Chemistry Paper 1 Questions And Answers - Form 4 Term 2 Opener 2021

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Chemistry Paper 2 Questions And Answers - Form 4 Term 2 Opener 2021

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INSTRUCTIONS

Answer all the questions in the spaces provided
Mathematical tables and silent electronic calculators may be used
All working must be clearly shown where necessary

The figure below shows the cooling curve for water is gaseous state.
1. Using the same axis draw a curve obtained if the water used in the experiment was impure. (1mk)
2. Name the process taking place between:
  1. S and T (1mk)
  2. U and V (1mk)
On addition of a few drops of aqeous sodium hydroxide to solution M a white precipitate forms which dissolves on a addition of excess sodium hydroxide. A white precipitate forms when solution M is reacted with sodium chloride solution. Suggest the identity of the cation present and explain. (2mks)
1g of sodium hydroxide is added to 30cm³ of 1M HCl. How many cm³ of 0.1M KOH solution will be needed to neutralize the excess acid. ( Na=40, O=16, H=1) (3mks)
Describe how you can prepare crystals of magnesium chloride starting with 50cm³ of 2M magnesium hydroxide. (3mks)
Use the following information to answer the questions that follow
∆H_lattice Mgcl² = -2489 KJ/ mol^-1
∆H_hydration Mg²⁺ = - 1891 kJ/ mol
∆H hydration Cl^- = -384 kJ/ mol
1. Calculate the heat of solution of magnesium chloride. (2mks)
2. Draw an energy level diagram for the dissolving of magnesium chloride. (2mks)
The reaction between hydrochloric acid and potassium dichromate can be used to demonstrate a reversible reaction. The ionic equation is given below
2Cro₄^2-_(aq) + 2H⁺_(aq) Cr₂O7^2- _(aq) + H₂0_(l)Yellow orange
Explain the observation that would be made when dilute hydrochloride acid is added to the equilibrium mixture. (2mks)
The table below gives the rate of decay for a sample of a radioactive element P

