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Solutions & Solubility

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Solutions & Solubility

Concentration

- Concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solution.
- Dilute solution– contains a low concentration of solute.
- Concentrated solution– contains a high concentration of solute.
- Molarity (M) – number of moles of a solute dissolved per liter of solution
- a.k.a. molar concentration

Molarity

- Calculate the number of moles in 1 L of the solution
Molarity (M) = moles of solute

liters of solution

Example 1

Calculate the molarity when 2 mol of glucose is dissolved in 5 L of solution, divide the number of moles by the volume in liters.

2 mol glucose

5 L solution

= 0.4 mol/L = 0.4 M

1. A solution has a volume of 2.0L and contains 36.0g of glucose. If the molar mass of glucose is 180 g, what is the molarity of the solution?

2. A solution has a volume of 250 mL and contains 0.70 mol NaCl. What is its molarity?

3. How many moles of ammonium nitrate are in 335 mL of 0.425M NH4NO3?

4. How many moles of solute are in 250 mL of 2.0M CaCl2? How many grams of CaCl2 is this?

Making Dilutions

- You can make a solution less concentrated by diluting it with solvent.
- A dilution reduces the moles of solute per unit volume, however, the total moles of solute in solution does not change
Moles of solute before dilution = moles of solute after dilution

M1× V1 = M2 × V2

You have the following stock solutions available: 2.00M NaCl, 4.00M KNO3 and 0.50M MgSO4. Calculate the volumes you must dilute to make the following solution.

5. 250.0 mL of 0.300M NaCl

6. 75.0 mL of 0.200M KNO3

7. 5.0 L of 0.2M MgSO4

Percent Solutions

- If both solute & solvent are liquids
Percent by volume (% v/v) = volume of solute × 100%

solution volume

- If a solid is dissolved in a liquid
Percent mass / volume (% m/v) = mass of solute (g) × 100%

solution volume (mL)

Must be the same unit: mL or L

Must be this unit

Practice ProblemsTitle: Percent Solution ProblemsYou do not have to write the problem. You MUST show your work.

8. What is the concentration, in percent (m/v), of a solution with 75g K2SO4 in 1500mL of solution?

9. A bottle of hydrogen peroxide antiseptic is labeled 3.0% (v/v). How many mL H2O2 are in a 400.0 mL bottle of this solution?

10. Calculate the grams of solute required to make 250 mL of 0.10% MgSO4 (m/v).