chem

Chocolatepistachio

if someone could help with this question
I have a bottle of HCl which is labelled 35% HCl w/w. NB assume the solution density is 1.200 g/cm and the MW of HCl is 36.46g.
what is the molarity of the solution?

Billzene

1% m/m = 1 g HCl / 100 g solution
35% m/m = 35 g HCl / 100 g solution
100 g solution = 100 g / [1.2 g mL^-1] = 83.333333333333... mL
35 g /83.3333333... mL = [35 x 12] g / 1000 mL = 420 g HCl /L

[HCl] = 420/36.46 = 11.52 M (12 M to 2 sig figs since 35% m/m was 2 sig figs)

Chocolatepistachio

why is it 1.2 g mL-1
and why is it 35x12/1000

Billzene

Chocolatepistachio
1.2 g mL^-1 is the density, since 1 cm³ = 1 mL

You multiplied 83.33333333333... mL by 12 to get to 1000 mL, so you must also multiply 35 g by 12 to find how many g of HCl in 1000 mL ie 1 L