Mass of P (g) number of days

48 0

18 90

6 180
1. Determine its half-life (2mks)
2. Complete the following nuclear equation. (1mk)
  233 0
  Pa + e
  91 -1
Study the following flow chart. Use it to answer the question that follow
1. Identify (3mks)
  1. Solid A
  2. Solid B
  3. Gas E
2. Name the reagents used in step (2mks)
  1. II
1. Name two salts responsible for permanent hardness of water. (2mks)
2. Explain the precipitation method used to remove water hardness. (1mk)
When steam was passed over heated charcoal as shown in the diagram, below, hydrogen and carbon (II) oxide gases were formed.
1. Write the equation for the reaction which takes place. (1mk)
2. Name two uses of carbon (II) oxide gas which are also uses of hydrogen gas. (2mks)
1. State and explain the observations made when a few drops of concentrated Sulphuric (vi) acid is added to sucrose ( C₁₂, H₂₂,O₁₁) (2mks)
2. Using an equation show how the above reaction takes place. (1mk)
Students from Sunshine Secondary School suspected that some water contained either sulphate or sulphite cons. Explain how the ion present can be determined. (3mks)
A mixture of ethane, oxygen and nitrogen are ignited. On cooling the residual gas occupied 58cm³ when shaken with aqeous alkali, the volume was reduced to 32cm³. A further 18cm³ of the product was absorbed by alkaline pyrogallo. Calculate the composition of the original mixture. ( C = 12, H = 1, N = 14, O = 16 and molar volume at r.t.p = 24dm³. (4mks)
0.24g of a divalent metal x dissolves in 50cm³ of 0.25 M sulphuric acid. The resulting solution required 5.0cm³ of 1.0 M sodium hydroxide solution to neutralize the excess acid. What is the reactive atomic mass of x.
Study the diagram below and answer the questions that follow.
1. Identify liquid x (1mk)
2. Write an equation for the reaction that occurs in the flask. (1mk)
3. Describe the confirmatory test for oxygen gas. (1mk)
When zinc metal is reacted with a solution of hydrogen chloride gas in water there is effervescence. When the experiment is repeated with a solution of hydrogen chloride gas in methylbenzene there is no observable change. Explain this observations. (3mks)
Compare the rate of diffusion of carbon dioxide (CO₂) & ozone (O₃) at the same temperature. (C = 12, O = 16 ) (3mks)
Starting with Lead metal describe how to prepare a solid sample of Lead (II) Sulphate salt. (3mks)
Given the following reaction
HCl_(aq) + NaOH_(aq) → NaCNl_(aq) + H₂O_(l)T₁ = initial temperature of solutions before additions = 18.0^oC
T₂ = final temperature of solution at neutralization = 19.2^oC
50cm³ 1M HCl
50cm³ 1M NaOH
Calculate Molar enthalpy of neutralization of hydrogen cyanide (3mks)
Compound K reacts with sodium hydroxide as shown
1. What type of reaction is represented by the equation. (1mk)
2. To what class of organic compounds does K belong. (1mk)
3. How is M separated from aqueous mixture of L and M. (1mk)
Draw a diagram to show how an aluminium spoon can be electroplated with pure copper. (2mks)
An ion of element Z can be represented as shown below,
Use the information to answer the questions that follow
1. Identify the period in which the element belong. (½mk)
2. Write the electron configuration of the ion of Z ( ½mk)
3. What would be the nature of the solution of the chloride of Z if dissolved in water. (1mk)
1. What is PH scale (1mk)
2. State whether the values of the following solution are strong or weak acids and bases.
  PH = 8 (½mk)
  PH = 5 (½ mk)
  PH = 2 (½ mk)
  PH = 13 (½mk)
Draw the structure of;
1. 1. Hydroxonium ion H₃O⁺ (1mk)
  2. Aluminium oxide (Al = 13, 0 = 8) (1mk)
2. Aluminium chloride has a melting point of 120°C while Aluminium oxide has a melting point of 2977°C. In terms of structure and bonding explain how the differences come about. (2mks)
State the use of the following laboratory apparatus
1. (1mk)
2. (1mk)
The diagram below shows heating of Lead nitrate
1. State the observations made in the above experiment (2mks)
2. Write an equation for the reaction that takes place. (1mk)
Give two differences between nuclear reactions and chemical reactions. (2mks)
3.1 g of an organic compound containing carbon, hydrogen and oxygen only produced 4.4 g of carbon oxide and 2.0 g of water on complete combustion:
1. Calculate its empirical formulae (2mks)
2. Calculate its molecular formulae if its formulae mass is 62. (2mks)
Two cleansing agents are represented below
1. R – COO⁻Na⁺ and
2. R – OSO₃⁻Na⁺
  1. Name the detergents (2mks)
  2. Select one of the detergents that would be suitable for washing in water containing magnesium chloride. Explain. (2mks)
Use the data below to calculate the enthalpy change for the reaction below
CH_4(g) + 2O_2(g) → CO_2(g) + 2H₂0_(l) (3mks)
Bond Energy (KJ)
C – H 413
O = O 489
C = O 805
H – O 464

