What is the mass fraction of calcium chloride in the solution obtained by mixing 5g. of this salt with 45g of water?

First of all, you need to find the mass of the solution.

To do this, add up the available masses of salt and water.

M solution = M salt + M water = 5 + 45 = 50 grams;

The mass fraction of salt in the solution will be equal to the ratio of the mass of salt to the mass of the solution and will be:

C salt = M salt / M solution = M salt / (M salt + M water) = 5 / (5 + 45) = 5/50 = 0.1 = 10%;