Limus or universal indicator paper:
Turns blue/ purple when hydroxide ions (OH-) are present.
Adding hydrochloric acid:
Bubbles of gas are given off if carbonate ions (CO3,2+) os sulphate ions (SO3,2-)are present.
E.g. 2HCl + Na2CO3 -> 2NaCl + CO2 +H2O
Identifying the gas formed:
If the gas turns limewater milky, the gas is carbon dioxide, and carbonate ions are present.
If the gass is acidic and has a chocking smell, the gas is sulphurdioxide, and a sulphite was present.
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