Chemistry Paper 1 Questions and Answers - Form 4 End Term 1 Exams 2021

CHEMISTRY
FORM 4
END TERM EXAMS
TERM 1 2021
PAPER 1
TIME 2 hrs

INSTRUCTIONS

Answer all the questions

1. State one disadvantage of using flower extracts as acid – base indicators. (1mk)
2. Name the indicator that can be used in the laboratory to tell the pH of lemon juice.(1mk)
3. Differentiate between strong and weak acids. (1mk)
1. What are isotopes? (1mk)
2. Determine the number of neutrons in (1mk)
When magnesium is burnt in air it reacts with both oxygen and nitrogen gas giving a white ash. Write two equations for the reactions that take place. (1mk)
A solution contains 29.1g per litre of aluminium Sulphate. Calculate the number of Sulphate ions in 350cm³ of the solution.(Al = 27, S = 32, O = 16) Avogadro’s constant = 6.0 x 10²³. (2mks)
When a solid B was heated in a test-tube, it gave off two gases. The two gases were seperates by passing them through a plug of glass wool in a test-tube as shown below.

The first gas which evolved turned moist red litmus paper to blue. Later the other gas involved turned the litmus back to red.
1. Identify solid B (1mk)
2. Write the equation for the reaction that take place in the test tube (1mk)
Hydrogen Sulphide gas was bubbled into two solutions of metallic nitrates as shown in the flow diagram below
1. Identify the black solid C (1mk)
2. Write an ionic equation for the formation of the green solution (1mk)
3. State the property of Hydrogen Sulphide shown by the formation of solution D (1mk)
The apparatus shown below was used to investigate the effect of Carbon (II) Oxide on Lead (II) Oxide.
1. State the observation made in the combustion tube during the experiment. (2mks)
2. Write the equation for the reaction that take place in test-tube E. (1mk)
1. Lime water is also used to soften hard water. Why is this method not preferred to soften hard water. (1mk)
2. Name a compound that causes temporary hardness of water. (1mk)
3. State one disadvantage of using hard water for domestic purpose. (1mk)
1. Name the compound below
  CH₃CH₂CH = CH₂
2. Draw and name other isomers of the compound in (a) above. (2mks
A white solid dissolve in water to form a colourless solution. The colourless solution forms a white precipitate with Ammonia solution but dissolve in excess alkali. The colourless solution forms a white precipitate with Lead (II) Nitrate solution. The white Precipitate dissolve on warming to form a colourless solution.
1. Write the chemical formulae for the ion formed when the colourless solution react with excess ammonia solution. (1mk)
2. Write the name of the ion present in the white solid. (1mk)
3. What is an alkali (1mk)
The solubility of Potassium Manganate (VII) at 20ºC is 13g per 100g of water and at 90ºC is 60g per 100g of water.
1. Determine the mass of Pottassium (VII) Manganate present in 80g of saturated solution at 90ºC. (1mk)
2. Calculate the mass of Pottassium (VII) Manganate that would crystallize out if the solution in (a) were cooled to 20ºC. (2mks)
1. Explain why concentrated Sulphuric (VI) acid is a poor electrolyte and has no effect on blue litmus paper whereas 2M Sulphuric (VI) acid conducts electricity and changes blue litmus paper red. (1mk)
2. What is a binary electrolyte. (1mk)
An element F has a relative atomic mass of 88. When a current of 0.5 amperes was persed through the fused chloride of F for 20 minutes and 20 seconds, 0.278g of F were deposited at the cathode. Determine the charge on ion of F (1Faraday = 96500C). (2mks)
Below is a cross- section of a charcoal burner
1. Charcoal is a form of impure carbon. Name any other two allotropes of carbon. (1mk)
2. Write an equation for the reaction taking place at the part marked B. (1mk)
The diagram below represents paper chromatogram of four types of sugar.
