False positive

If asked why dilute hydrochloric acid is added first, explain that it removes carbonate ions which could otherwise form another white barium precipitate and cause a false positive.

For sulfate, acidify with dilute hydrochloric acid before adding barium chloride. Do not use sulfuric acid because it would introduce sulfate ions and could cause a false positive.

For a sulfate test, acidify with hydrochloric acid rather than sulfuric acid; sulfuric acid would introduce sulfate ions and could cause a false positive.