A LevelChemistryOCRExam Questions2. Foundations in Chemistry2.2 Amount of Substance

Amount of Substance (OCR A Level Chemistry)

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2.2 Amount of Substance

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2.2 Amount of Substance

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11 mark

What is the molecular formula of naphthalene?
napthalene

  • C10H8

  • C10H10

  • C12H10

  • C12H12

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21 mark

What is the molecular formula of the compound below?

12-dimethylcyclopropane

  • C7H10

  • C7H12

  • C7H14

  • C7H16

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31 mark

Ethanol can be prepared by different reactions.

Which reaction has the highest atom economy?

  • C6H12O6 → 2C2H5OH + 2CO2

  • C2H4 + H2O → C2H5OH

  • C2H5Br + H2O → C2H5OH + HBr

  • CH3COOC2H5 + H2O → C2H5OH + CH3COOH

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4
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What is the number of molecules in 500 cm3 of oxygen under room conditions?

(The Avogadro constant, NA = 6.02 x 1023)

  • 3.01 x 1023

  • 3.01 x 1026

  • 1.20 x 1021

  • 1.26 x 1022

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5
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Ethane has the formula C2H6.

What is the mass in grams of one molecule of ethane? (Ar: C = 12.0; H = 1.0)

(The Avogadro constant, NA = 6.02 x 1023)

  • 1.81 x 1025

  • 4.98 x 10-23

  • 30.0

  • 2.99 x 10-23

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6
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A 5.62 g sample of anhydrous sodium sulfate, Na2SO4, is dissolved in water and the solution made up to 250 cm3 in a volumetric flask.

What is the concentration in mol dm-3 of the hydrated sodium sulfate solution?

  • 0.61

  • 1.6 x 10-4

  • 0.16

  • 0.016

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7
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A student prepared 250 cm3 of a 0.0800 mol dm-3 solution of borax, Na2B4O7 ·10H2O in water in a volumetric flask.

What is the mass of borax crystals needed to make up this solution?

  • 5.240 g

  • 4.384 g

  • 0.080 g

  • 7.624 g

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8
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How many moles of oxygen are there in 500 cm3 of gas at 298 K and 105 000 Pa?

(The gas constant R = 8.314 J K-1 mol-1)

  • 0.021 mol

  • 2.12 x 10-5 mol

  • 47.2 mol

  • 2.12 x 104 mol

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9
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Methane and steam can be used to prepare hydrogen and carbon monoxide as shown by the equation below.

CH4 (g) + H2O (g) →  3H2 (g) + CO (g)

200 g of methane was reacted with an excess of steam to produce 642 dm3 of hydrogen gas at RTP.

What is the percentage yield of hydrogen?

  • 71.3%

  • 46.7%

  • 33.3%

  • 140.2%

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101 mark

Which of the following statements is true about reactions with an atom economy of 100%?

  • There must be only one product

  • The reaction has a high percentage yield

  • It is more sustainable than a reaction with a low atom economy

  • The sum of molar masses of the desired products is equal to the sum of molar masses of all reactants

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1
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Which sample contains the greatest number of molecules?

  • 1 g of methanal, CH2O

  • 2 g of carbon dioxide, CO2

  • 3 g of sulfur, S6

  • 4 g of bromine, Br2

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2
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How many electrons are removed from 3.99 x 10-2 g of Ar (g) to form Ar+ (g) ions? 

  • 1.204 x 1024 

  • 1.33 x 1021 

  • 3.27 x 1020

  • 6.02 x 1020

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3
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Which magnesium compound contains the greatest percentage by mass of magnesium?

  • Magnesium carbonate, MgCO3 

  • Magnesium nitrate, Mg(NO3)2 

  • Magnesium hydroxide, Mg(OH)2 

  • Magnesium sulfate, MgSO4 

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4
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15.0 g of a compound contains 6.105 g of carbon, 0.765 g of hydrogen and 8.130 g of oxygen. The relative molecular mass of the compound is 118.0 g mol-1.

What is the molecular formula of the compound?

  • C2H3O2

  • C4H8O4

  • CH1.5O

  • C4H6O4

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5
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A copper compound has a formula CuSO4•xH2O and a molar mass of 231.6.

What is the value of x?

  • 2

  • 3

  • 4

  • 5

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6
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What mass of Na2CO3 is required to prepare 250 cm3 of a 0.150 mol dm-3 standard solution?

Your answer should be given to 3 significant figures.

  • 3.98 g

  • 6.63 g

  • 1.54 g

  • 3.11 g

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7
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0.0300 mol of magnesium oxide is reacted completely with 1.50 mol dm-3 HCl.

What is the volume, in cm3, of 1.50 mol dm-3 HCl required for this reaction?

  • 20

  • 25

  • 40

  • 50

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8
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What volume, in m3, of hydrogen gas is produced when 1.45 g of lithium reacts with water at 298 K and 100 kPa?

