A Level H1 Chemistry Practice Paper 5

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TuitionGoWhere Practice Paper - Chemistry H1 A-Level

TuitionGoWhere Practice Paper (AI) - Version 5

Subject: Chemistry H1
Level: A-Level
Paper: Practice Paper 2 (Structured & Free Response)
Duration: 2 Hours
Total Marks: 80
Name: __________________________ Class: __________ Date: __________

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Instructions to Candidates

1. Answer all questions.
2. Write your answers in the spaces provided.
3. Use a black or dark blue pen.
4. For calculations, show all working. Give your answers to 3 significant figures unless otherwise specified.
5. The data booklet provided contains necessary constants and values.

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Section A: Physical and Inorganic Chemistry (40 Marks)

Question 1 (a) Define the term amphoteric oxide. [1]

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(b) Aluminium oxide ($\text{Al}_2\text{O}_3$) is an amphoteric oxide. Write a balanced chemical equation, including state symbols, for the reaction of $\text{Al}_2\text{O}_3$ with hot, concentrated sodium hydroxide solution. [2]

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(c) Explain why $\text{Al}_2\text{O}_3$ is described as "sparingly soluble" in water. [1]

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Question 2 A student prepares a buffer solution by mixing $50.0\text{ cm}^3$ of $0.200\text{ mol dm}^{-3}$ ethanoic acid ($\text{CH}_3\text{COOH}$) and $50.0\text{ cm}^3$ of $0.100\text{ mol dm}^{-3}$ sodium ethanoate ($\text{CH}_3\text{COONa}$). (a) State the role of the conjugate base in this buffer system. [1]

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(b) Given that the $pKa$ of ethanoic acid is 4.76, calculate the pH of the resulting buffer solution. [3]

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(c) The student adds $1.00\text{ cm}^3$ of $0.100\text{ mol dm}^{-3}$ $\text{HCl}$ to the buffer. Calculate the new pH. [3]

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Question 3 (a) Distinguish between a strong acid and a weak acid in terms of their behavior in aqueous solution. [2]

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(b) Write the expression for the acid dissociation constant ($Ka$) for a diprotic acid $\text{H}_2\text{A}$. [1]

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(c) Calculate the pH of a $0.050\text{ mol dm}^{-3}$ solution of a weak monoprotic acid $\text{HA}$ with $Ka = 1.8 \times 10^{-5}$. [3]

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Question 4 (a) Describe the structure and bonding in solid sodium chloride. [2]

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(b) Explain why sodium chloride has a high melting point. [2]

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Question 5 (a) State the shape of the $\text{BF}_3$ molecule and explain this shape using VSEPR theory. [2]

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(b) $\text{BF}_3$ reacts with ammonia ($\text{NH}_3$) to form a white crystalline adduct. Draw a dot-and-cross diagram to illustrate the bonding in this adduct. [3]

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Section B: Organic and Applied Chemistry (40 Marks)

Question 6 (a) Draw the structures of the cis and trans isomers of but-2-ene. [2]

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(b) Explain why but-1-ene does not exhibit cis-trans isomerism. [2]

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Question 7 (a) Define nucleophilic substitution. [2]

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(b) Draw the mechanism for the reaction between bromoethane and aqueous $\text{NaOH}$ to form ethanol. Include all curly arrows and dipoles. [3]

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Question 8 (a) A compound $\text{X}$ with formula $\text{C}_3\text{H}_6\text{O}$ reacts with $2,4\text{-DNPH}$ to give an orange precipitate. (i) What does this test indicate about the functional group of $\text{X}$? [1]

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(ii) $\text{X}$ is then oxidized by acidified $\text{K}_2\text{Cr}_2\text{O}_7$ to form compound $\text{Y}$. Identify $\text{Y}$ and provide its structure. [2]

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Question 9 (a) State the effect of increasing temperature on the position of equilibrium and the value of $Kc$ for the following reaction: $\text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) \rightleftharpoons 2\text{NH}_3(\text{g}) \quad \Delta H = -92\text{ kJ mol}^{-1}$ [2]

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(b) Explain the effect of increasing the pressure on the yield of $\text{NH}_3$ in the reaction above. [2]

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Question 10 (a) Calculate the percentage by mass of oxygen in glucose ($\text{C}_6\text{H}_{12}\text{O}_6$). [2]

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(b) A sample of an unknown gas has a mass of $0.800\text{ g}$ and occupies $400\text{ cm}^3$ at $300\text{ K}$ and $1.00\text{ atm}$. Calculate the molar mass of the gas. ($R = 0.0821\text{ L atm K}^{-1}\text{ mol}^{-1}$) [3]