MARKING SCHEME

The figure below shows the cooling curve for water is gaseous state.
1. Using the same axis draw a curve obtained if the water used in the experiment was impure. (1mk)
2. Name the process taking place between:
  1. S and T (1mk)
    - Condensation
  2. U and V (1mk)
    - Freezing
On addition of a few drops of aqeous sodium hydroxide to solution M a white precipitate forms which dissolves on a addition of excess sodium hydroxide. A white precipitate forms when solution M is reacted with sodium chloride solution. Suggest the identity of the cation present and explain. (2mks)
- Pb²⁺
  When Pb²⁺ reacts with NaOH, itforms insoluble lead (II) hydroxide which dissolves in excess to form comlex ions. When reacted with chloride ions there is formation of PbCl.
1g of sodium hydroxide is added to 30cm³ of 1M HCl. How many cm³ of 0.1M KOH solution will be needed to neutralize the excess acid. ( Na=40, O=16, H=1) (3mks)
NaOH_(aq) + HCl_(aq) → NaCl_(aq) + H₂O_(l)
Moles of NaOH = ¹/₄₀ = 0.025moles
Moles of HCl = 1 × 30 = 0.003moles
1000
Moles of HCl to react with KoH
0.003 − 0.025 = 0.005moles
HCl_(aq) + KoH_(aq) → KCl_(aq) + H₂0_(l)
Moles of KoH used = 0.005moles
0.1moles → 1000cm³
0.005moles → ?
1000 × 0.005 = 50cm³
0.1
Describe how you can prepare crystals of magnesium chloride starting with 50cm³ of 2M magnesium hydroxide. (3mks)
Take 100cm³ of 2M HCl (or 200cm³ of 1M HCl) and add to 50cm³ of 2M MgCl₂ in a beaker to form Magnesium sulphate solution. heat the solution to saturation and allow to cool for crystals to form. Filter and dry the crystals between filter papaers
Use the following information to answer the questions that follow
∆H_lattice Mgcl² = -2489 KJ/ mol^-1
∆H_hydration Mg²⁺ = - 1891 kJ/ mol
∆H hydration Cl^- = -384 kJ/ mol
1. Calculate the heat of solution of magnesium chloride. (2mks)
  Heat os solution = ∆H_lattice + ∆H_hydration
  = +2489 + (−1891 +( 2×−384))
  =+2489 −2659 =−170KJ/mol
2. Draw an energy level diagram for the dissolving of magnesium chloride. (2mks)
The reaction between hydrochloric acid and potassium dichromate can be used to demonstrate a reversible reaction. The ionic equation is given below
2Cro₄^2-_(aq) + 2H⁺_(aq) Cr₂O7^2- _(aq) + H₂0_(l)Yellow orange
Explain the observation that would be made when dilute hydrochloride acid is added to the equilibrium mixture. (2mks)
The orange colour intensifies because the added H⁺ makes the equilibrium to shift to the right.
The table below gives the rate of decay for a sample of a radioactive element P