The gas constant, R = 8.314 J mol-1 K-1 

  • 5.203 x 10-3 

  • 2.601 x 10-3 

  • 2.601 x 10-4 

  • 2.601

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9
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A student reacts 21.76 g of 2-bromopropane in the reaction below.

CH3CHBrCH3  + NaOH  → CH3CHOHCH3  + NaBr
Mr= 122.9    Mr = 60.0  

The reaction produces 3.940 g of CH3CHOHCH3.

What is the percentage yield of CH3CHOHCH3?

  • 12.6%

  • 21.3%

  • 32.5%

  • 37.1%

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10
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Which reaction produces the largest atom economy of CaCl2?

  • Ca + 2HCl → CaCl2 + H2  

  • CaCO3 + 2HCl → CaCl2 + CO2 + H2O

  • CaO + 2HCl → CaCl2 + H2O 

  • CaCl2•2H2O → CaCl2 + 2H2O 

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11
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Sodium reacts with water as shown below.


2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

Which mass of sodium reacts with water to produce 960 cm3 of hydrogen gas at RTP?

  • 0.46 g 

  • 0.92 g

  • 1.84 g

  • 3.68 g

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12
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Silicon can be made by heating silicon tetrachloride, SiCl4, with zinc.


SiCl4 + 2Zn → Si + 2ZnCl2


8.50g of SiCl4 is reacted with an excess of zinc. The percentage yield of silicon is 90%. 


What is the mass of silicon made?

  • 1.26 g

  • 1.31 g

  • 1.40 g 

  • 1.55 g

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1
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An organic compound has the composition by mass:

C, 53.33 %; H, 11.11%; O, 35.56%.

What is the empirical formula of the organic compound?

  • C4H8O2

  • C4H10O2

  • C2H4O

  • C2H5O

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2
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Samples of four hydrocarbons are completely burnt under the same conditions of temperature and pressure.

Which sample produces the greatest volume of CO2?

  • 0.4 mol C2H6

  • 0.3 mol C3H8

  • 0.2 mol C4H10

  • 0.1 mol C5H12

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3
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Which reaction produces the smallest atom economy of BaCl2?

  • BaCl2 + 2H2O → BaCl2 + 2H2O

  • BaO + 2HCl → BaCl2 + H2O

  • BaCO3 + 2HCl → BaCl2 + CO2 + H2O

  • Ba + 2HCl → BaCl2 + H2

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4
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A compound has the composition by mass:

H, 5.00%;    N, 35.00%;   O, 60.00%.

Which compound has this composition?

  • HNO3 

  • NH4NO3 

  • HNO2 

  • NH2OH

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5
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Calcium nitrate, Ca(NO3)2, decomposes when heated, as shown below.

Ca(NO3)2 (s) → CaO (s) + 2NO2 (g) + 1⁄2O2 (g)

A student decomposes 0.00500 mol of Ca(NO3)2 and collects the gas that is produced.

Calculate the volume of gas that the student should expect to collect, measured at room temperature and pressure.

  • 60 cm3

  • 120 cm3

  • 240 cm3

  • 300 cm3

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6
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A sample of a compound M contains 1.46 g of carbon, 0.482 g of hydrogen and 1.69 g of nitrogen.
What is the empirical formula of M?

  • CH2N 

  • C4HN4

  • CH4N

  • C2H4N

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7
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A student mixes 100 cm3 of 0.200 mol dm–3 NaCl (aq) with 100 cm3 of 0.200 mol dm–3 Na2CO3 (aq).
What is the total concentration of Na+ ions in the mixture formed?

  • 0.100 mol dm–3

  • 0.200 mol dm–3

  • 0.300 mol dm–3

  • 0.400 mol dm–3

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8
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Which mass of substance contains the greatest number of atoms?

  • 3.00 g of ammonia

  • 3.00 g of chloromethane

  • 4.00 g of hydrogen sulfide

  • 4.00 g of hydrogen chloride

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9
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Which volume of oxygen gas, at room temperature and pressure, is required for the complete combustion of 1.25 × 10-3 mol of propan-1-ol?

  • 105 cm3

  • 120 cm3

  • 135 cm3

  • 150 cm3

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10
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Complete combustion of 40 cm3 of a gaseous hydrocarbon X requires 240 cm3 of oxygen. 160 cm3 of carbon dioxide forms. All gas volumes are at room temperature and pressure.

What is the formula of X?

  • C4H8

  • C4H10

  • C6H12

  • C6H14

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111 mark

0.1 mol of HOOCCH2COOH are reacted with 0.1 mol of aqueous NaOH.

How many molecules of water are formed?

  • 6.02 × 1022

  • 3.01 × 1022

  • 6.02 × 1023

  • 3.01 × 1023

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12
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What is the number of oxygen atoms in 88.0 g of CO2?

  • 3.01 × 1023

  • 1.20 × 1024

  • 2.41 × 1024

  • 4.82 × 1024 

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