Group 2 and Group 7

Question 1

What happens to the atomic radius as you go down group 2?

Answer 1

It increases as each element gets an extra main energy level.

Question 2

What happens to the first ionisation energy as you go down group 2?

Answer 2

It decreases because the atomic radius increases, more shielding, these decrease attraction between nucleus and outer shell electrons

Question 3

What happens to the melting point as you go down group 2?

Answer 3

Decreases because all of the metals donate two outer electrons to the delocalised sea. As you go down the group, the atomic radius increases so these electrons are further away from the nucleus so the force of attraction between them is less so the metallic bonds are weaker.

Question 4

What happens to the electronegativity as you go down group 2?

Answer 4

Decreases because atomic radius increases and there is more shielding, this decreases attraction between electrons and nucleus so it has a weaker ability to attract electrons.

Question 5

Observations and equation when Mg is reacted with water

Answer 5

Reacts with steam to form a white solid

Mg(s) + H2O(g) -> MgO(s) + H2(g)

Or reacts slowly with water in the general equation.

Question 6

Observations and equation when Ca is reacted with water

Answer 6

Fizzing with bubbles given off and a white precipitate

Ca(s) + 2H2O(l) -> Ca(OH)2(s) + H2(g)

Question 7

Observations and equation when Sr is reacted with water

Answer 7

Fizzes more in water and bubbles formed. Colourless solution

Sr + 2H2O -> Sr(OH)2 + H2

Question 8

Observations and equation when Ba is reacted with water

Answer 8

Fizzes more in water and bubble formed. Colourless solution.

Ba + 2H2O -> Ba(OH)2 + H2

Question 9

Trend for solubility of hydroxides (G2)

Answer 9

Mg is insoluble
Ca is partially soluble
Sr and Ba are both soluble

Question 10

Trend for solubility of sulfates (G2)

Answer 10

Mg is soluble
Ca is partially soluble
Sr and Ba are insoluble

Question 11

Uses for Mg(OH)2

Answer 11

Extracting titanium from TiCl4, indigestion treatment.

Question 12

Uses of Ca(OH)2

Answer 12

Limewater to neutralise acidic soil.

Question 13

Uses of BaSO4

Answer 13

Barium meal as it absorbs x-rays well

Question 14

Why is dilute nitric or hydrochloric acid added before testing for sulfate ions?

Answer 14

To remove carbonate ions as CO2 because barium carbonate is also a white solid so is indistinguishable from barium sulfate.

Question 15

Trend in electronegativity in group 7

Answer 15

Decreases down the group because atomic radius increases because the have more shells. This means more shielding so less attraction between nucleus and electrons in covalent bond

Question 16

Trend in boiling point in group 7

Answer 16

Increases down the group because the atoms are larger and have more electrons so have more and stronger Van der Waals forces between the molecules.

Question 17

Why is the F-F bond unexpectedly​ weak?

Answer 17

Goes against trend of bond enthalpy. The small size of F atom leads to repulsion between the non-bonding pairs as they are so close together.

Question 18

Oxidising agent

Answer 18

Something that takes electrons from another substance and is itself reduced

Question 19

Trend of oxidising power of halogens

Answer 19

Increases up the group because (same as trend in electronegativity)

Question 20

Reducing agent

Answer 20

Something that loses electrons to reduce another substance and is itself oxidised.

Question 21

Trend in reducing power of halides

Answer 21

Increases down the group because the ions are larger meaning the electrons in the outer shell are further from the nucleus so the attraction between them is less and the electrons are more easily lost.

Question 22

Observations of reaction with chloride ions and sulfuric acid.

Answer 22

Steamy fumes (HCl)

Question 23

Observations of reaction with bromide ions and sulfuric acid.

Answer 23

Steamy fumes (HBr), colourless gas (SO2), orange gas (Br2), water

Question 24

Observations of reaction with iodide ions and sulfuric acid.

Answer 24

Steamy fumes (HI), colourless gas (SO2), purple gas (I2), bad smell H2S, yellow solid (S), water.

Question 25

Method to test for halide ions

Answer 25

Add dilute nitric acid to remove any other ions that could form a precipitate with silver nitrate. Add silver nitrate until a precipitate forms. Add dilute ammonia to the precipitate (2cm^3). Dropwise, add concentrated ammonia.

Question 26

How can you tell there were chloride ions in a sample?

Answer 26

White precipitate, dissolved, dissolved

Question 27

How can you tell there were bromide ions in a sample?

Answer 27

Cream precipitate, not dissolved, dissolved

Question 28

How can you tell there were iodide ions in a sample?

Answer 28

Yellow precipitate, not dissolved, not dissolved

Question 29

Equation with chlorine reacting with cold, dilute NaOH

Answer 29

Cl2 + 2NaOH -> NaClO + NaCl + H2O

Question 30

Equation with chlorine reacting with water (no sunlight)

Answer 30

Cl2(g) + H2O(l) -> HClO(aq) + HCl(aq)

Question 31

Equation with chlorine reacting with water (sunlight)

Answer 31

2Cl2(g) + 2H2O(l) -> 4HCl(aq) + O2(g)

Question 32

Equation with water reacting with sodium chlorate

Answer 32

NaClO(s) +H2O(l) Na+(aq) + OH-(aq) + HClO(aq)

Question 33

How does chloric acid (HClO) purify water

Answer 33

It is an oxidising agent and kills bacteria by oxidation.

Question 34

Why is swimming pool water kept slightly acidic?

Answer 34

So that the equilibrium for the reaction with NaClO and H2O is to the right so more chloric acid is formed. Not too acidic to corrode metal components or affect swimmers.

Question 35

Test for sulfate ions

Answer 35

Add dilute nitric or hydrochloric acid. Then add barium chloride solution. If sulfate ions are present, a white precipitate of barium sulfate is formed.

Question 36

Test for hydroxide ions

Answer 36

Same as test for ammonium ions only you add the ammonium compound.

Question 37

Test for ammonium ions

Answer 37

Add sodium hydroxide solution and warm the mixture. If ammonium ions were present, ammonia gas will be formed which has a pungent smell and turns red litmus paper blue.

Question 38

Test for carbonate ions

Answer 38

Add dilute nitric or hydrochloric acid. If carbonate ions were present, there is effervescence due to CO2 gas forming. This gas turns limewater cloudy.