Group 2+7

Question 1

Why does a flame test work

Answer 1

When metal compound is heated electrons in the metal ion are excited to a higher energy level
As electrons return to normal energy level the energy is emitted as visible light
The colour of light emitted is due to the energy gap

Question 2

How does solubility of hydroxides change down the group

Answer 2

Hydroxides increase in solubility down the group

Question 3

How do sulfates change in solubility down the group

Answer 3

Sulfates decrease in solubility down the group

Question 4

Formula of a metal sulfate

Answer 4

XSO4

Question 5

Formula of group 2 hydroxide

Answer 5

X(OH)2

Question 6

Flame test colour of lithium

Answer 6

Crimson

Question 7

Flame test colour of sodium

Answer 7

Yellow

Question 8

Flame test colour of potassium

Answer 8

Lilac

Question 9

Flame test colour of beryllium

Answer 9

No change

Question 10

Flame test colour of magnesium

Answer 10

No change

Question 11

Flame test colour of calcium

Answer 11

Brick red

Question 12

Flame test colour of strontium

Answer 12

Red

Question 13

Flame test colour of barium

Answer 13

Green

Question 14

Why does thermal stability of group 2 carbonate change

Answer 14

As you go down group 2 ionic radius increases
Therefore charge density increases
Less able to polarise carbonate ion
Therefore more energy required to break C-O bond

Question 15

What is thermal decomposition

Answer 15

The breaking down of a substance using heat energy
Is exothermic

Question 16

Properties of group 7 elements

Answer 16

Non-metal
Reactive
Not found natively (as pure elements)
Usually found in compounds with metals eg halide salts

Question 17

How does the reactivity of group 7 elements change down the group

Answer 17

Less reactive down the group

Question 18

Why does reactivity change down group 7

Answer 18

Halogens form 1- ion by gaining outer shell electron
Further out outer shell makes it harder to gain an electron

Question 19

Why is ionic radii greater than atomic radii group 7

Answer 19

Because an electron has been gained and now more electrons than protons
Hence attraction between nucleus and each electron decreases

Question 20

Change in melting/boiling of group 7 and why

Answer 20

Increase down the group

Only London forces so bigger molecule creates stronger forces so more energy required to break

Question 21

Why do all halogens have similar chemical properties

Answer 21

All react to gain one outer shell electron

Question 22

Are group 7 elements oxidising or reducing agents

Answer 22

Tend to gain electrons in reaction so are likely to be oxidising agents and be reduced

Question 23

When will group 7 element not have negative oxidation state

Answer 23

When combined with oxygen as oxygen is more electronegative

Question 24

How does oxidising ability change down group 7

Answer 24

Decreases
Ability to gain electrons decreases down group as number of shells increases so outer electron further from nucleus and more shielding

Question 25

Why are group 7 poorly soluble with water

Answer 25

Unable to form hydrogen bonds with water so can’t release enough energy to overcome hydrogen bonds between water molecules

Question 26

Why are group 7 soluble in cyclohexane

Answer 26

Both have London forces as strongest intermolecular bonds Energy released by forming London forces between halogen and solvent releases enough energy to break London forces between halogen and solvent

Question 27

Physical state at room temp for Cl, Br and I and why

Answer 27

Cl- gas Br- liquid I- solid Increase in number of electrons so increase in strength of London forces

Question 28

Why has hydrogen flouride got higher boiling point than expected

Answer 28

Has intermolecular hydrogen binding and therefore intermolecular forces require more energy to break

Question 29

What happens in redox reaction of group 7 and 1/2 metal

Answer 29

Electrons transferred from metal to halogen to form metal halide

Question 30

Appearance of metal halide

Answer 30

Generally white solid

Question 31

What happens in reaction of chlorine and water

Answer 31

Produces a mixture of two acids H2O + Cl2 becomes HCl and HOCl

Question 32

Why does redox chlorine and water form two acids

Answer 32

Cl is oxidised to form HOCl and reduced to form HCl

Question 33

Reaction of chlorine and COLD alkali

Answer 33

Forms sodium chlorate (I) Cl2 + 2NaOH becomes NaCL + NaClO + H2O

Question 34

Reaction of chlorine and HOT alkali

Answer 34

Forms sodium chlorate (V) 3Cl2 + 6NaOH becomes 5NaCl + NaClO3 + 3H2O

Question 35

What is hydrogen halide displacement

Answer 35

A more reactive halogen will take the place of a less reactive halogen

Question 36

Reactivity of halogens from most reactive to least

Answer 36

Fluorine Chlorine Bromine Iodine

Question 37

What does bromine dissolve in

Answer 37

An organic solvent

Question 38

Precipitate colour reaction of silver nitrate and chlorine

Answer 38

White

Question 39

Precipitate colour reaction of silver nitrate and bromine

Answer 39

Cream

Question 40

Precipitate colour reaction of silver nitrate and iodine

Answer 40

Yellow

Question 41

How to differentiate between yellow and cream precipitate

Answer 41

Silver bromine (cream) will not dissolve in aqueous ammonia but will dissolve in conc ammonia Silver iodide (yellow) is insoluble in both aqueous and conc ammonia Therefore add concentrated ammonia

Question 42

Basic ionic formula for silver nitrate and halogen

Answer 42

Ag+(aq) + X-(aq) becomes AgX (s)

Question 43

Result of adding aqueous barium chloride followed by dilute hydrochloride acid

Answer 43

White pot insoluble in hydrochloric acid SO42- ions present

Question 44

Result of adding dilute acid to compound

Answer 44

Effervescence giving colourless gas and gas turning water guilty = CO3 2- ions present Pungent colourless gas on warming that decolourises potassium manganate = SO3 2- ions present

Question 45

Result of adding aqueous sodium hydroxide and heat

Answer 45

Gas that turns damp red litmus paper blue means NH4+ ions present

Question 46

Result of adding aqueous sodium hydroxide

Answer 46

White precipitate insoluble in excess reagent means insoluble metal hydroxide- group 2 metal ions likely

Question 47

Result of warm solid with aqueous sodium hydroxide and aluminium/zinc powder

Answer 47

Gas that turns damp red litmus paper blue means NO3- ions present reduced to NH3