Question

Compare the water hardness of the following three solutions as mg of calcium ions in 1 liter of water and answer the following questions:

a) 25 mg
b) 100 mg
c) 200 mg
According to the water hardness labels from EPA, Solution B is considered as
1)very hard
2)hard
3)soft
4)moderately hard

Answer 1

Moderately hard water has 60-120 mg/L of calcium. A water hardness of 175 mg CaCO3/L is considered hard, surpassing moderate levels. The molarity of Ca2+ ions in this context can be calculated from the molar mass of CaCO3.

Step-by-step explanation:

Water hardness is typically gauged by the presence of calcium ions (Ca2+), which are predominantly attributed to calcium carbonate (CaCO3) in the water. Moderately hard water contains about 60-120 mg/L of calcium or 60-120 ppm (parts per million) as CaCO3. On the contrary, a water sample with a hardness count of 175 mg of CaCO3 per liter indicates a higher level of hardness, surpassing the threshold for moderately hard water and delving into the category of hard water.

To understand the molar concentration of Ca2+ ions, we can calculate it based on the molar mass of CaCO3, which is 100.09 g/mol. By dividing the concentration by mass (175 mg/L) by the molar mass, then multiplying by 1000 to convert mg to grams, we arrive at a molarity for CaCO3 in water. However, since each molecule of CaCO3 produces one Ca2+ ion upon dissolution, the molarity of Ca2+ is equal to the molarity of CaCO3.