reactivity trends

Question 1

where are the two electron of the outer shell in a group 2 element found?

Answer 1

outer s sub shell

Question 2

what is the most common reaction in group 2 elements?

Answer 2

redox reactions, each metal ion is oxidised forming a 2+ ion. Another species will gain 2 electrons and become reduced therefore group 2 elements are also known as a reducing element.

Question 3

describe the redox reaction between group 2 elements and oxygen

Answer 3

metal oxide is formed e.g MgO is formed when using magnesium, made up go Mg2+ and O2- ions.

Question 4

what can you see when magnesium reacts with oxygen?

Answer 4

brilliant white light which forms white magnesium oxide

Question 5

describe the change in oxidation number when magnesium reacts with oxygen

Answer 5

as two magnesiums are needed to react with oxygen and each magnesium increases by +2, the total increase is +4. As two oxygen are in O2 (diatomic) and each oxygen decreases by 2 the total decrease is -2.

Question 6

Describe the redox reaction between group 2 elements and water

Answer 6

an alkaline hydroxide is formed with the general formula M(OH)2 and hydrogen gas.

Question 7

Describe the redox reaction between group 2 elements and dilute acids.

Answer 7

salt and hydrogen gas in formed

Question 8

why does reactivity increase going down the group 2 elements?

Answer 8

ionisation energies decrease down the group because the attraction between the nucleus and outer electron decreases as a result of its increasing atomic radius and shielding

Question 9

In group 2 elements what takes up most of the energy input?

Answer 9

first and second ionisation energy.

Question 10

Describe how group 2 oxides react with water?

Answer 10

hydroxide ions(OH-) are released therefore solution becomes more alkaline and filled with group 2 hydroxides. Group 2 hydroxides are only slightly soluble in water, they form a solid precipitate.

Question 11

Describe the trend in solubility of group 2 hydroxides

Answer 11

group 2 hydroxides become more soluble going down the group so the solutions more hydroxide ions (OH-) and are more alkaline.

Question 12

How are group 2 compounds used in agriculture?

Answer 12

Calcium hydroxide, Ca(OH)2 is added to fields to increase the pH of acidic soil. The calcium hydroxide neutralises the acid forming neutral water

Question 13

How are group 2 compounds used in medicine?

Answer 13

they are used as antacids to neutralise stomach acid to relieve indigestion.

Question 14

why does boiling point increase going down group 7 (halogens)?

Answer 14

• higher electron density
• stronger London forces
• more energy required to break the intermolecular forces
• boiling point increases

Question 15

where are the outer electrons found in halogens?

Answer 15

two electrons are in the outer s-sub shell and 5 in the outer p sub shell.

Question 16

what is the most common reaction in halogens?

Answer 16

redox reactions, each halogen atom gains one electron to form a 1- halogen ion. I becomes reduced however the other species becomes oxidised therefore halogens are known as a oxidising agent

Question 17

how can you test the trend in reactivity of halogens?

Answer 17

do a displacement reaction, a colour change indicates a displacement.

Question 18

what colour is chlorine and bromine?

Answer 18

chlorine is a pale green and bromine is orange

Question 19

what is the colour of iodine?

Answer 19

brown but for a positive result of iodine from a displacement reaction it is the colour, violet

Question 20

what is the colour of fluorine?

Answer 20

pale yellow gas that reacts with almost any substance

Question 21

what is the colour of astatine?

Answer 21

rare decays rapidly, has never been seen. Least reactive halogen

Question 22

why do halogens become less reactive going down the group?

Answer 22

• atomic radius increases
• sheilding increases
• less nuclear attraction to capture an electron
• reactivity decreases

Question 23

what is disproportionation?

Answer 23

a redox reaction where the same element is oxidised and reduced.

Question 24

how is the reaction of chlorine and water a disproportionate reaction?

Answer 24

in the chlorine molecule, one atom is oxidised and the other is reduced. Chloric (I) acid, HClO, and hydrochloric acid are made.

Question 25

why is chlorine commonly added to water?

Answer 25

to purify the water, the bacteria are killed by chloric acid.

Question 26

How can another disproportionate reaction occur?

Answer 26

if the water has sodium hydroxide, more chlorine dissolves. Sodium chlorate (I) is formed which is used as household bleach.

Question 27

what are the risks of chlorine?

Answer 27

chlorine gas is very irritant and can be fatal in large concentrations. Chlorine can react with organic hydrocarbons forming chlorinated hydrocarbons which are suspected of causing cancer.

Question 28

How do you test for carbonates?

Answer 28

add dilute nitric acid, if bubbles occur it may be carbon dioxide. To confirm it is carbon dioxide, bubble the gas through lime water. The positive result is a white precipitate which turns the lime water cloudy.

Question 29

most sulphates are insoluble in water except…

Answer 29

barium sulphate which forms a white precipitate

Question 30

how do you do halide tests?

Answer 30

add aqueous silver nitrate to an aqueous solution of halide. The silver halide precipitates are different colours- silver chloride is white, silver bromide is cream-coloured and silver iodide is yellow. You can add aqueous ammonia to test the solubility of the precipitate which is useful as the colours can be hard to tell apart.

Question 31

if you are asked to analyse an unknown inorganic compound, what is the order of tests you need to carry out?

Answer 31

1) carbonate test
2) sulphate test
3) halide test

Question 32

how do you carry out a sulphate test?

Answer 32

add a solution containing Ba2+ (aq) ions and the positive result is a white precipitate of BaSO4.

Question 33

why is it important to carry out the carbonate test before the sulphate test?

Answer 33

Barium carbonate, BaCo3 also makes a white precipitate in a sulphate test

Question 34

why is it important to carry out the carbonate test and sulphate test before the halide test?

Answer 34

although we are looking AgNO3 as a precipitate, silver carbonate and silver sulphate also form precipitates.

Question 35

how do you analyse a mixture of ions?

Answer 35

1) carbonate test- add dilute nitric acid until bubbling stops to remove all carbonate ions. Use dilute nitric acid, HNO3 as sulphuric acid contains sulphate ions and hydrochloric acid contains chloride ions which would show on the halide tests
2) sulphate test- add excess Ba(NO3) then filter off solution. Don’t use BaCl2 as chloride ions would show on halide test.
3) halide test

Question 36

Describe chloride, bromide and iodide ions solubility in ammonia, NH3

Answer 36

• chloride is soluble in dilute ammonia
• bromide is soluble in concentrated ammonia
• iodide is insoluble in concentrated ammonia

Question 37

How do you test for ammonium ions?

Answer 37

add sodium hydroxide and warm the mixture to release bubbles as ammonia is soluble in water . Test gas using moist pH indicator paper, blue is the positive result.