1. Identify the most stable sugar. (1mk)
2. On the diagram, show the chromatogram of R. Given that R contains all the other sugars(2mks)
The empirical formula of a hydrocarbon is C₂H₃. The hydrocarbon has a relative molecular Mass of 54. (H = 1, C = 12)
1. Determine the molecular formula of the hydrocarbon. (1mk)
2. Draw the structural formulae of the hydrocarbon in (a) (1mk)
3. To which homologous series does the hydrocarbon in (b) above belong? (1mk)
State three factors that increase the rate of reaction for the following reaction. (3mks)
CaCO_3(s) + 2HCl_(aq) CaCl_2(aq) + CO_2(g) + H₂O_(aq)
In terms of structure and bonding explain the following
1. Melting point of Magnesium is higher than that of Sodium. (3mks)
2. Melting point of Chlorine is lower than that of Iodine. (1mk)
The set-up below was used to prepare a solution of hydrogen chloride gas
1. Identify solid S (1mk)
2. Identify one mistake in the set up. (1mk)
3. Write an equation for the reaction taking place in the flask. (1mk)
1. State Gay-Lussac’s law (1mk)
2. 10cm³ of a gaseous hydrocarbon, C_xH_y required 30cm³ of oxygen for complete combustion. If steam and 20cm³ of Carbon (IV) oxide were produced, what is the value of x in C_xH_y. (2mks)
Starting with lead metal, describe how a dry sample of Lead(II) chloride can be prepared in the laboratory. (3mks)
An ion T^2- has an electronic arrangement of 2.8
1. What is the atomic number of the element. (1mk)
2. To which group and period does the element belong to;
  Group__________________________________________________ (1mk)
  Period__________________________________________________ (1mk)
Using dot (.) and cross (x) diagram show the type of bond present in hydrogen ion, H₃O⁺
(H = 1, O = 8) (2mks)
A mixture of Hydrogen gas and Carbon (IV) oxide are passed through Potassium hydroxide solution as shown below.
1. State the observation made in the conical flask. (1mk)
2. Write the equation for the reaction that takes place in:-
  1. the conical flask (1mk)
  2. the burning of gas x (1mk)
20cm³ of a solution containing 4g per litre of Sodium hydroxide was neutralized by 8cm³ of dilute Sulphuric (VI) acid. Calculate the concentration of the acid in moles per litre.(Na = 23, O = 16, H=1) (3mks)
Given that the hydration energies of Ca²⁺_(g) and Cl^-_(g) are -1562KJ/Mole and -364KJ/Mole respectively. The heat of solution (Hsoln) for one Mole of CaCl₂ is -82.9 KJ/Mole. Determine the lattice energy for CaCl₂. (2mks)
The diagram below is used to prepare nitrogen (IV) oxide gas.
1. Identify substance V (1mk)
2. State and explain one precaution taken when carrying out the experiment. (2mks)
Electrode potentials for the half cells are shown below. Use the information to answer the questions that follow.
Sn²⁺(aq)+2e^- Sn(s) ; = -0.14V
Cu²⁺(aq)+2e^- Cu(s) ; = -0.34V
1. Write the cell representation for the cell made up of two half cells. (1mk)
2. Write the cell equation for the cell reaction. (1mk)
3. Calculate the value for the cell. (1mk)
State the function of each of the following in the solvay process of production of Sodium Carbonate.
1. Coke (1mk)
2. Cold water on the carbonation. (1mk)
3. Ammonia a generator. (1mk)
1. A student in form three was given two gases C₂H₆ and C₂H₄. He added acidified Potassium Manganate (VII) to each solution. State the observations the student made. (2mks)
2. State one use of C₂H₄.

MARKING SCHEME

1. State one disadvantage of using flower extracts as acid – base indicators. (1mk)
  - The composition of the extract continuously changes with time so the acid or base and also changes with colour with time.
2. Name the indicator that can be used in the laboratory to tell the pH of lemon juice.(1mk)
  - Universal indicator
3. Differentiate between strong and weak acids. (1mk)
  - A strong acid is one that dissociate fully in aqueous solution A weak acid is one which dissociate partially in aqueous solution.
1. What are isotopes? (1mk)
  - Are atoms of the same element with the same atomic number but different mass number.
2. Determine the number of neutrons in ₁₈¹⁸O(1mk)|
  - 18 – 8 = 10 neutrons
When magnesium is burnt in air it reacts with both oxygen and nitrogen gas giving a white ash. Write two equations for the reactions that take place. (1mk)
- -2Mg_(s) + O2_(g)→2MgO_(s)
  -3Mg_(s) + N_2(g)→Mg₃N_2(s)
A solution contains 29.1g per litre of aluminium Sulphate. Calculate the number of Sulphate ions in 350cm³ of the solution.(Al = 27, S = 32, O = 16) Avogadro’s constant = 6.0 x 10²³. (2mks)
- Molar mass of Al₂(SO₄)₃ = 27 x 2 + (32 x 3) + (16 x 4 x 3) = 342
  Moles of Al₂(SO₄)₃ in 1000cm³ = ✓ ½
  Moles of Al2(SO₄)₃ in 350cm³ =
  Al₂(SO₄)_3(aq) →2Al³⁺_(aq) + 3SO₄^2-_(aq)
  1 mole of Al₂(SO₄)₃ produce 3 moles of SO₄^2- ions
  0.02979 moles → 0.02979 x 3 moles of SO42- ions
  Number of SO₄^2- ions = 0.08937 x 6.0 x 10²³ = ✓5.36 x 10²² ions.
