How many grams of CaCl2 are needed to make 100ml of a 15% solution in water if only the dihydrated (CaCl2⋅2 H2O) salt is available?
You want 15 g CaCl2. You will need
15 g CaCl2 x [(molar mass CaCl2.2H2O/molar mass CaCl2)] = ? g CaCl2.
To calculate the number of grams of CaCl2 needed to make a 15% solution in water, we'll need to know the molar mass of CaCl2⋅2 H2O and the density of the solution. Let's break down the steps to find the answer.
1. Determine the molar mass of CaCl2⋅2 H2O:
- The molar mass of calcium chloride (CaCl2) is 40.08 g/mol (40.08 grams per mole).
- The molar mass of water (H2O) is 18.02 g/mol (18.02 grams per mole).
- Since there are two water molecules in CaCl2⋅2 H2O, the molar mass of CaCl2⋅2 H2O is:
Mass of CaCl2 + (2 × Mass of H2O) = 40.08 g/mol + (2 × 18.02 g/mol) = 76.12 g/mol
2. Calculate the mass of the 15% solution:
- To make a 15% solution, 100 ml (or 100 grams, as 1 ml of water weighs approximately 1 gram) of the solution will contain 15 grams of CaCl2⋅2 H2O.
- Therefore, the desired mass of CaCl2⋅2 H2O is 15 grams.
3. Use the molar mass to determine the number of moles:
- Divide the mass of CaCl2⋅2 H2O by its molar mass:
Number of moles = Mass / Molar mass = 15 g / 76.12 g/mol ≈ 0.197 mol
4. Convert moles to grams of CaCl2:
- Since there is one calcium (Ca) ion in each formula unit of CaCl2, the number of grams of CaCl2 is the same as the number of grams of CaCl2⋅2 H2O.
- Therefore, 0.197 mol of CaCl2 is equal to 0.197 × 76.12 g/mol = 15 grams.
Hence, you will need 15 grams of CaCl2 to make 100 ml of a 15% solution in water using the dihydrated (CaCl2⋅2 H2O) salt.