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A-LEVEL CHEMISTRYIntroduction Some (but not all) students find the transition from GCSE to A-level Chemistry very challenging at first. This is because the topics we study at the beginning of the course are heavily mathematical and involve a significant jump in complexity from what you have studied at GCSE. To help make this transition smoother, we have prepared this booklet for you. Please try to complete all of the questions in each task. Some tasks can be completed on the sheets themselves, others will need to be done on lined paper. For each task, you have been given some webpages and videos which can help. The CGP book, Headstart to A-level Chemistry, is specifically designed to help bridge the gap between GCSE and A-level. It contains explanations of the relevant concepts, worked examples and some questions. Therefore, I have suggested some follow-up activities from the CGP book which you could complete after finishing each task in this booklet. Purchasing this book and completing the recommended questions would be useful additional preparation for the A-level course – it is not compulsory or essential to do so however. Further details on where to purchase this book can be found in the further reading section at the end of this booklet.
Schedule and Tasks This is just a suggested schedule - you do not have to complete all the tasks during the precise weeks that I have specified! The general idea however is to complete these tasks towards the end of your summer holiday so that you arrive at Strode with the knowledge and skills covered in this booklet fresh in your minds.
Week Task Title Follow up questions from the Head Start A-Level Chemistry Book
1 (w/b 9th August)
The structure of atoms P1Q1-3 P2Q1-3
The mass spectrometer P3Q1-3
2 (w/b 16th August)
Writing formulae P7 Q1-3
Writing Chemical equations P19Q1-3
Relative formula mass P3Q4-5
3 (w/b 23rd August)
Task 7 The mole P37Q1-3
Task 8 Moles and Equations
Task 9 Empirical and molecular formulae P38Q1-2 P39Q1-3
Task 10 Percentage Yields 4 (w/b 30th August) Additional
task a Royal Society of Chemistry: Starters for 10: chemistry, mathematical and practical competencies online tasks – see online resources section at the end of this booklet
P43Q1 P44Q1 P45Q1
Additional task b
Further useful sections from the Headstart Book
P8Q1-3 P11Q1-2 P12Q1-2 P13Q1 P14Q1-2 P22Q1-2
Task 1: The structure of atoms
and videos 7+8 from the MacChem Guy playlist to help with this task. https://www.youtube.com/playlist?app=desktop&list=PLi6oabjl6coxUlfu8syK3K0iFXQIjwDUM
In this task, you can write all your answers on the question sheets.
1 Complete the blanks:
Atoms consist of a central ______________ containing protons and _______________ .
The nucleus is surrounded by __________________ which are found in different energy
levels (also called ___ ). Atoms have no charge because they contain
equal numbers of protons and
3. Atomic number = number of .
Mass number = number of + number of .
Number of protons = ___
Number of neutrons = ___
Number of electrons = __
4. Complete the blanks:
Atoms of the same element always have the same number of _______ (e.g. all atoms with six protons are
___________ atoms). Atoms of different elements have different numbers of ______________ .
Isotopes are atoms of the same element. They contain the same number of ______________ but a different
number of _________________ .
5 Complete the table below containing data on some atoms.
number Mass number
Number of protons
Number of neutrons
Number of electrons
6 Complete the table below containing data on some ions:
number Mass number
Number of protons
Number of neutrons
Number of electrons
19 20 18
13 14 10
17 20 18
Task 2: The Mass Spectrometer Isotopes are atoms of the same element that have different numbers of neutrons. Hydrogen has 3 isotopes;
Isotopes occur naturally, so in a sample of an element you will have a mixture of these isotopes. We can accurately measure the amount of an isotope using a mass spectrometer.
To learn about a mass spectrometer, firstly watch this video:
https://www.youtube.com/watch?v=tOGM2gOHKPc (watch from 0-3.45 mins only)
The five processes that take place in a mass spectrometer can be summarised as:
VAPOURISATION IONISATION ACCELERATION DEFLECTION DETECTION
Answer these questions on lined paper. Use the following websites to help:
https://www.chemguide.co.uk/analysis/masspec/howitworks.html#top (q1-3) https://www.chemguide.co.uk/analysis/masspec/elements.html#top (q4) or https://www.bbc.co.uk/bitesize/guides/z3sg2nb/revision/6 (q4)
and video 10 from the MacChem Guy playlist. https://www.youtube.com/playlist?app=desktop&list=PLi6oabjl6coxUlfu8syK3K0iFXQIjwDUM
Q1 Why must the sample be vapourised?
