Solutions Part IIDHS Chemistry

Chapter 15

I. Concentrations of Solutions

• The concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solvent.

Amount of solute vs. amount of water

Dilute vs Concentrated

Little solute a lot of solute

Very Concentrated

Less Concentrated

Concentrated solutions

• A concentrated solution is one that contains a high concentration of solute.

Dilute solutions

• A dilute solution contains a small concentration of solute.

Pictorial Representation

Pictorial Representation

• There are several ways to express concentration. These include: percent solutions (by volume or mass), molarity, or molality.

A. Percent Solutions

Percent Solutions

% solute = amount of solute _ 100 TOTAL amount of solvent

solution

3 types: (%m/m) same units(%v/v) same units(%m/v) needs to be g/mL

How much vinegar is just acetic acid?

5% of vinegar is acetic acid

Percent by Volume% by volume (% (v/v)) = volume of solute

100 Volume of solution

units must be the same

Tip: watch out for the wording. You may need to add the volume of the solute and solvent to get the volume of the total solution

(solute + solvent)

Percent by Mass

% by mass (% (m/m)) = mass of solute 100 mass of solution

*units must be the same

Tip: watch out for the wording. You may need to add the mass of the solute and solvent to get the volume of the total solution

(solute + solvent)

Percent Mass by Volume

% mass by volume (% (m/v) = mass of solute (g)

100 volume of solution (mL)

*units must g/mL

Ex 1: 20 mL of alcohol is diluted with water to a total volume of 65

mL. What is the percentage of alcohol, by volume?%(v/v) = Volume of solute

100 Volume of solution

%(v/v)=

20 mL alcohol100 65 mL H2O? % = 30.8%Alcohol by

volume

65 mL alcohol + water

30.8% of this solution is alcohol. The rest is water.

20 mLalcohol

Ex 2 : A solution containing 7 g of NaCl in 165 g of

solution.

What is the percent of NaCl by mass?

7 g NaCl100 165 g solution? % NaCl (m/m)= 4.24%

Solution = Solute + solventSolution = 7 g + 158 g

158 g of solvent (water)

Children’s Dose vs Adult Dose

Diphenhydramine hydrochloride

(active ingredient in allergy medicine like Benadryl)

How do you feed a child medicine when one tablet is too

strong?

Liquid dose for children has been diluted to 12.5 mg for every 5 mL of medicine

What percent by mass of diphenhydramine hydrochloride

is in the solution?

Liquid dose for children has been diluted to 12.5mg for every 5mL of medicine

.0125 g = .250% (m/v)

5 mL 100

EX 3: A saline solution containing 3.5 g of NaCl in 62.5 mL of solution. What is

the percent of NaCl, by mass.

3.5 g NaCl100 62.5 mL solution? % = 5.60%

EX 3: A saline solution containing 3.5 g of NaCl in 62.5 mL of solution. What is

the percent of NaCl, by mass.

3.5 g NaCl100 62.5 mL solution? % = 5.60%

Ex 4: What volume of ethanol is needed to produce 120 mL of a 22.3% (v/v)

ethanol solution?

%(v/v)=

ethanol by volume (v/v)

? mL ethanol100 120 mL solution

22.3 % = 26.8 mL

Ex 5: What volume of a 2.8% (m/v) glucose solution would you need to

deliver to a patient who needs 750 mg of glucose?

glucose by volume (m/v) 0.750 g glucose

100 ? mL glucosesolution

2.8 % = 26.8 mL

Practice1. If 10 mL of pure acetone is diluted with

water to a total solution volume of 200 mL, what is the percent by volume of acetone in the solution?

2. A bottle of hydrogen peroxide is labeled 3.0% (v/v). How many mL of H2O2 are in a 400.0 mL bottle of this solution?

3. Calculate the grams of solute required to make 250 g of 0.10% MgSO4 (m/m).

4. A solution contains 2.7 g CuSO4 in 75 mL of solution. What is the percent (m/v) of the solution?

1. If 10 mL of pure acetone is diluted with water to a total solution volume of 200 mL, what is the percent by volume of acetone in the solution?

