AS Chemistry Paper 1

State and explain the trend in electronegativity of halogens as you go down the group.

As you go down the group, the electronegativity decreases, as the atoms get bigger, meaning there is more shielding between the nucleus and the electrons in the covalent bond, meaning the electrostatic attraction between them is weaker

State and explain the trend in boiling points of halogens as you go down the group.

As you go down the group, the boiling points increase, as the atoms get bigger, so the van der waals forces get stronger and take more energy to break

State and explain the trend in oxidising ability of group 7 elements.

As you go down the group, the oxidising ability of the halogen decreases, as their ability to attract electrons decreases due to more shielding and greater atomic radius

State the trend in displacement reactions of the halogens.

Each halogen will displace a halogen below it in the periodic table

State and explain the trend in reducing ability of halide ions.

As you go down the group, reducing ability increases, as electrons are easier to lose from larger atoms due to greater shielding and atomic radius

State the equation for the reaction of sodium fluoride with sulfuric acid.

NaF + H₂SO₄ —> NaHSO₄ + HF

State the equation for the reaction of sodium chloride with sulfuric acid.

NaCl + H₂SO₄ —→ NaHSO₄ + HCl

State the equations for the reactions of sodium bromide with sulfuric acid.

NaBr + H₂SO₄ —→ NaHSO₄ + HBr

2HBr + H₂SO₄ —→ Br + SO₂ + 2H₂O

State the equations for the reaction of sodium iodide with sulfuric acid.

NaI + H₂SO₄ —→ NaHSO₄ + HI

2HI + H₂SO₄ —→ I₂ + SO₂ + 2H₂O

6HI + SO₂ —→ H₂S + 3I₂ + 2H₂O

Describe how to test for halide ions.

1. Add a few drops of nitric acid to remove impurities

2. Add a few drops of silver nitrate and note the colour of the precipitate produced

3. Add dilute NH₃ and if the precipitate dissolved, chloride ions were present

4. If it does not dissolve, add concentrated NH₃ and if the precipitate dissolves then, bromide ions were present

5. If the precipitate does not dissolve, iodide ions are present

What colour is silver chloride ppt?

White

What colour is silver bromide ppt?

Cream

What colour is silver iodide ppt?

Yellow

State the trend in solubility of silver halides in ammonia.

The silver halides get less soluble in ammonia as you go down the group

Explain why silver nitrate is used to test for halide ions.

Halide ions combined with silver ions to form silver halide precipitates with different colours

Explain why nitric acid is added to the solution before silver nitrate.

To acidify the solution and remove impurities

State the reaction of chlorine with water in the absence of sunlight.

Cl₂ + H₂O —→ ClO- + CL- + 2H+

What is meant by a disproportionation reaction?

A reaction where the same substance is oxidised and reduced

State the reaction of chlorine with water in the presence of UV light.

2Cl₂ + 2H₂O —→ 4HCl + O₂

State the advantages and disadvantages of adding chlorine to water supplies.

It is useful to kill bacteria in swimming pools

However, it can be toxic in large quantities

State the equation for the production of bleach.

2NaOH + Cl₂ —→ NaClO + NaCl + H₂O

Describe how to test for sulfate ions.

Add BaCl₂ and a white ppt is formed if sulfate ions are formed

Describe how to test for hydroxide ions.

They will turn damp red litmus paper blue

Describe how to test for carbonate ions.

1. Add HCl

2. Bubble the gas produced through limewater

3. If the limewater turns cloudy, carbonate ions are present

Describe how to test for group 2 cations.

Dip a metal splint into the solution and hold in a flame

It will turn brick red if Ca²⁺ ions are present

It will turn red if Sr²⁺ ions are present

It will turn pale green if Ba²⁺ ions are present

Describe how to test for ammonium ions.

Hold red litmus paper over it, and it will turn blue if ammonium ions are present

How do you calculate the relative atomic mass of a substance?

average mass of one atom / mass of 1 atom of carbon 12 x 12

How do you calculate the relative molecular/formula mass of a substance?

average mass of one molecule / mass of 1 atom of carbon 12 x 12

Define relative atomic/formula mass.

The average mass of an atom/molecule of an substance relative to one twelfth of the mass of an atom of carbon 12.

What does Avogadro’s constant represent?

The number of particles in a mole.

State Avogadro’s constant.

6.022 x 10²³

What is concentration measured in?

mol dm ^-3

How do you calculate concentration?

Concentration = moles / volume

How do you calculate moles?

moles = mass / Mr

How do you calculate percentage atom economy?

Mr desired product / Mr total reactants x 100

What are the advantages of a high atom economy?

There is less waste going to landfill

It is cheaper

How do you calculate percentage yield?

% yield = experimental / theoretical x100

Why is % yield never 100%?

The reaction may be reversible

Some product may be lost when separating from the reaction mixture

Some reactants may react in other reactions

State the ideal gas equation.

pV = nRT

What are the units for pressure in the ideal gas equation?

