IGCSE Chemistry

State the method used to obtain sand from a mixture of sand and water

filtration

State the method used to obtain solid copper sulfate from aqueous copper sulfate

crystallisation

State the method used to obtain red food dye from a mixture of food dyes

paper chromatography

State the method used to obtain water from salt water

simple distillation

Draw a diagram to show equipment used in simple distillation

For what process is this equipment used?

State the method used to obtain kerosene from a crude oil.

fractional distillation

Draw the equipment used in fractional distillation in the lab

For what process is this equipment used?

Explain how fractional distillation is used to separate a mixture of different liquids

The different liquids have different boiling points

State the method used to extract the red dye from a sample of rose petals

dissolving

Describe how pure salt can be obtained from rock salt

1) Grind rock salt into a fine powder. 2) Add powder to hot water and stir to dissolve salt. 3) Filter mixture. Salt solution passes through the filter paper leaving behind the sand. 4) Boil filtrate to evaporate some of the water. 5) Leave saturated solution to cool so that crystals of salt form. 6) Filter cold mixture to separate the crystals from the remaining solution.

Ethanol is a flammable liquid. Suggest how it could be heated safely

Use a water bath

Explain how a chromatogram shows that different dyes are different from each other

Each dyes has a different mixture

State the expression for calculating molar concentration

Molar concentration = Amount (in moles)/volume (in dm^³)

Which cation gives a crimson red flame colour?

Li⁺

Which cation gives a orange flame colour?

Na⁺

Which cation gives a lilac flame colour?

K⁺

Which cation gives a brick red flame colour?

Ca²⁺

Describe how you would carry out a flame test

Put solid onto a wire. Put into a blue flame

How would you test for the ammonium ion?

Add sodium hydroxide. If ammonium ions were present, ammonia gas will form which will turn damp red litmus paper blue

Describe how you would test for Cu²⁺ ions

Add sodium hydroxide and a blue precipitate will form

Give the formula of the blue precipitate formed when sodium hydroxide is added to a solution containing Cu²⁺

Cu(OH)₂

Describe how you would test for Fe²⁺ ions

Add sodium hydroxide and a green precipitate will form

Write a word equation for the reaction between sodium hydroxide and iron(II) sulfate

sodium hydroxide + iron(II) sulfate -> iron (II) hydroxide + sodium sulfate

Describe how you would test for Fe³⁺ ions

Add sodium hydroxide and a brown precipitate will form

What 2 things are added to a solution to test for chloride ions? What is observed if they are present?

Add dilute nitric acid and silver nitrate. A white precipitate of silver chloride is formed.

Describe the test for bromide ions.

Add dilute nitric acid and silver nitrate. A cream precipitate of silver bromide is formed.

After adding nitric acid and silver nitrate to a solution containing iodide ions, what colour precipitate is formed?

A yellow precipitate (of silver iodide) is formed.

Why is hydrochloric acid added before barium chloride solution in testing for sulfate ions?

To remove carbonate ions

Describe how you would test for sulfate ions

Add dilute HCl, followed by BaCl₂. A white precipitate will form

Write an chemical equation for the reaction between barium chloride and lithium sulfate (Li₂SO₄). Include state symbols. Also, what would you see?

BaCl₂ (aq) + Li₂SO₄ (aq) -> BaSO₄ (s)+ 2LiCl (aq). Observe a white precipitate of barium sulfate.

Describe how you would test for carbonate ions, CO₃²⁻

Add nitric acid and see if carbon dioxide bubbles form

Describe the test for ammonia gas

Turns damp red litmus paper blue

State the expression for calculating % yield. (Triple science only!)

% yield = (actual amount of products/theoretical amount of products) x100

Describe the chemical test for water

Add water to anhydrous copper(II) sulfate which will change from white to blue if water is present

What is the symbol for a reversible reaction?

The addition of water to anhydrous copper sulfate can be used to test for the presence of water. The reaction is reversible. What is the word equation? Describe the colour change.

anhydrous copper sulfate (white) + water <-> hydrated copper sulfate (blue)

Ammonia and hydrogen chloride react together in a reversible reaction to produce a white solid. What are the word and symbol equations?

ammonia + hydrogen chloride <-> ammonium chloride NH₃ + HCl <-> NH₄Cl

State two features of a reaction that is in dynamic equilibrium

1) The rate of the forward reaction is equal to the rate of the backward reaction. 2) There is no overall change in concentrations.

