Laboratory Solutions

Solute

• The substance that is being dissolved

• NaCl

Solvent• The liquid in

which the solute is dissolved.

• Water

Percentage Concentrations

Weight/Volume Percent

Weight/Volume % = grams of solute x 100

volume of solution

A weight per volume percent concentration is the weight of the solute in grams per 100 mL of solution. It can be abbreviated as w/v.

A student adds 20.0 grams of NaCl to volumetric flask and fills it to the 100mL mark. What is the weight per volume (w/v) percent concentration of the solution?

Weight % = grams of solute x 100 volume of solution

Weight % = 20.0 grams x 100 100mL of solution

Weight % = 20% NaCl solution

How many grams of NaCl would be needed to prepare 500 ml of a 5% solution of NaCl?

Grams of solute = Volume of solution x Weight %

Grams of solute = 500mL x 5%

Grams of solute = 500mL x 5g/100mL

Grams of solute = 25 g of NaCl

Volume/Volume Percent

volume % = volume of solute x 100 volume of solution

Volume % = mL of solute x 100 100 mL of solution

In a percent by volume expression, both the amount of solute and the total solution are expressed in volume units. It can be abbreviated as v/v.

A student adds 20.0 ml of ethanol to a volumetric flask and fills it to the 1L mark. What is the percent volume (v/v) concentration of the solution?

Volume % = volume of solute x 100 volume of solutionVolume % = 20.0 mL of solute x 100

1000mL of solutionVolume % = 2%

How many milliliters of ethanol would you need to make 10.0 mL of a 10% by volume solution of ethanol in water?

volume of solute = Volume of solution x Volume /volume %

volume of solute = 10.0 ml x 10%

volume of solute = 1.0 ml ethanol

Weight Percent

Weight % = weight of solute weight of solution x

100

In a Weight (mass) Percent the numerator is the mass of solute and the denominator is mass of total solution.

What is the weight percent of glucose in a solution made by dissolving 4.6 g of glucose in 145.2 g of water?

Determine total weight of solution: 4.6 g glucose

+ 145.2 g water 149.8 g solution

Calculate Weight % glucose =   4.6 g glucose x 100 = 3.1% glucose149.8 g solution

20. What is the weight percent of sucrose in a solution made by dissolving 29.89 g of sucrose in 1000 g of water?

29.89 + 1000 = 1029.98 solution

29.89/1029.98 x 100 =

2.90 %

How much NaCl would you need to prepare 400 g of a 2.50% solution of sodium chloride?

Grams of solute = Gram of solution x Weight/Weight %

Grams of solute = 400 g x 2.50 %

Grams of solute = 10.0 g salt

Homework Problems

1. A chemist adds 78.5 grams of MgCl2 to volumetric flask and fills it to the 1L line. What is the weigh per volume percent of the solution?

Weight % = grams of solute x 100 volume of solution

Weight % = 78.5 g x 100 1000mL of solution

7.85 %

2. How many grams of NaCl would be needed to prepare 600 ml of a 34% solution?

Grams of solute = Volume of solution x W/V %

Grams of solute = 600ml x 34 %

204 grams NaCl

3. How many grams of KCl would be needed to prepare .4 L of a 25% solution?

400 mL x 25%

100 grams KCl

4. How many grams would be needed to prepare an 11% solution of sucrose in 350 ml?

350 x 11%

38.5 grams

5. Find amount of milligrams present in: 75 mL CaCo3 solution with a concentration of 3 mg/ml.

75ml x 3mg/ml

225mg

6. A student adds 20 ml of methanol to 400ml flask and fills it to the mark. What is the percent per volume (v/v) concentration of the solution?

20ml/400ml x 100

5%

7. 37ml of a substance is put into a 500 ml flask filling it. What is the v/v concentration of the solution?

37 ml/500ml x 100

7.4%

8. 50 ml of a substance is added into a 1.25 L flask, filling it. What is the percent volume concentration of the solution?

50ml/1250 x 100

4%

9. How many milliliters of ethanol would you need to make 100 mL of a 23% by volume solution?

100ml x 23ml/100ml

23 ml ethanol

10. What is the weight percent of NaCl in a solution made by dissolving 480 g of NaCl in 1000 g of water?

Weight % = weight of solute weight of solution x

100

480/1480 x 100

32.43%

11. How much MgCO3 would you need to make 120g of an 8.5% solution of MgCO3?

120g x 8.5%

10.2g

12. What is the weight percent of sucrose in a solution made by dissolving 50 g in 350 g of water?

Weight % = weight of solute weight of solution x

100

50g/ 400g x 100

12.5%