transition pack for a level...

Rednock School Science Department.

You will be tested on this material in the week beginning 12th September 2016 1

Transition Pack

for A Level

Chemistry

A guide to help you get ready for A-level Chemistry.



This booklet contains background reading materials, links to useful websites, activities and

resources to prepare you to start an A level in Chemistry in September. It is aimed to be used

after you complete your GCSE, throughout the remainder of the summer term and over the

Summer Holidays to ensure you are ready to start your course in September.

Book Recommendations

Periodic Tales: The Curious Lives of the Elements (Paperback) Hugh Aldersey-Williams

ISBN-10: 0141041455

http://bit.ly/pixlchembook1

This book covers the chemical elements, where they come from and how they are used.

There are loads of fascinating insights into uses for chemicals you would have never

even thought about.

The Science of Everyday Life: Why Teapots Dribble, Toast Burns and Light Bulbs Shine (Hardback) Marty

Jopson

ISBN-10: 1782434186


The title says it all really, lots of interesting stuff about the things around you home!

Calculations in AS/A Level Chemistry (Paperback) Jim Clark (HIGHLY RECOMMENDED)

ISBN-10: 0582411270


If you struggle with the calculations side of chemistry, this is the book for you. Covers

all the possible calculations you are ever likely to come across. Brought to you by the

same guy who wrote the excellent chemguide.co.uk website.






30 Definitions you need to Learn

Word Definition

Acid A species that releases H+ ions in aqueous solution.

Alkali A type of base that dissolves in water forming OH-

(aq) ions.

Anhydrous Containing no water molecules.

Aqueous Substance dissolved in water

Avagadro’s constant The number of atoms per mole of the Carbon-12 isotope. (6.02x1023 mol-1)

Base A compound that neutralises an acid to form a salt.

Bonded pair A pair of electrons shared between two atoms to form a covalent bond.

Concentration The amount of solute, in moles, dissolved in 1dm3 of solution.

Covalent bond The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

Dative covalent (coordinate bond) A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only.

Dipole A separation in electrical charge so that one atom of a polar covalent bond, or one end of a polar molecule, has a small positive charge δ+ and the other has a small negative charge δ-.

Empirical formula The formula that shows the simplest whole-number ratio of atoms of each element present in a compound.

First Ionisation Energy The energy required to remove one electron from each atom in mole mole of gaseous atoms of an element to form one mole of gaseous 1+ ions.

Hydrated A crystalline compound containing water molecules.

Hydrocarbon A compound of Hydrogen and Carbon only.

Intermolecular force An attractive force between molecules. Intermolecular forces can be London forces, permanent dipole-dipole interactions or hydrogen bonding.

Ionic bonding The electrostatic attraction between positive and negative ions.

Isotopes Atoms of the same element with different numbers of neutrons and different masses.



Lone pair An outer shell pair of electrons that in not involved in chemical bonding.

Metallic bond The electrostatic attraction between positive metal ions and delocalised electrons.

Mass number The sum of the protons and neutrons in the nucleus – also referred to as Nucleon number.

Mole The amount of any substance containing as many elementary particles as there are carbon atoms in exactly 12g of the Carbon-12 isotope, which is 6.02 x 1023 particles.

Neutralisation A chemical reaction in which an acid and base react together to form a salt.

Oxidation Loss of electrons or an increase in oxidation number (also addition of oxygen)

Redox reaction A reaction involving reduction and oxidation.

Reduction Gain of electrons or a decrease in oxidation number (also loss of oxygen)

Relative atomic mass The weighted mean mass of an atom of an element compared with one twelfth of the mass of an atom of Carbon-12.

Relative Isotopic mass The mass of an atom of an isotope compared with one twelfth of the mass of an atom of Carbon-12.

Salt The product of a reaction in which the H+ ions from the acid are replaced by metal or ammonium ions

Saturated Containing single bonds only.

Unsaturated Containing a multiple carbon-carbon bond.



Brushing up your GCSE knowledge

Many of the topics we cover below will be familiar to you from GCSE but at A level you need

to be able to apply your knowledge quickly and so the following sections are to help you

boost your existing knowledge and to allow you to tackle exam questions of these types

without worry.

Chemical Formula

Table of common ions.

