Concentration, Yield and Atom Economy - Worksheets, Questions and Revision

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GCSE · Chemistry

C3b Concentration, Yield and Atom Economy

AQA 8464 · Calculator allowed · about 100 minutes
Total Marks
Name: _______________________________    Date: ____ / ____ / ______
Answer ALL questions. Show all your working.
1
A required practical investigates the volume of dilute hydrochloric acid needed to exactly neutralise a fixed volume of sodium hydroxide solution, using a suitable indicator.
(a)Name one piece of apparatus used to measure accurately a fixed volume of 25.0 cm3 of sodium hydroxide solution.(1)
(b)Name the piece of apparatus, marked in cm3, that is used to add the acid gradually and to measure the volume of acid added.(1)
(c)Give one safety precaution that should be taken when carrying out this titration.(1)
(Total for Question 1 is 3 marks)
2
A technician, Priya, dissolves 8.0 g of sodium chloride in water to make 250 cm3 of solution.
(a)State the formula linking concentration, mass of solute and volume of solution.(1)
(b)Convert 250 cm3 to dm3.(1)
(c)Calculate the concentration of the solution in g/dm3.(2)
(Total for Question 2 is 4 marks)
3
A student, Callum, prepares copper sulfate crystals, CuSO4.5H2O. The theoretical (maximum possible) yield is 12.5 g. Callum actually obtains 9.6 g of crystals.
(a)State the formula used to calculate percentage yield.(1)
(b)Calculate the percentage yield of copper sulfate crystals.(2)
(Total for Question 3 is 3 marks)
4
Give three reasons why the percentage yield of a reaction is usually less than 100%.
(Total for Question 4 is 3 marks)
5
Ethene, C2H4, reacts with steam in the only reaction taking place, forming ethanol, C2H5OH, as the sole product:
C2H4 + H2O -> C2H5OH
Mr: C2H4 = 28, H2O = 18, C2H5OH = 46
(a)State the formula used to calculate atom economy.(1)
(b)Calculate the atom economy for the production of ethanol in this reaction. Give your answer to 1 decimal place.(3)
(Total for Question 5 is 4 marks)
6
A pharmacy technician, Fatima, needs to prepare a salt solution of concentration 20 g/dm3.
(a)Calculate the mass, in g, of salt needed to make 1.5 dm3 of this solution.(2)
(b)Fatima only has 12 g of salt available. Calculate the maximum volume, in dm3, of this solution that can be made at the same concentration.(2)
(Total for Question 6 is 4 marks)
7
A reaction has a theoretical yield of 25.0 g of product. The percentage yield obtained is 88%.
(a)Rearrange the percentage yield formula to make actual yield the subject.(1)
(b)Calculate the actual mass of product obtained.(2)
(Total for Question 7 is 3 marks)
8
Match each key term to its correct definition by writing the correct definition letter (A-E) next to each term (i-v).
Terms: (i) concentration (ii) atom economy (iii) percentage yield (iv) molar volume (v) concordant titres
Definitions:
A. titres that agree closely with each other (within 0.10 cm3 of one another)
B. the volume occupied by one mole of any gas at a stated temperature and pressure
C. the mass of solute dissolved per unit volume of solution
D. the percentage of the total mass of all reactants that is converted into a desired/useful product
E. the actual yield of a reaction expressed as a percentage of the maximum theoretical yield
(Total for Question 8 is 5 marks)
9
A stock solution of copper sulfate has a concentration of 40 g/dm3. A technician, Kwame, dilutes 50 cm3 of this stock solution with distilled water to a total volume of 200 cm3.
(a)Calculate the concentration of the diluted solution, in g/dm3.(2)
(b)State what would happen to the concentration of the diluted solution if Kwame had instead diluted the same 50 cm3 of stock solution to a total volume of 400 cm3. Justify your answer without further calculation.(2)
(Total for Question 9 is 4 marks)
10
In the industrial production of vinegar, ethanol is oxidised by oxygen to form ethanoic acid as the only desired product:
C2H5OH + O2 -> CH3COOH + H2O
Mr: C2H5OH = 46, O2 = 32, CH3COOH = 60, H2O = 18
(Total for Question 10 is 3 marks)
11
Describe how a student could carry out a titration to find the volume of dilute hydrochloric acid needed to exactly neutralise 25.0 cm3 of sodium hydroxide solution, using a suitable indicator.
(Total for Question 11 is 6 marks)
12
A student, Aaliyah, carries out a titration and records the following burette readings:
Rough titration: 23.20 cm3
Titration 1: 22.60 cm3
Titration 2: 22.55 cm3
Titration 3: 22.65 cm3
(a)State why a rough (preliminary) titration is carried out before the accurate titrations.(1)
(b)Identify, using the data given, which titre(s) should be used to calculate the mean titre. Give a reason for your answer.(2)
(c)Calculate the mean titre, giving your answer to 2 decimal places.(2)
(d)Give one reason why a pipette, rather than a measuring cylinder, is used to measure the 25.0 cm3 of alkali.(1)
