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Solution Concentration and Calculations Guide

Learn about different measurements and calculations related to solution concentration, including weight %, mole fraction, molarity, molality, and more. Understand the solution process, solvation, hydration, and the role of energy in solutions.

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Solution Concentration and Calculations Guide

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  1. Definitions • Solution – homogeneous mixture of solids, liquids, or gases • Solvent – component of mixture whose phase doesn’t change • Solute – the other part of the mix

  2. Concentration • Amount of solute per solvent • Different measurements exist of this • “dilute” vs. “concentrated”

  3. Weight % • (mass solute)/ (mass solution) x 100 • A solution is made of 6.9g of NaHCO3 per 100g of water. What is its weight %?

  4. Mole Fraction • (moles solute)/ (moles solution) • Calculate the mole fraction of HCL in a solution containing 36% HCL by weight.

  5. Molarity • (moles solute)/ (L solution) • Calculate the molarity of ascorbic acid (C6H8O6) prepared by dissolving 1.80g in water to make 125 ml of solution. • How many ml is needed to provide .0100 mole of ascorbic acid?

  6. Molality • (moles solute)/ (kg solvent) • What is the molality of a solution made by dissolving 5.0g toluene (C7H8) in 225g of benzene (C6H6)?

  7. Example • Given the density of the 5.0g toluene in 225g benzene is .876g/ml. Calculate a) the molarity b) the mole fraction and c) the weight %.

  8. Solution Process • Solutions are formed when one substance uniformly disperses in another • ..\Program Files\General Chemistry 4.0\General Chemistry 4.0.exe • Solvation- when the solute particles are broken up into small pieces • Hydration – when the solute particles are surrounded by water molecules

  9. Energy • Total energy of the solution process is actually the sum of the energies of the different parts of the solution process • ΔH1 – always endothermic – energy required to break intermolecular forces in solute • ΔH2 – always endothermic – energy required to break intermolecular forces in solvent • ΔH3 – always exothermic – energy released when solute is surrounded by polar water molecules

  10. Total Heat • ΔHt = ΔH1 + ΔH2 + ΔH3 • If ΔH3 is greater than ΔH1 and ΔH2, then the overall process is exothermic • If not, then process is endothermic • Sometimes endothermic dissolving will occur spontaneously if the entropy is increasing (all things tend toward disorder)

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