I- Group 2- Alkaline Earth Metals

Question 1

Trend in 1st IE down group 2

Answer 1

↓
- bigger atoms
- ↑ shielding
- ↓ attraction from nucleus to outer shell e-

• 2nd IE- easier to remove both s e- in outer shell (even though nuclear charge↑)

Question 2

Trend in reactivities in group 2

Answer 2

↑ down the group
- ↓ IE
- ↓ a.e. for reactions
- faster, ↑ vigorous reactions

Question 3

Trend in melting points down group 2

Answer 3

Be ↓ Mg ↑ Ca ↓ Sr ↓ Ba

• metallic structures
• bigger metal ions
• sea of delocalised e- further from nuclei down the group
• ↓ electrastatic attraction
• weaker metallic bonds

Question 4

Trend in atomic radius

Answer 4

↑ down the group
- ∵ ↑ shells

Question 5

Trend in electronegativity

Answer 5

↓ down the group
- ∵ ↑ shielding

Question 6

Reaction of Beryllium with water

Answer 6

x react- even w/ steam

Question 7

pH of solution with Calcium + water

Answer 7

~pH12 (alkaline)

Question 8

Reaction of magnesium with steam

Answer 8

Mg (s) + H2O(g) -> MgO(s) + H2(g)​

• burns w/ a bright white flame
• white solid forms

Question 9

Reaction of magnesium with cold water

Answer 9

• ## no visible changevery clean Mg
• slight reaction –> soon stops
• ∵ Mg(OH)2 forms- insoluble
• barrier on Mg –> prevents further reaction

Question 10

Reactions of calcium, strontium, barium with cold water

Answer 10

X(s) + 2H2O(l) -> X(OH)2 (aq or s) + H2(g)​
- react w/ increasing vigor

(strontium & barium ~ reactivities as Li)

Question 11

Explain the trend in reactivities down group 2.

Answer 11

• ↑ atomic radius
• ↑ shielding of nucleus by e-
• ↓ attraction for outer e- in s orbital
• e- lost ↑ easily
• ↑ reactive
  :)
• Beryllium x fit trend- unreactive
• ∵ strong resistant layer of oxide on its surface–> lowers its reactivity

Question 12

What is a precipitate?

Answer 12

• solid
• forms when 2 dissolved ionic compounds react
• to form an insoluble product

Question 13

Atypical prperties of Beryllium

Answer 13

• Beryllium chloride- covalent ​
• Dative covalent bonds form between Be & Cl​
  :)
• Beryllium hydroxide is amphoteric​
• can react w/ both acids & bases to form salts​
  (other group 2 hydroxides are alkaline​)

Question 14

Main use of magnesium metal

Answer 14

Mineral extraction of Titanium from ore rutile (TiO2)
- TiO2 + 2C + Cl2 –>TiCl4 + 2CO​
- TiCl4 + 2Mg –>Ti + 2MgCl2
:)
- very expensive ∵ Mg is expensive + long process

Question 15

Use of Magnesium hydroxide

Answer 15

**Milk of magnesia **
* insoluble
- antacid- neutralises acid in stomach
- treats indigestion + constipation

Question 16

Use of calcium hydroxide

Answer 16

Slaked slime
- powder to neutralise acidic soil- agriculture
–> good crop prod. + maintain food supply

Question 17

Use of magnesium sulfate

Answer 17

Epsom salts
- treat magnesium deficiency

Question 18

Uses of calcium carbonate/ calcium oxide

Answer 18

Flue gas desulfurisation
- remove SO2 from flue gases (neutralisation of acidic SO2)
- CaCO3(s) + SO2(g) → CaSO3(s) + CO2(g)

Question 19

Use of barium sulfate

Answer 19

Barium meal
-** absorbs X-rays** –> shows outline of guts

• Ba2+ ions- toxic
• BaSO4- insoluble–> harmless

Question 20

Which 3 group 2 metal compounds have uses in medicine?

Answer 20

1. barium sulfate
2. magesium hydroxide
3. magnesium sulfate

Question 21

What happens when an ionic substance dissolves?

Answer 21

• ions separate + mix w/ water (random positions)
• // ppt forms

Question 22

Precautions when testing for solubilities of group 2 hydroxides & sulphates

Answer 22

• wear safety goggles
• wash hands if in contact w/ :
  BaCl2- toxic
  NaOH + H2SO4 - corrosive

Question 23

Trend in solubilities of group 2 hydroxides down the group

Answer 23

↑ soluble down the group

• Mg2+ - INSOLUBLE white ppt
  {Mg2+(aq) + 2OH- (aq)–> Mg(OH)2(s)​}
  (solution is alkaline so somw must have dissolved)
• Ca2+ - SPARINGLY SOLUBLE white ppt
  {Ca2+(aq) + 2OH- (aq)–> Ca(OH)2(s)}
• Ba2+ - no visible change

Question 24

Trend in solubilities of group 2 sulfates down the group

Answer 24

↓ soluble down the group

• Mg2+ - x visible change
• Ca2+ - SPARINGLY SOLUBLE white ppt
  {Ca2+(aq) + SO42-(aq) → CaSO4(s)​}
• Ba2+ - INSOLUBLE white ppt
  {Ba2+(aq) + SO42-(aq) → BaSO4(s)}

Question 25

Test for sulfate ions

Answer 25

1. acidify solution w/ HCl
2. add BaCl2
3. white ppt of insoluble barium sulphate
   {Ba2+(aq) + SO42-(aq)–> BaSO4(s)​}

Question 26

Why do we acidify the solution first before testing for sulfate ions?

Answer 26

• Carbonates in H2O ∵ dissolved CO2 in air
• would form barium carbonate - insoluble white ppt –> false +ve result
• acid reacts w/ carbonates –> H2O + CO2
• x carbonates to give false results
• use acid w/o sulphate ions–> x false result

Why HCl?
- same ions (Cl-) as BaCl2