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Period 3 elements for AQA A-level Chemistry

Period 3 elements

This page covers the following topics:

1. Reactions of water with period 3 elements
2. Reactions of oxygen with period 3 elements
3. Oxides of period 3 elements

Both sodium and magnesium react with water steam to produce a metal oxide and hydrogen gas.
2Na(s) + Hโ‚‚O(g) โ†’ Naโ‚‚O(s) + Hโ‚‚(g)
Mg(s) + Hโ‚‚O(g) โ†’ MgO(s) + Hโ‚‚(g)

Sodium reacts vigorously with water to produce a metal hydroxide and hydrogen.
2Na + 2Hโ‚‚O โ†’ 2NaOH + Hโ‚‚

When hydrogen is produced in the two aforementioned reactions, bubbles are observed in a solution.

Reactions of water with period 3 elements

Most period 3 elements can burn in the presence of oxygen producing different coloured flames and forming a corresponding oxide.
4Na + Oโ‚‚ โ†’ 2Naโ‚‚O
2Mg + Oโ‚‚ โ†’ 2MgO
4Al + 3Oโ‚‚ โ†’ 2Alโ‚‚Oโ‚ƒ
Si + Oโ‚‚ โ†’ SiOโ‚‚
Pโ‚„ + 5Oโ‚‚ โ†’ Pโ‚„Oโ‚โ‚€
S + Oโ‚‚ โ†’ SOโ‚‚, 2SOโ‚‚ + Oโ‚‚ โ†’ 2SOโ‚ƒ

Reactions of oxygen with period 3 elements

Most period 3 oxides react with water to produce either alkaline or acidic solutions. The acidic properties of period 3 oxides increase going towards the right throughout the period. A solution can be tested for acidity with a litmus paper; if it turns blue, a solution is alkaline, if red, it is acidic.

Naโ‚‚O + Hโ‚‚O โ†’ 2NaOH, alkaline
MgO + Hโ‚‚O โ†’ Mg(OH)โ‚‚, alkaline
Alโ‚‚Oโ‚ƒ + Hโ‚‚O โ†’ no reaction
SiOโ‚‚ + Hโ‚‚O โ†’ no reaction
Pโ‚„Oโ‚โ‚€ + Hโ‚‚O โ†’ Hโ‚ƒPOโ‚„, acidic
SOโ‚‚ + Hโ‚‚O โ†’ Hโ‚‚SOโ‚ƒ, acidic
SOโ‚ƒ + Hโ‚‚O โ†’ Hโ‚‚SOโ‚„, acidic

Oxides of period 3 elements

1

Write a balanced equation for the reaction of magnesium oxide and water.

Magnesium oxide reacts with water to form magnesium hydroxide.

MgO + Hโ‚‚O โ†’ Mg(OH)โ‚‚

Write a balanced equation for the reaction of magnesium oxide and water.

2

Magnesium readily reacts with steam. Write a balanced equation for this chemical reaction, including physical states.

Magnesium reacts with water steam to produce magnesium oxide and hydrogen gas.

Mg(s) + Hโ‚‚O(g) โ†’ MgO(s) + Hโ‚‚(g)

Magnesium readily reacts with steam. Write a balanced equation for this chemical reaction, including physical states.

3

Sodium burns spontaneously in oxygen. Provide a balanced equation for this reaction.

Sodium can burn in the presence of oxygen producing sodium oxide.

4Na + Oโ‚‚ โ†’ 2Naโ‚‚O

Sodium burns spontaneously in oxygen. Provide a balanced equation for this reaction.

4

White phosphorus (Pโ‚„) burns spontaneously in excess oxygen to form the phosphorous(V) oxide, Pโ‚„Oโ‚โ‚€. Write a balanced equation for this reaction.

The reaction includes phosphorus (Pโ‚„) and oxygen as the reactants and phosphorus(V) oxide as the product.

Pโ‚„ + 5Oโ‚‚ โ†’ Pโ‚„Oโ‚โ‚€

White phosphorus (Pโ‚„) burns spontaneously in excess oxygen to form the phosphorous(V) oxide, Pโ‚„Oโ‚โ‚€. Write a balanced equation for this reaction.

5

How would you distinguish between sodium and magnesium in a flame test?

Sodium burns with a yellow flame and magnesium burns with a white flame.

yellow sodium flame, white magnesium flame

How would you distinguish between sodium and magnesium in a flame test?

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