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Concentration

Concentration. Concentration is the amount of solute dissolved in an amount of solution. Molar concentration is called Molarity, or M. M = moles of solute volume of solution in L

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Concentration

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  1. Concentration • Concentration is the amount of solute dissolved in an amount of solution. • Molar concentration is called Molarity, or M. • M = moles of solute volume of solution in L • If 2.0 moles NaCl is dissolved in 1 L of solution, its concentration is “two molar” and is expressed as 2.0 M NaCl.

  2. Steps to make a 1 M solutionExample: 1 M NaOH solution • Calculate the mass needed. 1 mol NaOH 40.01 g NaOH = 40.01 g NaOH 1 mol NaOH • Measure this amount of NaOH into a beaker, then add about 200 mL solvent to dissolve it. • Pour the solution into a 1.0 L volumetric flask. • Rinse the beaker with more solvent and add to the flask. • Add solvent until the solution meets the line indicating 1.0 L. • Stopper the flask and swirl, mix thoroughly.

  3. Find Molarity Example 1: What is the molarity of a solution made with 3.66 moles solute in 0.500 L? M = mol = 3.66 mol = L .500 L 7.32 M

  4. Find Molarity, given mL Ex. 2: What is the molarity of a solution made with1.50 mole solute in 250 mL? In order to find M, need volume in L: 250 mL | 1 L____ = _____L | 1000 mL (or move decimal to left 3 places) M = mol = 1.50 mol = ______ M _____ L .250 L 6.0 M

  5. Find Molarity, given grams Ex. 3: What is the molarity of a solution made with 55.0 g KCl in 0.250 L? In order to find M, need moles first: 55g KCl | 1 mol KCl = _____mol KCl | 74.5 g KCl M = mol = . mol = ______ M KCl L .500 L .738 mol 1.48 M

  6. Find Moles Ex. 4: How many moles of KCl are in a 100 mL sample of 0.67 M solution? In order to find moles, rearrange the molarity equation: M = mol →mol = (M)(L) = (0.67mol)(0.100L) = L L .067 mol

  7. Find Grams Ex. 4: How many grams of KCl are in a 100. mL sample of 0.670 M solution? Find moles, then convert to grams using periodic table masses. In order to find moles, rearrange the molarity equation: M = mol →mol = (M)(L) = (0.67mol)(0.100L) = L L 0.67 mol | 74.5 g KCl = | 1mol KCl .067 mol 4.99 g

  8. Find Volume To produce 23.4 g of K2CrO4 from 6.0 M K2CrO4, what volume of the solution is needed? Given: 23.4 g K2CrO4 needed concentration of solution = 6 moles K2CrO4 per 1 L Want: volume of K2CrO4 in solution 23.4 g K2CrO4 1mol K2CrO4 = 194.2g K2CrO4 0.120 mol K2CrO4 1 L = 6 mol K2CrO4 0.120 mol K2CrO4 0.020 L K2CrO4 soln

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