2.2 Group 2

Question 1

Why do group 2 metals have high melting points?

Answer 1

• Giant metallic lattice structure held together by strong metallic bonds
• very strong attraction between positive metal ions and delocalised electrons
• lots of energy needed to break the bonds

Question 2

Why are group 2 metals denser than group 1 metals?

Answer 2

• stronger bonding as the ions have a 2+ charge so stronger attraction to delocalised electrons
• ions are smaller and heavier so can be packed together more densely

Question 3

Why do group 2 metals have similar chemical reactions?

Answer 3

• all have 2 electrons in outer shell
• all good reducing agents

Question 4

Appearance of group 2 metals:

Answer 4

White solids that form colourless solutions

Question 5

What is the trend in atomic radius down group 2?

Answer 5

• atomic radius increases
• number of shells increases
• nuclear attraction on the outer electron decreases

Question 6

What is the trend in first IE down group 2?

Answer 6

• decreases down the group
• atomic radius and shells/shielding increase
• greater distance between nucleus and outer electron
• less nuclear attraction on outer electron
• less energy needed to remove outer electron

Question 7

What is the trend in melting points down group 2?

Answer 7

• melting points decrease
• size of ions increases but 2+ charge does not change
• attraction between ions and delocalised electrons gets weaker
• less energy needed to break the bonds

Question 8

What is the trend in reactivity down group 2?

Answer 8

• increases down the group
• shells/shielding increases, nuclear attraction on outer electrons decreases
• electrons are lost more easily

Question 9

Magnesium + cold water

Answer 9

Forms Mg(OH)2 (s) + H2

*very slight effervescence, very slow reaction

Question 10

Magnesium + steam

Answer 10

Forms MgO (s) + H2

• bright white light/flare
• white solid

Question 11

Calcium + cold water

Answer 11

Ca(OH)2 (aq) + H2

• vigorous effervescence
• Ca dissolves
• solution turns deep blue (alkaline pH 10-12)

Question 12

Strontium + cold water

Answer 12

Sr(OH)2 (aq) + H2

*very vigorous effervescence
*Sr dissolves

Question 13

Barium + cold water

Answer 13

Ba(OH)2 (aq) + H2

• most vigorous effervescence of group 2
• Ba dissolves

Question 14

Describe the extraction of titanium from its ore:

Answer 14

1) titanium oxide ore is reacted with carbon and chlorine - produces titanium tetrachloride

2) TiCl4 is reduced with magnesium metal to produce titanium

Question 15

Give 2 equations that occur when extracting titanium from its ore:

Answer 15

1) Tio2 + 2Cl2 + 2C&raquo_space;> TiCl4 + 2CO

2) TiCl4 + 2Mg&raquo_space;> Ti + 2MgCl2

Question 16

What is the trend in solubility of group 2 hydroxides?

Answer 16

• solubility increases down the group

Examples:
* Mg(OH)2 is insoluble (white solid)
* Ba(OH)2 is soluble

Question 17

What is the trend in the pH of the hydroxides?

Answer 17

• pH increases down the group

Question 18

Describe a use of magnesium hydroxide:

Answer 18

*in medicine as an antacid for children (milk of magnesia)

• neutralises stomach acid

Question 19

Describe a use of calcium hydroxide:

Answer 19

• in agriculture, to neutralise acid soil

Question 20

What is trend in solubility of group 2 sulphates?

Answer 20

• solubility decreases down the group

Examples:
* MgSO4 is soluble
* BaSO4 is insoluble (white solid)

Question 21

Describe the changes in oxidation states when group 2 metals react with cold water:

Answer 21

• the metal is oxidised (0»>+2)
• hydrogen is reduced (+1»>0)

Question 22

State the roles of the metal and hydrogen in this reaction:

Answer 22

• metal - reducing agent
• hydrogen - oxidising agent

Question 23

Describe a method to confirm the presence of Mg2+ ions:

Answer 23

• add aqueous sodium hydroxide to a solution of the group 2 compound being tested
• observe the precipitate formed (thick white)

Question 24

What suggests the presence of Mg2+ ions?

Answer 24

• the pH of the solution turns slightly alkaline (because Mg(OH)2 is sparingly soluble)
• indicates a small amount of OH- ions have dissolved

Question 25

Describe a method to confirm the presence of Ba2+ ions:

Answer 25

* add sulfuric acid (or aqueous sodium sulphate) to a solution of the group 2 compound being tested * observe the precipitates formed (thick white)

Question 26

Describe a method, using barium salts, to test for sulphate ions:

Answer 26

* add 1cm3 hydrochloric acid to 1cm3 of an unknown solution * add 1cm3 of an aqueous barium salt (Ba(NO3)2) * white precipitate (BaSO4) will form if sulphate ions are present

Question 27

Why is it important to add an acid to the unknown solution?

Answer 27

* to remove CO3(2-) ions that may interfere with the test

Question 28

Give an equation to show the removal of CO3(2-) ions using HCl:

Answer 28

2H(+) + CO3(2-) >> CO2 + H2O

Question 29

Describe a use of barium sulphate:

Answer 29

* in medicine (barium meal) is ingested * allows for x-rays to be taken of soft tissue

Question 30

Even though it is toxic, why is barium sulphate able to be safely ingested?

Answer 30

* barium sulphate is insoluble so the Ba2+ ions are not absorbed into the blood

Question 31

Describe a method, using magnesium salts, to test for hydroxide ions:

Answer 31

* add 1cm3 of a magnesium salt (MgCl2) to 1cm3 of an unknown solution * a white precipitate (Mg(OH)2) forms if hydroxide ions are present

Question 32

Describe a use of calcium compounds:

Answer 32

* CaO / CaCO3 cam be used to remove sulphur dioxide from flue gas * chimneys lined with CaO / CaCO3 (bases), neutralise the SO2 to prevent acid rain (H2SO4) forming

Question 33

Give equations to show the removal of SO2 from flue gas using calcium compounds:

Answer 33

* CaO + SO2 >> CaSO3 * CaCO3 + SO2 >> CaSO3 + CO2