Pa (pascals)

What are the units for volume in the ideal gas equation?

m³ (cubic metres)

What is the ideal gas constant?

8.31 J K^-1 mol^-1

What are the units for temperature in the ideal gas equation?

K (kelvin)

Rearrange the ideal gas equation to find p.

p = nRT/V

Rearrange the ideal gas equation to find V.

V = nRT/p

Rearrange the ideal gas equation to find n.

n = pV/RT

Rearrange the ideal gas equation to find T.

T = pV/nR

How do you convert from cm³ to m³?

x10^-6

How do you convert from dm³ to m³?

x10^-3

How do you convert from degrees celsius to Kelvin.

Add 273

What are the features of a chemical reaction at equilibrium?

Forward and reverse reactions occur at the same rate
The concentrations of reactants and products remain constant

The system is closed

What is Le Chatelier’s principle?

If a change is made to a system in dynamic equilibrium, the position of equilibrium will move to counteract the change

How does a catalyst effect the position of equilibrium?

It has no effect, but allows it to be reached faster

How does an increase in temperature effect the yield of the reaction?

The position of equilibrium moves in the endothermic direction, increasing the yield of the endothermic products

How does an increase in concentration effect the yield of the reaction?

Increasing the concentration of the reactant will increase the yield of the products

How does an increase in pressure effect the yield of a reaction using gases?

It favours the side of the reaction with fewer moles, increasing the yield of these products

Why must a compromise of pressure and temperature be reached in an industrial reaction?

A high temperature is needed to give a high rate of reaction, but can be expensive and decrease the yield in an endothermic reaction

A high pressure is needed to give a high rate of reaction and may increase yield, but can be expensive

What are the compromise conditions for the haber process?

400*

200atm

What is Kc?

An equilibrium constant that indicates the position of equilibrium for a reaction at a certain temperature

How is concentration represented in a Kc equation?

[X]

State the Kc formula for the reaction aA + bB —> cC + dD

[C]^c x [D]^d / [A]^a x [B]^b

How do concentration and catalysts effect Kc?

They have no effect

How does change in temperature effect Kc?

If a temperature increase causes an increase in products, Kc increases

Define activation energy.

The minimum energy required for a reaction to occur

Why do most collisions not lead to a reaction?

The particles have an energy that is less than the activation energy

The particles do not collide in the correct orientation

What does the peak of a maxwell-boltzmann curve represent?

The most common energy of the particles

Where is the average energy on a maxwell-boltzmann curve?

To the right of the peak

What does the area to the right of the Ea represent on a maxwell-boltzmann curve?

The particles with an energy greater than the Ea

What does the area under a maxwell-boltzmann curve represent?

The total number of particles in the reaction

Why does the curve never touch the x-axis?

There is no maximum energy

Define rate of reaction.

The change in concentration of a reactant of product over time

How does particle energy change with increasing temperature?

It increases

State and explain how the maxwell-boltzmann curve changes with an increase in temperature.

The curve gets broader and flatter as there is a greater spread of values

How does an increase in temperature effect rate of reaction?

It increases as more of the particles have an energy that is greater than the activation energy so there are more successful collisions

How does an increase in concentration/pressure effect rate of reaction?

It increases, as there are more particles present, so more particles have an energy greater than the activation energy, so there are more successful collisions

How does the use of a catalyst effect rate of reaction?

It provides an alternate route with a lower activation energy, so more particles have an energy greater than the activation energy, so there are more successful collisions

What is a catalyst?

A substance that increases the rate of a chemical reaction without being changed in chemical composition or amount

What is a redox reaction?

A reaction where one substance is reduced and the other is oxidised

What is oxidation?

Loss of electrons

What is reduction?

Gain on electrons

What is a spectator ion?

An ion that does not take part in the reaction

What does a reducing agent do?

Donates electrons

What does an oxidising agent do?

Removes electrons

What is an oxidation state?

A number that shows whether a substance is oxidised and by how much

Which element in a compound is given the negative oxidation state?

The more electronegative element

What is the oxidation state of an element?

0

What is the oxidation state of hydrogen and what are the exceptions?

+1 unless it is a metal hydride where it is -1

What is the oxidation state of a group 1 element?

+1

What is the oxidation state of a group 2 element?

+2

What is the oxidation state of aluminium?

+3

What is the oxidation state of oxygen and what are the exceptions?

-2

-1 in peroxides

+2 in F2O

What is the oxidation state of Fluorine?

-1

What is the oxidation state of chlorine and what are the exceptions?

-1

positive in F and O compounds

What is the sum of the oxidation states in a compound?

0

What is the sum of the oxidation states in an ion?

The charge of the ion

What 2 things must be balanced in a redox equation?

The number of atoms on each side

The total charge on each side

What 2 substances can be added to balance a redox equation?

Water and H+ ions

How do you work out half equations from balanced redox equations?

Split the compounds into their oxidation states and work out what has been oxidised and reduced, and by how much

How can you tell from an equation if it is a redox reaction?

If oxidation states have changed, a redox reaction has occurred