Edexcel iGCSE Chemistry
Experiment for Diffusion? - ANS 1) HCl placed at one end of the test tube, ammonia solution at the
other.
2) Where they meet, a ring of Ammonium Chloride appears.
3) The diagram shows that the ammonia is closer to the ring, showing that ammonia must have travelled
faster, showing it's a lighter gas.
Experiment for Dilution? - ANS 1) Put a coloured substance in a solvent e.g food colouring in water.
2) Over the time, the colour levels out but is weaker than the original solution- Dilution
3) More heat = more kinetic energy = happens faster, rate of dilution quicker.
What is filtration? - ANS Making a barrier which one component of a mixture can pass through but the
other is caught by.
What is distillation? - ANS When one substance is evaporated off while the other remains.
What is fractional distillation? - ANS A mixture is evaporated and rises up a tube. Different substances
have different boiling points and so will condense at different temperatures. As the mixture travels up
the tube, the temperature decreases, substances are collected at different places. Separates a mixture
into its different parts.
What is crystallisation? - ANS A solution is warmed, allowing the solvent to evaporate; the solution is
now left to cool and will form crystals.
What is chromotography? - ANS Chromotography paper is placed in a substance, the different
components of the substance will travel at different speeds due to the size of the particles.
,How can information from chromatograms be used to identify the composition of a mixture? - ANS
Chromotography paper is placed in a solvent- the different compounds will travel at different speeds
due to the size of their particles.
What is the atomic number? - ANS Number of protons (same as the number of electrons)
What is the atomic mass number? - ANS Number of neutrons & protons together
What are isotopes? - ANS Atoms of an element with the same number of protons but a different
number of neutrons
What is the RAM (relative atomic mass)? - ANS The mass of one atom of an element in relation to
Carbon
How do you work out the relative formula mass (Mr) from the relative atomic mass (RAM)? - ANS
(Number of that element in a molecule x its RAM) + (Number of other element in a molecule x its RAM)
Triangle for carrying out equations using Ar & Mr - ANS Moles (mol) = Mass (g) / RFM (Mr)
How do you work out moles for a gas? - ANS Moles = Mass (g) / 24,000 cm3 (24dm3)
Difference between a liquid (l) and an aqueous solution? - ANS An aqueous solution is a solid dissolved
in a liquid.
How can you obtain the formula of a simple compound experimentally? - ANS 1) Weigh your compound
of two elements.
2) Remove an element through a reaction. Weigh again. This gives you the individual mass of both
elements in the compound.
3) Work out the formulae by dividing the weight by its Ar.
,eg 22g with an Ar of 11 = 22/11 = 2
How to work out the empirical formula? - ANS 1) Find the masses of each element in a compound by
taking each element out and weighing.
2) Turn these masses into percentages of the compound.
3) Divide each % by the element's Ar & you will have the number of atoms of it in a molecule.
4) Put these values in the formula, giving you the *molecular formula*
5) To get the *empirical formula*, divide the values by their smallest factor.
eg C6.7H20 = Molecular
CH₃ = Empirical
Calculate reacting masses using experimental data and chemical equations? - ANS If we react 2 moles of
A(Ar=24) and 5 moles of B(Ar=25) we get 2x24 + 5x25 = 173g
Calculate percentage yield? - ANS % yield = actual yield/theoretical yield.
1) See how many moles of the reactant it takes to give the number of moles of the product eg Fe₂O₃ =
2Fe (one molecule of Iron Oxide gives two molecules or Iron)
2) Thus the mass of Fe will be my yield
3) If I am told the weight of Fe₂O₃ is 100g, I work out its moles (Mol = Mass/Mr) = Mol = 100/160 =
0.625mol
4) Because the molar ratio between Fe₂O₃ & 2Fe is 1:2, I multiply 0.625 by 2 = 1.25 mol
5) I then need to work out the theoretical mass of Fe using mass = mol x Mr = 1.25 x 56 = 70g
6) If I in fact got 82g, I divide 70 by 82 and put it over 100 = 85.4%
How do you work out the molar concentration? - ANS Concentration = Moles/Volume
, Why do electrons transfer from one atom to another? - ANS Electrons are transferred from one atom to
another in an attempt to fill or empty their outermost shell to become stable.
Describe the formation of ions - ANS An atom has no charge. If it loses or gains an electron it becomes
an ion and then has a charge. Losing an electron will give it a charge of +1, gaining an electron will give it
a charge of -1. If two ions meet with opposite charges, they are attracted to eachother and form an ionic
compound.
What is oxidation? - ANS Oxidation is when an atom loses an electron - OILRIG
It is also when there is a gain of oxygen
What is reduction? - ANS Reduction is when an atom gains an electron - OILRIG
It is also when oxygen is lost.
Name the 7 common cations. - ANS K⁺, Na⁺, Ca²⁺, Li⁺, H⁺, Mg²⁺, Al³⁺
Group 1 & 2 elements, Hydrogen & Aluminium
Name the 8 common anions - ANS Cl⁻, Br⁻, I⁻, F⁻, OH⁻, NO3⁻, CO₃²⁻, SO₄²⁻
The halogens, Sodium Hydroxide & OHNOCOSO
What is ionic bonding? - ANS It happens between 2 ions which are attracted to one another due to their
opposite attractions. Thus the ions have electrostatic attraction. The attraction makes an ionic bond.
