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First, a little review…

First, a little review…. Solution =. A homogenous mixture of two or more substances in a single phase. Solute =. The substance dissolved in a solution. Solvent =. The dissolving medium in a solution.

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First, a little review…

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  1. First, a little review… Solution = A homogenous mixture of two or more substances in a single phase. Solute = The substance dissolved in a solution. Solvent = The dissolving medium in a solution. The amount of a substance required to form a saturated solution with a specific amount of solvent at a specified temperature. Solubility =

  2. Factors Affecting Rates of Dissolution (how quickly a substance dissolves: 1. Size of the Particles: The smaller the particles = quicker dissolution. Why? Dissolution (dissolving) occurs at the surface of the solute and the solvent. When a crystal (like sugar, CuSO4, or salt) is broken up more solute molecules are in contact with the solvent (water) and are able to be dissolved. A.k.a. More surface area to the solvent = quicker dissolution. 2. Agitation of solution: the more agitation (shaking) = quicker dissolution Why? Shaking causes more solvent to come into contact with the solute causing quicker dissolution. 3. Temperature: the warmer the solution = the quicker dissolution Why? The warmer something is (i.e water) more its molecules are moving around. The more they are moving around the more solute molecules with which they will come into contact causing a quicker dissolution rate.

  3. Concentration Units Concentration = measure of the amount of solute dissolved in a given quantity of solvent. (will be measured in g solute/100 g solution) A diluted solution contains a small amount of solute A concentrated solution contains a large amount of solute Molarity (M) = the number of moles of solute dissolved in 1 L of solution Molarity (M) = moles of solute liters of solution

  4. Molarity Example: Intraveneous (IV) saline solutions are often administered to patients in the hospital. One saline solution contains .90g NaCl in exactly 100. mL of solution. What is the molarity of the solution? Known: Mass = .90g NaCl Volume = 100mL solution Unknown: Molarity M = mol solute L soln *We have L, but not moles, but we do have the mass so we can convert mass to moles: mass/molar mass = moles .90g NaCl / 58.443 g/mol = .015 mol NaCl To find Molarity: M = .015 mol NaCl = .15 M solution .100 L

  5. Molality Molality (m) = the number of moles of solute per kilogram of solvent. Molality = moles of solute kilograms of solvent Example Problem: How many grams of potassium iodide must be dissolved in 500.0g of water to produce a 0.060 molal KI solution? Known: mass of water = 500.0g Solution concentration = .060m Unknown: Mass of solute = ? g KI 0.060 m = X mole KI = 0.060 m * .5000kg = X mole KI .5000kg H2O .030mol * 165.998g/mol = 5.0 g KI X = .030 mole KI Now, convert from mole to grams (* by molar mass)

  6. ppm, ppb, Both are used to represent very dilute solutions. ppm = parts per million = one part solute in 1,000,000 parts water (solvent) This is like 1 sec. of time in 11.5 days ppb = parts per billion = one part solute in 1,000,000,000 parts water. This is like 1 sec. of time in 31.7 years! How to calculate: mass solute X 106 = ppm mass H2O For ppb multiply by 109 instead of 106.

  7. Solubility curves use concentrations in g/100 g H2O. How to calculate: mass solute (in grams) x 100g H2O mass H2O (in grams) % Concentration : mass solute (in g) x 100% (mass solute + mass solvent)

  8. Normality Normality (N) = the gram equivalent weight of a solute per liter of solution. • typically a multiple of the molarity of a solution • Depends upon the two compounds that are reacting • You’ll see it later in the acid base unit! (that’s next!)

  9. % by mass % by mass = mass of solute divided by the mass of the solution then multiplied by 100. % by mass = g solute * 100 g soln Example: Determine the percent composition by mass of a 80 g salt solution which contains 20 g salt. % by mass = 20. g salt * 100 = 20% salt (80+20) solution = 100. g soln

  10. 3 Types of Solutions • Saturated Solution = A solution that contains the maximum amount of dissolved solute. • Unsaturated Solution = A solution that contains less solute than a saturated solution at same existing conditions. • 3. Supersaturated Solution = A solution that contains more solute than a saturated solution at the same conditions.

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