5 M NaOH solution has density 1.50g ml. Calculate its molality.
Answers
Answer:
Explanation:
If all you are given is Molarity, then you also need to know the density of the solution to calculate molality, m (mol/kg solvent).
The easiest way to understand the process is to assume you have 1L of solution which is 1000 mL. Think of the units of molarity and molality. So here is an example:
What is the molality of a
3.00 M
solution of
NaCl
? The density of the solution is
1.12 g/mL
.
We know that in
1.00 L
of solution, there are
3.00
mol of
NaCl
, since that is the meaning of
3.00 M
.
If we figure out how many kg of water there are in
1.00 L
of this solution, we are almost done! Many students are confused between solution and solvent, so be careful.
First let's figure out the mass of the solution using dimensional analysis and density:
? g soln
=
1.00
L
×
1000
mL
1
L
×
1.12 g
1
mL
=
1120 g solution
Now we need to know the mass of just the water.
? g water
=
mass of the solution
−
mass of NaCl in the solution
=
1120 g soln
−
(
3.00
mol NaCl
×
58.4 g
1 mol NaCl
)
=
1120 g soln
−
175 g NaCl
=
945 g water
=
0.945 kg of water
Now, use the units of molality as an equation:
molality
(
mol solute
kg solvent
)
=
no. moles NaCl
no. kg water
So,
molality
=
3.00 mol NaCl
0.945 kg water
=
3.17 m NaCl
Answer:
to calculate the molarity of a solution, you need to know the number of moles of ... a total of 225 mL of solution? Solution: 1 mol of NaOH has a mass of 40.00 g, so