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chemistry A - level > moles etc exam questions > Flashcards

moles etc exam questions Flashcards

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1
Q

The student rinses the burette with deionised water before filling with sodium hydroxide solution. State and explain the effect, if any, that this rinsing will have on the value of the titre.

A

Titre value would increase / larger value
Because the sodium hydroxide solution would be more dilute

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2
Q

A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen by mass.
Which could be the molecular formula of this compound?
A C2H2O2
B C2H2O
C C2H4O2
D C2HO2

A

C

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3
Q

When driving a car, a legal limit for ethanol (Mr = 46.0) is 80 mg per 100 cm3 of blood. What is this concentration in mol dm–3?
A 1.74 × 10–1
B 1.74 × 10–2
C 1.74 × 10–3
D 1.74 × 10–4

A

B

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4
Q

What is the percentage atom economy for the production of ethanol from glucose?
C6H12O6 → 2 C2H5OH + 2 CO2
A 25.6%
B 27.1%
C 51.1%
D 54.2%

A

C

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5
Q

Nitration of 1.70 g of methyl benzoate (Mr = 136.0) produces methyl 3-nitrobenzoate (Mr = 181.0). The percentage yield is 65.0%
What mass, in g, of methyl 3-nitrobenzoate is produced?
A 0.830
B 1.10
C 1.47
D 2.26

A

C

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6
Q

Which compound needs the greatest amount of oxygen for the complete combustion of 1 mol of the compound?
A ethanal
B ethanol
C ethane-1,2-diol
D methanol

A

B

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7
Q

The student noticed that some of the liquid injected into the gas syringe did not vaporise.
Explain the effect that this has on the Mr calculated by the student.

A
  • Calculated Mr value would be greater than actual
  • A lower volume would have been recorded
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8
Q

The total uncertainty from two readings and an end point error in using a burette is ± 0.15 cm3
What is the total percentage uncertainty in using the burette in this experiment?
Tick (✓) one box.
0.45%
0.90%
1.34%

A

0.45%

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9
Q

The equation below represents the complete combustion of butane.
20 cm3 of butane are completely burned in 0.20 dm3 of oxygen.
Which statement is correct?
All volumes are measured at the same temperature and pressure.
A 40 cm3 of carbon dioxide are formed
B 0.065 dm3 of oxygen react
C 70 cm3 of oxygen remain
D 0.50 dm3 of steam are formed

A

c

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10
Q

The heat released when 1.00 g of ethanol (Mr = 46.0) undergoes complete combustion is 29.8 kJ
What is the heat released by each molecule, in joules, when ethanol undergoes complete combustion?
(the Avogadro constant L = 6.022 × 1023 mol–1)
A 2.28 × 10–18 J
B 4.95 × 10–20 J
C 2.28 × 10–21 J
D 4.95 × 10–23 J

A

A

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11
Q

Identify the diagram in the figure below that shows the correct relative sizes of the ions in sodium fluoride.
Justify your answer.

A

B
Both Na+ and F– same electron arrangement
Sodium (ion) has more protons so attracts (outer) electrons closer

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12
Q

The correct value for x is 10.
Suggest a reason for the difference between the experimental value for x and the correct value.

A

Not heated to constant mass

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13
Q

Suggest how the procedure could be improved, using the same apparatus, to give a more accurate value for x. justify your answer.
Suggestion
Justification

A

Heat to constant mass
You can be sure all the water has been driven off

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14
Q

Some of the liquid injected did not evaporate because it dripped into the gas syringe nozzle outside the oven.
Explain how this would affect the value of the Mr of Y calculated from the experimental results.

A

Lower volume recorded
Mr would be greater (than the real Mr)

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15
Q

How many protons are there in 6.0 g of nitrogen gas?
Avogadro constant, L = 6.022 × 1023 mol–1
A
1.3 × 1023
B
9.0 × 1023
C
1.8 × 1024
D
3.6 × 1024

A

c

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16
Q

A 30 cm3 sample of nitrogen was reacted with a 60 cm3 sample of fluorine according to the equation
What is the volume of the gas mixture after the reaction, at constant temperature and pressure?
A
20 cm3
B
30 cm3
C
40 cm3
D
50 cm3

A

d

17
Q

The student rinsed the burette before filling it with the sodium hydroxide solution.
State why the student should use sodium hydroxide solution rather than water for the final rinse of the burette.

