A Level H1 Chemistry Practice Paper 3

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TuitionGoWhere Practice Paper - Chemistry H1 A-Level

TuitionGoWhere Practice Paper (AI)

Subject: Chemistry H1
Level: A-Level
Paper: Practice Paper (Version 3)
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 calculator where necessary.
4. The total mark for this paper is 80.
5. All calculations should be carried out to 3 significant figures unless otherwise stated.

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Section A: Atomic Structure and Bonding [25 Marks]

Question 1 (a) The element X in Period 3 forms an oxide that is amphoteric and sparingly soluble in water. (i) Identify element X. [1]

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(ii) Write a balanced equation, including state symbols, for the reaction of this oxide with hot aqueous sodium hydroxide. [2]

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(b) Consider the molecule $\text{PCl}_5$. (i) State the shape of the $\text{PCl}_5$ molecule. [1]

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(ii) Explain why the molecule has this shape using the VSEPR theory. [2]

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(c) Draw a dot-and-cross diagram to illustrate the bonding in the triiodide ion, $\text{I}_3^-$. Include all lone pairs and the overall charge. [3] [Space for Diagram]

Question 2 (a) Describe the structure and bonding in solid magnesium. [2]

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(b) $\text{BF}_3$ reacts with trimethylamine, $(\text{CH}_3)_3\text{N}$, to form a white crystalline compound. (i) State the type of bond formed between the boron and nitrogen atoms. [1]

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(ii) Explain why this bond forms, referring to the electronic configuration of boron. [2]

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(c) Compare the boiling points of $\text{HCl}$ and $\text{HF}$. Explain the difference in terms of intermolecular forces. [3]

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Question 3 (a) Complete the table for the following species. [4]

Species	Nucleon Number	Atomic Number	Protons	Neutrons	Electrons
$^{37}\text{Cl}^-$	37	17
$^{24}\text{Mg}^{2+}$	24	12

(b) Draw the structures of the cis and trans isomers of but-2-ene. [4] [Space for Diagrams]

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Section B: The Mole Concept and Energetics [25 Marks]

Question 4 (a) A sample of an unknown noble gas with a mass of 2.10 g occupies $600\text{ cm}^3$ at 300 K and 1.00 atm. Calculate the molar mass of the gas. [3]

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(b) Polyethylene terephthalate (PET) has the formula $(\text{C}_{10}\text{H}_8\text{O}_4)_n$. Calculate the percentage by mass of carbon in PET. [2]

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(c) A patient is prescribed four 500 mg tablets of a medication per dose. The active ingredient has a molar mass of $180\text{ g mol}^{-1}$. Calculate the number of moles of the active ingredient the patient receives in one dose. [3]

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Question 5 (a) Given the following enthalpy data:

• $\Delta H_f[\text{CO}_2(\text{g})] = -393.5\text{ kJ mol}^{-1}$
• $\Delta H_f[\text{H}_2\text{O}(\text{l})] = -285.8\text{ kJ mol}^{-1}$
• $\Delta H_f[\text{C}_3\text{H}_8(\text{g})] = -103.8\text{ kJ mol}^{-1}$ Calculate the enthalpy of combustion of propane ($\text{C}_3\text{H}_8$). [4]

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(b) Explain why the actual enthalpy change of a reaction may differ from the value calculated using average bond enthalpies. [2]

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Question 6 (a) A mixture of $^{12}\text{CO}_2$ and $^{14}\text{CO}_2$ was analyzed. If the average molar mass of the sample is $44.12\text{ g mol}^{-1}$, calculate the percentage of $^{14}\text{CO}_2$ in the mixture. [4]

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(b) State the effect of increasing the pressure on the position of equilibrium for the reaction: $\text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) \rightleftharpoons 2\text{NH}_3(\text{g})$. Explain your answer. [3]

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Section C: Chemistry of Aqueous Solutions and Organic Chemistry [30 Marks]

Question 7 (a) What is meant by the term weak acid? Illustrate your answer with an equation for the dissociation of ethanoic acid in water. [2]

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(b) A $0.150\text{ mol dm}^{-3}$ solution of a weak monoprotic acid HA has a pH of 3.20. (i) Calculate the concentration of $\text{H}^+$ ions. [1]

