Making
Molar
Solutions
From
Solids
What are molar solutions?
A molar solution is one that expresses
“concentration” in moles per volume
Usually the units are in mol/L
mol/L can be abbreviated as M or [ ]
Molar solutions are prepared using:
a balance to weigh moles (as grams)
a volumetric flask to measure litres
L refers to entire volume, not water!
Because the units are mol/L,
we can use the equation M = n/L
Alternatively, we can use the factor label method
Calculations with molar solutions
Q: How many moles of NaCl are required to
make 7.5 L of a 0.10 M solution?
M=n/L, n = 0.10 M x 7.5 L = 0.75 mol
# mol NaCl = 7.5 L x 0.10 mol NaCl = 0.75 mol
1L
But in the lab we weigh grams not moles, so …
Q: How many grams of NaCl are required to
make 7.5 L of a 0.10 M solution?
# g NaCl =
7.5 L x 0.10 mol NaCl x 58.44 g NaCl =43.83 g
1L
1 mol NaCl
Read pages 288 – 290. Do Q 19 - 22
19. # g NaOH =
3.00 L x 0.125 mol NaOHx 40.00 g NaOH =15.0 g
1L
1 mol NaOH
20. # g NaCl =
5.0 L x 0.56 mol NaCl x 58.44 g NaCl = 164 g
1L
1 mol NaCl
21. 355 ppm = 355 mg/L or 0.355 g/L
# g CO2 = 1.00 Lx 0.355 g CO2 =.355 g
1L
0.355 g CO2x 1 mol CO2 = 8.07 x 10–3 mol
44.0 g CO2  1L = 8.07 x 10–3 mol/L
22. a) 235 g  3000 mL x 100% =7.83 % W/V
b) mol/L = 4.02 mol / 3.00 L = 1.34 mol/L
Practice making molar solutions
1. Calculate # of grams required to make 100 mL
of a 0.10 M solution of NaOH (see above).
2. Get volumetric flask, plastic bottle, 100 mL
beaker, eyedropper. Rinse all with tap water.
3. Fill a beaker with distilled water.
4. Pour 20 - 30 mL of H2O from beaker into flask.
5. Weigh NaOH. Add it to flask. Do step 5 quickly.
6. Mix (by swirling) until the NaOH is dissolved.
7. Add distilled H2O to just below the colored
line.
8. Add distilled H2O to the line using eyedropper.
9. Place solution in a bottle. Place label (tape) on
bottle (name, date, chemical, molarity). Place
More Practice Questions
For more lessons, visit
www.chalkbored.com
1. How many grams of nitric acid are present in 1.0 L
of a 1.0 M HNO3 solution? 63 g
2. Calculate the number of grams needed to produce
1.00 L of these solutions: a) 1.00 M KNO3 101 g
b) 1.85 M H2SO4 181 g c) 0.67 M KClO3 82 g
3. Calculate the # of grams needed to produce each:
a) 0.20 L of 1.5 M KCl b) 0.160 L of 0.300 M HCl
c) 0.20 L of 0.09 mol/L AgNO3 a) 22 g b) 1.75 g
d) 250 mL of 3.1 mol/L BaCl2
c) 3 g d) 0.16 kg
4. Give the molarity of a solution containing 10 g of
each solute in 2.5 L of solution: a)H2SO4 b)Ca(OH)2
5. Describe how 100 mL of a 0.10 mol/L
a) 0.041 mol/L
NaOH solution would be made.
b) 0.054 mol/L