Making Molar

SolutionsFrom Solids

What are molar solutions?What are molar solutions?A molar solution is one that expresses

“concentration” in moles per volumeUsually the units are in mol/Lmol/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/LAlternatively, we can use the factor label method

Calculations with molar solutionsCalculations with molar solutionsQ: How many moles of NaCl are required to

make 7.5 L of a 0.10 M solution?

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?

M=n/L, n = 0.10 M x 7.5 L = 0.75 mol# mol NaCl =7.5 L x 0.10 mol NaCl

1 L= 0.75 mol

# g NaCl =7.5 L x 0.10 mol NaCl

1 L=43.83 gx 58.44 g NaCl

1 mol NaClRead pages 288 – 290. Do Q 19 - 22

19. # g NaOH =3.00 L x 0.125 mol NaOH

1 L=15.0 gx 40.00 g NaOH

1 mol NaOH20. # g NaCl =

5.0 L x 0.56 mol NaCl1 L

= 164 gx 58.44 g NaCl1 mol NaCl

21. 355 ppm = 355 mg/L or 0.355 g/L

22. a) 235 g 3000 mL x 100% =7.83 % W/Vb) mol/L = 4.02 mol / 3.00 L = 1.34 mol/L

# g CO2 = 1.00 Lx 0.355 g CO2

1 L=.355 g

x 1 mol CO2

44.0 g CO2

= 8.07 x 10–3 mol 1L = 8.07 x 10–3 mol/L

0.355 g CO2

Practice making molar solutionsPractice making molar solutions1. 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 bottle at front. Rinse & return equipment.

More Practice QuestionsMore Practice Questions1. How many grams of nitric acid are present in 1.0 L

of a 1.0 M HNO3 solution?

2. Calculate the number of grams needed to produce 1.00 L of these solutions: a) 1.00 M KNO3

b) 1.85 M H2SO4 c) 0.67 M KClO3

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 HClc) 0.20 L of 0.09 mol/L AgNO3

d) 250 mL of 3.1 mol/L BaCl2

4. Give the molarity of a solution containing 10 g of each solute in 2.5 L of solution: a)H2SO4 b)Ca(OH)25. Describe how 100 mL of a 0.10 mol/L NaOH solution would be made.

63 g

101 g181 g 82 g

a) 22 g b) 1.75 gc) 3 g d) 0.16 kg

a) 0.041 mol/Lb) 0.054 mol/L

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