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A Level Chemistry > Incorrect Test Answers > Flashcards

Incorrect Test Answers Flashcards

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1
Q

Describe the process of electrospray ionisation? [4 marks]

A

1) Dissolved in solvent.
2) Injected through a needle.
3) A high voltage is applied.
4) This causes a proton to be gained.

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2
Q

State the meaning of the term periodicity. [1 mark]

A

Repeating patterns of physical and chemical properties.

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3
Q

What is the equation for the reaction of solid sodium chloride with concentrated sulphuric acid?

What is the role of sulphuric acid?

A

2NaCl + H₂SO₄ —-> Na₂SO₄ + 2HCl

Proton donor.

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4
Q

What reaction(s) occurs when NaF reacts with H₂SO₄?

What is observed?

A

NaF + H₂SO₄ —-> NaHSO₄ + HF

Misty fumes of HF gas.

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5
Q

What reaction(s) occurs when NaCl reacts with H₂SO₄?

What observations are there?

A

NaCl + H₂SO₄ —-> NaHSO₄ + HCl

Misty fumes of HCl.

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6
Q

What reaction(s) occur when NaBr reacts with H₂SO₄?

What observations are there?

A

NaBr + H₂SO₄ —-> NaHSO₄ + HBr

2HBr + H₂SO₄ —-> Br₂ + SO₂ + 2H₂O

Misty fumes of HBr and brown gas (Br₂).

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7
Q

What reaction(s) occur when NaI reacts with H₂SO₄?

What observations are there?

A

NaI + H₂SO₄ —-> NaHSO₄ + HI

2HI + H₂SO₄ —-> I₂ + SO₂ + 2H₂O

6HI + SO₂ —-> H₂S + 3I₂ + 2H₂O

Fumes of H₂S and solid iodine (purple).

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8
Q

What is the equation for AgBr reacting with concentrated ammonia solution?

A

AgBr + 2NH₃ —-> Ag(NH₃)₂⁺ + Br⁻

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9
Q

What is the shape of a ClF₄⁻ ion?

A

Square planar.

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10
Q

Explain why Mg(OH)₂ is only weakly alkaline.

A

It is only sparingly soluble and so less dissolves and less is therefore dissociated.

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11
Q

State whether a solution containing [Fe(H₂O)₆]³⁺ ions has a higher or lower pH than a solution containing an equal concentration of [Fe(H₂O)₆]²⁺ ions and explain why. [3 marks]

A

A lower pH.

Fe³⁺ has a higher charge density than Fe²⁺ which means it attracts the bonding electrons more. This weakens the O-H bonds which makes it more likely to dissociate.

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12
Q

How do you test for an alcohol?

A

React with acidified potassium dichromate with heat.

It should turn from orange to green.

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13
Q

Why is fluted filter paper used?

A

Large surface area which allows the solution to travel quickly through the filter paper.

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14
Q

What is the value of a H-O-H bond angle in water?

Explain the bond angle. [4 marks]

A

104.5 degrees.

There are two lone pairs and two bonding pairs of electrons. Lone pairs have a greater repulsion than bonding pairs of electrons. This causes a bent shape to be formed and the bond angle reduced from 109.5 degrees to 104.5 degrees.

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15
Q

What is the purpose of a salt bridge?

A

Allows ions to pass freely between the two electrolytes.

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16
Q

How can an electrochemical cell reaction be changed in order to go to completion?

A

Replace voltmeter with lamp.

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17
Q

What effect does changing temperature have on Kₚ and yield?

A

It shifts the position of equilibrium to favour the endothermic reaction and therefore affects the yield.

It also affects the value of Kₚ.

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18
Q

What effect does changing pressure have on Kₚ and yield?

A

It shifts the position of equilibrium to the side with the fewest number of moles and therefore affects the yield.

It does NOT affect Kₚ.

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19
Q

What effect does a catalyst have on Kₚ and yield?

A

It neither affects the yield or value of Kₚ.

It will make the equilibrium be reached faster.

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20
Q

What is the definition of empirical formula?

A

The simplest ratio of atoms of each element in a compound.

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21
Q

What is the definition of relative molecular mass?

A

The average mass of a molecule on a scale where an atom of carbon-12 is exactly 12.

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22
Q

What is the colour change at the end point of the titration between iron and manganate (VII) ions?

A

Colourless —-> Pink.

23
Q

What are the reagents for a dehydration reaction?

A

Concentrated sulphuric acid.

24
Q

A calculation of the enthalpy of lattice formation of silver iodide based on a perfect ionic model gives a smaller numerical value than the experimental value.

Explain this difference. [2 marks]

A

AgI contains some covalent character.

The forces holding the lattice together are stronger.

25
Q

Calculate the pH of a 0.0131 mol dm⁻³ solution of calcium hydroxide at 10°C.

Kw = 2.93 x 10⁻¹⁵ mol² dm⁻⁶ at 10°C. [3 marks]

A

12.95

26
Q

State the type of crystal structure shown in sulphur trioxide. [1 mark]

A

Molecular

27
Q

Explain why silicon dioxide has a higher melting point than sulphur trioxide. [4 marks]

A

Covalent bonds between atoms in SiO₂.

Van der Waals forces <b> between molecules </b> in SO₃.

Covalent bonds are stronger than van der Waals forces.

Covalent bonds take more energy to be <b> broken</b>.

28
Q

Write an equation for the reaction of sulphur trioxide with potassium hydroxide solution. [1 mark]

A

SO₃ + 2KOH —-> K₂SO₄ + H₂O

29
Q

Solution A is [Cu(H₂O)₆]Cl₂.

