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Molarity

Molarity. Molarity is a measure of molar concentration. Molarity equals moles over liters 1 M = 1mol/L The symbol M is read molar so “1 M HCl” is read “one molar hydrochloric acid”. Sample problem #1.

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Molarity

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  1. Molarity

  2. Molarity is a measure of molar concentration. • Molarity equals moles over liters • 1 M = 1mol/L • The symbol M is read molar so “1 M HCl” is read “one molar hydrochloric acid”.

  3. Sample problem #1 0.0292 mol Cane sugar (sucrose)is dissolved in 0.200 L of water. What is the concentration of the sugar solution? Answer: 0.146 M sucrose

  4. Basic Molarity Step-by-step • If you are given grams, turn it into moles. • If you are given a volume in units other than liters, convert to liters. • Plug the numbers into the equation M=mol/L and solve.

  5. Sample Problem #2 • A student prepared a solution by dissolving 1.345 g of potassium nitrate, KNO3 in enough water to prepare 25.00 mL of solution. What is the molarity of the solute? • Answer: 0.5321 M KNO3

  6. Try this in your seat • Calculate the molarity of sodium chloride in a solution made by dissolving 2.357 g NaCl in enough water to make 50.00 mL of solution. • Answer: 0.8066 M NaCl

  7. Now try to calculate moles • Find the number of moles of sucrose in 15 mL of 0.10 M sucrose solution. • Answer: 0.0015 mol sucrose

  8. Can you calculate the volume? • Suppose we have a bottle of 0.0380 M potassium permanganate and want to measure out 7.60 x 10-4 mol potassium permanganate. What volume of the solution should we use? • Answer: 0.0200 L KMnO4

  9. Dilution • To dilute something means to reduce its concentration. • The formula we use in dilution calculations is; MinitialVinitial = MfinalVfinal The volume must be in liters.

  10. Sample Dilution Problem • Calculate the volume of a 0.0380 M KMNO4 solution that we should use to prepare 0.250 L of 1.50 X 10-3 M KMNO4 • Answer: 9.87 X 10-3 L

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