Laboratory Solutions

Laboratory SolutionsIn the laboratory, we will be using different concentration of chemical solutions. Each protocol will require different solutions in varying concentrations.

Revised 9/06/2006

Concentration• The amount of a particular

substance in a stated volume (or sometimes mass) of a solution or mixture.

• Ratio where the numerator is the amount of the material of interest and the denominator is the volume or mass of the entire mixture.

Concentrations

•weight per volume•Percents

•Molarity

Weight per Volume

Weight per Volume• The simplest way to represent

concentration of a solution is as the mass in grams per unit of volume.

Weight = mass of solute

volume volume of solution

2g NaCl

1L• Means that 2 g of NaCl is dissolved

in enough liquid so that the total volume is 1L.

Solute

• The substance that is being dissolved

• NaCl

Solvent• The liquid in

which the solute is dissolved.

• Water

Amount vs. Concentration

• Amount is how much substance is present.

• Concentration is ratio with a numerator (amount) and a denominator (usually volume)

Proportions

1mg = 10mg

10 mL 100mL

Example 1: How could you make 300 mL of a solution that has a concentration of 10g of NaCl in 100 mL total solution?

10 g = ?100 mL 300 mL300 mL x 10 g = ?

100 mL .30 g = ?

Question

1. Your mother gives you 250mg of acetaminophen and a cup containing 500ml of water. What is the concentration of the solution if you dissolve the Tylenol in the water?

Question

2. If a solution requires a concentration of 3g of NaCl in 250 mL total volume, how much NaCl is required to make 100mL?

Question

3. How many milligrams of NaCl are present in 50 mL of a solution that has a concentration of 2mg/mL NaCl?

Question 4. If the concentration of MgSO4 in a

solution is 25 g/L, how much magnesium sulfate is present in 100mL of this solution?

Question5. If a solution requires .005 g of Tris

base per Liter, how much Tris Base is required to make 10-3 Liters of this solution?

Percentage Concentrations

Percentage Concentrations When concentration is expressed in

terms of percent, the numerator is the amount of solute and the denominator is 100 units of total solution.

• weight/volume percent • volume percent• weight percent

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.

Example 2A 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

6. A student adds 13.5 grams of KCl to volumetric flask and fills it to the 1000mL mark. What is the weight per volume percent of the solution?

7. A student adds 45.6 grams of MgCl2 to volumetric flask and fills it to the 1000mL mark. What is the weight per volume percent of the solution?

By rearranging the equation we can determine how much chemical we needed to add to the desired volume to prepare a solution of the correct concentration.

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

Example 3How 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

8. How many grams of NaCl would be needed to prepare 250 ml of a 5% solution of NaCl?

9. How many grams of Glucose would be needed to prepare 200 ml of a 2% solution of glucose?

10. How many grams of EDTA would be needed to prepare 475 ml of a 15% solution of EDTA?

11. How many grams of Pb(NO3)2 would be needed to prepare 500 ml of a 5% solution of Pb(NO3)2?

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.

Example 4A student adds 20.0 ml of ethanol to 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%

12. A student adds 10.0 ml of ethanol to 100mL volumetric flask and fills it to the mark. What is the percent volume (v/v) concentration of the solution?

13. A student adds 3.5 ml of isopropanol to 50mL volumetric flask and fills it to the mark. What is the percent volume (v/v) concentration of the solution?

14. A student adds 1.5 ml of methanol to 100mL volumetric flask and fills it to the mark. What is the percent per volume (v/v) concentration of the solution?

By rearranging the equation we can determine the volume the chemical solution we needed to add to the desired volume to have a solution of the correct concentration.

Volume of solute = Volume of solution x Volume %

Example 5How 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

15. How many milliliters of ethanol would you need to make 20.0 mL of a 10% by volume solution of ethanol in water?


16. How many milliliters of isopropyl alcohol would you need to make 100 mL of a 75% by volume solution of isopropyl alcohol in water?


17. How many milliliters of methanol would you need to make 1L of a 90% by volume solution of methanol in water?


18. How many milliliters of bleach would you need to make 1L of a 20% by volume solution of bleach water?


19. How many milliliters of SDS solution would you need to make 1L of a .1 % by volume solution of SDS buffer?


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.

Example 6: 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?

21. What is the weight percent of NaCl in a solution made by dissolving 123.5 g of NaCl in 898 g of water?

By rearranging the equation we can determine the mass of the chemical we needed to make the solution of the correct concentration.

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

Example 7: How much NaCl would you need to prepare 400 g of a 2.50% solution of sodium chloride?


Grams of solute = 400 g x 2.50 %

Grams of solute = 10.0 g salt

22. How much KCl would you need to prepare 300g of a 25% solution of KCl?


23. How much AgNO3 would you need to prepare 150 g of a 3.0% solution of Ag NO3?


24. How much resin would you need to prepare 200 g of a 75% solution of resin in acetone?


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

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 %

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

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

5. Find amount of milligrams present in: 75 mL CaCO3 solution with a concentration of 3 mg/ml.

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?

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

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?

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

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


100

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

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


100

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Laboratory Solutions