Mass of P (g) number of days

48 0

18 90

6 180
1. Determine its half-life (2mks)
2. Complete the following nuclear equation. (1mk)
  233 0 233
  Pa + e → y
  91 -1 90
Study the following flow chart. Use it to answer the question that follow
1. Identify (3mks)
  1. Solid A - Iron(Fe)
  2. Solid B - Iron (II) Sulphide (FeS)
  3. Gas E - Hydrogen sulphide (H₂S)
2. Name the reagents used in step (2mks)
  1. II Dilute Hydrochloric acid
1. Name two salts responsible for permanent hardness of water. (2mks)
  - Calcium sulphate
  - Magnesium sulphate
2. Explain the precipitation method used to remove water hardness. (1mk)
  Sodium Carbonate is added to precipitate Ca²⁺ or Mg²⁺ ions
  Mg²⁺ + CO₃²⁻→ MgCO_3(s)
  OR
  Ca²⁺(aq)+ CO₃²⁻→MgCO_3(s)
When steam was passed over heated charcoal as shown in the diagram, below, hydrogen and carbon (II) oxide gases were formed.
1. Write the equation for the reaction which takes place. (1mk)
  H₂O_(g) + C_(s) → CO_(g) + H_2(g)
2. Name two uses of carbon (II) oxide gas which are also uses of hydrogen gas. (2mks)
  1. As a fuel
  2. As a redusing agent in hte extraction of metals such as iron fron that ore.
1. State and explain the observations made when a few drops of concentrated Sulphuric (vi) acid is added to sucrose ( C₁₂, H₂₂,O₁₁) (2mks)
  - Black masss of substance is formed. This is because the concentrated sulphuric (V) acid removes the atom which forms water from the sucrose i.e Hydrogen and oxygen leaving behind Carbon which is black.
2. Using an equation show how the above reaction takes place. (1mk)
  Conc.H₂SO_4(l)
  C₁₂H₂₂O_11(S)12C_(s) + 11H₂O_(l)
Students from Sunshine Secondary School suspected that some water contained either sulphate or sulphite cons. Explain how the ion present can be determined. (3mks)
- To a certain sample of water, add a few drops of Barium Nitrate solution followed by drops of dilute nitric(V) acid. If a white precipitate soluble on addition of the acid is formed the water contains sulphite ions and if a white precipitate insoluble on addition of the acid is formed the water contains sulphate.
A mixture of ethane, oxygen and nitrogen are ignited. On cooling the residual gas occupied 58cm³ when shaken with aqeous alkali, the volume was reduced to 32cm³. A further 18cm³ of the product was absorbed by alkaline pyrogallo. Calculate the composition of the original mixture. ( C = 12, H = 1, N = 14, O = 16 and molar volume at r.t.p = 24dm³. (4mks)
1C₂H₄ + 2O₂ → 2O_2(g) + 2H₂O_(l)
Volume of CO₂ = 58 − 32
= 26
Volume of O₂ unreacted =18cm³
Mole ratio of CO₂ : H₂O
2 : 1
26 : ?
26 × 1 =13cm³ volume of C₂H₄
2
volume of O₂ used
Mole ration of O₂: CO₂2 : 2
? : 26
26 × 2 =26cm³ of O₂ used
2
Total O₂ present
26+18 =44cm³
Residual = Nitrogen + CO₂ + used O₂
58= N + 26 + 18
58 − 44 =14cm³ Nitrogen
Original mixture
44cm³ - oxygen
13cm³ - ethene
14cm³ - Nitrogen
0.24g of a divalent metal x dissolves in 50cm³ of 0.25 M sulphuric acid. The resulting solution required 5.0cm³ of 1.0 M sodium hydroxide solution to neutralize the excess acid. What is the reactive atomic mass of x.
H₂SO_4(aq) + 2NaOH_(aq) → Na₂SO_4(aq) + 2H₂O_(l)
Moles of NaOH = 0.005 × 1 = 0.005moles
Mole ratio of NaOH : H₂SO₄ =
2 : 1
0.005 0.0025 moles of H₂SO₄
X(s) + H₂SO_4(aq) → XSO_4(aq) + H_2(g)
Available moles of H₂SO₄ = 0.25 × 0.05 = 0.0125moles
Moles of H₂SO₄ reacted with X = 0.0125-0.0025 = 0.01
Mole ratio of X : H₂SO₄
1 : 1
0.01 : 0.01
Moles = mass
RFM
RFM = Mass = 0.24
Moles 0.01
=24
Study the diagram below and answer the questions that follow.
1. Identify liquid x (1mk)
  - Water
2. Write an equation for the reaction that occurs in the flask. (1mk)
  2Na₂O_2(g) + 2H₂O_(l) → 4NaOH_(aq) + O_2(g)
3. Describe the confirmatory test for oxygen gas. (1mk)
  - Insert a glowing splint to a gas jar containing the gas, If it relights the gas is confirmed to be Oxygen.
When zinc metal is reacted with a solution of hydrogen chloride gas in water there is effervescence. When the experiment is repeated with a solution of hydrogen chloride gas in methylbenzene there is no observable change. Explain this observations. (3mks)
- Solution of Hydrogen Chloride in water ionizes product hydrogen ions which makes the solution acidic hence reacting with zinc to produce hydrogen gas while a solution of hydrogen chloride in methylbenzene is in molecular form hence no reaction with zinc.
Compare the rate of diffusion of carbon dioxide (CO₂) & ozone (O₃) at the same temperature. (C = 12, O = 16 ) (3mks)
CO₂ = 12+ 32 =44
O₃ = 16 × 3 = 48

