and heated lead (II) oxide. (1mk)
27. State one use of:
    1. Calcium nitrate (1 mrk)
    2. Magnesium hydroxide (1 mrk)
28. Coloured flower placed in a gas jar containing gas X immediately turned colourless. A solution of gas X in water formed a white precipitate with silver nitrate solution. The precipitate was insoluble in nitric (V) acid but dissolved in excess aqueous ammonia.
    1. What is the identity of gas X? (1mk)
    2. Write down the balanced chemical equation of the reaction that took place when:
       1. Solution of gas X in water reacted with silver Nitrate solution. (1mk)
       2. Aqueous ammonia was added to the resulting mixture in b(i) above. (1mk)
29. Study the flow chart below and answer the questions that follow.
    
    
    1. Identify solid G (1mk)
    2. Write the formula of the complex ion in solution F (Imk)
30. Describe how you would obtain solid sample of sodium carbonate from a mixture of lead carbonate and sodium carbonate powders. (2mks)

MARKING SCHEME

1.  NaCl – by mobile ions
   Graphite – by mobile electrons /delocalized electrons
2.  
   1.   
      
   2. The hydroxide of R has a molecular structure with van-derwaals forces in
      between the molecules. (1mk)
3.  
   1.  
      1. Barium sulphite 1mk
      2. Gas Y – Sulphur (IV) oxide 1mk
4. 2^nd ionization energy is greater than first ionization energy of magnesium. second electron is attracted more because protons are more than electrons
5.  
   1. Direction of flow of cold water into and out of the Liebig condenser is wrong
   2. Distillation 
   3. Ethanol and water are miscible
      Their boiling points are different 
6.  
   1. Isotopes are atoms of the same element with the same atomic number but different mass numbers 
   2. = 20.2 
7. KOH_(aq) + HNO_3(aq) →KNO_3(aq) + H2O_(l)
   R.F.M of KOH = 56
   Moles of HNO3 = 50 x 2 = 0.1
                                1000
   Mole ratio is 1:1
   Hence moles of KOH in 50cm³ = 0.1
   In 100cm³ is 0.2 moles
   Mass of X = 0.2 x 56 = 11.2g
8.  
   1. Blue 
   2. SO_2(g) + H₂O_(l) H₂SO_3(aq)
   3. Bleaching agent 
9.  
   1. Outer part of non-luminous flame is hotter as there is complete combustion of gas
       Inner part contains unburnt gases since there is no supply of enough air, paper is unburnt
   2. Produces soot  not hot due to incomplete combustion of gas 1mk
10.  
    1. chlorine reacts vigorously with hot iron forming dark-brown crystals of iron (III) chloride. (1mk)
    2.  
       1. To collect the iron (III) chloride which is a sublimate (1mk)
       2. It reacts with excess chlorine gas to avoid emission of poisonous chlorine gas into the air (1mk)
11.  
    1. – Zn²⁺ 
       - Cl -
    2. Pb²⁺ _(aq) + 2CL-_(aq) → PbCl_2(s) 
    3. [Zn ( NH₄)] ²⁺
12.  
    1. Liquid m = water
    2. CO₂  formed by burning candle,
       slightly soluble  forming an acidic 
       solution
    3. H₂O_(l) + Na₂O_2(s) →2 NaoH_(aq) + O2_(g)
13.  
    1. Alkali metals lose one electron hence require less energy than alkaline earth meals which lose 2 electrons
    2. Alkali metals down group increase in atomic radius hence decrease in strength of metallic bond
       Halogens increase in size down the  group increase strength of van der waals forces
    3. Exist as mono atomic molecules with weak van der waals forces
14. Heat the mixture  iodine sublimes and is collected in the cooler part of the vessel leaving lead(II) sulphate behind
15.  
    1. C
    2. A – weak acid ionizes partially
    3. E
16.  
    1. Q- The melting point is below 25oc while melting point is above 25^oc(1mk)
    2. 1. P Giant atomic structure
       2. R Metallic structure (1mk)
    3. R -Has low density with high melting and boiling points.
       Is good conductor of electricity
17. Ram = RamY₁ x Abudance + Ram Y₂ x abundance
                                 100
    6.939 = 6.015y + 7.016Y2
                   100
    6.939 = 6.015y₁ + 7.016(100-Y₁)
                   100
    693.9 = 6.015Y₁ + 701.5 – 7.016Y₁
    Y₁ = 7.7%
    Y₂ = 100 – 7.7 = 92.3%
    Method II 
    
18.  
    1. Methylethanoate
    2.   
       
19.  
    1.   
       
    2. Wet cotton when heated produce steam which react with hot magnesium to form magnesium oxide and hydrogen gas
20.  
    1. X – 2.8.6
       Y – 2.8.8.1
    2. Ionic / electrovalent  because X is a non metal element while Y is a metal
21.  
    1. Hydrogen chloride gas is acidic, therefore dissolved in water to give an acidic solution of hydrochloric acid which turned blue litmus paper red.
    2. To prevent sucking back   1mk
22.  
    1. Chromium (III) ion
       Copper (II) ions
    2.   
       
    3. Check on the diagram
23.  
    1. Carbon(IV) oxide
    2. To absorb excess /unreacted carbon(IV) oxide gas
    3. Carbon (II) oxide is poisonous
24.  
    1. -1 R
    2.  
25.  
    1.  
       1. Covalent bond
       2. Hydrogen bond 
    2.   
       
       Diagram
       Correct electron distribution
       Change and brackets 
26.  
    1.  
       1. Water
       2. Use anhydrous copper(II)sulphate white if it changes to blue crystals then its water
       3. Anhydrous cobalt (II) chloride blue changes to pink
    2. Grey solid
    3. PbO_(s) + H2_(g) Pb_(s) + H2O_(l) 
27.  
    1. nitrogenous fertilizer
    2. in anti-acid medicine
28.  
    1. Chlorine gas /Cl₂
    2.  
       1. HCl_(aq) + AgNO_3(aq) → AgCl_(s) + HNO_3(aq)
       2. AgCl_(s) + 2NH_3(aq) →[Ag(NH₃)₂]⁺_-(aq) + Cl_-(aq)
          AgCl_(s) + 2NH_3(aq) →Ag(NH₃)₂Cl_(aq)
29.  
    1. Lead (II) nitrate /Pb(NO₃)₂
    2. [Pb(OH)₄] _2-
30.  
    1. Add distilled water to the mixture and stir
    2. Filtre to obtain a filtrate of sodium carbonate and insoluble lead carbonate
    3. Heat the filtrate to dryness to obtain dry sodium carbonate solid