When a solid B was heated in a test-tube, it gave off two gases. The two gases were seperates by passing them through a plug of glass wool in a test-tube as shown below.

The first gas which evolved turned moist red litmus paper to blue. Later the other gas involved turned the litmus back to red.
1. Identify solid B (1mk)
  - Ammonium Carbonate
2. Write the equation for the reaction that take place in the test tube (1mk)
  (NH⁴)₂ CO_3(S) 2NH_3(g) + CO_2(g) + H₂O_(l)
Hydrogen Sulphide gas was bubbled into two solutions of metallic nitrates as shown in the flow diagram below
1. Identify the black solid C (1mk)
  Copper(II) Sulphide.
2. Write an ionic equation for the formation of the green solution (1mk)
  Fe³⁺_(aq)→Fe²⁺_(aq)+e^-
3. State the property of Hydrogen Sulphide shown by the formation of solution D (1mk)
  Reducing agent
The apparatus shown below was used to investigate the effect of Carbon (II) Oxide on Lead (II) Oxide.
1. State the observation made in the combustion tube during the experiment. (2mks)
  - Yellow solid changes to✓ orange then to grey✓1
2. Write the equation for the reaction that take place in test-tube E. (1mk)
  CO_2(g)+CO₂(OH)_2(aq)→CaCO_3(s)+H₂O_(l)
1. Lime water is also used to soften hard water. Why is this method not preferred to soften hard water. (1mk)
  - Only remove temporary✓1 water hardness and not permanent water hardness.
2. Name a compound that causes temporary hardness of water. (1mk)
  - Calcium hydrogen Carbonate
  - Magnesium hydrogen carbonate
3. State one disadvantage of using hard water for domestic purpose. (1mk)
  - Wastes soap due to formation of scum
1. Name the compound below
  CH₃CH₂CH = CH₂
  - But-1-ene (1mk)
2. Draw and name other isomers of the compound in (a) above. (2mks)
A white solid dissolve in water to form a colourless solution. The colourless solution forms a white precipitate with Ammonia solution but dissolve in excess alkali. The colourless solution forms a white precipitate with Lead (II) Nitrate solution. The white Precipitate dissolve on warming to form a colourless solution.
1. Write the chemical formulae for the ion formed when the colourless solution react with excess ammonia solution. (1mk)
  - [Zn(NH₃)₄]^2- (1mk)
2. Write the name of the ion present in the white solid. (1mk)
  - Chloride ion (1mk)
3. What is an alkali (1mk)
  - An alkali is a soluble base (1mk)
The solubility of Potassium Manganate (VII) at 20ºC is 13g per 100g of water and at 90ºC is 60g per 100g of water.
1. Determine the mass of Pottassium (VII) Manganate present in 80g of saturated solution at 90ºC. (1mk)
  - 60g per 100g of water;total mass of saturated solution = 16g
  - 160g of saturated solution→13g of KMnO4
  - 80g of saturated solution→^80x60/₁₆₀ 30g ✓ ½ of KMnO4 1mk
2. Calculate the mass of Pottassium (VII) Manganate that would crystallize out if the solution in (a) were cooled to 20ºC. (2mks)
  - At 20ºC:
    113g of saturated solution →13g of KM_nO₄
    80g of saturated solution → 80x13/113=9.204
    At 90ºC:
  - 80g of saturated solution →30g of KM_nO₄
  - At 200C:80g of saturated solution →9.204g
  - Mass of KM_nO₄ crystalizes out
  - 30-9.204g ✓ ½ (2mks)
1. Explain why concentrated Sulphuric (VI) acid is a poor electrolyte and has no effect on blue litmus paper whereas 2M Sulphuric (VI) acid conducts electricity and changes blue litmus paper red. (1mk)
  - Concentrated Sulphuric (iv) acid has no ions ✓ ½ (it is covalent) 2M of Sulphuric (vi) acid has H⁺ ions and SO₄^2- ions ✓ ½ (1mk)
2. What is a binary electrolyte. (1mk)
  - A substance in molted form conducts electricity but contains only two specifically one type of cation ion and specially one type of anion.(1mk)
An element F has a relative atomic mass of 88. When a current of 0.5 amperes was passed through the fused chloride of F for 20 minutes and 20 seconds, 0.278g of F were deposited at the cathode. Determine the charge on ion of F (1Faraday = 9650ºC). (2mks)
- Quantity of electricity Q=It
  =0.5x[(20x60)+20]
  =61ºc ✓ ½
  9650ºc→ 1 Faraday ✓ ½
  61º → ^{0.006321244 x 88}/_0.278
  The change on the ion is +2 ✓ ½ (2mks)
Below is a cross- section of a charcoal burner
1. Charcoal is a form of impure carbon. Name any other two allotropes of carbon. (1mk)
  - Diamond ✓ ½
  - Graphite ✓ ½ (1mk)
2. Write an equation for the reaction taking place at the part marked B. (1mk)
  CO_2(g)+C_(s) →2CO_(g) (1mk)
The diagram below represents paper chromatogram of four types of sugar.