Q2. (a) How are the atoms ionised?
(b) Why is it necessary to turn them into ions?
Q3. Explain why the different isotopes are deflected by different amounts in a mass spectrometer.
A mass spectrum for the element chlorine will give a spectrum like this: 75% of the sample consist of chlorine-35, and 25% of the sample is chlorine-37. We can calculate what the mean mass of the sample will be: Mean mass = 75 x 35 + 25 x 37 = 35.5 100 100
If you look at a periodic table this is why chlorine has an atomic mass of 35.5.
Given the percentage of each isotope you can calculate the accurate atomic mass (or relative atomic mass) for that element. Q4. Use the percentages of each isotope to calculate the accurate atomic mass of the following elements.
a) Gallium has 2 isotopes: 60.2% Ga-69 and 39.8% Ga-71 b) Thallium consists of 29.5% Tl-203 and 70.5% Tl-205. c) Strontium has 4 isotopes: 0.56%Sr-84, 9.86% Sr-86, 7.02% Sr-87 and 82.56% Sr-88
Task 3: Writing formulae
Simple ions Sodium Na+
Potassium K+ Calcium Ca2+
Transition metal ions Copper Copper (I) Cu+
Copper (II) Cu2+ Iron Iron (II) Fe2+
Iron (III) Fe3+
Zinc Zinc Zn2+
Complex ions Ion Charge Ammonium NH4
1. Use the tables shown above to write the formula of the following ionic compounds. You can also use
these websites for help: https://www.bbc.co.uk/bitesize/guides/zg6bmsg/revision/2
MacChem Guy video 6 https://www.youtube.com/playlist?app=desktop&list=PLi6oabjl6coxUlfu8syK3K0iFXQIjwDUM
Answer the questions on lined paper.
(a) potassium iodide (b) sodium oxide (c) aluminium bromide
(d) magnesium chloride (e) iron (II) oxide (f) iron (III) oxide
(g) calcium sulfide (h) copper (I) chloride (i) potassium fluoride
(j) sodium nitrate (k) calcium hydroxide (l) potassium sulphate
(k) magnesium nitrate (l) calcium carbonate (m) ammonium sulphate
Task 4: Balancing equations
Use this webpage if you need help: https://www.bbc.co.uk/bitesize/guides/zg6bmsg/revision/3 Or this video tutorial: https://www.youtube.com/watch?v=eNsVaUCzvLA Balance the following equations: (complete this task on the sheet)
a. H2 + 02 H20
b. S + 02 S03
c. HgO Hg + 02
d. Zn + HCl ZnCl2 + H2
e. Na + H20 NaOH + H2
f. Fe + 02 Fe203
g. C6H14 + 02 C02 + H20
h. Al + FeO Al2O3 + Fe
i. Br2 + KI → KBr + I2
Task 5: Writing chemical equations
Write chemical equations for the following reactions taking place(write your answers below each question). You will first need to convert the names of the materials into formulae and then balance the equation.
1. magnesium metal reacts with copper(II) sulphate solution to produce solid copper
metal and magnesium sulphate solution.
2. Solid calcium hydroxide reacts with solid ammonium chloride on heating to produce solid calcium chloride, steam and ammonia gas.
