topic 4A

Question 1

atomic radius down group 2

Answer 1

increases because the atoms have more shells of electrons

Question 2

melting points down group 2

Answer 2

decreases becuase metallic bonding weakens as atomic size increases. Distance between positive ions and delocalised electrons increases so electrostatic force of attraction between them weakens

Question 3

what happens to 1st ionisation energy down the group

Answer 3

outermost electrons are held more weakly as they are further from the nucleus.
outer shell electrons become more shielded
so it decreases

Question 4

reactivity of group 2 metals down a group

Answer 4

increases as the atomic radii increases hence there is more shielding. Nuclear attraction decreases so it’s easier to remove outer electrons

Question 5

reactions with oxygen

Answer 5

• they burn in oxygen

Question 6

Magnesium?

Answer 6

burns with white flame

Question 7

Barium reactivity?

Answer 7

most reactive

Question 8

Berylium?

Answer 8

no reaction

Question 9

Calcium?

Answer 9

burns with a red flame producing calcium oxide

Question 10

barium?

Answer 10

burns with green flame

Question 11

react with chlorine?

Answer 11

group 2 metals will react with chlorine

Question 12

reactions with water - Mg

Answer 12

reacts in steam to produce magnesium oxide and hydrogen
also reacts with warm water giving a different magnesium hydroxide product (very slow reaction)

Question 13

reactions with water - other group 2 metals

Answer 13

react with cold water with increasing effervescence down the group to form hydroxides

Question 14

observations

Answer 14

fizzing
metal dissolving
solution heating up

Question 15

observation with calcium

Answer 15

white precipitate forming

Question 16

solubility of hydroxides

Answer 16

become more soluble down the group.
when not soluble they appear as white precipitate

Question 17

is magnesium hydroxide soluble?

Answer 17

insoluble
MgOH is used in medicine to neutralise excess acid in stomach and treat constipation
safe to use because it is weakly alkaline

Question 18

is calcium hydroxide soluble

what is it used for

Answer 18

reasonably soluble
used in agriculture to neutralise acidic soils
lime water is an aqueous solution of CaOH which is used as a test for CO2

Question 19

is barium hydroxide soluble?

Answer 19

would easily dissolve
hydroxide ions present would make solution strongly alkaline

Question 20

solubility of sulfates

Answer 20

group 2 sulfates become less soluble down the group
BaSO4 is least soluble

Question 21

what would happen if barium reacted with sulfuric acid

Answer 21

would react slowly as the insoluble barium sulfate produced would cover the surface of the metal and act as a barrier to further attack

Question 22

thermal decomposition

Answer 22

use of heat to break down a reactant into more than 1 product

Question 23

what happens to group 2 carbonates when heated

Answer 23

they decompose to produce group 2 oxides and carbon dioxide gas

Question 24

ease of thermal decomposition down group 2?

Answer 24

decreases
become more thermally stable
cations get bigger - less polarising effect - CO bond weakens - less easily break down

Question 25

investigating ease of thermal decomposition

Answer 25

heat known mass of carbonate in a boiling tube and pass the gas through limewater. Time for the first permanent cloudiness to appear in the lime-water. Repeat for different carbonates using same moles and same volume of lw

Question 26

thermal decomposition of group 2 nitrates

Answer 26

they decompose to produce group 2 oxides, oxygen and nitrogen dioxide gas

Question 27

word equation for thermal decomposition of group 2 nitrates

Answer 27

metal nitrate -> metal oxide + nitrogen dioxide + oxygen

Question 28

change in thermal stability explanation

Answer 28

Magnesium nitrate decomposes the easiest because the Mg2+ ion is smallest and has the greater charge density. Causes more polarisation of the nitrate anion and weakens N-O bond

Question 29

Group 1 nitrates decomposition

Answer 29

metal nitrate –> nitrate salt + oxygen

Question 30

method for flame test

Answer 30

• use nichrome wire
• dip in concentrated HCl and heat under Bunsen flame
• If sample is not powdered, grind it up
• Dip wire in solid and put in Bunsen flame and observe flame colour

Question 31

flame colour for Lithium

Answer 31

carmine red

Question 32

flame colour for sodium

Answer 32

orange

Question 33

flame colour for potassium

Answer 33

lilac

Question 34

flame colour for rubidium

Answer 34

purple

Question 35

flame colour for caesium

Answer 35

violet

Question 36

flame colour for magnesium

Answer 36

no colour

Question 37

flame colour for calcium

Answer 37

brick red

Question 38

flame colour for strontium

Answer 38

crimson

Question 39

flame colour for barium

Answer 39

green

Question 40

flame colour for berylium

Answer 40

no colour

Question 41

flame colour for copper

Answer 41

blue/green

Question 42

explanation for occurence of flame colours

Answer 42

heat causes electron to move to higher energy level
electron is unstable at higher energy level so drops back down.
as it drops from high energy to low energy, energy is emitted in the form of visible light with wavelength of observed light

Question 43

problems with flame tests

Answer 43

• many compounds contain small amounts of sodium impurities
• colours are subjective as different levels of colour vision in people
• ‘brick’ red depends on the brick
• lilac/lavender/ mauve/ purple are similar

Question 44

reaction of group 2 elements with dilute acids

Answer 44

• they form a salt and hydrogen gas

Question 45

reaction of group 2 hydroxides with dilute acids

Answer 45

• they form a salt