If the original solution contained 0.12 mol hcl, what amount of hcl, in moles, will remain when the reaction is complete? 1.4 g zn reacted.

First, we have to know the reaction between HCl and Zn. This is a single replacement reaction as shown below:

2 HCl + Zn → ZnCl₂ + 2  H⁺

The molar mass for zinc is 65.38 g/mol. Convert mass to moles and compute for moles of HCl needed to completely react.

Mole of Zn = 1.4 g * 1 mol/65.38 g = 0.0214 moles Zn
Moles of HCl reacted =  0.0214 mol Zn * ( 2 mol HCl/1 mol Zn) = 0.0428 mol
Moles HCl remaining = 0.12 - 0.0428 = 0/077 moles HCl