Predict what will happen to the equilibrium position in the following reaction when the pressure is increased. Give a reason for your prediction: CH₄(g) + H₂O(g) <-> CO(g) + 3H₂(g) ΔH = +210 kJ mol⁻1

Equilibrium will move to the left because there are fewer molecules on the left hand side

Predict what will happen to the equilibrium position in the following reaction when the temperature is increased. Give a reason for your prediction: CH₄(g) + H₂O(g) <-> CO(g) + 3H₂(g) ΔH = +210 kJ mol⁻1

Equilibrium will move to the right because the forward reaction is endothermic

Predict what will happen to the rate of reaction in the following reaction when the temperature and pressure is increased. Give a reason for your prediction: CH₄(g) + H₂O(g) <-> CO(g) + 3H₂(g) ΔH = +210 kJ mol⁻1

The rate will increase

Predict what will happen to the equilibrium position in the following reaction when the temperature is increased. Give a reason for your prediction: CO(g) + H₂O(g) <-> CO₂(g) + H₂(g) ΔH = -42 kJ mol⁻1

Equilibrium will move to left the because the reaction is exothermic

Predict what will happen to the equilibrium position in the following reaction when the temperature is decreased. Give a reason for your prediction: CO(g) + 2H₂(g) <-> CH₃OH(g) ΔH = -91 kJ mol⁻1

Equilibrium will move to right the because the reaction is exothermic

Predict what will happen to the equilibrium position in the following reaction when the pressure is decreased. Give a reason for your prediction: CO(g) + 2H₂(g) <-> CH₃OH(g) ΔH = -91 kJ mol⁻1

Equilibrium will move to left the because there are more molecules on the left hand side

State the raw materials used in the manufacture of ammonia

nitrogen from air and hydrogen from natural gas

State a use for N₂

making ammonia

The following reaction is used to manufacture ammonia in the Haber process: N₂ + 3H₂ -> 2NH₃ ΔH = -92KJ/mol. The reaction is carried out at 450⁰C but the reaction would be faster if a higher temperature were used. Suggest why a higher temperature is not used in the Haber process

Yield would decrease and energy costs would increase

State the temperature used for the manufacture of ammonia by the Haber process

450°C

State the pressure used for the manufacture of ammonia by the Haber process

200 atm

State the catalyst used for the manufacture of ammonia by the Haber process

Iron

How is ammonia separated from unreacted hydrogen and nitrogen in the Haber process?

The reaction mixture is cooled until the ammonia condenses into a liquid

What happens to the unreacted hydrogen and nitrogen in the Haber process?

Recycled

State the uses of ammonia

manufacture of nitric acid and fertilisers

Suggest the names of two elements, other than nitrogen, that are likely to be present in NPK fertiliser

potassium and phosphorous

Write a chemical equation for the reaction between ammonia and nitric acid

NH₃ + HNO₃ -> NH₄NO₃

State the raw materials used in the manufacture of sulfuric acid. (Triple science only!)

sulphur (from ores) and oxygen (from air)

Describe the manufacture of sulfuric acid by the contact process. (Triple science only!)

1) Making of sulfur dioxide: S + O₂ -> SO₂, 2) Reversible step: 2SO₂ + O₂ <-> 2SO₃ (exothermic), 3) H₂SO₄ + SO₃ -> H₂S₂O₇, 4) H₂S₂O₇ + H₂O -> 2H₂SO₄

State the temperature used for the manufacture of sulfuric acid by the contact process. (Triple science only!)

450°C

State the pressure used for the manufacture of sulfuric acid by the contact process. (Triple science only!)

2 atm

State the catalyst used for the manufacture of sulfuric acid by the contact process. (Triple science only!)

Vanadium(V) oxide

State the uses of sulfuric acid. (Triple science only!)

manufacture of detergents, fertilisers and paints

In Chemistry, what is the meaning of the word Group? What does that tell us about the electron configuration?

A Group is a vertical column of similar elements (same number of electrons in the outer shell)

In Chemistry, what is the meaning of the word Period? What does that tell us about the electron configuration?

A Period is a horizontal row of elements (same number of electron shells)

Where are the metals in the Periodic Table? Where are the Non-Metals?

Metals on the left of the Periodic Table. Non-Metals on the top-right, plus Hydrogen.

If an element conducts electricity, is it a metal or a non-metal?

Metal

If an element doesn't conducts electricity, is it a metal or a non-metal?

Non-Metal

Are metal oxides acidic or basic?

Basic

Are non-metal oxides acidic or basic?

Acidic

Why do elements in the same group of the periodic table have the same chemical properties?

