Group 2 - the alkaline metals

Question 1

How reactive are they?

Answer 1

Fairly reactive, less reactive than group 1

Question 2

Atomic radius trend down group 2

Answer 2

• Increases down group 2 due to more electron shielding so electron becomes further away from nucleus

Question 3

Ionisation energy trend down group 2

Answer 3

• 1st ionisation energy decreases down, as atomic radius and shielding increases so electron is easier to remove as less attraction between electron and nucleus

Question 4

Melting point trend down group 2

Answer 4

• Decrease down group
• Because delocalised electrons further away from nucelus
• Further down the group the weaker the attraction between between nucleus and delocalised electrons

Question 5

How does magnesium react with water and give the equation?

Answer 5

• Very slowly
• Magnesium hydroxide formed
• Mg + 2H2O(l) –> Mg(OH)2 + H2

Question 6

How does magnesium react with steam and give the equation?

Answer 6

• Reacts readily with steam
• Magnesium oxide formed
• Mg + H20(g) –> MgO + H2O

Question 7

Why is magensium oxide formed rather than magnesium hydroxide with steam?

Answer 7

• As hydroxide not stable at higher temperatures
• It thermally decomposes to give magnesium oxide and water

Question 8

How do calcium, strontium and barium react with water?

Answer 8

• They produce metal hydroxides and hydrogen
• The reactivity of the reaction increases as group descends
• Calcium releases bubbles of hydrogen and a white ppt
• Strontium more reactive than calcium, less white ppt formed, barium even less white ppt formed

Question 9

Give equations of Ba, Sr, and Ca with water

Answer 9

• Ca + 2H2O —> Ca(OH)2 + H2
• Sr + 2H2O —> Sr(OH)2 + H2
• Ba + 2H2O —> Ba(OH)2 + H2

Question 10

Solubility of group 2 hydroxides in water

Answer 10

• Become more soluble down the group
  
  • Magnesium hydroxide sparingly soluble as solution slightly alkaline indicating some hydroxide ions are dissolved in the water

Question 11

Observations of Ca2+ with sodium hydroxide

Answer 11

White ppt of calcium hydroxide

Question 12

Observations of Mg2+ with sodium hydroxide

Answer 12

Thick white ppt of magnesium hydroxide

Question 13

Observations of Sr2+ with sodium hydroxide

Answer 13

Thin white ppt of strontium hydroxide

Question 14

Observations of Ba2+ sodium hydroxide

Answer 14

Very thin white ppt of barium hydroxide

Question 15

Solubility of group 2 sulfates in water

Answer 15

• Decrease in solubility down the group
• Calcium sulfate said to be sparingly soluble and barium sulfate insoluble

Question 16

Observation of Mg2+ with sodium sulfate

Answer 16

No ppt

Question 17

Observation of Ca2+ with sodium sulfate

Answer 17

Thin white ppt

Question 18

Obsevation of Sr2+ with sodium sulfate

Answer 18

White ppt

Question 19

Observation of Ba2+ with sodium sulfate

Answer 19

Thick white ppt

Question 20

The test of barium salts for a sulfate

Answer 20

1. Add 1cm3 of dilute HCl
2. Add 1cm3 aqueous barium chloride solution
3. If thick white ppt formed then sulfate ions present

Question 21

Simplest ionic equation for test for sulfate ions with barium salts

Answer 21

Ba2+(aq) + SO42- (aq) –> BaSO4(s)

Question 22

What is magnesium used for?

Answer 22

• Extraction of titanium
• Titanium can be used for aerospace, marine and motor vehicles due to high corrosion resistance

Question 23

Equation of magnesium extracting titanium

Answer 23

TiCl4 + 2Mg —> Ti + 2MgCl2

Question 24

Magnesium hydroxide use

Answer 24

• ‘Milk of magnesia’ given to alleviate constipation and as an antacid
• Solution only slightly alkaline so does not irritate oesophagus

Question 25

Calcium hydroxide use

Answer 25

• ‘Slaked slime’ neutralises acidic soil, reducing the acidity so plants can grow without nasty side effects
• Improves availabitlity of nutrients like phosphorus and improves texture of soil so smaller seedlings can break through soil surface

Question 26

Cacium oxide use

Answer 26

• Neutralises sulfure dioxide to prevent formation of acid rain.
• Calcium carbonate can also be used

Question 27

Barium sulfate use

Answer 27

• ‘Barium meal’
• Barium good at absorbing x-rays and can outline the gut
• Barium ions toxic but technique is harmless as barium sulfate insoluble and cannot be absorbed into blood

Question 28

Electronegativity down group 2

Answer 28

• Decreases down the group
• More inner energy levels of electron shielding the attractive power of the nucleus which combined with increase in atomic radius leads to decrease in electronegativity despite increased nuclear charge

Question 29

Why is water never added to burning Mg

Answer 29

Hydrogen could explode

Question 30

Any group 2 metal with water equation

Answer 30

Mg (s) + 2H2O —> Mg(OH)2 + H2

Question 31

Any group 2 metal with oxygen

Answer 31

2Ca + O2 —> 2CaO

Question 32

Any group 2 metal with acid

Answer 32

2Sr + 2HCl —> SrCl2 + H2

Question 33

Any group 2 metal with TiCl4

Answer 33

2Mg + TiCl4 —> 2MgCl2 + Ti

Question 34

Ionisation energy graph down group 2

Answer 34