Question

How many molecules of HCl are in 4.91 L of HCl acid at 25°C if the density equals 1.096 g/mL?

Answer 1

4.91L=4910mL. The mass is 4910×1.096g=5381.36g.

Using Avogadro’s number 6.022×10²³ which relates the molecular mass to mass in grams, and using H=1 and Cl=35.5 as atomic weights, the molecular mass is 36.5 approx, so 36.5g contain 6.022×10²³ molecules.

Therefore 5381.36g contain 5381.36/36.5×6.022×10²³=887.85×10²³=8.8785×10²⁵ molecules. Round this because of approximations to 8.88×10²⁵ molecules.