%(v/v)=

acetone by volume (v/v)

10 mL acetone100 200 mL solution

? % = 5.00 %

2. A bottle of hydrogen peroxide is labeled 3.0% (v/v). How many mL of H2O2 are in a 400.0 mL bottle of this solution?

%(v/v)=

H2O2 by volume (v/v)

? mL H2O2

100 400. mL solution3.00 % = 12.0 mL

3. Calculate the grams of solute required to make 250 g of 0.10% MgSO4 (m/m).

%(m/m)=

MgSO4 by volume (v/v)

? g MgSO4

100 250 g solution0.10 % = 0.250 g

4. A solution contains 2.7 g CuSO4 in 75 mL of solution. What is the percent (m/v) of the solution?

%(m/v)=

CuSO4 by volume (m/v)

2.7 g CuSO4

100 75 mL solution ? % = 3.60 %

Practice1. If 10 mL of pure acetone is diluted with

water to a total solution volume of 200 mL, what is the percent by volume of acetone in the solution?

2. A bottle of hydrogen peroxide is labeled 3.0% (v/v). How many mL of H2O2 are in a 400.0 mL bottle of this solution?

3. Calculate the grams of solute required to make 250 g of 0.10% MgSO4 (m/m).

4. A solution contains 2.7 g CuSO4 in 75 mL of solution. What is the percent (m/v) of the solution?

5.00% acetone (v/v)

12.0mL H2O2

0.250g MgSO4

3.60% (m/v)

B. Molarity

Molarity

• Molarity (M) is the number of moles of a solute dissolved per liter of solution.

Molarity

• Molarity is also known as molar concentration and is read as “ __#__ molar” (Ex. a 2M HCl solution is read as two molar HCl”

• Note that the volume involved is the total volume of solution, not just the solvent.

Molarity

Molarity (M) = moles of solute M = mol Liters of solution 1 L

*if given grams, convert if to moles using the molar mass of the substance

Why are grams important?

• You can not directly measure moles, you must calculate the mass in grams first

Grams MolesMolar mass

___g = 1 mole

How to Prepare a SolutionTo make 1.00 liter of a 1.00 molar (1.0

M) solution:

1) add 1.0 mol of solute to a volumetric flask

2) add about ¼ flask of distilled water. Swirl the flask till the solute is dissolved.

3) slowly add water until the final volume reads 1.00 L

Molarity EX 1. What is the molarity of a

solution that contains 8 moles of CaCl2 in 50 mL of solution?

M =1

molL

8 mol0.05 L

160M CaCl2

MolarityEX 2. How many grams of NaCl are

needed to make 500mL of a 0.2 M solution?

M =1

? molL

.2 M 0.5 L

.1 mol

0.1 mol NaCl

1 mol NaCl

58.443 g NaCl=5.84 mol NaCl

Using MolarityEx 3: A saline solution contains 0.90 g

NaCl in exactly 100 mL of solution. What is the molarity of the solution?

0.90g NaCl x

1 mol NaCl

58.443 g NaCl

=0.0154 mol NaCl

100 mL x 1 L

1000 mL

= 0.100 L NaCl

Step 1: Calculate # moles

Step 2: mL L

Ex 3 continued

Step 3: Calculate Molarity

M =1

0.0154 molL

? M 0.1 L

0.154 M

Ex 2: How many grams of solute are present in 562 mL

of 0.24 M Na2SO4?

M = mol mol = M L L

mol =

0.24M Na2SO4 x .562L

= 0.135mol

Convert from Moles to Grams

0.135mol Na2SO4 | 142g Na2SO4 = | 1 mol Na2SO4

= 19.2g Na2SO4

Practice1. A solution has a volume of 2.0 L and contains

36.0 g of glucose. If the molar mass of glucose is 180 g/mol, what is the molarity of the solution? 0.100M glucose

2. How many moles of ammonium nitrate are in 335 mL of 0.425 M NH4NO3? 0.142mol NH4NO3

3. How many grams of solute are in 250 mL of 2.0 M CaCl2 solution? 55.5gCaCl2

4. Describe how you would prepare 250 mL of a 0.2 M NaOH solution. Need 2.00g NaOH in 250mL of solution

1. A solution has a volume of 2.0 L and contains 36.0 g of glucose. If the molar mass of glucose is 180 g/mol, what is the molarity of

the solution?

