www.cksciencetuition.com 1 How to use this booklet: Go back over some of the calculations topic if you need to: The videos I have provided will not go through every type of mole calculation but will instead focus on useful techniques for improving your confidence in calculations. Have a look at the list of different types of calculation in Section A and recap anything you think you have forgotten. Choose which questions you are going to try: • Section A: The Basics These questions are clearly labelled and give examples of the most common types of calculation encountered at A Level. There should be no sneaky surprises and they are there for you to build your confidence or as a reminder for some equations you may have forgotten. Written answers to these questions are at the back of the booklet to allow you to self-check. Timing – allow about one minute per mark • Section B: Applied Calculations These questions are more challenging, unstructured questions where you are given no extra clues. Pay attention to the marks awarded as they may guide you in the expected number of steps. Also pay attention to any requirement for units or significant figures. Timing – allow about one minute per mark • Section C: Multiple Choice Many students struggle with multiple choice calculation questions because they don’t write it down and work it out fully! Never leap to conclusions as all the alternative answers are deliberately designed to distract you. Timing – allow about 1.5 minutes per mark Complete the questions under exam conditions: Once you’ve chosen your questions, time yourself and don’t look at your notes! Even if you are struggling, try to stick to your resolve and provide answers that are as complete as possible in the time limit provided. Check your answers: Answers to Section A are provided at the end of the booklet with some working out to help you see if you made a mistake. Answers to Sections B and C will be given in video format to help talk through the calculations. Materials required: • Scientific calculator • A Level periodic table, with relative atomic mass values given to 1 decimal place Constants used: Avogadro’s constant, NA: 6.02 x 10 23 mol -1 Gas constant, R: 8.31 J mol -1 K -1
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www.cksciencetuition.com 1
How to use this booklet: Go back over some of the calculations topic if you need to: The videos I have provided
will not go through every type of mole calculation but will instead focus on useful
techniques for improving your confidence in calculations. Have a look at the list of
different types of calculation in Section A and recap anything you think you have
forgotten.
Choose which questions you are going to try:
• Section A: The Basics
These questions are clearly labelled and give examples of the most common types
of calculation encountered at A Level. There should be no sneaky surprises and
they are there for you to build your confidence or as a reminder for some equations
you may have forgotten. Written answers to these questions are at the back of the
booklet to allow you to self-check. Timing – allow about one minute per mark
• Section B: Applied Calculations
These questions are more challenging, unstructured questions where you are given
no extra clues. Pay attention to the marks awarded as they may guide you in the
expected number of steps. Also pay attention to any requirement for units or
significant figures. Timing – allow about one minute per mark
• Section C: Multiple Choice
Many students struggle with multiple choice calculation questions because they
don’t write it down and work it out fully! Never leap to conclusions as all the
alternative answers are deliberately designed to distract you. Timing – allow about
1.5 minutes per mark
Complete the questions under exam conditions: Once you’ve chosen your questions,
time yourself and don’t look at your notes! Even if you are struggling, try to stick to your
resolve and provide answers that are as complete as possible in the time limit provided.
Check your answers: Answers to Section A are provided at the end of the booklet with
some working out to help you see if you made a mistake. Answers to Sections B and C will
be given in video format to help talk through the calculations.
