concentration of solution (prelim chem - water) (1 Viewer)

[jnney]

calculate concentrattion in molL-1

0.71g of calcium chloride-2-water in 250ml of water.


Attempt:

From - C=n/v

n = moles of cacl2.2.h2o

n = .71/(40.04+35.45x2)+2(1.008x2+16)

n = 4.8 x 10^-3 mol

therefore Concentration = 4.8 x 10^-3 / .250

C = 0.0192 mol L-1.

Is this right? the answer seems a bit funny .

Thank you .

 

[ohexploitable]

I think you're missing the point of the question, when CaCl₂.2H₂O dissolves the trapped 2H₂O will become part of the water i.e. total volume of water = 250mL + the trapped water.

I think the question is asking you to find the concentration of CaCl₂

 

[jnney]

How do you find the volume of 2h2o?

 

[ohexploitable]

How do you find the volume of 2h2o?

There are 2 moles of H₂O for every mole of CaCl₂.2H₂O.

Calculate the number of moles of H₂O (2 x 4.8 x 10³ according to your calculations), then find the mass, then find the volume (1g=1mL at room temp).