1+

1- 2+ 2- 3+

Lithium Li+ Chloride Cl- Magnesium Mg2+

Sulphate SO42- Aluminium

Al3+

Sodium Na+ Bromide Br- Calcium Ca2+ Carbonate CO3

2-

Iron III Fe3+

Potassium K+

Iodide I- Zinc Zn2+ Oxide O2-

Silver Ag+

Hydroxide OH- Copper Cu2+ Sulphide S2-

Ammonium NH4

+

Nitrate NO3- Lead Pb2+

Hydrogen H+

Hydrogencarbonate HCO3

-

Iron II Fe2+

Writing a chemical formula – the rules

Ionic compounds are neutral, so the number of positively charged ions and negatively charged ions in a formula must always be equal.

Charges are never written in a chemical formula

The number of ions in a formula is written after the symbol and below the line, eg. MgCl2 is made of 1 Mg ion and 2 Cl ions.

Some ions contain more than one atom, such as NO3-. If you more than one of these

ions in a formula, brackets must be used, eg. (NO3)2



Now use these rules to work out the formulae of the following compounds

Balancing equations

Balancing chemical equations is the stepping stone to using equations to calculate masses in chemistry. The

guidelines are:

Calculate how many atoms of each type of are on either side of the equation

If it is the same then it is balanced – job done.

If it is not the same then the quantities of each part of the equation may need to be changed to make

them balance. You can only change quantities by using a large number in front of the reactant or

product and NOT small subscript numbers in the formula as the FORMULA MUST stay the SAME. (start

with the elements that are not balanced first but remember you change the quantity of every atom in

the molecule)

Keep doing this until the numbers of each type of atom are the same on either side

Check and make sure that these numbers are the smallest ratio they can be.

NB – Atoms cannot be created or destroyed so what you have at the beginning, you must have at the end.



Beginner level



Intermediate Level



Challenge



The MOLE

Counting atoms and molecules

Chemists are able to count atoms and molecules of different elements and compounds by weighing them. This is because atoms of different elements have different masses. We call the mass of an atom, the relative atomic mass, Ar. This is defined as the average mass of all the atoms of an element relative to the mass of the carbon-12 isotope which is given exactly the mass of 12.

The mole is a number. It is equal to the number of atoms in 12g of the carbon 12 isotope. All relative atomic and molecular masses are compared to the mass of the carbon 12 isotope. So for all atoms and molecules, the atomic/molecular mass in grams always contains 1 mole of particles. This mass is often referred to as the molar mass, relative atomic mass or relative molecular mass. The number of particles in one mole of a substance is called Avogadro’s Constant and is equal to 6 x 1023. Equal numbers of moles always contain the same number of particles and so the mole can be used as a link between chemical equations showing number of particles (stoichiometry) and reacting quantities (ie. masses of substances). The link between mass and number of moles can be written as: n = m m n = number of moles Mr n Mr m = mass in grams (g) Mr = relative molecular mass Let’s start of simply – Formula mass Work out the formula mass of the following:



Moles calculations

Exercise 1

Calculate the number of moles in the following:

Exercise 2

Calculate the mass of the following:



Reacting Masses

Try using what you know about moles to answer the following questions.



Reacting masses – Challenge

Try these as a bit more of a challenge:



Percentage Yields

Percentage Yield Calculations

We have seen how to work out how much product should be produced in a reaction using

relative molecular mass (mole) calculations. This is called the theoretical yield. In reality,

some product is always lost during the process of making the product so we never actually

get the full amount. The amount of product actually made in an experiment is called the

actual yield. We can calculate the actual yield as a percentage of the theoretical yield as

follows:

Percentage yield = actual yield x 100

theoretical yield

Now try these:



Percentage composition


Sometimes the mass of an element in a compound can be given as a percentage. This can be

worked out quite easily.

Example.

Calculate the % by mass of magnesium and oxygen in Magnesium Oxide.