An excess of ammonia was added to solution A to form solution B.

Write an ionic equation for the reaction that occurs. [1 marks]

A

[Cu(H₂O)₆]²⁺ + 4NH₃ —-> [Cu(NH₃)₄(H₂O)₂]²⁺ + 4H₂O

30
Q

Solution A is [Cu(H₂O)₆]Cl₂.

Reagent D was added to another sample of solution A to form a yellow-green solution.

Write an ionic equation for the reaction that occurs when the yellow-green solution is formed from solution A. [1 mark]

A

[Cu(H₂O)₆]²⁺ + 4Cl⁻ —-> [CuCl₄]²⁻ + 6H₂O

31
Q

Explain why the reaction between the aldehyde, CH₃CH₂CH₂CH₂CHO, and KCN and dilute acid forms a racemic mixture. [3 marks]

A

The carbonyl group is planar.

Attack from either side has equal probability.

32
Q

Write an equation for the reaction of concentrated nitric acid with concentrated sulphuric acid to form the species that reacts with nitrobenzene. [1 mark]

A

2H₂SO₄ + HNO₃ —-> NO₂⁺ + 2HSO₄⁻ + H₃O⁺

33
Q

Why is an aromatic amine less basic than an aliphatic amine?

A

The lone pair of electrons on the nitrogen atom is <b> delocalised</b> into the benzene ring.

Therefore, it is less available to donate or accept a H⁺ ion.

34
Q

What reagents and conditions are required to convert a haloalkane into a nitrile?

A

Alcoholic and aqueous KCN.

35
Q

What reagents are required to reduce a nitrile into an amine?

A

LiAlH₄ in dry ether.

Or H₂ with a nickel catalyst.

36
Q

Concentrated sulphuric acid reacts with solid sodium chloride.

State the role of the sulphuric acid. [1 mark]

A

Proton donor.

37
Q

Describe the method the student should use to purify the benzoic acid [6 marks]

A

1) Dissolve crude product in hot water of a minimum volume.
2) Filter to remove insoluble impurities.
3) Cool to recrystallise.
4) Filter under reduced pressure with Buchner apparatus.
5) Wash with cold solvent <b> and</b> dry.

38
Q

V₂O₅ can be used as a catalyst in the Contact Process.

Which is a step in the Contact Process in which the vanadium is oxidised?

A) SO₂ + V₂O₅ —-> SO₃ + 2VO₂
B) SO₃ + 2VO₂ —-> SO₂ + V₂O₅
C) 2VO₂ + 1/2 O₂ —-> V₂O₅
D) V₂O₅ —-> 2VO₂ + 1/2 O₂

A

C.

39
Q

Explain why the enthalpy of hydration becomes less exothermic from Li⁺ to K⁺. [2 marks]

A

The size increases and so the charge density decreases.

The electrostatic attraction between metal ion and Oδ⁻ of water decreases.

40
Q

Explain, with the aid of an equation, why a solution containing [Al(H₂O)₆]³⁺ has a pH less than 7. [3 marks]

A

[Al(H₂O)₆]³⁺ + H₂O ⇌ [Al(H₂O)₅(OH)]²⁺ + H₃O⁺

<b>Al³⁺</b> has a high charge density which weakens the OH bond in water, releasing H⁺ ions.

41
Q

Solid sodium chloride reacts with concentrated sulphuric acid.

State the role of the chloride ions in the reaction. [1 mark]

A

Base.

42
Q

Give an equation for the redox reaction between solid sodium bromide and concentrated sulphuric acid. [1 mark]

A

2NaBr + 2H₂SO₄ → Na₂SO₄ + Br₂ + SO₂ + 2H₂O

43
Q

Give two ways of maximising the yield of propanal obtained by distillation of the reaction mixture. [2 marks]

A

Keep the temperature to below the boiling point of the other products.

Cool the distillate / reaction vessel.

44
Q

Explain how stereoisomerism occurs. [1 marks]

A

C=C bond cannot <u>rotate</u> <b> and</b> each carbon has two different groups attached.

45
Q

How does adding water to an equilibrium mixture affect the amount of products and reactants?

A

Adding water causes the concentrations to fall.

The equilibrium moves to the side with more moles to oppose the decrease in concentration.

46
Q

Suggest a value for the enthalpy of hydrogenation of cyclohexa-1,3-diene and justify your value. [3 marks]

A

Between -239 and -121.

Double bonds separated by one single bond which allows some delocalisation/overlap of p-orbitals.

47
Q

What type of compounds does thermal cracking make?

A

Produces lots of alkenes

48
Q

What type of compounds does catalytic cracking make?

A

Mostly aromatic hydrocarbons and the alkanes needs to produce motor fuels

49
Q

How are nitrous oxides created inside a car engine?

A

N₂ + O₂ => 2NO

2NO + O₂ => 2NO₂

50
Q

What are the equations for how a catalytic converter works?

A

2NO => N₂ + O₂

2NO + 2CO => N₂ + 2CO₂

51
Q

What two monomers is Nylon 6,6 made from?

A

Hexanedioic acid and 1,6-diaminohexane.

52
Q

What two monomers is Kevlar made from?

A

Benzene-1,4-dicarboxylic acid and 1,4-diaminobenzene.

53
Q

What two monomers is Terylene made from?

A

Benzene-1,4-dicarboxylic acid and ethane-1,2-diol.

A Level Chemistry (24 decks)

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