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Ch 14: Solutions• Solutions are homogeneous mixtures (solute + solvent).

• Solute is the dissolved substance.– Seems to “disappear” in the solvent.

• Solvent is the substance in which the solute dissolves.– Does not appear to change state.

• Aqueous solutions– Have water as the solvent.– Water is called the universal solvent because it dissolves so many substances.

• Metal solutions (one metal dissolved in another) are called alloys (ex: steel, brass, bronze).

• See table 14.1 for all types of solutions

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14.1 Solubility• When one substance (the solute) dissolves in another (the solvent) it

is said to be soluble.– Ex: salt and ethanol are both soluble in water

• When one substance does not dissolve in another it is said to be insoluble.– Ex: oil is insoluble in water

• When a solute and solvent have the same state (gas, liquid, or solid), the solvent is the component present in the highest percentage.

• Metal solutions (one metal dissolved in another) are called alloys.

• Ionic Compounds

– Dissociate into ions when dissolved in water– Polar water molecules interact with positive and negative ions to

dissolve the compound (fig 14.1, 14.2)– ions surrounded by water molecules are hydrated

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• Covalent Compounds

– Polar covalent compounds have “polar” groups that tend to be soluble in water.

• Ethanol (a liquid) or sucrose (table sugar), for example, have polar O-H bonds that interact with water to enhance solubility.

• See fig 14.3, 14.4

– Nonpolar covalent compounds have molecules that do not form attractions to water molecules because all their bonds are essentially non-polar, which prevents them from being soluble in water.

• Petroleum products or vegetable oil molecules are examples.

• See figs 14.5, 14.6

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• Molecules that are similar in structure tend to form solutions: “like dissolves like”

• A given solvent dissolves solutes that have polarities similar to its own.

– Water (a polar molecule) dissolves most polar solutes (liquids or solids).

– Non-polar solvents dissolve nonpolar solutes. Gasoline, for example, dissolves in oil since they are both nonpolar compounds. However, neither gasoline nor oil will dissolve in water because water is polar.

• Gases are always soluble in each other.

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14.2 Solution Composition• Concentration = amount of solute in a given amount of

solution.

• A concentrated solution has a high proportion of solute to solution.

• A dilute solution has a low proportion of solute to solution.

• A saturated solution contains the maximum amount of solute that will dissolve in the solvent at a particular temperature. (The higher the temperature the greater the saturation.)

• An unsaturated solution contains less solute than the saturation limit.

• A supersaturated solution contains more solute than the saturation limit. – Unstable; the solute easily precipitates out of solution.

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14.3 Solution Composition: Mass Percent

• Mass percent is an expression of the mass of solute present in a given mass of solution.

• Mass Percent = (grams of solute ÷ mass of solution) x 100 – Remember, the mass of the solution is the sum of the masses of

the solute and the solvent.

• See examples 14.1, 14.2

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14.4 Solution Composition: Molarity• Describes a solution in terms of concentration, or the amount of

solute in a given volume.

• Molarity (M) = moles of solute per 1 liter of solution.

• A standard solution is a solution whose concentration is accurately known. See Fig 14.7 for preparation.

• Molarity calculations: See examples 14.3, 14,4, 14.6, 14.7 in text

– Calculate molarity

– Calculate moles/mass of solute

– Calculate volume of solution

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14.5 Dilution• Dilution is adding solvent to decrease the concentration

of a solution. See Fig 14.8 and example 14.8.

• The amount of solute stays the same, but the solute concentration decreases due to the added solvent.

• Dilution Formula: M1 x V1 = M2x V2

M1V1 = before dilution; M2V2 = after dilution

• Since molarity is defined in terms of liters, change any volume in milliliters to liters to solve dilution problems.

• Examples: