Glossary for AS Level Chemistry
Module 1
Amount of Substance
Useful terms needed for A level chemistry
Avogrados Number (L)
1 mole of substance contains
6.023x 1023 particles
Empirical formula the simplest
whole number ratio of atoms present in
a molecule
Kelvin
A unit of temperature
OàC = 273 Kelvin
RAM (Ar)
The average mass of one atom
compared to the mass of one atom of
carbon-12
Ar = the average mass of an atom x12
The mass of 1 atom of carbon-12
Relative Molecular mass (Mr)
The average mass of a molecule
compared to the mass of one atom of
carbon-12
Mass = VM x Mr
Mass no. (n)
Sum of protons and neutrons
Mr= the average mass of an entity
The mass of 1 atom of carbon-12
Molarity (M)
The concentration in mol/dm3
Standard solution
A solution whose concentration is
known exactly
M=n x 1000
V
Molar mass
Mass of 1 mole of atoms
Also moles = VM
1000
Molar mass = mass of 1 atom x
Avogrados number
Molar Solution
Contains 1 mol dm-3
Number of moles can be calculated
Number of moles = mass in grams
Relative atomic mass
Mole
The working quantitative unit used in
calculations. One mole of substance is
the amount of that substance which can
contains as many particles as there are
atoms in exactly 12g of carbon 12
Molecular formula
A formula which shows actual number
of atoms present in a molecule
Pascal
A unit of pressure
n = m/Mr
Standard temperature and Pressure
Temperature =273 Kelvin, pressure =
100kpa
At STP a volume of gas occupies 22.4
dm3
Therefore 1 mole of gas occupies 22.4
dm3 at standard temperature and
pressure
Oxidation
A reaction in which the species looses
electrons
J McDougall
AS level Chemistry
Alfreton Grange College
1/4
Ideal Gas Equation
pV=nRT
pressure (Pascal’s)
Volume (m3)
Temperature (Kelvin)
R=8.31JK-1
Number of moles
Mr=mRT/pV
Shielding
The effect of the inner electrons
screening the outer electrons from the
nuclear charge
Volume = moles x 1000/Molarity
Oxidation state
The number of electrons of an atom
used in forming bonds
Moles = VM
In volumetric calculations
Species
A general term used to donate an atom,
an ion or molecule
Oxidising Agent
An electron pair acceptor
Mass =VM x Mr
Titration
Can be preformed to find the
concentration of a solution
Concentration of the solution is
calculated using molar ratios.
Reflux
A method of prolonged heating
Redox reaction
A reaction in which oxidation and
reduction occurs
Halogen
Any element in group 7
Reducing agent
An electron donor
Electro-negativity
A measure of the ability of an atom to
for attract a pair of electrons in a
covalent bond
Reduction
A reaction in which a species gains a
electron
Element
A substance that contains only those
atoms
Ionisation energy
The energy required to remove one
mole of electrons from one mole of
gaseous atoms.
Lone pair
A pair of electrons in the outer
occupied energy level which are not
involved in bonding.
Polar bond
A covalent bond in which the lone pair
are not shared equally
Transition metal
An element with a partially filled d
shell
Enthalpy change
The heat energy change in a reaction
occurring at constant pressure
Equilibrium
A reaction in which the rates of
forward and backward reaction are
equal
Hess Law
The enthalpy change in a reaction is
independent of the route of the reaction
J McDougall
AS level Chemistry
Alfreton Grange College
2/4
Co-ordinate bond (Dative Bond)
A covalent bond in which both
members of the pair of electrons are
provided by one of the atoms
Amount in moles of sodium hydroxide
= Volume (dm-3) x concentration (mol dm-3)
= 25.0 x 10-3 x 0.10= 2.5 x 10-4 mol
Covalent Bond
A bond formed by sharing of electrons
2) Find the number of moles of
hydrochloric acid that react with
sodium hydroxide
Ionic bond
The force of attraction between
opposite charged atoms
HCl (aq) + NaOH (aq)
Example calculations
Calculating moles from gas volume
How many moles of oxygen are there
in 500cm3 of gas at 25àCand at
100 KPa
NaCl (aq)+ H2O(l)
1 mol HCl reacts with 1 mol of NaOH
So 2.5 x 10-3 mol of HCl reacts with
2.5 x 10-3 of NaOH
3) Find the concentration of
hydrochloric acid
Concentration = mol dm-3 = mol/ dm-3
1) Convert the units to the units of
the ideal gas equation
100KPa = 100 000 Pa = p
500cm3 = 500 x 10-6 m3= V.
25àC = 298 K= T
= 2.5 x 10-4
19.8 x 10-3
2) rewrite the ideal gas equation
Calculating the volume of the acid
used in a titration
n= pV
RT
3) insert the values
n = 100 000 x 500 x 10-6
8.31 x 298
Moles of oxygen = 0.020 mol
Calculating the concentration of an
acid solution
3
In a titration, 25.0 cm of sodium
hydroxide solution is neutralised by
19.8 cm3 of hydrochloric acid.
1) Find the number of moles of
sodium hydroxide in 25.0 cm3
So concentration of hydrochloric acid
= 0.127 mol dm-3
Sodium carbonate is readily soluble
compound used as washing soda.
Calculate the volume of 0.1 M HCl
needed to react exactly with 25cm-3 of
0.22 M Sodium carbonate
2HCl + Na2CO3
2NaCl + CO2 +H2O
2 moles of HCl reacts with 1 mole of
Na2CO3
Volume of 0.1 M HCl that would react
with 25cm3 of 0.1 M Na2CO3 =50 cm3
Volume of 0.1 M HCl that reacts with
25 cm3 0.22 M Na2CO3
= 50 x0.22
0.1
= 110 cm-3
J McDougall
AS level Chemistry
Alfreton Grange College
3/4
Questions
The table shows the accurate masses of
two atoms
1
Mass/g
H
1.6734 x 10-24
12
C
1.9925 x 10-23
1.Calculate the accurate values for the
mass of one mole of each atom.
Avogrados number (L) is 6.0225 x
1023
2.Why is 12C referred to when defining
relative atomic mass of an element
3.In an experiment 1.54g of carbon
dioxide were produced and then
absorbed in 50cm3 of sodium
hydroxide solution forming sodium
carbonate. Calculate the molar
concentration of the sodium
carbonate in the solution.
4.Define the term relative atomic mass
5.The mass of one atom of 12C is 1.99
x 10-23 g. use this mass to calculate a
value for the Avogrados constant (L)
6.During fermentation using yeast 1.8
g of glucose (C6H12O6) can be
converted into 0.92 g of ethanol
(C2H6O) and 448cm3 of carbon
dioxide measured at STP
I.
Calculate the number of moles
of glucose used in the experiment
II.
Calculate the number of moles
of ethanol and carbon dioxide
produced in this experiment
7 Calculate the mass of helium needed
to fill a weather balloon which has a
volume of 120 dm3 at standard
pressure and a temperature of 18àC
8 Hydrated sodium carbonate
(Na2CO3 x H20) is sold commercially
as washing soda. A student carried out
an experiment to determine the value
of x which represents the number of
moles of crystallisation present in 1
mole of hydrated sodium carbonate.
The following method was used:2.995 g of hydrated sodium carbonate
were dissolved in water and the
solution made up exactly to 250cm3 in
a volumetric flask. 25cm3 samples of
this solution were measured by pipette
and titrated against a standard solution
of 0.113 M hydrochloric acid.
The average value of acid required to
completely neutralise the sodium
carbonate solution was 21.20 cm3
Given the equation for the reaction is
2HCl + Na2CO3
2NaCl + CO2 +H2O
I. Calculate the mass of sodium
carbonate in the sample using
the titration results
II. Using the answer from I above
and the original mass of
hydrated solution. Calculate
the value for x
A road tanker has crashed and 73kg of
pure HCl are spilling onto a motorway.
There are different methods to
neutralise the acid. The 1st was 5M
NaOH
I. Write an equation for the
reaction between hydrochloric
acid and sodium hydroxide
II. How many moles of acid are
there in 73Kg
III. What volume of sodium
hydroxide in dm3, is needed to
neutralise this amount of acid
J McDougall
AS level Chemistry
Alfreton Grange College
4/4