[kenny1999]

I have a question from a chemistry exercise book

it has detailed solution, but I suspect that it's answer is wrong.

Question is

A mixture contains copper and zinc. 5.00g of the mixture are added to excess HCl.
When the reaction is complete, the solid residue is dried and weighed. The mass of the
solid residue is 3.80g

one of the questions after this background is

- Calculate the percentage by mass of zinc in the mixture.

It's detailed solution is


Since only zinc reacts with HCl, decrease in mass is due to the disappearance of Zn. and Thus, percentage by mass of zinc = (5.00-3.80)/5.00 x 100%

and that's all

I doubt it's correct...

my reasoning is that the solid residue is Zinc chloride, so 3.80 gram includes the mass of Chloride which is not the mass of Zn although there mole ratio in the reaction of Zn with HCl is 1:1. but mole ratio =/= mass ratio.

Is the book wrong or I wrong?

[Borek]

Solid residue means solid that was left. Zinc chloride is soluble and was removed with the solution.