Other alkaline solutions
3 marks · NormalExplain why a solution of sodium carbonate in water is alkaline, even though sodium carbonate does not contain hydroxide ions in its original formula.
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Must show: Sodium carbonate reacts with water., Hydroxide ions (OH^-) are produced in the process., Alkalinity is due to these OH^- ions.
Common mistakes: Claiming carbonate ion itself is OH^-; Saying only carbonate ions are present
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Marking points
M1 · 1 mark · States or describes sodium carbonate reacts with water.
M1 · 1 mark · Mentions hydroxide ions (OH^-) are produced.
A1 · 1 mark · Explains that alkaline property comes from the OH^- ions in solution.
Worked solution
Sodium carbonate reacts with water to form sodium hydroxide and sodium hydrogencarbonate, both of which produce hydroxide ions (OH^-). The solution is alkaline due to the presence of these hydroxide ions.