if the concentration of NaCl is 0.25M, calculate

sarah1004 · #1 Nov 7, 2009, 04:07 PM

if the concentration of NaCl is 0.25M, calculate
a.how many moles of NaCl there are in 20mL of the solution
0.005mol
b.what volume of the NaCl must be taken to contain 0.1mol of NaCl.
0.4L

Are these are correct ??

Thnk you

Perito · Nov 7, 2009, 05:37 PM

1. The concentration of NaCl is 0.25 molar. That's 0.25 moles per liter. You have 20 mL of that solution

$0.25\,\frac {moles}{\cancel {Liter}}\,\times\, 20\,\cancel {mL} \,\times\, \frac {1\,\cancel {Liter}}{1000\,\cancel {mL}}= \frac {0.25\,\times\,20}{1000}\,moles = 0.005\, moles$

Yup. Looks right.

2.
$0.25 \,\frac {moles}{Liter}\,V = 0.1\,mol$

$V = 0.1 \cancel {mol} \times \frac {Liter}{0.25 \, \cancel {mol}} = 0.4\,Liter$

Yup. That looks right, too.

Congratulations.