INORGANIC topic 4 period 3 and oxides

Question 1

Give an equation for the reaction of phosphorus(V) oxide with water.

Suggest a pH for the solution formed {2}

Answer 1

.P4O10 + 6 H2O → 4 H3PO4

. ‒1 to + 1

Question 2

Give an equation and two observations made for the reaction that occurs when sodium is
heated in oxygen. {2}
Equation :
Observation 1 :
Observation 2:

Answer 2

.4Na + O2 → 2Na2O
Ignore state symbols
Allow multiples and fractions
Allow 2Na + O2 → Na2O2

.Yellow/orange flame/light AND white solid/powder/smoke/fumes/ash

Question 3

Explain the increase in melting point from sodium oxide to magnesium oxide. {2}

Answer 3

. Greater/increased charge/charge density on magnesium ion/Mg2+ (specific mention of
ion(s) can be scored from M2)
Allow magnesium ion is smaller (than sodium ion);
Ignore atomic radius

.Stronger attraction for anions/oxide ion / stronger attraction between oppositely charged
ions/ stronger attraction between Mg2+ and O2– / stronger ionic bonding

Question 4

Describe a test you could carry out in a test tube to distinguish between sodium oxide and phosphorus oxide {3}

Answer 4

.React with water / add water / solution (of substances in question)

.Add litmus paper / universal indicator / measure pH (with pH meter)

.If red litmus added sodium (hydr)oxide goes blue
-Universal Indicator: blue/ purple with sodium oxide (solution) and red with phosphorus oxide (solution)
-pH meter or Universal Indicator: sodium (hydr)oxide (solution) has a higher pH (than phosphorus oxide (solution))
-sodium (hydr)oxide pH (12 to 14) and phosphorus oxide (solution) pH (-1 to 2)