(Total for Question 12 is 6 marks)
13
A solution contains 4.9 g of sulfuric acid, H2SO4 (Mr = 98), dissolved in 200 cm3 of solution.
(a)State the equation that links number of moles, concentration and volume for a solution.(1)
(b)Calculate the number of moles of sulfuric acid in the solution.(2)
(c)Calculate the concentration of the solution in mol/dm3.(2)
(Total for Question 13 is 5 marks)
14
A solution of potassium hydroxide, KOH (Mr = 56), has a concentration of 2.0 mol/dm3.
(a)Calculate the concentration of this solution in g/dm3.(2)
(b)A different solution of potassium hydroxide has a concentration of 84 g/dm3. Calculate its concentration in mol/dm3.(2)
(Total for Question 14 is 4 marks)
15
Calcium carbonate decomposes on heating to form calcium oxide and carbon dioxide:
CaCO3 -> CaO + CO2
Mr: CaCO3 = 100, CaO = 56, CO2 = 44
The desired product of this reaction is calcium oxide.
(a)Calculate the atom economy for the production of calcium oxide. Give your answer to 1 decimal place.(3)
(b)A different method of making calcium oxide has an atom economy of 82%. Explain why a chemical company would prefer to use the method with the higher atom economy.(3)
(Total for Question 15 is 6 marks)
16
Magnesium reacts with excess dilute hydrochloric acid:
Mg + 2HCl -> MgCl2 + H2
Mr: Mg = 24, MgCl2 = 95
A student, Rhys, reacts 3.6 g of magnesium with excess acid and collects 13.8 g of magnesium chloride.
(a)Calculate the number of moles of magnesium used.(1)
(b)Use the equation to calculate the maximum (theoretical) mass of magnesium chloride that could be made.(3)
(c)Calculate the percentage yield of magnesium chloride obtained by the student.(2)
(Total for Question 16 is 6 marks)
17
At room temperature and pressure (rtp), the volume of one mole of any gas is 24 dm3.
Calcium carbonate reacts with excess dilute hydrochloric acid:
CaCO3 + 2HCl -> CaCl2 + H2O + CO2
Mr: CaCO3 = 100
A student reacts 5.0 g of calcium carbonate with excess dilute hydrochloric acid.
(a)State the volume occupied by one mole of any gas at rtp.(1)
(b)Calculate the number of moles of calcium carbonate used.(1)
(c)Use the equation to state the number of moles of carbon dioxide gas produced.(1)
(d)Calculate the volume of carbon dioxide gas produced at rtp, in dm3.(2)
(e)Calculate this volume in cm3.(1)
(Total for Question 17 is 6 marks)
18
A sample of hydrogen gas, H2 (Mr = 2), has a volume of 600 cm3 at rtp (molar volume = 24 dm3 at rtp).
(a)Calculate the number of moles of hydrogen gas in this sample.(2)
(b)Calculate the mass of hydrogen gas in this sample.(1)
(Total for Question 18 is 3 marks)
19
In a titration, 25.0 cm3 of sodium hydroxide solution of unknown concentration is pipetted into a conical flask with a few drops of phenolphthalein indicator. Dilute hydrochloric acid of concentration 0.100 mol/dm3 is added from a burette until the indicator just changes colour. The mean (concordant) titre of acid used is 22.50 cm3.
NaOH + HCl -> NaCl + H2O
Mr of NaOH = 40
(a)Calculate the number of moles of HCl used.(2)
(b)Use the equation to state the number of moles of NaOH that reacted.(1)
(c)Calculate the concentration of the sodium hydroxide solution, in mol/dm3.(2)
(d)Calculate the concentration of the sodium hydroxide solution in g/dm3.(2)
(Total for Question 19 is 7 marks)
20
A pharmaceutical company can manufacture ibuprofen using either Route 1 (six reaction steps, atom economy 40%) or Route 2 (three reaction steps, atom economy 77%). Both routes give a percentage yield of about 65%.
Evaluate the advantages of using Route 2 rather than Route 1 to manufacture ibuprofen.
(Total for Question 20 is 6 marks)
21
Sulfuric acid reacts with sodium hydroxide:
H2SO4 + 2NaOH -> Na2SO4 + 2H2O
In a titration, 20.0 cm3 of sodium hydroxide solution of concentration 0.500 mol/dm3 is exactly neutralised by 16.00 cm3 of dilute sulfuric acid.
(a)Calculate the number of moles of sodium hydroxide used.(2)
(b)Use the equation to calculate the number of moles of sulfuric acid that reacted.(1)
(c)Calculate the concentration of the sulfuric acid, in mol/dm3. Give your answer to 3 significant figures.(2)
(Total for Question 21 is 5 marks)
22
Excess magnesium ribbon is added to 50 cm3 of dilute hydrochloric acid of concentration 2.0 mol/dm3:
Mg + 2HCl -> MgCl2 + H2
(molar volume = 24 dm3 at rtp)
(a)Calculate the number of moles of HCl in the 50 cm3 of acid used.(2)
(b)Use the equation to calculate the number of moles of hydrogen gas produced.(1)
(c)Calculate the volume of hydrogen gas produced at rtp, in dm3.(2)
(Total for Question 22 is 5 marks)
Mark scheme · C3b Concentration, Yield and Atom Economy

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Question 12

Question 13

Question 14

Question 15

Question 16

Question 17

Question 18

Question 19

Question 20

Question 21

Question 22