4 Inorganic Chemistry and the Periodic Table

Question 1

Describe the reaction between alkali metals and chlorine

Answer 1

• all form white solid compounds
• depending on the metal the colour of flame varies

Question 2

Describe the reaction between alkali metals and water

Answer 2

• the metals floats, fizzes and dissolves
• flame colour depends on the metal
• sodium forms a spherical shape
• resulting solution turns UI blue, which indicates alkali solution

Question 3

Describe the reaction between alkali metals and oxygen

Answer 3

Group 1 metals react violently with O₂ to form a white solid

Question 4

Describe the hydroxides of alkali metals

Answer 4

• white solids
• commonly supplied as pellets or flakes
• soluble in water to form alkaline solutions
• strong bases as they fully ionise in water, giving solutions containing hydroxide ions

Question 5

Describe the carbonates of alkali metals

Answer 5

• white in colour
• unusual metal carbonates as they dissolve in water
• alkaline solution is from as the carbonate ions remove H⁺ ions from water molecules to form hydrogencarbonate ion and hydroxide ions
• do not decompose on heating besides lithium carbonate which forms the oxide and CO₂ when hot

Question 6

Describe the nitrates of alkali metals

Answer 6

• white crystalline solids
• very soluble in water
• decomposes on heat to form the nitrite and oxygen besides lithium nitrate which forms the oxide, nitrogen dioxide and oxygen

Question 7

Describe sodium and potassium compounds

Answer 7

• widely used as chemical reagents
• ions of alkali metals are in reactions which act as spectator ions
• soluble in water including their hydroxides and carbonates
• ions of alkali metals are colourless in aqueous solution so do not hide or interfere with colour changes

Question 8

Describe flame tests

Answer 8

• an analytic technique used to identify metal ions
• HCl is used as it reacts with the salt to form a metal chloride which evaporates easily on a Bunsen flame
• when a metal ion is heated, an electron with gain energy and become promoted form its ground state energy level to a higher energy level; when it returns to its original shell, the excess energy it had gain is released in the form of visible light

Question 9

Steps of flame test?

Answer 9

1. Sterilise the nichrome wire by holding it in the blue flame of a Bunsen and let it glow red
2. Dip the nichrome wire in concentrated HCl (aq)
3. Dip the nichrome wire in the solid to be tested
4. Hold the wire in the blue flame of a Bunsen and note the colour

Question 10

Describe the Group 2 elements

Answer 10

• known as alkaline earth metals
• occur as minerals in rocks
• insoluble in water
• harder and denser than Group 1 metals
• higher melting temperatures
• surface is covered with a layer of oxide

Question 11

Describe the reaction between Group 2 metals and oxygen

Answer 11

• burn in oxygen in heating to form white ionic oxides besides beryllium
• barium burns in excess oxygen or air with a green flame to form BaO₂

Question 12

Describe the reactions between Group 2 metals and water

Answer 12

• metals Mg to Ba in Group 2 react
• not as vigorous as the reactions of Group 1 metals
• rate of reaction increases down the group
• magnesium reacts very slowly with cold water producing the hydroxide, it reacts more rapidly with steam
• calcium reacts with cold water to form limewater and hydrogen, but the solubility is low that the solution becomes saturated over time

Question 13

Describe the oxides of Group 2 metals

Answer 13

• basic oxides besides beryllium oxide
• white solid

Question 14

Describe the hydroxides of Group 2 metals

Answer 14

• soluble in water forming alkaline solutions from Mg to Ba
• solubility increases down the group
• barium hydroxide is sometimes used as an alkali in chemical analysis as its carbonate would not cause contamination

Question 15

Describe the carbonates of Group 2 metals

Answer 15

• insoluble in water
• react with dilute acids
• decompose on heating to give the oxide and carbon dioxide
• thermal stability increases down the group

Question 16

Describe the nitrates of Group 2 metals

Answer 16

• colourless crystalline solids
• very soluble in water
• decompose to the oxide on heating
• thermal stability increases down the group

Question 17

Describe the sulfates of Group 2 metals

Answer 17

• colourless solids
• solubility decreases down the group
• soluble barium salt can be used to test for sulfate ions where a white precipitate forms

Question 18

How to test for carbonate ions?

Answer 18

• add dilute acid to the carbonate to observe fizzing
• pass the gas through limewater, which should turn milky
• this confirms the presence of CO₂ and so the CO₃^2-

Question 19

How to test for sulfate ions?

Answer 19

• add dilute HCl (aq) followed by BaCl₂ (aq) to the solution of the sulfate
• a white precipitate of BaSO₄ is produced

Question 20

How to test for nitrate ions?

Answer 20

• add FeSO₄ (aq) to the nitrate solution followed by conc. H₂SO₄
• a brown ring of NO₂ gas is formed at the interface

Question 21

Define “thermal decomposition ”

Answer 21

The process of breaking down a substance using heat energy

Question 22

What are the two factors that affect thermal stability?

Answer 22

• ionic charge
• ionic radius