Molarity and Dilutions Practice Problems
Molarity =
Molarity1 xVolume1 = Molarity 2 xVolume2
M1V1 = M 2V2
moles solute
Liters solution
1)
How many grams of potassium carbonate, K2CO3, are needed to make 250 mL of a 2.5 M
solution?
€
€
1st calculate
the moles of solute
2nd use moles of solute to convert to grams of solute
1) 2.5M =
€
x
0.25L
x = 0.625molesK 2CO3
2) 0.625moles x
138g K 2CO3
= 86.25g K 2CO3
1mole K 2CO3
2)
How many liters of 4.0
€ M solution can be made using 125 grams of lithium bromide, LiBr?
st
1 convert mass LiBr to moles LiBr
2nd Use moles LiBr to calculate liters solution
1.44mole
4.0M =
1moleLiBr
1) 125gLiBr x
= 1.44moleLiBr 2)
x
86.8gLiBr
x = 0.36L or 360mL
€
3)
What is the concentration of a solution that has a volume of 2.5 L and contains 660 grams of
calcium phosphate, Ca3(PO4€
)2 ?
st
1 convert mass to moles
2nd use moles to calculate molarity.
1) 660gCa3 (PO4 ) 2 x
1moleCa3 (PO4 ) 2
2.1molesCa3 (PO4 ) 2
= 2.1moleCa3 (PO4 ) 2 2) M =
= 0.84 M
309.8gCa3 (PO4 ) 2
2.5L
4)
€
How many grams of copper (II) fluoride, CuF2, are needed to make 6.7 liters of a 1.2 M
solution?
€
1st calculate the moles of solute
nd
2 convert from moles to grams
x
101.53gCuF2
= 810g CuF2
1)
2) 8.0moles CuF2 x
6.7L
1moleCuF2
x = 8.0moles CuF2
1.2M =
5)
€
A 50.0 gram sample of NaOH is dissolved in 0.600 L of water. What volume of this solution
would be€needed to create a 1.5 L solution that is 0.200 M NaOH?
1st convert mass to moles
2nd calculate molarity of solution
3rd solve for V1 using M1V1=M2V2
1) 50.0gNaOH x
€
1.25molesNaOH
1moleNaOH
= 2.08M NaOH
= 1.25moleNaOH 2) M =
0.600L
40.0gNaOH
€
3)
€
2.08M ⋅ V1 = 0.200M ⋅1.5L
V1 = 0.144L or 144mL
6)
What is the concentration, in moles per liter, of a solution with a volume of 3.3 mL that contains
12 grams of ammonium sulfite, (NH4)2SO3?
st
1 convert mass solute to moles solute
2nd calculate molarity of solution
1) 12g(NH 4 ) 2 SO3 x
€
7)
0.10moles(NH 4 ) 2 SO3
1mole(NH 4 ) 2 SO3
= 30.M
= 0.10mole(NH 4 ) 2 SO3 2) M =
0.0033L
116g(NH 4 ) 2 SO3
A concentrated solution of sulfuric acid, H2SO4, has a concentration of 18.0 M. How many
€
milliliters of the concentrated acid would be required to make 250. mL of a 1.00 M H2SO4
solution?
M1V1=M2V2
18.0M ⋅ V1 = 1.00M ⋅ 250mL
V1 = 13.9mL
€
8)
A 50 L baby pool has a chlorine concentration of 0.200 M. If 20 L of water evaporated on a hot
summer day, what is the final concentration of the pool?
1st calculate moles of chlorine in baby pool.
2nd calculate molarity using moles Cl2 and the new volume
1)
x
50L
x = 10.0molesCl€
0.200M =
2) M =
10molesCl
= 0.5M
20L