[DarkS]

During a chemistry lesson, almost all of the students got the answer for a question wrong. When the lesson had ended the teacher hadn't yet told us the problem with our method and most of us are quite passionate to find the correct answer now.

Mass of solute: 12g of MgCl₂
The volume of liquid:?
Concentration mol/dm³: 1.5 mol/dm³
Concentration g/dm³: 19.6/dm³

In a previous lesson, we had learnt that:

Concentration mol/dm³ = number of moles / volume (dm³)

so rearranging this gives:

Volume = number of moles / Concentration

To work out the number of moles I had taken the mass (12g) and divided it by its relative formula mass (95):

Number of moles = 12/95 = 0.12631578947

then I substituted it into the earlier equation: Volume = number of moles / Concentration

Volume = 0.126 / 1.5 = 0.0084dm³

However, the teacher's answer was 8dm³, though I'm pretty sure my answer is wrong I don't know where I went wrong. All help is appreciated

I've attached the worksheet as pdf where the question is from but it has my messy writing over some of it so it may be unclear.

[chenbeier]

Neither 0,0084 dm³ nor 8 dm³ is correct.
The  result is 0,084 dm³

Die teachers value is to large yours to small.

Also die concentration 19.6 g/ dm³ is wrong.

1.5 mol/dm³ x 95 g/mol = 142,5 g/dm³

[DarkS]

Thanks, it seems I made a careless calculating mistake. I will wait for my teacher's explanation on how she got 8 to see her points.