Final answer:
To find the percent by mass of water in BaCl2·2H2O, you calculate the mass of the water present in the compound, divide it by the molar mass of the compound, and multiply by 100. The calculated percentage (14.83%) does not match any of the given options, suggesting an error in the question.
Step-by-step explanation:
The percent by mass of water in BaCl2·2H2O is calculated by firstly determining the mass of the water within the compound. Water has a molar mass of 18.015 (2 hydrogen atoms at 1.008 each and one oxygen atom at 15.999), and since there are two water molecules, we double this to get 36.03 g/mol for the mass of water. The overall molar mass of BaCl2·2H2O is given as 243 g/mol.
The percentage of water by mass is calculated by taking the mass of the water, dividing it by the total mass of the compound, and then multiplying by 100 to convert to percentage.
So, percentage of water by mass =
(36.03 g / 243 g) × 100 = 14.83%
Looking at the given options, none of them matches our calculated value, which suggests there might be an error in the choices provided or that the formula mass for BaCl2·2H2O may have been incorrectly stated. If you encounter such a situation during an exam or homework, it is advisable to review your calculations and, if the discrepancy remains, bring it up with your teacher for clarification.