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(ii) Calculate the acid dissociation constant, $K_a$, for acid HA. [3]

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(c) A buffer solution is prepared by mixing $0.10\text{ mol dm}^{-3}$ of ethanoic acid ($\text{p}K_a = 4.76$) and $0.20\text{ mol dm}^{-3}$ of sodium ethanoate. Calculate the pH of this buffer. [3]

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Question 8 (a) Carbonic acid ($\text{H}_2\text{CO}_3$) is formed when $\text{CO}_2$ dissolves in rainwater. (i) Write the balanced equation for the first dissociation of $\text{H}_2\text{CO}_3$ in water. [1]

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(ii) Write the expression for $K_{a1}$ for this dissociation. [1]

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(b) Explain why high acidity (low pH) reduces the effectiveness of enzymes in fermentation tanks. [2]

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(c) Describe a chemical test to distinguish between a solution of $\text{NaCl}$ and $\text{Na}_2\text{CO}_3$. State the observation for each. [3]

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Question 9 (a) Bromoethane reacts with aqueous $\text{NaOH}$ to form ethanol. (i) Name the mechanism of this reaction. [1]

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(ii) Draw the mechanism for this reaction, including all curly arrows and dipoles. [3] [Space for Diagram]

(b) Explain why ethanol is more soluble in water than ethane. [2]

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(c) Describe the reaction of ethanol with propanoic acid in the presence of concentrated $\text{H}_2\text{SO}_4$. State the name and formula of the organic product formed. [3]

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Question 10 (a) Given $E^\circ(\text{Zn}^{2+}/\text{Zn}) = -0.76\text{V}$ and $E^\circ(\text{Cu}^{2+}/\text{Cu}) = +0.34\text{V}$, predict whether zinc metal can displace copper from a solution of $\text{CuSO}_4$. Explain your answer. [3]

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(b) State the effect of a catalyst on the value of the equilibrium constant $K_c$. [1]

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(c) Compare the nature of the oxides of $\text{Na}$ and $\text{Si}$ in Period 3. Provide an equation for the reaction of $\text{Na}_2\text{O}$ with water. [3]

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Answer Key - Chemistry H1 Practice Paper (Version 3)

Section A: Atomic Structure and Bonding

Q1 (a)(i) Aluminium (Al) [1] (a)(ii) $\text{Al}_2\text{O}_3(\text{s}) + 2\text{NaOH}(\text{aq}) + 3\text{H}_2\text{O}(\text{l}) \to 2\text{Na}[\text{Al}(\text{OH})_4](\text{aq})$ [2] (b)(i) Trigonal bipyramidal [1] (b)(ii) Phosphorus has 5 bonding pairs of electrons and 0 lone pairs. [1] These 5 pairs repel each other to be as far apart as possible to minimize repulsion. [1] (c) Diagram showing central I with one lone pair and two bonds to terminal I atoms. Terminal I atoms with three lone pairs each. Overall charge [I$_3$]$^-$ indicated. [3]

Q2 (a) Giant metallic structure [1]. $\text{Mg}^{2+}$ cations and mobile/delocalized valence electrons held together by strong electrostatic forces. [1] (b)(i) Coordinate covalent bond (or dative bond) [1] (b)(ii) Boron has an empty 2p orbital (or is electron deficient with only 6 valence electrons). [1] It accepts a lone pair of electrons from the nitrogen atom of trimethylamine. [1] (c) $\text{HF}$ has a significantly higher boiling point than $\text{HCl}$. [1] $\text{HF}$ can form hydrogen bonds due to the high electronegativity of F, which are much stronger than the permanent dipole-dipole forces in $\text{HCl}$. [2]

Q3 (a)

• $^{37}\text{Cl}^-$: P=17, N=20, E=18 [2]
• $^{24}\text{Mg}^{2+}$: P=12, N=12, E=10 [2] (b) Cis: Methyl groups on same side of C=C. [2] Trans: Methyl groups on opposite sides of C=C. [2]