1. Identify the most stable sugar. (1mk)
  Q
2. On the diagram, show the chromatogram of R. Given that R contains all the other sugars(2mks)
The empirical formula of a hydrocarbon is C₂H₃. The hydrocarbon has a relative molecular Mass of 54. (H = 1, C = 12)
1. Determine the molecular formula of the hydrocarbon. (1mk)
  - (C₂H₃)x =54 ✓ ½
    x[12x2 + 3x1] =54
    24x+3x=54
    24x=54
    x =⁵⁴/₂₇
    x=2
    (C₂H₃)2 =C₄H₆ ✓ ½ (1mk)
2. Draw the structural formulae of the hydrocarbon in (a) (1mk)
3. To which homologous series does the hydrocarbon in (b) above belong? (1mk)
  - Alkynes ✓ 1(reject alkyne without ( s))
State three factors that increase the rate of reaction for the following rection. (3mks)
CaCO_3(s) + 2HCl_(aq) CaCl_2(aq) + CO_2(g) + H₂O_{_(aq)}
- Surface area of CaCO₃ ✓1
- Concentration of HCl ✓1
- Temperative increase ✓1
In terms of structure and bonding explain the following
1. Melting point of Magnessium is higher than that of Sodium. (3mks)
  - Magnesiun metal has storage metalic✓ ½ bond than sodium in its giant metallic✓ ½ structure due to increase in number of delocalized electrons in magnesium✓1 (2mk)
2. Melting point of Chlorine is lower than that of Iodine. (1mk)
  - Iodine has strong vander walls✓ ½ forces in its molecular structure,chlorine has weak vander waals✓ ½ forces in its molecular structure.(1mk)
The set-up below was used to prepare a solution of hydrogen chloride gas
1. Identify solid S (1mk)
  Sodium chloride or any other chloride of metal. (1mk)
2. Identify one mistake in the set up. (1mk)
  Delivery tube to dissolve HCl_(g) in water (1mk)
3. Write an equation for the reaction taking place in the flask. (1mk)
  NaCl_(s)+H₂SO_4(l)→NaHSO_4(s)+HCl_(g) (1mk)
1. State Gay-Lussac’s law (1mk)
  - When gases react they do so in volumes which are in whole number ratio and to the volume of the products if gaseous at constant temperature and pressure.
2. 10cm³ of a gaseous hydrocarbon, C_xH_y required 30cm³ of oxygen for complete combustion. If steam and 20cm³ of Carbon (IV) oxide were produced, what is the value of x in C_xH_y. (2mks)
  - C_xH_y(g)+O_2(g)→CO_2(g)+H₂O_(g) ✓ ½
    10cm³ 30cm³ 20cm³
    Their volumes to mole ratio
    C_xH_y(g)+O_2(g)→CO_2(g)+H₂O_(g) ✓ ½
    1mole 3moles 2moles
    C_xH_y(g)+3O_2(g)→2CO_2(g)+H₂O_(g) ✓
    Then 2 atoms of carbon were present in CxHy and 4 atoms of Hydrogen.
    C₂H_4(g)+3O_2(g)→2CO_2(g)+2H₂O_(g)
    Thus x = 2✓ ½ (2mks)
Starting with lead metal, describe how a dry sample of Lead(II) chloride can be prepared in the laboratory. (3mks)
- React excess✓ ½ Lead metal with dilute nitric(v) acid.Then filter of the unreacted lead metal to Lead (II) nitrate as filtrate.Add a solution of sodium chloride to the filtrate.A white precipitate forms✓ ½ which is Lead (II) chloride.Filter the precipitate✓ ½ and wash it with distilled water then dry it between filter paper. (3mks)
An ion T^2- has an electronic arrangement of 2.8
1. What is the atomic number of the element. (1mk)
  8 (1mk)
2. To which group and period does the element belong to;
  Group VI (1mk)
  Period 2(1mk)
Using dot (.) and cross (x) diagram show the type of bond present in hydrogen ion, H3O⁺
(H = 1, O = 8) (2mks)
A mixture of Hydrogen gas and Carbon (IV) oxide are passed through Potassium hydroxide solution as shown below.