3. When octane (C8H18) is burned with excess air carbon dioxide and water vapour are produced.
4. Calcium metal reacting with phosphoric acid(H3PO4) to form calcium phosphate solution and hydrogen gas
Task 6: Relative Formula mass
Element Ar Element Ar Element Ar
aluminium Al 27 Hydrogen H
1 Phosphorus P
bromine Br 79.9 Iodine I 126.9 Potassium K
calcium Ca 40.1 Iron Fe 55.8 Silver Ag 107.9
carbon C 12 Magnesium Mg
24.3 Sodium Na
chlorine Cl 35.5 Nitrogen N 14 Sulphur S 32.1
copper Cu 63.5 Oxygen O 16 Zinc Zn 65.4
fluorine F 19
1. Calculate the relative formula mass of the following substances You will need to use the relative atomic masses (Ar) shown above. Use this webpage to help: https://www.bbc.co.uk/bitesize/guides/zgcyw6f/revision/1 Write your answers on this sheet:
(a) Mg(OH)2 (b) Ca(HCO3)2
(c) (NH4)2SO4 (d) C2H5COOH
Task 7: THE MOLE
Example 1: Calculation of the number of moles of material in a given mass of that material NUMBER OF MOLES = MASS MOLAR MASS Eg Calculate the number of moles of chlorine in 17.75 g of chlorine gas Cl2. The first stage of this calculation is to calculate the molar mass of chlorine molecules. Molar mass of Cl2 = 2 x 35.5 = 71 g number of moles of chlorine = 17.75 = 0.25 moles
71 Example 2: Calculation of the mass of material in a given number of moles of that material MASS OF SUBSTANCE = NUMBER OF MOLES X MOLAR MASS Eg Calculate the mass of 3 moles of sulfur dioxide SO2. 1 mole of sulfur dioxide has a mass = 32.1 + (2 x 16) = 64.1 g mol−1 ∴ 3 moles of SO2 = 3 x 64.1 = 192.3 g QUESTIONS Use https://www.bbc.co.uk/bitesize/guides/z24xcj6/revision/2 to help (it has a useful video on p1 and some examples and explanations on p2-3).
Answer q1 on lined paper but complete q2 on this sheet.
1. (a) How many moles are in 85.2g of phosphorus pentoxide (P2O5)? (b) How many moles in 73.56g of potassium chlorate (V) (KClO3)? (c) What is the mass of 0.125 moles of tin sulfate (SnSO4)? (d) What is the mass of 0.040 moles of Na2S2O3 (e) 0.05 moles of a substance has a mass of 4g. What is its molar mass?
2. Complete the blank parts of the following table (except the greyed out boxes).
Substance Formula Mr Mass Moles
carbon monoxide CO 560 g
propane C3H8 0.2
0.104 g 0.0005
methane CH4 6 kg
sodium Na2CO3 2.5
0.1 g 0.0025
Task 8: Moles and Equations Now that you can balance chemical equations and calculate numbers of moles, we need to use both skills to work out masses of chemicals involved in reactions.
For example: magnesium + sulfur magnesium sulfide Mg + S MgS
We can see that one atom of magnesium will react with one atom of sulfur. From the periodic table: Mg = 24.3 and S = 32.1 If I weigh out exactly 24.3g of magnesium this will be 1 mole of magnesium, if I weigh out 32.1g of sulfur then I would have 1 mole of sulfur atoms. So 24.3g of Mg will react precisely with 32.1g of sulfur, and will make 56.4g of magnesium sulfide.
For further guidance, see this webpage: https://www.bbc.co.uk/bitesize/guides/z3kg2nb/revision/4
and video 19 from the MacChem Guy playlist: https://www.youtube.com/playlist?app=desktop&list=PLi6oabjl6coxUlfu8syK3K0iFXQIjwDUM
Questions (answer on lined paper)
Q1. 2Mg +O2 MgO
(a) If I have 2.4g of magnesium, what mass of oxygen(O2) will I need to react completely with the magnesium?
(b) What mass of magnesium oxide will be formed?
2. Al + Fe2O3 Fe + Al2O3
(a) Balance the equation (b) If I have 150g of iron oxide, what mass of aluminium will I need to react completely
with this? (c) What mass of aluminium oxide will be formed?
3. K2CO3 + HCl → KCl + H2O + CO2
(a) Balance the equation (b) If I react 5g of potassium, carbonate with ex cess HCl, what mass of potassium chloride will be formed
(b) What mass of carbon dioxide will be formed? (c) If one mole of carbon dioxide occupies 24000cm3, what volume of carbon dioxide
will be formed?
