What is the most suitable reagent for detecting the presence of carbonate ions in the presence of an excess of sulfate ions? A dilute NaOH(aq) B dilute H2SO4(aq) C BaCl2(aq) D NaCl(aq) - AQA - A-Level Chemistry - Question 19 - 2019 - Paper 3

The most suitable reagent for detecting carbonate ions in the presence of excess sulfate ions is dilute H2SO4. Upon addition of dilute H2SO4 to a solution containing carbonate ions (CO3^2-), a reaction occurs that produces carbon dioxide gas (CO2) and water (H2O). The reaction can be represented as follows:

ightarrow ext{H}_2 ext{O} + ext{CO}_2(g)$$ This effervescence (bubbling) indicates the presence of carbonate ions in the solution. In contrast, NaOH or NaCl would not specifically react with carbonate ions in a way that allows for clear detection in the presence of sulfate.