Solution Concentration Notes CP Chemistry Chapter 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 concentration % by mass % by volume dilutions molarity

Percent by Mass & Percent by Volume

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?

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%)  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: Where ‘M’ = Molarity 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 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= 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒 𝐿𝑖𝑡𝑒𝑟𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦= 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒 𝐿𝑖𝑡𝑒𝑟𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦= # 𝑜𝑓 𝑔𝑟𝑎𝑚𝑠 𝑠𝑜𝑙𝑢𝑡𝑒 𝑀𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 𝑠𝑜𝑙𝑢𝑡𝑒 𝐿𝑖𝑡𝑒𝑟𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛

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?