An unknown hydrate of sodium dichromate,Na₂Cr₂O₇ • XH₂O,is heated to give 12.1% water.What is the water of crystallization (X)for the hydrate?

Question

Quizplus · Accepted Answer

The molar mass of anhydrous sodium dichromate (Na₂Cr₂O₇) is approximately 262 g/mol. Given that the hydrate loses 12.1% of its mass as water upon heating, we can calculate the mass of water lost per 100 g of hydrate. This is 12.1 g of water, which corresponds to 12.1 g / 18 g/mol (molar mass of water) = 0.672 moles of water. The closest whole number to this is 2, indicating that there are 2 moles of water (XH₂O) for every mole of Na₂Cr₂O₇, making the correct answer 2 moles of water of crystallization (X).

An Unknown Hydrate of Sodium Dichromate,Na₂Cr₂O₇ • XH₂O,is Heated to Give