Chapter 8

Question 1

Does the reactivity increase or decrease as you go down group 2?

Answer 1

Reactivity increases down group 2 when each element has a redox reaction carried out with it this occurs as the element loses two electrons forming at 2+ ion

Question 2

Does the ionisation energies decrease or increase as you go down the group?

Answer 2

They decrease because the nuclear attraction decreases as a result of increasing atomic radius and shielding

Question 3

What can you say about group 2 elements as you go down the group?

Answer 3

They become stronger and more reactive as well as stronger reducing agents.

Question 4

What is the use of group 2 compounds in agriculture?

Answer 4

Calcium hydroxide is added to fields as lime by farmers to increase the pH of acidic salts, the calcium hydroxide neutralises the acid found within the soil forming neutral water.

Question 5

What is the use of group 2 compounds in medicine?

Answer 5

Group 2 bases are often used as anti-acid for treating acid indigestion. Many indigestion tablets use magnesium and calcium carbonate as the main ingredients whereas ‘milk of magnesia’ is a suspension of white magnesium hydroxide in water. The acid in your stomach is mainly hydrochloric

Question 6

What do group 2 oxides form when they react with water?

Answer 6

They release hydroxide ions and form alkaline solutions of the metal hydroxide
e.g CaO +H2O –> Ca2+ + 2OH-

Question 7

Are group 2 hydroxide’s soluble or not?

Answer 7

They are only slightly soluble in water so when the solution becomes saturated any further metal and hydroxide ions will form a solid precipitate. The solubility of hydroxide increases as you go down the group so contain more 0H minus ions and a more alkaline.

Question 8

Describe the experiment used to show the solubility of hydroxides in group 2?

Answer 8

1. Add a spatula of each group 2 oxide to water in a test tube
2. Shake. There is insufficient water to dissolve all the metal hydroxides which form, each metal hydroxide will be saturated, with some white solid at the bottom of the tube
3. Measure the pH, with the alkalinity increasing as you go down the group

Question 9

What is the most common type of reaction for a group 2 metals?

Answer 9

Redox reactions: as each metal is oxidised forming a 2+ ion with an electron configuration of a noble gas.

Question 10

What is the group 2 element described as in a redox reaction?

Answer 10

The group to element is the reducing agent as it has produced another species. The other species has to gain these two electrons and will be reduced.

Question 11

What do group 2 elements react with water to form?

Answer 11

An alkaline hydroxide and hydrogen gas (general formula for the hydroxide is M(OH)2 )

Question 12

Does reactivity increase or decrease as you go down the group?

Answer 12

Reactivity increases as you go down the group. Water and magnesium reacts very slowly but as you go down the reaction comes more vigourous.

Question 13

What do group 2 elements react with oxygen to form?

Answer 13

Metal oxide with the general formula MO which is made up of M2+ and O2- ions

Question 14

What is the redox reaction for group to metals with dilute acid?

Answer 14

They form a salt and hydrogen.

Question 15

Are halogens reactive or not?

Answer 15

They are the most reactive nonmetallic group where they occur as stable halide ions.

Question 16

Describe the boiling point of halogens?

Answer 16

At RTP all halogens exist as diatomic molecules. The group contains elements in all three states changing from gas to liquid to solid down the group. In a solid state they form lattices with simple molecular structures.

Question 17

Describe the trend in halogens in terms of the boiling point?

Answer 17

As you go down there are more electrons so have stronger London forces so more energy is required to break the intermolecular forces therefore the boiling point increases.

Question 18

Describe the reactivity of halogens?

Answer 18

They decrease in reactivity as you go down the group. Chlorine is the most reactive than bromine and then iodine which is the least reactive.

Question 19

What does chlorine react with?

Answer 19

Br- and I-
When chlorine reacts with the bromine ion, it forms an orange colour from the Br2 formation.
When chlorine reacts with the iodine ion, if forms a violet colour from the I2 formation.

Question 20

What does bromine react with?

Answer 20

I- only

When bromine reacts with the iodine ion, if forms a violet colour from the I2 formation.

Question 21

What does iodine react with?

Answer 21

Nothing

Question 22

What is the most common reaction for halogens?

Answer 22

A redox reaction as each atom is reduced as it gains one electron forming a one minus halide ions with the electron configuration of the nearest noble gases. The halogens are known as the oxidising agent because it has oxidised another species. Another species has to lose electrons to halogen atoms so are oxidised.

Question 23

What do you halogen – halide displacement reactions show?

Answer 23

They show that the reactivity decreases down the group.

Question 24

Describe the halogen halogen displacement reaction?

Answer 24

The solution of each halogen is added to aqueous solution of the other halides e.g. chlorine is added to solutions containing Br- and I- ions. If the halogen is added the more reactive substance will obtain in the reaction. If the halogen is more reactive than the ion the reaction will take place the halogen displacing from the solution with the solution changing colour.

Question 25

What is added to the solution in order to tell the difference between iodine and bromine?

Answer 25

As they are similar colours when in water a non polar solvent e.g. cyclohexane can be added and the mixture is shaken. The non polar halogens dissolve more readily than water. In cyclohexane the colours that are easily identifiable with iodine being dark purple.

Question 26

How do halogens react?

Answer 26

They react by gaining an electron as you go down the group the tendency to gain an electron decreases mean in the halogen is less reactive. The trend shows as the atomic radius increases, shielding increases so less nuclear attraction to capture an electron from another species so reactivity decreases.

Question 27

Which of the halogens is the strongest oxidising agent.

Answer 27

Fluorine is the strongest as it can gain electrons to the species more readily than in the other halogens. They become weaker oxidising agents as you go down the group.

Question 28

What does aqueous halide ions react with aqueous silver ions to form?

Answer 28

Precipitate of silver halides

Question 29

What does silver chloride form?

