Multiple choice Curdy white precipitates formed, when soap solution is used with hard water, is due to calsium and magnesium ions present in hard water. potassium and sodium ions present in hard water. calcium and sodium ions present in hard water. magnesium and potassium ions present in hard water. Reveal answer Fill a bubble to check yourself A Correct answer Explanation Hard water contains calcium and magnesium ions. When soap is used with hard water, these ions react with soap to form insoluble calcium and magnesium salts of fatty acids, appearing as curdy white precipitates.