Elements in the same group of the periodic table have the same number of electrons in their outer shell

Explain, in terms of the arrangement of electrons in its atoms, why neon is very unreactive

Neon has 8 electrons in the outer shell, so it is full. Therefore it does not easily gain or lose electrons

Write the chemical equation for the reaction betweem sodium and water

2Na + 2H₂O -> 2NaOH + H₂

State 5 observations when potassium reacts with water

1) fizzing occurs 2) potassium moves around 3) potassium melts 4) lilac flame is seen 5) potassium disappears 6) potassium floats

Complete the equation for the reaction by inserting the state symbols: 2Li(....) + 2H₂O(....) -> 2LiOH(...) + H₂(....)

2Li(s) + 2H₂O(l) -> 2LiOH(aq) + H₂(g)

State 4 observations when sodium reacts with water

1) fizzing occurs 2) sodium moves around 3) sodium melts 4) sodium disappears 5) sodium floats

How should group 1 elements be stored

Under oil

Describe the relative reactivities of the elements in Group 1

The reactivity increases as you go down the group, e.g. Li

Explain, by referring to the electronic configurations of sodium and potassium, why potassium is more reactive than sodium. (Triple science only!)

Sodium has the electronic configuration 2,8,1 and potassium has 2,8,8,1. The outer electron lost from potassium is further from the nucleus therefore the electron is less attracted by the nucleus

State the colour and physical state of chlorine at room temperature

Green gas

State the colour and physical state of bromine at room temperature

Orange brown liquid

State the colour and physical state of iodine at room temperature

Grey solid

Suggest how the reactivity of astatine compares to that of iodine. Explain your answer.

Astatine is less reactive because group 7 elements get less reactive with increasing atomic number.

State the most reactive element in group 7

Fluorine

Why does chlorine react with hydrogen bromide?

Chlorine is more reactive and so displaces the bromine.

Hydrogen bromide is reacted with chlorine to form bromine. Write a chemical equation.

2HBr + Cl₂ -> 2HCl + Br₂

State the colour change observed when bromine is added to an aqueous solution of potassium iodide

Colourless to brown

Identify the element that is displaced in this reaction: 2HBr + Cl₂ -> 2HCl + Br₂

Bromine

Why would there be no reaction when iodine was added to sodium bromide solution?

Iodine as it is less reactive than bromine

Name the substance with the brown colour that forms whem chlorine is added to potassium iodide solution

Iodine as it is less reactive than chlorine

Identify the species that is oxidised in the following reaction. Explain your answer: 2Br⁻ + Cl₂ -> 2Cl⁻ + Br₂

Bromide. Loses electrons

Identify the species that is reduced in the following reaction. Explain your answer: 2Br⁻ + Cl₂ -> 2Cl⁻ + Br₂

Chlorine. Gains electrons

When chlorine gas is bubbled into an aqueous solution of potassium iodide, the colourless solution turns brown. Complete the following ionic equation: Cl₂(g)+ ___I⁻(aq) -> 2Cl⁻(aq) + ___(aq)

Cl₂(g) + 2I⁻(aq) -> 2Cl⁻(aq) + I₂(aq)

Describe the test for chlorine gas

Turns moist litmus paper white (bleaches)

Describe, in terms of electrons, the formation of sodium chloride

An atom of sodium loses one electron. An atom of chlorine gains one electron

Explain the term ionic bond

An ionic bond is the strong electrostatic attraction between oppositely charged ions

Explain, in terms of structure and bonding, why sodium chloride has a very high melting point

NaCl has a giant ionic structure with strong electrostatic forces between oppositely charged ions that require a lot of energy to break

Explain, in terms of structure and bonding, why magnesium oxide has a higher melting point than sodium chloride (Triple science only!)

NaCl and MgO both have a giant ionic structure with strong electrostatic forces between oppositely charged ions. The Ions in MgO have a charge of 2 and -2, but in NaCl the charges are 1 and -1. So the bonds in MgO require more energy to break

Explain why magnesium oxide has a higher melting point than sodium chloride. (Triple science only!)

Mg²⁺ and O²⁻ ions have a higher charge than sodium and chloride therefore the electrostatic forces between the ions are much stronger. This requires more energy to break.

Describe the structure of an ionic compound, e.g NaCl. (Triple science only!)

A giant structure held together by the attraction between oppositely charged ions

Draw a diagram to represent the positions of the ions in a crystal of sodium chloride.

A - sodium ions. B - Chloride ions

Describe the formation of a covalent bond

The sharing of a pair of electrons between two nuclei