what would the right answer be

Question

Gold dissolves in the acid mixture known as aqua regia according to the following balanced reaction:

Au + HNO3 + 3 HCl --> AuCl3 + NO + 2H2O

If 1.25mg of gold can dissolve what mass of Hydrochloric acid will also be reacted to completely dissolve this gold.

A

7.72 X 10-5 g HCl

B

3.75 mg HCl

C

6.95 X 10 -4 g HCl

D

0.6947 g HCl

Answer 1

Answer is "c". Molar ratio of HCl/Au is 3/1. convert 1.25 mg Au=0.00125 g Au, divide by the molar mass of Au (196.97 grams/mole) and then multiply by 3 to find moles of Hcl. Then multiply by the molar mas of HCl (36.45 grams/mole) and obtain the result, 6.94 x10^-4 grams.