Answer 29

White precipitate which is soluble in dilute ammonia

Question 30

What does silver bromide form?

Answer 30

A cream precipitate which is soluble and concentrated ammonia.

Question 31

What does silver iodine form?

Answer 31

Yellow precipitate insoluble in concentrated ammonia.

Question 32

What is diproportion?

Answer 32

It is when the same element is both oxidised and reduced e.g chlorine with water and with cold dilute sodium hydroxide.

Question 33

What is the reaction of chlorine with water?

Answer 33

When small amounts of chlorine is added to water a disproportionate reaction occurs. For each molecule one chlorine atom is reduced and another is oxidised. Both products are acids: chloric acid, HClO and hydrochloric acid HCl.

Question 34

What are the uses of chloric acid and chlorate ions, ClO- ?

Answer 34

Bacteria is killed by both chloric acid and chloride ions with chloric acid acting as a weak bleach.

Question 35

What is the reaction of chlorine with cold dilute sodium hydroxide?

Answer 35

If water use contains dissolved sodium hydroxide much more chlorine can dissolve so another disproportion occurs. The reaction between H2O and CO2 is limited due to low solubility. This solution results in a large concentration of chloride ions from the sodium chlorate which forms.

Question 36

The solution produced by chlorine with cold, dilute sodium hydroxide is used in?

Answer 36

Household bleach

Question 37

What are the benefits of chlorine?

Answer 37

Chlorine is beneficial in ensuring the water is fit to drink and that bacteria is killed. The risk of not adding chlorine to water supply is greater. The quality of water will be compromised and diseases such as typhoid and cholera would break out. The benefits outweigh the risk.

Question 38

What are the risks of chlorine use?

Answer 38

Chlorine is extremely toxic in gas form. In small concentration it is a respiratory irritant and in large concentrations it can be fatal. Chlorine and water can react with organic hydrocarbons e.g. methane. Chlorinated hydrocarbons are suspected in causing cancer.

Question 39

How do you test for a carbonate?

Answer 39

1. Add dilute nitric acid to the solid or solution in a test tube.
2. If you see bubbles the unknown compound could be a carbonate.
3. In order to prove that CO2 has been produced bubble the gas through lime water (saturated Ca(OH)2 (aq)). Carbon dioxide reacts to form a fine white precipitate of calcium carbonate which turns lime water cloudy.

Question 40

How do you test for sulphate?

Answer 40

Most sulphates are soluble in water but barium sulphate is very insoluble which forms a white precipitate. Aqueous barium ions are added to the solution of the unknown compound. Usually the barium ions are added as barium chloride or nitrate. If you intend to do a halide test afterwards you need to add barium nitrate instead of barium chloride as it introduces chloride ions

Question 41

How do you test for halides?

Answer 41

Most halides are soluble in water but silver halides are insoluble. Aqueous silver ions react with aqueous halide ions to form precipitate of silver halides.

1. Add aqueous silver nitrate AgNO3 to an aqueous halide solution.
2. Silver halide precipitates are different colours.
3. Add aqueous ammonia to test the solubility of the precipitates this means they can be told apart

Question 42

What are the sequence of tests?

Answer 42

Carbonate, sulphate, Halide

Question 43

What colour precipitate will chloride ions form and its solubility?

Answer 43

White precipitate, which is soluble in dilute ammonia

Question 44

What colour precipitate will bromide ions form and its solubility?

Answer 44

Cream precipitate, which is soluble in concentrated ammonia.

Question 45

What colour precipitate will iodide ions form and its solubility?

Answer 45

Yellow Precipitate, which is insoluble in dilute nitric acid.

Question 46

When doing a sequence of tests describe the carbonate test?

Answer 46

You add dilute acid what are you looking effervescence from CO2. Both sulfate and halide ions don’t produce bubbles with dilute acid. This test is carried out without the possibility of an incorrect conclusion. No bubbles no carbonate and you can move on.

Question 47

When doing a sequence of tests describe the sulfate test?

Answer 47

You had a solution of Ba2+ ions looking for a white precipitate of BaSO4. Barium carbonate is white and insoluble in water therefore it is important to do the carbonate test first and then proceed as no carbonate will be present.

Question 48

When doing a sequence of tests describe the halide test?

Answer 48

You add a solution of silver ions as silver nitrate and are looking for a precipitate. Silver carbonate and silver sulphate are both insoluble in water so will form precipitates. It is then important to carry this test out last as all possibilities would’ve been ruled out.

Question 49

What do you do if you need to analyse a mixture of chemicals when carrying out the same tests?

Answer 49

1. Carbonate test – if you see bubbles continue adding dilate nitric acid until the bubbles stop. All carbonate ions will then be removed so they have been none to react any other test. If you intend on doing a sulfate and halide test, dilute nitric acid should be used as sulphuric acid contains sulphate and hydrochloric acid contains chloride ions which would show up on the other tests.
2. Sulphate test – you add excess barium nitrate to the solution. Any sulphate ions will precipitate out as barium sulphate which could be filtered out. If you intend to test for halides, barium chloride should not be used as the chloride would show up on the halide test. 3. Halide test – finally you add silver nitrate, any other ions initially present would have been removed or any precipitate formed would be halide ion, add ammonia to confirm which halide.

Question 50

Describe the test for ammonium ions?

Answer 50

When heated together aqueous ammonium ions in aqueous ions react to form ammonia gas, NH3.
1. Add aqueous sodium hydroxide to a solution of the ammonium ion.
2. Ammonia gas is produced. You are unlikely to to see any bubbles as ammonia is very soluble.
3. The mixture is warmed and the ammonia gas is released.
4You can test the presence of ammonia with moist pH indicator paper. Ammonia is alkaline so its presence within the solution will turn the paper blue.