JEE Main 2021 · 26 February · evening · Single correct · +4 / −1
Calgon is used for water treatment. Which of the following statement is NOT true about Calgon?
- (a) It is also known as Graham's salt.
- (b) It is polymeric compound and is water soluble.
- (c) It does not remove Ca²⁺ ion by precipitation.
- (d) Calgon contains the 2ⁿᵈ most abundant element by weight in the Earth's crust.
Answer and solution
Answer (d) Calgon contains the 2ⁿᵈ most abundant element by weight in the Earth's crust.
Solution
Chemistry ma’am · 3 steps
Write Calgon's formula and list its elements: silicon, second in the Earth's crust, is not one of them.
- What Calgon is. Calgon is sodium hexametaphosphate, (NaPO₃)₆, often written as Na₂[Na₄(PO₃)₆]. Its only elements are Na, P and O.
- How it softens. It holds Ca²⁺ and Mg²⁺ in a soluble complex and releases Na⁺ into the water. Nothing settles out as a precipitate.
Na₂[Na₄(PO₃)₆] + 2Ca²⁺ → Na₂[Ca₂(PO₃)₆] + 4Na⁺
Statement Check True? (a) Graham's salt Sodium hexametaphosphate is also called Graham's salt true (b) Polymeric, water soluble It is a chain of PO₃⁻ units, and it dissolves in water true (c) No precipitation of Ca²⁺ Ca²⁺ stays in solution, held in a soluble complex true (d) Contains the 2nd most abundant crustal element Crust order is O, then Si, then Al. Calgon has no Si false - So. Statement (d) is the one that is NOT true. Calgon contains oxygen, which is the most abundant element in the crust, but it does not contain silicon, which is the second.
The idea to keep. Calgon softens water by holding Ca²⁺ and Mg²⁺ in a soluble complex, not by precipitating them. In the Earth's crust the order is O, then Si, then Al.
Answer from the NTA final answer key. Solution by PrepWiser.