SOLUTIONS

Classification of Matter Solutions are homogeneous mixtures Classification of Matter

Solute - substance being dissolved Definitions Solution - homogeneous mixture (remember, the particles are so tiny they don’t settle out like in heterogeneous mixtures) Solute - substance being dissolved Solvent - present in greater amount

Definitions Solute - KMnO4 Solvent - H2O

Solubility Solubility tells us how well something dissolves Soluble: Dissolves Insoluble: Doesn’t dissolve Solubility definition: maximum grams of solute that will dissolve in 100 g of solvent at a given temperature Related to the saturation of a solution

Saturation Unsaturated: Saturated Supersaturated Not full More solute can be dissolved in the solvent Saturated Full More solute CANNOT be dissolved in the solvent Supersaturated Over Full More solute has been added than normal Usually because you’ve added heat to the solvent.

Solubility UNSATURATED SOLUTION more solute dissolves no more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form concentration

Factors that affect Solubility & Dissolving Surface Area If the solute covers more surface area, it will dissolve faster Ex. Cube of sugar vs sugar particles Stirring Stirring speeds up dissolving time Think of how long you would have to wait if you didn’t stir your chocolate syrup into your milk Temperature Hotter temperatures= Faster Hotter temperatures = More soluble For gases, colder temperatures are more favorable

Polarity (again) If a solute will dissolve in a solvent depends on the polarity Remember: Like Dissolves Like Polar dissolves Polar Non-Polar dissolves Non-Polar If things don’t mix then they have different polarities Some definitons Miscible: Liquids that mix together Immiscible: Liquids that don’t mix together

“Like Dissolves Like” NONPOLAR POLAR

Colligative Properties properties that depend on the concentration of solute particles but not on their identity Boiling points and freezing points of solutions differ from those of pure solvent.

Change in Freezing Point Ethylene glycol/water solution Pure water The freezing point of a solution is LOWER than that of the pure solvent Protects engine from Freezing

Change in Freezing Point Common Applications of Freezing Point Depression Ethylene glycol – deadly to small animals Propylene glycol

Change in Boiling Point Ethylene glycol/water solution Pure water The boiling point of a solution is HIGHER than that of the pure solvent Protects engine from overheating

Concentration Concentration: The amount of solute dissolved in a given amount of solvent Dilute= low concentration of solute Concentrated= High concentration of solute Three ways to calculate concentration Molarity (M) THE MOST COMMON!! Percent Concenrtation (%m/v), (%m/m) , (%v/v) Molality (m)

Concentrated vs. Dilute

Calculations of Solution Concentration: Mass Percent Mass percent is the ratio of mass units of solute to mass units of solution, expressed as a percent

Mass % by Volume Sometimes you will see Mass % as a function of volume of solvent instead of mass of solvent

A Simplifying Assumption 1 ml of water = 1 gram of water 1000 ml of water = 1 liter = 1000 grams Assume that solutions with water as the solvent have the density of pure water (1 mL = 1 gram) It’s not true, but it’s close enough 

VOLUME % is the ratio of volume units of solute to volume units of solution, expressed as a percent

What is the percent concentration of 2 What is the percent concentration of 2.7 g of glucose in 75 mL of water?

85 mL of ethanol is diluted to 250 mL of solution 85 mL of ethanol is diluted to 250 mL of solution. What is the % concentration of ethanol?

How many mL of H2O2 are in a 400 mL bottle of 3.0% (v/v) solution?

Molality mass of solvent only 1 kg water = 1 L water

75 g MgCl2 1 mol MgCl2 95.21 g MgCl2 0.25 kg water = 3.2m MgCl2 Molality Find the molality of a solution containing 75 g of MgCl2 in 250 mL of water. 75 g MgCl2 1 mol MgCl2 95.21 g MgCl2 0.25 kg water = 3.2m MgCl2

0.500 kg water 1.54 mol NaCl 1 kg water 58.44 g NaCl 1 mol NaCl Molality How many grams of NaCl are req’d to make a 1.54m solution using 0.500 kg of water? 0.500 kg water 1.54 mol NaCl 1 kg water 58.44 g NaCl 1 mol NaCl = 45.0 g NaCl

M = mol L Molarity The most common way we measure concentration Moles of solute per Liters of Solution (not just solvent, but amount solute+solvent) In some problems: you may need to convert grams to moles first You may need to convert mL to L M = mol L

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

substance being dissolved total combined volume

What is the concentration of a solution made from 0 What is the concentration of a solution made from 0.2 moles of KCL in 0.6 L of water?

You have 5. 50 L of solution that contains 190 g of NaCl You have 5.50 L of solution that contains 190 g of NaCl. What is the molarity of the solution?

How much distilled water (in mL) would be required to make a 0 How much distilled water (in mL) would be required to make a 0.4 M solution using 32 g of NaNO3?

Dilution Preparation of a desired solution by adding water to a concentrate. Moles of solute remain the same.

GIVEN: M1 = 15.8M V1 = ? M2 = 6.0M V2 = 250 mL WORK: M1 V1 = M2 V2 Dilution What volume of 15.8M HNO3 is required to make 250 mL of a 6.0M solution? GIVEN: M1 = 15.8M V1 = ? M2 = 6.0M V2 = 250 mL WORK: M1 V1 = M2 V2 (15.8M) V1 = (6.0M)(250mL) V1 = 95 mL of 15.8M HNO3

DILUTION How many milliliters of a stock (or standard) solution of 4.00M KI would you need to prepare 250 mL of 0.760M KI?

DILUTION Suppose you need 250 mL of a a0.20 M NaCl, but the only supply of sodium chloride you have is a solution of 1.0 M NaCl. How do you prepare the required solution solution?

Preparing Solutions Weigh out a solid solute and dissolve in a given quantity of solvent. Dilute a concentrated solution to give one that is less concentrated.

Solution Stoichiometry Just like you have done before! STEPS Write the balanced equation for the reaction Calculate the moles of reactants Determine which reactant is limiting Calculate the moles of other reactants or products, as required Convert to grams or other units, if required

Calculate the mass of solid NaCl that must be added to a 1.50 L of a 0.100 M AgNO3 solution to precipitate all of the Ag+ ions in the form of AgCl. Calculate the Mass of AgCl Formed. AgNO3 + NaCl  AgCl + NaNO3

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 0.01000 M of K2CrO4 solution