Question

The hardness of water (hardness count) is usually expressed in parts per million (by mass) of CaCO₃, which is equivalent to milligrams of CaCO₃ per liter of water. What is the molar concentration of Ca²⁺ ions in a water sample with a hardness count of 175 mg CaCO₃/L?

a) 0.0017 M
b) 0.0042 M
c) 0.0083 M
d) 0.0167 M

Answer 1

The molar concentration of Ca²⁺ ions in a water sample with a hardness count of 175 mg CaCO₃/L is 0.001749 M. The correct option is (A).

Step-by-step explanation:

The molar concentration of Ca²⁺ ions in a water sample with a hardness count of 175 mg CaCO₃/L can be calculated as follows:

First, we need to convert the hardness count from mg CaCO₃/L to moles of CaCO₃/L.

Given that the molar mass of CaCO₃ is 100.09 g/mol, we can calculate:

175 mg CaCO₃/L * (1 g / 1000 mg) * (1 mol CaCO₃ / 100.09 g) = 0.001749 mol CaCO₃/L

Since the molar ratio between Ca²⁺ ions and CaCO₃ is 1:1, the molar concentration of Ca²⁺ ions is the same as the molar concentration of CaCO₃, which is 0.001749 M.