Section B: The Mole Concept and Energetics

Q4 (a) $n = PV/RT = (1.00 \times 0.600) / (0.0821 \times 300) = 0.02436\text{ mol}$ [1] $M = m/n = 2.10 / 0.02436 = 86.2\text{ g mol}^{-1}$ [2] (b) $M(\text{PET unit}) = 10(12.0) + 8(1.0) + 4(16.0) = 192\text{ g mol}^{-1}$ [1] $\% \text{C} = (120 / 192) \times 100 = 62.5\%$ [1] (c) Total mass = $4 \times 500\text{ mg} = 2.0\text{ g}$ [1] $n = 2.0 / 180 = 0.0111\text{ mol}$ [2]

Q5 (a) $\Delta H = [3(-393.5) + 4(-285.8)] - [-103.8] = [-1180.5 - 1143.2] + 103.8 = -2219.9\text{ kJ mol}^{-1}$ [4] (b) Average bond enthalpies are based on a mean value across many different compounds [1], whereas actual bonds in a specific molecule may be stronger or weaker. [1]

Q6 (a) Let $x$ be fraction of $^{14}\text{CO}_2$. $44(1-x) + 46(x) = 44.12$ $44 - 44x + 46x = 44.12 \implies 2x = 0.12 \implies x = 0.06$ Percentage = $6\%$ [4] (b) Shifts to the right (products) [1]. There are 4 moles of gas on the left and 2 on the right; increasing pressure favors the side with fewer moles to reduce pressure. [2]

Section C: Chemistry of Aqueous Solutions and Organic Chemistry

Q7 (a) An acid that only partially dissociates/ionizes in water. [1] $\text{CH}_3\text{COOH}(\text{aq}) \rightleftharpoons \text{CH}_3\text{COO}^-(\text{aq}) + \text{H}^+(\text{aq})$ [1] (b)(i) $[\text{H}^+] = 10^{-3.20} = 6.31 \times 10^{-4}\text{ mol dm}^{-3}$ [1] (b)(ii) $K_a = [\text{H}^+][\text{A}^-] / [\text{HA}] = (6.31 \times 10^{-4})^2 / (0.150 - 6.31 \times 10^{-4}) \approx 2.65 \times 10^{-6}\text{ mol dm}^{-3}$ [3] (c) $\text{pH} = 4.76 + \log(0.20/0.10) = 4.76 + 0.30 = 5.06$ [3]

Q8 (a)(i) $\text{H}_2\text{CO}_3(\text{aq}) \rightleftharpoons \text{HCO}_3^-(\text{aq}) + \text{H}^+(\text{aq})$ [1] (a)(ii) $K_{a1} = [\text{HCO}_3^-][\text{H}^+] / [\text{H}_2\text{CO}_3]$ [1] (b) High acidity denatures the enzyme [1], changing the shape of the active site so the substrate cannot bind. [1] (c) Add dilute $\text{HCl}(\text{aq})$. [1] $\text{NaCl}$: No visible reaction. [1] $\text{Na}_2\text{CO}_3$: Effervescence/bubbles of $\text{CO}_2$ gas. [1]

Q9 (a)(i) Nucleophilic Substitution ($\text{S}_{\text{N}}2$) [1] (a)(ii) Diagram showing $\text{OH}^-$ attacking the $\text{C}$ atom, $\text{C}-\text{Br}$ bond breaking, $\text{Br}^-$ leaving, with $\delta+$ on $\text{C}$ and $\delta-$ on $\text{Br}$. [3] (b) Ethanol can form hydrogen bonds with water molecules [1] due to the polar $-\text{OH}$ group, whereas ethane only has weak London dispersion forces. [1] (c) Esterification reaction [1]. Product: Propyl ethanoate (or ethyl propanoate depending on acid/alcohol used - here it is ethyl propanoate) $\text{CH}_3\text{CH}_2\text{COOCH}_2\text{CH}_3$ [2].

Q10 (a) Yes [1]. Zn has a more negative $E^\circ$ than Cu, making it a stronger reducing agent. [1] Zn will be oxidized and $\text{Cu}^{2+}$ will be reduced. [1] (b) No effect [1]. (c) $\text{Na}_2\text{O}$ is basic, $\text{SiO}_2$ is acidic. [1] $\text{Na}_2\text{O}(\text{s}) + \text{H}_2\text{O}(\text{l}) \to 2\text{NaOH}(\text{aq})$ [2].