Experiment for Diffusion? - ANS 1) HCl placed at one end of the test tube, ammonia solution at the
other.
2) Where they meet, a ring of Ammonium Chloride appears.
3) The diagram shows that the ammonia is closer to the ring, showing that ammonia must have travelled
faster, showing it's a lighter gas.
Experiment for Dilution? - ANS 1) Put a coloured substance in a solvent e.g food colouring in water.
2) Over the time, the colour levels out but is weaker than the original solution- Dilution
3) More heat = more kinetic energy = happens faster, rate of dilution quicker.
What is filtration? - ANS Making a barrier which one component of a mixture can pass through but the
other is caught by.
What is distillation? - ANS When one substance is evaporated off while the other remains.
What is fractional distillation? - ANS A mixture is evaporated and rises up a tube. Different substances
have different boiling points and so will condense at different temperatures. As the mixture travels up
the tube, the temperature decreases, substances are collected at different places. Separates a mixture
into its different parts.
What is crystallisation? - ANS A solution is warmed, allowing the solvent to evaporate; the solution is
now left to cool and will form crystals.
What is chromotography? - ANS Chromotography paper is placed in a substance, the different
components of the substance will travel at different speeds due to the size of the particles.
,How can information from chromatograms be used to identify the composition of a mixture? - ANS
Chromotography paper is placed in a solvent- the different compounds will travel at different speeds
due to the size of their particles.
What is the atomic number? - ANS Number of protons (same as the number of electrons)
What is the atomic mass number? - ANS Number of neutrons & protons together
What are isotopes? - ANS Atoms of an element with the same number of protons but a different
number of neutrons
What is the RAM (relative atomic mass)? - ANS The mass of one atom of an element in relation to
Carbon
How do you work out the relative formula mass (Mr) from the relative atomic mass (RAM)? - ANS
(Number of that element in a molecule x its RAM) + (Number of other element in a molecule x its RAM)
Triangle for carrying out equations using Ar & Mr - ANS Moles (mol) = Mass (g) / RFM (Mr)
How do you work out moles for a gas? - ANS Moles = Mass (g) / 24,000 cm3 (24dm3)
Difference between a liquid (l) and an aqueous solution? - ANS An aqueous solution is a solid dissolved
in a liquid.
How can you obtain the formula of a simple compound experimentally? - ANS 1) Weigh your compound
of two elements.
2) Remove an element through a reaction. Weigh again. This gives you the individual mass of both
elements in the compound.
3) Work out the formulae by dividing the weight by its Ar.
,eg 22g with an Ar of 11 = 22/11 = 2
How to work out the empirical formula? - ANS 1) Find the masses of each element in a compound by
taking each element out and weighing.
2) Turn these masses into percentages of the compound.
3) Divide each % by the element's Ar & you will have the number of atoms of it in a molecule.
4) Put these values in the formula, giving you the *molecular formula*
5) To get the *empirical formula*, divide the values by their smallest factor.
eg C6.7H20 = Molecular
CH₃ = Empirical
Calculate reacting masses using experimental data and chemical equations? - ANS If we react 2 moles of
A(Ar=24) and 5 moles of B(Ar=25) we get 2x24 + 5x25 = 173g
Calculate percentage yield? - ANS % yield = actual yield/theoretical yield.
1) See how many moles of the reactant it takes to give the number of moles of the product eg Fe₂O₃ =
2Fe (one molecule of Iron Oxide gives two molecules or Iron)
2) Thus the mass of Fe will be my yield
3) If I am told the weight of Fe₂O₃ is 100g, I work out its moles (Mol = Mass/Mr) = Mol = 100/160 =
0.625mol
4) Because the molar ratio between Fe₂O₃ & 2Fe is 1:2, I multiply 0.625 by 2 = 1.25 mol
5) I then need to work out the theoretical mass of Fe using mass = mol x Mr = 1.25 x 56 = 70g
6) If I in fact got 82g, I divide 70 by 82 and put it over 100 = 85.4%
How do you work out the molar concentration? - ANS Concentration = Moles/Volume
, Why do electrons transfer from one atom to another? - ANS Electrons are transferred from one atom to
another in an attempt to fill or empty their outermost shell to become stable.
Describe the formation of ions - ANS An atom has no charge. If it loses or gains an electron it becomes
an ion and then has a charge. Losing an electron will give it a charge of +1, gaining an electron will give it
a charge of -1. If two ions meet with opposite charges, they are attracted to eachother and form an ionic
compound.
What is oxidation? - ANS Oxidation is when an atom loses an electron - OILRIG
It is also when there is a gain of oxygen
What is reduction? - ANS Reduction is when an atom gains an electron - OILRIG
It is also when oxygen is lost.
Name the 7 common cations. - ANS K⁺, Na⁺, Ca²⁺, Li⁺, H⁺, Mg²⁺, Al³⁺
Group 1 & 2 elements, Hydrogen & Aluminium
Name the 8 common anions - ANS Cl⁻, Br⁻, I⁻, F⁻, OH⁻, NO3⁻, CO₃²⁻, SO₄²⁻
The halogens, Sodium Hydroxide & OHNOCOSO
What is ionic bonding? - ANS It happens between 2 ions which are attracted to one another due to their
opposite attractions. Thus the ions have electrostatic attraction. The attraction makes an ionic bond.