Task 9: Empirical and molecular formulae The empirical formula shows the simplest whole number ratio of the atoms of each element present in a compound. The molecular formula shows the actual number of atoms of each element present in a compound – i.e. it is the ‘real formula’. For some compounds, the empirical formula and molecular formula, will be the same- but not for all. For example: COMPOUND MOLECULAR FORMULA EMPIRICAL FORMULA Carbon dioxide CO2 CO2 Methane CH4 CH4 Hexane C6H14 C3H7 Ethanoic acid C2H4O2 CH2O Phosphorus oxide
The empirical formula is usually calculated from data showing the % composition of each element present in a compound - or the masses of each element present in a compound. If you also have the molar mass of the compound, you can then calculate it’s molecular formula too. The method used for the calculations can be found here: https://www.bbc.co.uk/bitesize/guides/z8d2bk7/revision/4 The method is the same whether you are given % data or mass data. If you’re given % data, in step 4, you simply divide the % by the Ar instead of the mass by the Ar QUESTIONS (do these on lined paper please)
1 Find the empirical formula of each of the following substances
(a) H 5%, F 95%
(b) Na 3.71g, O 1.29 g
(c) Pb 90.7%, O 9.3%
(d) C 60.0%, H 13.3%, O 26.7%
2. Analysis of a compound consisting of carbon, hydrogen and oxygen showed it to contain 0.273g C, 0.046 g H and 0.182 g O.
It has a relative molecular mass (Mr) of 88.
(a) Calculate the empirical formula of the compound. (b) Calculate the molecular formula of the compound.
Task 10: Percentage Yields Use https://www.bbc.co.uk/bitesize/guides/z8wkh39/revision/2 and video 20 from the MacChem Guy playlist to help with this task:
https://www.youtube.com/playlist?app=desktop&list=PLi6oabjl6coxUlfu8syK3K0iFXQIjwDUM Answer the questions on this sheet
1 The equation for the thermal decomposition of limestone is: CaCO3 CaO + CO2
a Calculate the theoretical mass of calcium oxide that can be made by heating 500 g of
b In the reaction, only 261 g of calcium oxide was produced. Calculate the percentage yield.
2 Hydrazine (N2H4) is used as rocket fuel. It is made by the reaction of ammonia (NH3) with sodium chlorate (NaOCl)
ammonia + sodium chlorate hydrazine + sodium chloride + water
2 NH3 + NaOCl N2H4 + NaCl + H2O
a Calculate the theoretical mass of hydrazine that can be made by reacting 5100 g of ammonia with an excess of sodium chlorate.
b In the reaction, only 4200 g of hydrazine was produced. Calculate the percentage yield.
Head Start Book The CGP book, Headstart to A-level Chemistry, contains questions and explanations on a variety of topics and is specifically designed to bridge the gap between GCSE and A-level. You can purchase the paperback book from Amazon for £4.95 – or the Kindle version for £4.70 Link to amazon webpage: https://www.amazon.co.uk/Head-Start-level-Chemistry-Level-ebook/dp/B00VE2NIGG/ref=sr_1_2?dchild=1&keywords=Head+start+Chemistry&qid=1587483366&s=digital-text&sr=1-2 Reading and completing the questions from the recommended sections of this book would be useful additional preparation for the A-level course – it is not essential or compulsory however.
The further books below are suggested as they are just very interesting reads explaining the significance of Chemistry and the elements to the wider world. Reading these is not compulsory or essential.
Periodic Tales: The Curious Lives of the Elements Hugh Aldersey-Williams
This book covers the elements: where they come from and how they are used. There are loads of fascinating insights into uses for chemicals you would never even thought about.
The Disappearing spoon (and other extraordinary true tales from the Periodic Table) Sam Kean The tales in this book describes how many elements have played their parts in human history, finance, mythology, conflict, the arts, medicine and the lives of the scientists who discovered them. Online Resources Royal Society of Chemistry: Starters for 10: chemistry, mathematical and practical competencies https://edu.rsc.org/resources/basic-chemistry-competencies-starters-16-18/4010256.article
This is a great resource to both make students aware of the competencies they need to carry through into A Level Chemistry and give them some opportunities to practise these skills.
The resource comes in three sections. The first section, basic chemistry competencies, covers balancing equations, writing ionic equations, and writing chemical equations from text. The second resource, basic mathematical competencies, includes some practice of general mathematical skills and unit conversions, before drilling down into calculations involving moles, mass, and concentrations. The third resource, basic practical competencies, covers lab equipment that students should be familiar with, as well as good practice in recording results and plotting graphs.