A

use of water would dilute the NaOH OR
use of water would change the concentration of NaOH OR
to ensure the concentration of the NaOH is not changed OR

18
Q

Copper can be produced from rock that contains CuFeS2
(b) Suggest two reasons why the sulfur dioxide by-product of this process is
removed from the exhaust gases.
Reason 1
Reason 2

A
  • Prevents acid rain
  • Toxic OR causes breathing problems
  • Reduces waste product
  • Reduces need for sulfur mining
19
Q

Which of these contains the greatest number of atoms?
A
127 mg of iodine
B
1.54 × 10−4 kg of phosphorus
C
81.0 mg of carbon dioxide
D
1.70 × 10−4 kg of ammonia

A

d

20
Q

A 20.0 cm3 sample of a 0.400 mol dm−3 aqueous solution of a metal bromide (MBrn) reacts exactly with 160 cm3 of 0.100 mol dm−3 aqueous silver nitrate.
What is the formula of the metal bromide?
A MBr
B MBr2
C MBr3
D MBr4

A

b

21
Q

The student used a wash bottle containing deionised water when
approaching the end-point to rinse the inside of the conical flask.
Explain why this improved the accuracy of the titration.

A

Idea that it ensures all ethanedioic acid / reactants are in the mixture / solution / reaction or the idea that
some of the ethanedioic acid/ reactants would be on the sides of the flask

22
Q

(c) Give the meaning of the term concordant titres.

A

Titres that are within 0.1 cm3 of each other

23
Q

Suggest a reason, other than apparatus inaccuracy, why the Mr value determined from the experimental results differs from the actual Mr. Explain your answer.

A

M1 The volume of the gas in the syringe (V) is greater than the true volume (because some air leaked into the syringe)

24
Q

Suggest, with a reason, an appropriate safety precaution that the student should take when using the toxic chloroalkane, X, in the experiment.
Safety precaution
Reason

A

Carry out in a fume cupboard
To avoid toxic vapour

25
Q

What is the volume of 0.200 mol dm−3 Ba(OH)2 (aq) required to neutralise exactly 30.0 cm3 of 0.100 mol dm−3 HCl(aq)?
A
150.0 cm3
B
75.0 cm3
C
15.0 cm3
D
7.50 cm3

A

D

26
Q
A
  1. Fill up a burette with acid.
  2. Use a pipette to add alkali to a conical flask.
  3. Add an indicator to the alkali.
  4. Slowly add the acid into the alkali. swirling constantly to ensure the reactants mix well.
  5. Slow the adding of acid when the indicator changes colour.
  6. Stop adding acid when there is a permanent colour change.
  7. Record the titre.
  8. Repeat the titration. The titration is repeated until concordant (within 0.1 cm³) titres are obtained.
27
Q

What is the IUPAC name for this compound?
A 2-dimethyl-3-fluoropentane
B 2,2-dimethyl-3-fluoropentane
C 3-fluoro-2,2-dimethylpentane
D 3-fluoro-2-dimethylpentane

A

C

28
Q

Which compound has the lowest relative molecular mass?
A ethanoic acid
B 1-fluoropropane
C propanenitrile
D propylamine

A

C

29
Q

Which does not contain an asymmetric carbon atom?
A CH3CH(CH3)CH2CH3
B CH3CH2CH(CH3)CH2CH2CH3
C CH3CH(OH)CH2OH
D CH3CH2CHClCH3

A

A

30
Q

Which compound is not an isomer of the following compound?
A CH3CH2COCH3
B CH3CH═CHCH2OH C (CH3)2CHCHO
D CH2═CHCH2CHO

A

D

31
Q

How many isomers are there of C3H9N?
A 2
B 3
C 4
D 5

A

C

32
Q

How many structural isomers with an unbranched carbon chain have the molecular formula C4H8Br2?
A 4
B 5
C 6
D 7

A

C

33
Q

Which can be both an empirical and molecular formula of a stable compound?
A CH2O
B P4O10
C NH2
D CH3

A

A

34
Q

Which compound is a structural isomer of Z-but-2-ene?
A butane
B E-but-2-ene
C cyclobutane
D methylbut-2-ene

A

C

35
Q

How many structural isomers are there with the molecular formula C3H6BrCl?
A 4
B 5
C 6
D 7

A

B

chemistry A - level (16 decks)

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