group 2 and group 7 elements

Question 1

what is the trend in atomic radius down group 2?

Answer 1

increases, more electrons so extra electron shells

Question 2

what is the trend in ionisation energy down group 2?

Answer 2

decreases, extra electron shell causes shielding so outer electron is further away from nucleus

Question 3

what is the trend in reactivity down group 2?

Answer 3

increases, ionisation energy decreases, the easier it is to lose electrons the more reactive

Question 4

what is the trend in melting points down group 2?

Answer 4

general decrease, atomic radius increases so negative electrons are further from the positive nucleus so less energy is needed to break bonds.
(Mg has a small increase due to crystal structure)

Question 5

what happens when group 2 elements react with water?

Answer 5

-give a metal hydroxide and hydrogen.

e.g. Ca(s) + 2H2O(I) –> Ca(OH)2(aq) + H2(g)

-elements react more readily down the group as ionisation energies increase
-when Mg reacts with steam MgO is produced

e.g. Mg(s) + 2H2O(g) –> MgO(s) + H2(g)

Question 6

what is the solubility of group 2 elements and hydroxides (OH-)?

Answer 6

least soluble –> most soluble
Mg(OH)2 is sparingly soluble

Question 7

what is the solubility of group 2 elements and sulphates (SO42-)?

Answer 7

most soluble –> least soluble
BaSO4 is insoluble

Question 8

what is the test for sulphate ions?

Answer 8

-add HCl to remove any carbonate ions
-add barium chloride (BaCl2)
-white precipitate formed

Ba2+(aq) + SO42-(aq) –> BaSO4(s)

Question 9

what is the use of barium?

Answer 9

BaSO4 in insoluble and is opaque to x-rays, so its used in barium meals to diagnose problems in the oesophagus, stomach or intestines

Question 10

describe the extraction of titanium.

Answer 10

-titanium ore (TiO2) is converted to titanium chloride (TiCl4) by heating it with carbon in a steam of chlorine gas.
-purified by fractional distillation
-reduced by magnesium in a furnace

TiCl4(g) + 2Mg(I) –> Ti(s) + 2MgCl2(I)

Question 11

what other uses of group 2 compounds are there?

Answer 11

-calcium hydroxide (Ca(OH)2) is used to neutralise acidic soils.
-magnesium hydroxide (Mg(OH)2) is used in indigestion tablets as an antacid, neutralises stomach acid.

Question 12

describe the removal of sulphur dioxide from flue gases.

Answer 12

-wet scrubbing, reacting with alkali
-calcium oxide (lime CaO) or calcium carbonate (limestone CaCO3) is mixed with water
-then sprayed onto flue gases
-sulphur dioxide reacts with alkaline and produces a solid waste product calcium sulphite

CaO(s) + 2H2O(I) +SO2(g) –> CaSO3(s) +2H2O(I)
CaCO3(s) + 2H2O(I) + SO2(g) –> CaSO3(s)
+ 2H2O(I) + CO2(g)

Question 13

what are the properties of the first 4 halogens?

Answer 13

-F2, pale yellow, gas
-Cl2, green, gas
-Br2, red-brown, liquid
-I2, grey, solid

Question 14

what is the trend in boiling points down group 7?

Answer 14

increase, stronger van der waals forces as size and relative mass increases

Question 15

what is the trend in electronegativity down group 7?

Answer 15

decreases, larger atoms attract electrons less as the outer electron is further from the nucleus and more shielded

Question 16

what is the trend in reactivity down group 7?

Answer 16

-when halogens react they gain an electron, oxidising agents
-decreases, the outer shell is further from the nucleus, halogens become less oxidising down the group

Question 17

what happens when Cl2(aq) reacts with KBr(aq) ?

Answer 17

orange solution is formed (Br2)

e.g. Cl2(aq) + 2KBr(aq) –> 2KCl(aq) + Br2(aq)
Cl2(aq) + 2Br-(aq) –> 2Cl-(aq) + Br2(aq)

Question 18

what happens when Cl2(aq) reacts with KI(aq) ?

Answer 18

brown solution is formed (I2)

e.g. Cl2(aq) + 2KI(aq) –> 2KCl(aq) + I2(aq)
Cl2(aq) + 2I-(aq) –> 2Cl-(aq) + I2(aq)

Question 19

what happens when Br2(aq) reacts with KI(aq) ?

Answer 19

brown solution is formed (I2)

e.g. Br2(aq) + 2KI(aq) –> 2KBr(aq) + I2(aq)
Br2(aq) + 2I-(aq) –> 2Br-(aq) + I2(aq)

Question 20

how is bleach formed?

Answer 20

-chloride gas with cold, dilute sodium hydroxide, sodium chlorate(I) solution (NaClO(aq)) is produced
-chlorine is oxidised and reduced, disproportionation

2NaOH(aq) + Cl2(g) –> NaClO(aq) + NaCl(aq) + H2O(I)

Question 21

what happens when you mix chlorine and water?

Answer 21

undergoes disproportionation, end up with a mixture of chloride ions and chlorate(I) ions

Cl2(g) + H2O(I) ⇌ 2H+(aq) + Cl-(aq) + ClO-(aq)

Question 22

what happens to chlorine in sunlight?

Answer 22

decomposes water to form chloride ions and oxygen

Cl2(g) + H2O(I) ⇌ 2H+(aq) + 2Cl-(aq) + ClO-(aq)

Question 23

how can water be treated with bleach?

Answer 23

chlorate(I) ions kill bacteria, making water safe to drink or swim in

Question 24

what are the downside of chlorine?

Answer 24

-toxic
-chlorine gas, irritates respiratory system
-liquid chlorine, causes severe chemical burns
-reacts with organic compounds to form chlorine hydrocarbons that are cancer-causing

Question 25

what is the trend in reducing power of halides?

Answer 25

increases, the attraction between outer electrons and nucleus decreases as ions get bigger, as well as increased shielding

Question 26

what happens when halides react with sulphuric acid?

Answer 26

-produce a hydrogen halide e.g. NaCl(s) + H2SO4(I) --> NaHSO4(s) + HCl(g) -some are strong enough to reduce sulphuric acid to water and sulphur dioxide e.g. 2HBr(s) + H2SO4(I) --> Br2(g) + SO2(g) + 2H2O(I) 2Br-(g) --> Br2(s) + 2e- H2SO4 + 2H+ + 2e- --> SO2 + 2H2O

Question 27

what is the test for halides?

Answer 27

-add nitric acid (HNO3) -add silver nitrate (AgNO3(aq)) -white precipitate, chloride, most soluble cream precipitate, bromide pale yellow precipitate, iodide, least soluble e.g. Ag+(aq) + Cl-(aq) --> AgCl(s)

Question 28

what is the flame test for group 2 ions?

Answer 28

-dip nichrome wire in concentrated HCl -dip in unknown compound -hold over blue flame -brick red, calcium red, strontium barium, pale green

Question 29

what is the tube test for group 2 ions?

Answer 29

-add NaOH to tube containing metal ion -keep adding until in excess -white precipitate, magnesium/calcium/strontium no change, barium

Question 30

what is the test for ammonium ions?

Answer 30

-add sodium hydroxide to solution -gently heat tube -damp (so ammonia can dissolve) litmus paper turns blue NH4+(aq) + OH-(aq) --> NH3(g) + H2O(I)

Question 31

what is the test for hydroxide ions?

Answer 31

dip red litmus paper into solution, turns blue

Question 32

what is the test for carbonate ions?

Answer 32

-add HCl, causes fizz (carbon dioxide) or -bubble gas through test tube of limewater, turns cloudy