Question

The hardness of water (hardness count) is usually expressed as parts per million (by mass) of calcium carbonate. What is the molar concentration of calcium ions in a water sample with a hardness count of 175ppm?

Answer 1

1 ppm = 1 mg/L; therefore, 175 ppm = 175 mg CaCO3/L.
Convert to grams Ca ions.
Convert to mols Ca
M = mols Ca/L solution.

Answer 2

PPM

Answer 3

Answer:

1.75 × 10⁻³ M

Explanation:

Given:

Hardness = 175 mg CaCO₃/L

or mass of CaCO₃ in 1 L = 175 × 10⁻³ grams

Now,

Molar mass of CaCO₃ = 40 + 12 + ( 3 × 12 ) = 100 grams/mol

The concentration of CaCO₃ = number of moles / volume

or

= (175 × 10⁻³ / 100) / 1

or

= 1.75 × 10⁻³ M

Now,

CaCO₃ ⇒ Ca²⁺ + CO₃²⁻

1.75 × 10⁻³ M 1.75 × 10⁻³ M 1.75 × 10⁻³ M

thus,

the concentration of Ca²⁺ ions in water = 1.75 × 10⁻³ M