we desire to prepare 100cm³ 0.4 M solution MGCl² ,how much MGCl² is needed
Answers
Explanation:
For starters, we know that a
1-M
solution contains
1
mole of solute for every
1.0 L
of solution.
This implies that a
4.5-M
magnesium chloride solution will contain
4.5
moles of magnesium chloride, the solute, for every
1.0 L
of solution.
So all you have to do now is figure out how many moles of magnesium chloride would be equivalent in
2.0 L
of solution to
4.5
moles in
'
1.0
L
of solution.
?
.
moles MgCl
2
2.0 L solution
=
= 4.5 M solution
4.5 moles MgCl
2
1.0 L solution
Use cross multiplication to get
?
=
2.0
L solution
1.0
L solution
⋅
4.5 moles MgCl
2
This will be equal to
?
=
9.0 moles MgCl
2
So, you know that you can get a
4.5-M
magnesium chloride solution by dissolving
9.0
moles of magnesium chloride in enough water to have a total volume of
2.0 L
of solution.
To convert this to grams, use the compound's molar mass
9.0
moles MgCl
2
⋅
95.211 g
1
mole MgCl
2
=
860 g
−−−−−
The answer is rounded to two sig figs, the number of sig figs you have for your values.