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Laboratory Solutions

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Laboratory Solutions

- The substance that is being dissolved
- NaCl

- The liquid in which the solute is dissolved.
- Water

Percentage Concentrations

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

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 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 solution

Volume % = 20.0 mL of solute x 100

1000mL of solution

Volume % = 2%

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 % = 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.

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% glucose

149.8 g solution

29.89 + 1000 = 1029.98 solution

29.89/1029.98 x 100 =

2.90 %

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 %

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

Grams of solute = 600ml x 34 %

204 grams NaCl

400 mL x 25%

100 grams KCl

350 x 11%

38.5 grams

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%

37 ml/500ml x 100

7.4%

50ml/1250 x 100

4%

100ml x 23ml/100ml

23 ml ethanol

Weight % = weight of solute weight of solution x 100

480/1480 x 100

32.43%

120g x 8.5%

10.2g

Weight % = weight of solute weight of solution x 100

50g/ 400g x 100

12.5%