Final answer:
The percent by mass of water in the hydrated crystal is calculated by dividing the mass of water lost during heating (2.7 grams) by the initial mass of the hydrated crystal (8.60 grams) and multiplying by 100%, resulting in approximately 31.4% water by mass.
Step-by-step explanation:
To calculate the percent by mass of water in the hydrated crystal, you subtract the mass of the anhydrous (dry) crystal from the mass of the hydrated crystal to find the mass of water that was lost. So, 8.60 grams (initial hydrated mass) minus 5.9 grams (constant mass after heating) equals 2.7 grams, which is the mass of water lost. To find the percent by mass, you divide the mass of water by the initial mass of the hydrated compound and then multiply by 100%.
Percent by mass of water = (mass of water / mass of hydrated crystal) x 100%
Percent by mass of water = (2.7 g / 8.60 g) x 100% = approximately 31.4%
Therefore, the hydrated crystal consists of approximately 31.4% water by mass.