1. State the observation made in the conical flask. (1mk)
  - Bubbles are observed (1mk)
2. Write the equation for the reaction that takes place in:-
  1. the conical flask (1mk) -
    CO_2(g)+2KOH_(aq)→K₂CO_3(aq)+H₂O_(l) (1mk)
  2. the burning of gas x (1mk) -
    2H_2(g)+O_2(g)→2H₂O_(g) (1mk)
20cm³ of a solution containing 4g per litre of Sodium hydroxide was neutralized by 8cm³ of dilute Sulphuric (VI) acid. Calculate the concentration of the acid in moles per litre.(Na = 23, O = 16, H=1) (3mks)
- Molar mass of NaOH = 40✓ ½
  Moles of NaOH per littre = 4/40 = 0.4M ✓ ½
  Moles of NaOH reacted = ✓ ½
  H₂SO₄(aq)+2NaOH(aq)→Na₂SO₄(aq)+H₂O(l) ✓ ½
  2moles of NaOH react with 1mole of H₂SO₄
  Moles of H₂SO₄ reacting ✓ ½
  Molarity of the acid =✓ ½ (3mks)
Given that the hydration energies of Ca²⁺_(g) and Cl^-_(g) are -1562KJ/Mole and -364KJ/Mole respectively. The heat of solution (Hsoln) for one Mole of CaCl₂ is -82.9 KJ/Mole. Determine the lattice energy for CaCl₂. (2mks)
∆Hydr of CaCl2 = ∆Hydr Ca2+ +∆Hydr Cl-
=-1562+(-364x2)
=-1562+-728
=-2290Kjmol-1✓
∆Hsol = ∆Hlaq+∆Hydr
∆Hlath = ∆Hsol-∆Hydr✓ ½
= -82.9 = (-2290)✓ ½
= -82.9+2290
= +2207.1Kjmole-1 ✓ ½ (2mks)
The diagram below is used to prepare nitrogen (IV) oxide gas.
1. Identify substance V (1mk)
  - Concentrated Sulphuric(VI) acid//H₂SO_4(l) (1mk)
2. State and explain one precaution taken when carrying out the experiment. (2mks)
  - The experiment should be done in a fume chamber or in open air✓1
  - The gas (NO₂) is poisonous✓1 (2mks)
Electrode potentials for the half cells are shown below. Use the information to answer the questions that follow.
Sn²⁺(aq)+2e^- Sn(s) ; = -0.14V
Cu²⁺(aq)+2e^- Cu(s) ; = -0.34V
1. Write the cell representation for the cell made up of two half cells. (1mk)
  Sn_(s) /Sn²⁺_(aq) //Cu²⁺_(aq)/Cu_(s) (1mk)
2. Write the cell equation for the cell reaction. (1mk)
  Sn_(s)+Cu²⁺_(aq)→Cu_(s)+Sn²⁺_(aq) (1mk)
3. Calculate the value for the cell. (1mk)
  E^θcell = E^θreduced E^θoxidation
  = +0.34 – ( -0.14)✓ ½
  = +0.34++0.14
  = +0.48v✓ ½ (1mk)
State the function of each of the following in the solvay process of production of Sodium Carbonate.
1. Coke (1mk)
  - Produce heat energy to decompose CaCO₃// Produce Carbon(iv)
    Oxide when burnt in the kiln. (1mk)
2. Cold water on the carbonation. (1mk)
  - Cold water cools the carbonator (1mk)
3. Ammonia a generator. (1mk)
  - Recovers ammonia used in the initial stages(1mk)
1. A student in form three was given two gases C₂H₆ and C₂H₄. He added acidified Potassium Manganate (VII) to each solution. State the observations the student made. (2mks)
  - C₂H₆ did not have effect on acidified potassium manganate(VII)✓1 which C₂H₄ turned purple potassium manganate(VII) to colourless✓1 (2mks)
2. State one use of C₂H₄.
  - manufacture of plastics (any one ) (1mk)
  - manufacture of ethanol
  - used in ripening of fruits
  - preparation of ethan – 1,2 –diol.