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Chapter 15 Solutions

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15.1 Solubility Solution: homogeneous mixture or mixture in which components are uniformly intermingled Solute: substance that is being dissolved in solvent Solvent: substance that dissolves solvent and present in a large amount Aqueous solutions: solutions with water as the solvent

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**Table 15.1 – Various Types of Solutions**

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**15.2 Solution Composition: An Introduction**

Saturated: A solution in which the maximum amount of solvent has been dissolved. Any more solute added will sit as crystals on the bottom of the container Unsaturated: A solution in which more of solute can be dissolved Concentrated: a relative large amount of solute is being dissolved in solvent Diluted: a relative small amount of solute is being dissolved in solvent

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**15.3 Solution Composition: Mass Percent**

mass of solute Mass percent (m/m%) = x 100 mass of solution

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Examples A solution is prepared by mixing 1.00 g of ethanol, C2H5OH, with g water. Calculate the mass percent of ethanol in this solution A 135 g sample of seawater is evaporated to dryness, leaving 4.73 g of solid residue (the salts formerly dissolved in the seawater). Calculate the mass percent of solute present in the original seawater

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**Example: Determine Mass of Solute**

Although milk is not a true solution (it is really a suspension of tiny globules of fat, protein, and other substrates in water), it does contain a dissolved sugar called lactose. Cow’s milk typically contains 4.5 % by mass of lactose, C12H22O11. Calculate the mass of lactose present in 175 g of milk

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15.4 Solution Composition Molarity: the number moles of solute per volume of solution in liters moles of solute Molarity = Liters of solution unit = moles/L or M (molar) Standard solution: is a solution whose concentration is accurately known.

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Examples Calculate the molarity of a solution prepared by dissolving 11.5 g of solid NaOH in enough water to make 1.50 L of solution Calculate the molarity of a solution prepared by dissolving 1.56 g of gaseous HCl into enough water to make 26.8 mL of solution Determine how much volume (in ml) will be needed to dissolved 2.50 g of solid NaCl to make 0.050M solution.

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**E.g Solution Composition: Calculating Ion Concentration**

Give the concentration of all the ions in each of the following solutions: 0.50 M Co(NO3)2 1.0 M FeCl3

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**E.g Solution Composition: Calculating Number moles from Molarity**

How many moles of Ag+ ions are present in 25.0 mL of a 0.75 M AgNO3 solution? How many moles of Na+ ions are present in 42.0 mL of 0.350M NaCl?

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**Examples: Calculating mass from molarity**

To analyze the alcohol content of a certain wine, a chemist needs 1.00L of an aqeuous M K2Cr2O7 (potassium dichromate) solution. How much solid K2Cr2O7 (molar mass = g) must be weighed out to make this solution? Formalin is an aqueous solutions of formaldehyde, HCHO,, used as a preservative for biological speciments. How many grams of formaldehyde must be used to prepare 2.5 L of 12.3 M formalin?

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15.5 Dilution Reducing the original concentration of a chemical solution A process of transferring solution to achieve a the desired molarity by diluting with solvent Moles of solute after dilution = moles of solute before dilution Formula M1 V1 = M2 V2

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Examples What volume of 16 M sulfuric acid must be used to prepare 1.5L of 0.10 M of H2SO4 solution? Calculate the new molarity if a dilution is made for: 25.0 ml of water is added to 10.0 mL of M CaCl2

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**15.6 Stoichiometry of Solution Reactions**

Steps for solving stoichiometric problems involving solutions Step 1: Write a balanced equation for the reaction. For each reactions involving ions, it is best to write the net ionic equation. Step 2: Calculate the moles of reactant Step 3: Determine which reactant is limiting Step 4: Calculate the moles of other reactants or products, as required Step 5: Convert to grams or other units, if required

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Examples When Ba(NO3)2 and K2CrO4 react in aqueous solution, the yellow solid BaCrO4 is formed. Calculate the mass of BaCrO4 that forms when 3.50 x 10-3 mole of solid Ba(NO3)2 is dissolved in 265 mL of M K2CrO4 solution

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Examples When aqueous solutions of Na2SO4 and Pb(NO3)2 are mixed, PbSO4 precipitates. Calculate the mass of PbSO4 formed when 1.25 L of M Pb(NO3)2 and 2.00 L of M Na2SO4 are mixed

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**Neutralization Reaction**

Use stoichiometry to determine how much of acid or base must be used to reach neutralization Strong acid: HCl(aq) H+(aq) + Cl-(aq) Strong base: NaOH(s) Na+(aq) + -OH(aq) Net equation: H+(aq) + -OH(aq) H2O(l)

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Example What volume of a M HCl solution is needed to neutralize 25.0 mL of a M NaOH? Calculate the volume of 0.10 M HNO3 needed to neutralize 125 mL of MKOH

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**15.8 Solution Composition: Normality**

Normality is another unit of concentration sometime used when dealing with acid and base H+ and –OH Equivalent of an acid: the mount of acid that can be furnish 1 mol of H+ ions Equivalent of a base: the amount of that base that can furnish 1 mol of –OH ions

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**Equivalent E.g 1 mol HCl = 1 equiv HCl**

molar mass (HCl) = equivalent weight (HCl) 1 mol KOH = 1 equiv KOH molar mass KOH = 1 equiv KOH ½ mol H2SO4 = 1 equiv H2SO4 ½ molar mass H2SO4 = 1 equiv H2SO4

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**Solution Stoichiometry: Calculating Equivalent Weight**

Phosphoric acid, H3PO4 can furnish three H+ ions per molecule. Calculate the equivalent weight of H3PO4. Calculate the equivalent weight of HBr

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Normality (N) Normality (N) = number of equivalent of solute per liter of solution Knowing Normality can help us calculate The number of equivalents The volume of solution

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**Calculating Normality**

A solution of sulfuric acid contains 86 g of H2SO4 per liter of solution. Calculate the normality of this solution Calculate the normality of a solution containing 23.6 g of KOH in 755 ml of solution

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Neutralization The number of H+ ions furnished by the sample of acid is the same as the number of –OH ions furnished by the sample of base reacts exactly with n equiv acid n equiv base Nacid x Vacid = Nbase x Vbase

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