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Molarity and Molality

Molarity and Molality. Solutions= Molarity. A Molarity. Molarity = # of moles of a solute per liter of Solution. Solute and Solvent. substance being dissolved. total combined volume. A. Molarity = M. Concentration of a solution. Molarity.

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Molarity and Molality

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  1. Molarity and Molality

  2. Solutions= Molarity A Molarity

  3. Molarity = # of moles of a solute per liter of Solution Solute and Solvent

  4. substance being dissolved total combined volume A. Molarity = M • Concentration of a solution.

  5. Molarity • To make a 0.5-molar (0.5M) solution, first add 0.5 mol ofsolute to a 1-L volumetric flask half filled with distilled water.

  6. Molarity • Swirl the flask carefully to dissolve the solute.

  7. Molarity • Fill the flask with water exactly to the 1-L mark.

  8. A. Molarity (M) 2M HCl What does this mean?

  9. MASS IN GRAMS MOLES NUMBER OF PARTICLES LITERS OF SOLUTION Molarity Calculations 6.02  1023 (particles/mol) molar mass (g/mol) Molarity (mol/L)

  10. M = Ex: Molarity Calculations • What is the molarity of a solution in which 15.0 g NaCl are dissolved in 400 mL of solution. 15.0 g 1 mol 58.5 g = 0.256 mol NaCl 400 ml = 0.400 L of Solution 0.236 mol .400 L = 0.640 NaCl

  11. M = Ex. Molarity Calculations • Find the molarity of a 250 mL solution containing 10.0 g of NaF. 10.0 g 1 mol 41.99 g = 0.238 mol NaF 0.238 mol 0.25 L = 0.95M NaF

  12. Ex. Molarity Calculations • How many grams of NaCl are needed to produce a 1.56 M solution if you have 500mL of solution? .5 x 1.56 = __ X __ x .5 = .78 mole of Solute .500 L 500 mL = .500 solution = 45.6 g NaCl 58.5 g 1 mol 0.78 mol

  13. Ex. Molarity Calculations • How many grams of NaCl are required to make 0.500L of 0.25M NaCl? 0.500 L 0.25 mol 1 L 58.44 g 1 mol = 7.3 g NaCl

  14. Molality B. Molarity

  15. Molality = # of moles of solute dissoved per Kg of solvent • Molality = m • M = mole of solute Kg of Solvent

  16. moles of solute liters of solution moles of solute m = mass of solvent (kg) M = Concentration Units Continued Molarity(M) Molality(m) 12.3

  17. m = Ex: MolaLity Calculations • How many grams of KI must be dissolved in 500.O g of H20 to produce a 0.060 molal solution of KI? 1 Kg 1000 g 500 g = 0. 5 kg M = mol kg .5 * .060 = x/.5 Kg Solv. * .5 .03 mol 1 166 g 1mol . KI = 4.98 g KI

  18. moles of solute moles of solute m= m= moles of solute M = mass of solvent (kg) mass of solvent (kg) liters of solution 5.86 moles C2H5OH = 0.657 kg solvent What is the molality of a 5.86 M ethanol (C2H5OH) solution whose density is 0.927 g/mL? • Assume 1 L of solution: • 5.86 moles ethanol = 270 g ethanol • 927 g of solution (1000 mL x 0.927 g/mL) mass of solvent = mass of solution – mass of solute = 927 g – 270 g = 657 g = 0.657 kg = 8.92 m 12.3

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