Reacting acids with bases
4 marks · NormalAnswer the following about soluble and insoluble metal oxides.
Name one metal oxide that is soluble in water.
Write the chemical equation for its reaction with water.
State the product that makes the resulting solution an alkali.
Explain why most other metal oxides do not form alkalis when mixed with water.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Sodium oxide (Na2O) · must show Correct Group 1 oxide
(b) Na2O(s) + H2O(l) → 2NaOH(aq) · must show Correct reactants and products, Balanced
(c) Sodium hydroxide / NaOH (produces hydroxide ions, OH−) · must show NaOH or hydroxide ions
(d) Most other metal oxides are insoluble, so do not dissolve in water and cannot produce hydroxide ions. · must show Reference to insolubility, No alkali formed
Also accept: Allow calcium oxide for part a (with correct equation)
Common mistakes: Incorrect formulae in chemical equation; Misnaming metal hydroxide; Assuming all oxides are soluble
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Names a Group 1 metal oxide (e.g., sodium oxide, potassium oxide) as soluble.
A1 (b) · 1 mark · Correct chemical equation (e.g., Na2O(s) + H2O(l) → 2NaOH(aq)).
B2 (c) · 1 mark · States that sodium hydroxide/NaOH or hydroxide ions (OH−) are the product that makes the solution alkaline.
M1 (d) · 1 mark · Explains that most other metal oxides are insoluble and do not produce hydroxide ions in water.
Worked solution
a) Sodium oxide (Na2O) is soluble in water.
c) The product that makes the solution an alkali is sodium hydroxide (NaOH), which produces OH− ions.
d) Most other metal oxides are insoluble in water, so they do not produce hydroxide ions and do not make alkaline solutions.