=0.957
O₃ diffuse 0.957 times fast than CO₂

=1.044
CO₂ diffuse 1.044 times fast than O₃
Starting with Lead metal describe how to prepare a solid sample of Lead (II) Sulphate salt. (3mks)
- Heat lead in air to form PbO.
- React excess PbO with dilute HNO₃.
- Filter the excess PbO to get Pb(NO₃)₂ as filtrate.
- React Pb(NO₃)₂ with Na₂SO₄/K₂SO₄.
- Filter to get PbSo4 as the precipitate.
- Dry between filter paper.
Given the following reaction
HCl_(aq) + NaOH_(aq) → NaCNl_(aq) + H₂O_(l)T₁ = initial temperature of solutions before additions = 18.0^oC
T₂ = final temperature of solution at neutralization = 19.2^oC
50cm³ 1M HCl
50cm³ 1M NaOH
Calculate Molar enthalpy of neutralization of hydrogen cyanide (3mks)
∆H = MC∆T
M = (50+50)cm³ × 1g/cm = 100 = 0.1
1000
C = 4.2
∆T = 19.2 − 18.0 = 1.2
∆H = 0.1 × 4.2 × 1.2
= 0.504KJ
Mole of HCl = 50 × 1 =0.05moles
1000
0.05 = 0.504
1m = ? 0.504
0.05
= − 10.08 KJmol⁻¹
Compound K reacts with sodium hydroxide as shown
1. What type of reaction is represented by the equation. (1mk)
  - Saponification/Neutralization
2. To what class of organic compounds does K belong. (1mk)
  - Carboxylic acid
3. How is M separated from aqueous mixture of L and M. (1mk)
  - Adding Sodium Chloride, C₁₇H₃₅COONa precipitates
Draw a diagram to show how an aluminium spoon can be electroplated with pure copper. (2mks)
An ion of element Z can be represented as shown below,
Use the information to answer the questions that follow
1. Identify the period in which the element belong. (½mk)
  - Period 3
2. Write the electron configuration of the ion of Z ( ½mk)
  - 2.8.8
3. What would be the nature of the solution of the chloride of Z if dissolved in water. (1mk)
  - Acidic
1. What is PH scale (1mk)
  - Range of values running from 0-14 used to distinguish acids from bases and give theri strength/weakness.
2. State whether the values of the following solution are strong or weak acids and bases.
  PH = 8 weak base (½mk)
  PH = 5 weak acid (½ mk)
  PH = 2 strong acid (½ mk)
  PH = 13 strong base (½mk)
Draw the structure of;
1. 1. Hydroxonium ion H₃O⁺ (1mk)
  2. Aluminium oxide (Al = 13, 0 = 8) (1mk)
2. Aluminium chloride has a melting point of 120°C while Aluminium oxide has a melting point of 2977°C. In terms of structure and bonding explain how the differences come about. (2mks)
  - Aluminium Chloride forms a dimer with co-ordinate bonds (covalent) between the molecules which can easily dissociate with minimum heat. Aluminium oxide forms an ionic compound with strong ionic bonds throughout the structure(giant ionic bonds)
State the use of the following laboratory apparatus
1. (1mk)
  Used to deliver liquid substances into vessels
2. (1mk)
  Deliver liquids drop-wise into vessels
The diagram below shows heating of Lead nitrate
1. State the observations made in the above experiment (2mks)
  - An orange solid left behind which turns to yellow after cooling.
  - Brown fumes at the mouth of the boiling tube.
2. Write an equation for the reaction that takes place. (1mk)
  2Pb(No₃)_2(s)→ 2PbO_(s) + 4NO_2(g) + O_2(g)

Give two differences between nuclear reactions and chemical reactions. (2mks)

Nuclear Reactions	Chemical reactions
-Takes place within the nucleus and involves protons and neutrons -A lot of energy is involved -Not affected by environmanteal factors	-Takes place within the energy levels and involves electrons -No much energy -Affected by environmental factors

3.1 g of an organic compound containing carbon, hydrogen and oxygen only produced 4.4 g of carbon oxide and 2.0 g of water on complete combustion:
1. Calculate its empirical formulae (2mks)
  
  Empirical Formulae = CH₂O
2. Calculate its molecular formulae if its formulae mass is 62. (2mks)
  n=⁶²/₃₀ = 2
  Molecular formulae = 2 (CH₂O)
  =C₂H₄O₂
Two cleansing agents are represented below
1. R – COO⁻Na⁺ and
2. R – OSO₃⁻Na⁺
  1. Name the detergents (2mks)
    1. Soap
    2. Soapless detergents
  2. Select one of the detergents that would be suitable for washing in water containing magnesium chloride. Explain. (2mks)
    R – OSO₃⁻Na⁺ - Forms a soluble salt of Magnesium
Use the data below to calculate the enthalpy change for the reaction below
CH_4(g) + 2O_2(g) → CO_2(g) + 2H₂0_(l) (3mks)
Bond Energy (KJ)
C – H 413
O = O 489
C = O 805
H – O 464
Bond Breaking
4 × 413 = 1652
2 × 489 = 978
+2630KJ
Bond Formation
2 × 805 = 1610
4 × 464 = 1856
−3466
2630 − 3466 = −836KJ/mol