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Answer Key - Chemistry H1 Practice Paper (Version 5)

Section A: Physical and Inorganic Chemistry

Question 1 (a) An oxide that reacts with both acids and bases to form salts and water. [1] (b) $\text{Al}_2\text{O}_3(\text{s}) + 2\text{NaOH}(\text{aq}) + 3\text{H}_2\text{O}(\text{l}) \to 2\text{Na}[\text{Al}(\text{OH})_4](\text{aq})$ [2] (1 mark for correct formula of aluminate, 1 mark for balanced equation/states). (c) It has a giant covalent/ionic lattice with very strong bonds that are not easily overcome by hydration in water. [1]

Question 2 (a) It reacts with any added $\text{H}^+$ ions to prevent a significant drop in pH. [1] (b) $\text{pH} = pKa + \log([\text{salt}]/[\text{acid}])$ $\text{pH} = 4.76 + \log(0.100/0.200) = 4.76 - 0.30 = 4.46$ [3] (c) $\text{moles } \text{H}^+ = 0.001\text{ L} \times 0.100\text{ mol dm}^{-3} = 1.0 \times 10^{-4}\text{ mol}$. Initial $\text{moles acid} = 0.050 \times 0.200 = 0.01\text{ mol}$; $\text{moles salt} = 0.050 \times 0.100 = 0.005\text{ mol}$. New $\text{moles acid} = 0.01 + 0.0001 = 0.0101$; New $\text{moles salt} = 0.005 - 0.0001 = 0.0049$. $\text{pH} = 4.76 + \log(0.0049/0.0101) = 4.76 - 0.31 = 4.45$ [3]

Question 3 (a) Strong acid: completely dissociates/ionizes in water. Weak acid: partially dissociates/ionizes in water. [2] (b) $Ka_1 = [\text{HA}^-][\text{H}^+] / [\text{H}_2\text{A}]$ [1] (c) $[\text{H}^+] = \sqrt{Ka \times c} = \sqrt{1.8 \times 10^{-5} \times 0.050} = \sqrt{9.0 \times 10^{-7}} = 9.49 \times 10^{-4}\text{ mol dm}^{-3}$. $\text{pH} = -\log(9.49 \times 10^{-4}) = 3.02$ [3]

Question 4 (a) Giant ionic lattice. [1] Consisting of $\text{Na}^+$ and $\text{Cl}^-$ ions held by strong electrostatic forces of attraction. [1] (b) High energy is required to break the strong electrostatic attractions between the oppositely charged ions throughout the giant lattice. [2]

Question 5 (a) Trigonal planar. [1] Boron has 3 bonding pairs and 0 lone pairs; these repel each other to be as far apart as possible (120°). [1] (b) Diagram should show $\text{B}$ and $\text{N}$ with a dative bond (arrow from $\text{N}$ lone pair to $\text{B}$ empty orbital). [3]

Section B: Organic and Applied Chemistry

Question 6 (a) Cis: methyl groups on same side of $\text{C}=\text{C}$. Trans: methyl groups on opposite sides. [2] (b) One of the carbons in the $\text{C}=\text{C}$ bond is attached to two identical hydrogen atoms. [2]

Question 7 (a) A reaction where an electron-rich species (nucleophile) attacks an electron-deficient carbon atom, replacing a leaving group. [2] (b) Curly arrow from $\text{OH}^-$ lone pair to $\text{C}$ ($\delta+$); curly arrow from $\text{C}-\text{Br}$ bond to $\text{Br}$ ($\delta-$). Dipoles $\delta+/\delta-$ clearly marked. [3]

Question 8 (a) (i) Carbonyl group ($\text{C}=\text{O}$), either aldehyde or ketone. [1] (ii) Propanoic acid. Structure: $\text{CH}_3\text{CH}_2\text{COOH}$. [2]

Question 9 (a) Position shifts to the left (reactants). [1] $Kc$ decreases. [1] (b) Increase in pressure shifts equilibrium to the side with fewer moles of gas (right). [2] This increases the yield of $\text{NH}_3$.

Question 10 (a) $\text{Mr} = 180.16$. $\text{Mass of O} = 16 \times 6 = 96$. $\% \text{O} = (96/180.16) \times 100 = 53.3\%$ [2] (b) $V = 0.400\text{ L}$. $n = PV/RT = (1.00 \times 0.400) / (0.0821 \times 300) = 0.0162\text{ mol}$. $M = m/n = 0.800 / 0.0162 = 49.4\text{ g mol}^{-1}$. [3]