Molarity = mol L

Glucose = C6H12O6

Molar mass = 6(12.01g) + 12(1.008g) + 6(15.999g) =

Calculate moles: 36.0g C6H12O6 | 1 mol C6H12O6 = mol C6H12O6

| XXX g C6H12O6

Calculate Molarity: XXXmol C6H12O6 = 0.100M glucose 2.0 L

C. Dilutions

C. Dilutions

• You can make a less concentrated solution by diluting it with solvent.

• The dilution reduces the grams of solute per unit volume, but the total amount of solute in solution does not change.

Diluted Solutions

Before After

Dilutions Dilutions

Moles of solute before dilution = Moles of solute after dilution

Moles of solute = Molarity x volume

Dilutions:

M1V1 = M2V2

Ex: How many mL of a stock solution of 2.00 M MgSO4 would you need to

prepare 100.0 mL of 0.400 M MgSO4?

(2M)(V1) = (0.400M)(100mL)

m1 v1 m2 v2

V1 = 20mL of stock solution

Stock soln

Ex. 2: Describe how to prepare 100 mL of 0.400M MgSO4 from 2M MgSO4.

(see previous example)

Add 20mL of 2M stock solution in a container and add solvent up to the 100mL mark

Practice1. How many mL of a stock solution of

4.00 M KI would you need to prepare 250.0 mL of 0.760 M KI? 47.5mL of 4.00MKI

2. What volume must you dilute to make 50.0 mL of 0.20 M KNO3 from 4.0 M KNO3? 2.5mL of 4M KNO3

3. What is the molarity of a solution formed when you add 200 mL of water to 50 mL of 5.0 M HCl? 1.00M

1. How many mL of a stock solution of 4.00 M KI would you need to prepare

250.0 mL of 0.760 M KI?

(4M) (V1) = (0.760M) (250mL)

m1 v1 m2 v2

V1 = 47.5mL of 4M stock solution

2. What volume must you dilute to make 50.0 mL of 0.20 M KNO3 from 4.0

M KNO3?

(4M) (V1) = (0.20M) (50mL)

m1 v1 m2 v2

V1 = 2.5mL of 4M solution

3. What is the molarity of a solution formed when you add 200 mL of water

to 50 mL of 5.0 M HCl?

(5.0M) (50mL) = (M2) (250mL)

m1 v1 m2 v2

M2 = 1M of solution

EX. A chemist starts with 50 mL of a 0.40M NaCl solution and dilutes it to

1000 mL. What is the concentration of the dilute solution?

(0.4 M)(50 mL) = (?M)(1000 mL)

M1 V1 M2 V2

M2 = 0.0200 M is the concentration of the diluted

solution

Stock soln

Practice1) What volume of a 3.00M KI stock solution

would you use to make 0.300 L of a 1.25 M KI solution? 0.125 L

2) How many milliliters of a 5.0M H2SO4 stock solution would you need to prepare 100.0 mL of a 0.25M H2SO4?

5.00 mL3) If you dilute 20.0 mL of a 3.0M solution

to make 100.0 mL of solution, what isthe molarity of the dilute solution?0.600M

Practice 1

(3.00M) (V1) = (1.25M) (.300)

m1 v1 m2 v2

V1 = .125 L of 3M stock solution

Practice 2

(5M) (V1 mL) = (0.25M) (100 mL)

m1 v1 m2 v2

V1 = 5.00mL of 5M solution

Practice 3

(3.0M) (20mL) = (M2) (100mL)

m1 v1 m2 v2

M1 = 0.600M is the new concentration