Materials required:
• Scientific calculator
• A Level periodic table, with relative atomic mass values given to 1 decimal place
Contents How to use this booklet: ........................................................................................................................ 1
Section A: Basic calculation practice – Total 50 marks ......................................................................... 3
A1. Moles, mass and molar mass ............................................................................................................ 3
A2. Gas volumes and the ideal gas equation .......................................................................................... 3
A3. Solution and concentration .............................................................................................................. 3
A4. Empirical formulae and calculations from experiments ................................................................... 3
A5. Percentage yield and atom economy ............................................................................................... 4
A6. Avogadro constant and non-standard units calculations ................................................................. 4
Section B: More complex calculations – Total 30 marks ...................................................................... 5
Section C: Multiple choice questions – Total 10 marks ........................................................................ 7
Answers to Section A: .......................................................................................................................... 10
A1. Moles, mass and molar mass .......................................................................................................... 10
A2. Gas volumes and the ideal gas equation ........................................................................................ 10
A3. Solution and concentration ............................................................................................................ 11
A4. Empirical formulae and calculations from experiments ................................................................. 11
A5. Percentage yield and atom economy ............................................................................................. 13
A6. Avogadro constant and non-standard units calculations ............................................................... 13
6. Fermentation is used to make ethanol. The equation for the reaction is as follows. The Mr values of each compound are also given. C6H12O6(aq) = 2C2H6O(aq) + 2CO2(g) Mr values: g mol-1 180 46 44
Which expression represents the atom economy for the reaction? A (2 x 46 + 2 x 44) x 100
180 B (2 x 46) x 100 180 C 46 x 100 180 D (2 x 44) x 100 180
7. 5 dm3 of carbon monoxide, CO(g), and 2 dm3 of oxygen, O2(g), at the same
temperature and pressure are mixed together. Assuming complete reaction
according to the equation given, what is the maximum volume of carbon dioxide in
dm3 that can be formed?
2CO (g) + O2 (g) → 2CO2
A. 3
B. 4
C. 5
D. 7
8. Which of the following solutions would react exactly with a solution containing
0.0500 mol sulfuric acid?
A. 50.0 cm3 of 1.00 mol dm−3 KOH
B. 100.0 cm3 of 2.00 mol dm−3 KOH
C. 100.0 cm3 of 2.00 mol dm−3 Ba(OH)2
D 50.0 cm3 of 1.00 mol dm−3 Ba(OH)2
9. A student is provided with a 5.00 cm3 sample of 1.00 × 10–2 mol dm–3 hydrochloric
acid. The student is asked to devise a method to prepare a hydrochloric acid
solution with a concentration of 5.00 × 10–4 mol dm–3 by diluting the sample with
water. Which of these is the correct volume of water that should be added?
A5. Percentage yield and atom economy a) A student produced some magnesium sulfate crystals, MgSO4.7H2O by reacting 1.20
g magnesium with a slight excess of sulfuric acid. After crystallisation the mass of
crystals collected was 9.84 g. Calculate the percentage yield of the reaction. (3)
Moles Mg = 1.2 / 24.3 = 0.0494
1 moles of Mg makes 1 mole of hydrated salt
Mr hydrated salt = 246.4
Maximum mass of hydrated salt = 0.0494 x 246.4 = 12.17 g
Percentage yield = 9.84 / 12.17 x 100 = 81 %
b) Titanium is manufactured by heating titanium (IV) chloride with magnesium (at
1200 °C) according to the following equation:
TiCl4 (g) + 2Mg (l) → Ti (s) + 2MgCl2 (l)
Calculate the atom economy of this process, and suggest one way in which the
atom economy can be improved. (3)
Ar Ti = 47.9 Total Mr products = 47.9 + (95.3 x 2) = 238.5 Atom economy = 47.9 / 238.5 x 100 = 20 % Ways to improve atom economy: Use a different, lighter metal such as lithium in place of magnesium, or find a use for the magnesium chloride so that both products are useful.
A6. Avogadro constant and non-standard units calculations Avogadro constant used in these calculations = 6.02 x 1023 mol-1. You are not required to
learn the Avogadro constant; therefore make sure that you use the value given to you in
the question or on your data sheet rather than memorising the value.
a) Calculate the number of hydrogen atoms in 1 g of water. (2)
moles water molecules = 1 / 18 = 0.0556
Number of water molecules = 0.0556 x 6.02 x 1023 = 3.34 x 1022
Number of hydrogen atoms = 3.34 x 1022 x 2 = 6.68 x 1022
b) How many nitrate ions are there in one drop of a 0.05 mol dm-3 solution of calcium
nitrate, Ca(NO3)2? (Assume one drop has a volume of 0.050 cm3.) (3)
moles calcium nitrate = 0.05 x (0.050/1000) = 2.5 x 10-6
Each mole of Ca(NO3)2 produces two moles of nitrate ions when dissolved so moles of
nitrate ions = 5.0 x 10-6
Number of nitrate ions = 5.0 x 10-6 x 6.02 x 1023 = 3.01 x 1013