M3 Knowledge gaps

Question 1

Periodic table is arranged… (3)

Answer 1

Increasing atomic (proton) number
Periods showing repeating trends in physical/chemical properties
Groups according to similar chemical properties

Question 2

First ionisation energy across period 3

Answer 2

Overall: increasing (increased nuclear charge and attraction)
Small decrease to Al (p-block) and again to S (first p-block with paired electron)

Question 3

First ionisation energy across period 2

Answer 3

Overall: increasing (increased nuclear charge and attraction)
Small decrease entering p-block (B) and first full p-orbital (O)

Question 4

Trend in pH of group 2 metal hydroxides

Answer 4

More soluble down the group
Higher concentration of OH- so increased alkalinity down the group
i.e., Mg(OH)2 around 8-9 and Ba(OH)2 around 12-12

Question 5

Group 2 compound used as ‘antacid’

Answer 5

Magnesium hydroxide Mg(OH)2
Calcium carbonate CaCO3

Question 6

Use of a group 2 compound in agriculture

Answer 6

Calcium hydroxide Ca(OH)2 used to neutralise acidic soils

Question 7

Chlorine - colour in aqueous / organic conditions

Answer 7

Pale green in both

Question 8

Bromine - colour in aqueous / organic conditions

Answer 8

(aq) - orange/yellow
organic - red/brown/orange

Question 9

Iodine - colour in aqueous / organic conditions

Answer 9

(aq) - brown
organic - violet

Question 10

AgCl / AgBr / AgI precipitate colours

Answer 10

AgCl: white
AgBr: cream
AgI: yellow

Question 11

Silver halide precipitates in ammonia solutions

Answer 11

AgCl redissolves in dilute NH3
AgBr redissolves in concentrated NH3
AgI does not redissolve in NH3 of any concentration

Question 12

Test for ammonia (NH4+) ion

Answer 12

Add warm NaOH
Forms NH3 (g)
Turns damp red litmus paper blue

Question 13

Enthalpy change of reaction

Answer 13

Enthalpy change associated with a stated equation under std. conditions

Question 14

Enthalpy change of formation

Answer 14

Formation of 1mol of a compound from its elements in their std. states

Question 15

Enthalpy change of combustion

Answer 15

Enthalpy change when 1mol of a substance undergoes complete combustion under std. conditions

Question 16

Enthalpy change of neutralisation

Answer 16

Enthalpy change when 1mol of H2O produced by an acid-base neutralisation under std. conditions

Question 17

Bond enthalpy

Answer 17

Mean energy needed to break 1mol of covalent bonds in gaseous molecules

Question 18

Effect of increasing temp. (operating conditions)

Answer 18

Increases rate of reaction
Increases yield of endothermic reaction
Higher fuel costs / CO2 contributes to global warming and uses up fossil fuels

Question 19

Effect of increasing pressure (operating conditions)

Answer 19

Increases rate of reaction
Increases yield of reaction which produces fewest gaseous moles
Unsafe / expensive fuel costs to maintain

Question 20

Effect of catalyst (operating conditions)

Answer 20

Increases rate of reaction
No effect on equilibrium yield
Reduces fuel costs as lower temperature and pressure can be used