Solution Concentration

NotesCP ChemistryChapter 14

Concentration• definition: the measure of how much solute is

dissolved in a specific amount of solvent• can be dilute to concentrated• can use specific numerical quantities to measure

concentrationo % by masso % by volumeo dilutionso molarity

Percent by Mass & Percent by Volume

100solution

soluteionconcentratpercent

100)(

solventsolute

soluteionconcentratpercent

Percent by Volume Practice I

1. What is the percent by volume of ethanol in a solution that contains 35 mL of ethanol dissolved in 115 mL of water?

100)(

solventsolute

soluteionconcentratpercent

Percent by Volume Practice I cont’d

2. If you have 100 mL of a 30% aqueous solution of ethanol, what volume of ethanol and water are in the solution?

Percent by Volume Practice I cont’d

3. What is the percent by volume of isopropyl alcohol in a solution that contains 24 mL isopropyl alcohol in 1100 mL of water?

Percent by Volume Practice I cont’d

4. What is the percent by volume of 140 mL of isopropyl alcohol dissolved in 60 mL of water?

Percent by Volume Practice I cont’d

5. A bottle of hydrogen peroxide is labeled 3%. If you pour out 50 mL, what volume of hydrogen peroxide have you poured out?

Percent by Volume Practice I cont’d

6. If 50 mL of pure acetone is mixed with 450 mL of water, what is the percent by volume?

Percent by Volume Practice I cont’d

7. If you have 500 mL of a 10% solution of tetracycline, what is the volume of tetracycline and water?

Percent by Volume Practice I cont’d

8. If you pour out 60 mL of a 30% alcohol solution, how much pure alcohol have you poured?

Percent by Mass Practice I

1. What is the % concentration by mass of 8.3 g of NaCl dissolved in 300 g of water? (2.7%) 

2. What is the % concentration by mass of 65 g of C6H12O6 dissolved in 500 g of water? (11.5%)

3. You have a 1000 g bleach solution. The % concentration by mass of the solute NaOCl is 6.02 % . How many grams of the NaOCl are in the solution? (60.2 g)

 4. How many grams of water would you have to add to 50 g of NaCl to produce a solution concentration of 5%? (950 g)  5. What is the solution concentration by mass of 12 grams of NaCl dissolved in 300 grams of water? (3.8%)   6. If you need to produce 500 grams of an 8.3% saline solution, how many grams of salt and how many grams of water would you use to form the solution? (41.5 g of salt, 458.5 g H2O)

Diluting Solutions• Concentrated stock solutions of chemicals are

purchased in the laboratory because they are much more economical to buy

• These solutions are diluted to desired concentrations that are required by the labs we perform in class

• To properly dilute solutions we use the following equation:

o Where ‘M’ = Molarityo Where ‘V’ = Volume

Diluting Solutions Examples

1. What volume of a 3M KI solution would you use to make .3 L of a 1.25M KI solution?  2. How many milliliters of a 5M H2SO4 solution would you need to prepare 100 mL of .25 M H2SO4?

  3. If you dilute 20 mL of a 3.5M solution to make 100 mL of solution, what is the molarity of the dilute solution?  125 mL, 5 mL, .7M

Molarity• concentration expressed as the number of moles

of solute per liter of solution• use M, molar

o ex. 2.5 M solution is a 2.5 molar solution

• Conversion reminder: to convert mL to L, must divide by 1000 (1000 mL = 1 L)

Molarity Equations

Molarity Example Problem #1

What is the molarity of a solution containing 158 grams of sodium chloride, NaCl, in 2.5 liters of water?

Molarity Example Problem #2

Calculate the molarity of 250 mL solution containing 75 grams of H2SO4.

Molarity Example Problem #3

How many grams of NaCl would be dissolved in 1.75 L of a 0.85 M solution of NaCl?