[Ar (Mg) = 24, Ar (O) = 16]

(i) First work out the Relative molecular mass of Magnesium oxide

MgO Mr = 24 + 16 = 40

(ii) Next, work out how much of the total relative formula mass of the compound comes from each element

Total mass = 40

Mass of magnesium = 24

Mass of oxygen = 16

(iii) Now, work out for each element the fraction of the total mass of the compound as a percentage:

% composition = Mass of element x 100

Total mass of compound

So for Magnesium Oxide (MgO)

Magnesium = ( 24/40 ) x 100 = 60%

Oxygen = ( 16/40 ) x 100 = 40%



Now try these:

Empirical Formula

Calculating empirical and molecular formula using composition by mass. Analysis of compounds will give the composition of the constituent elements by mass. To find the simplest ratio of the different elements, the different atomic masses have to be taken into account. Example: A hydrocarbon was found to have a molecular mass of 58 and to contain 82.76% carbon by mass. The following steps find

the number of moles of the different elements (=mass/molar mass.) this is then used to find the ratio of different elements by dividing by the smallest value a whole number ratio is then obtained. (It may be necessary to multiply all the values obtained by another number to obtain a whole number ratio. If 0.2, 0.4, 0.6 appears, multiply all by 5, if 0.25 or 0.75 appears, multiply all by 4, if 0.33 or 0.66 appears multiply all by 3, and if 0.5 appears multiply all by 2)

The mass of the empirical formula is compared with the molecular mass to determine how

many empirical formulae make up the molecular formula. The molecular formula is then derived.

Element Analysis Ar n=m/M Ratio Whole number ratio

Carbon 82.76% 12.0 82.76/12.0 = 6.90

6.90/6.90 = 1.0

2

Hydrogen 100-82.76 = 17.24%

1.0 17.24/1.0 = 17.24

17.24/6.90 = 2.5

5

Empirical formula = C2H5 Mass = (2x12) + (5x1) = 29 Number of empirical formulae in the molecular formula = 58/29 = 2 Therefore, molecular formula = 2 x empirical formula = C4H10



Try these ratio questions:

Empirical formula:



Do you know your Salt?

At A level we expect you to know the 4 reactions of acids that produce salts. In the space

below, write out the general word equations for these reactions and then add an example

of a specific reaction with an acid to get the salt.

+

+ +

+ +

+ +



Places to visit

1. Go outdoors!

Have you actually spent any time observing the geology of the area you live in? What rocks or

minerals are found in your area? Does your area have a history of extracting minerals? If so what

were they, what were they used for, how did they obtain them? Are there any working or remains of

mineral extraction industries?

2. Are there any chemical or chemistry based businesses in your area? A big ask, but one that could be

really beneficial to you, write them a letter explaining that you are taking A level chemistry and you

want to see how chemistry is used in industry and you would like to visit / have some work

experience. You never know this could lead to great things!!!!

3. You could also try writing to / searching for your nearest university to see if they are running any

summer schools for chemistry – they are usually free and give you the opportunity to experience the

laboratories in a university.

4. Science museums.

You could visit your nearest science museum. They often have special exhibitions that may be of

interest to you.

https://en.wikipedia.org/wiki/List_of_science_museums#United_Kingdom

5. Somerset Earth Science Centre:

http://www.earthsciencecentre.org.uk

6. The UK Association for Science and Discovery Centres (ASDC) This association brings together over 60 major science engagement organisations in the UK. http://sciencecentres.org.uk/centres/weblinks.php

7. Chemguide

www.chemguide.co.uk

8. Doc Brown’s http://www.docbrown.info/

9. Knock Hardy www.knockhardy.org.uk

https://en.wikipedia.org/wiki/List_of_science_museums#United_Kingdom

http://www.earthsciencecentre.org.uk/

http://sciencecentres.org.uk/centres/weblinks.php

http://www.chemguide.co.uk/

http://www.docbrown.info/

http://www.knockhardy.org.uk/



Chemical formula

Beginners



Intermediate



Challenge



Formula mass

Moles

Exercise 1

Exercise 2



Reacting masses

Reacting masses –Challenge

Percentage Yields




Ratios

a) 5:2 b) 4:3 c) 3:8 d) 3:2 e) 5:3 f) 2:5 g) 5:3 h) 7:4

Empirical formula

a) NH3 b) C2H5 c) Al2O3 d) NaHCO3 e) H3PO4 f) Na2CO3

Do you know your salt?

transition pack for a level...

Documents