Solutions & SolubilityFactors Affecting

Solubility

What is a Solution?

•A solution is the same thing as a homogeneous mixture (a mixture with the exact same composition throughout).

Parts of a Solution

•Solute-the substance that is being dissolved in a solution

•Solvent-the substance in a solution that is being dissolved into.

Solution of Two Liquids

• When two liquids are able to dissolve into each other, they are called miscible.

• If not, they are called immiscible.

What can be dissolved?• Remember the saying “like dissolves

like”• Polar solvents (like water) will only

dissolve polar or ionic compounds.

*

How does solvation occur?• IMFs between polar molecule pull

ions away from solid.

*

Solubility Rules• The solubility rules will tell you if

a compound will be soluble in water.

• Note, this does not tell us how soluble it is, just whether or not it will dissolve.

Soluble or Insoluble?NaNO3

KClO4

PbBr2

K2CrO4

Ca(OH)2

Fe2S3

AgClNa3PO4

Hg2SO4

Fe(CN)3

Ba(C2H3O2)2

SrS

Precipitation• Precipitation is the formation of a

solid in a solution during a chemical reaction.

• The precipitate is the solid formed due to creation of an insoluble compound.

• The remaining liquid is called the supernatant.

• Lead (II) nitrate and potassium iodide solutions are mixed together. The yellow stuff is a solid, insoluble

compound. What could it be?

• The positive lead ion could go with the negative iodide ion and the positive potassium ion could go with the negative nitrate ion. Are either of the resulting compounds insoluble?

• PbI2 is insoluble, KNO3 is not, so we say lead (II) iodide precipitates!

What precipitate forms between:• Barium nitrate and sodium sulfate• Potassium chloride and silver acetate

• Ca(ClO3)2 and (NH4)2CrO4

• KClO4 and Li2Cr2O7

• FeCl3 and Ba(OH)2

Solubility•Solubility is the amount of a

substance that will dissolve into a quantity of solvent (at a given temperature)

Solubility, cont’d

•A solvent (like water, for example) can only hold so much of a solute.

•If a solvent cannot hold any more of a solute (at that temperature) it is called saturated.

•If the solvent can hold more solute, it is called unsaturated.

•Sometimes, a solution can hold more of a solute than it should theoretically hold. This type of solution is called supersaturated.

•How could this occur?

Factors Affecting Solubility

•Generally, a substance’s solubility increases as temperature is increased. (This is not true of most gases).

•Why? The solvent’s particles are moving faster, and so they have more energy to break bonds.

• In gases, pressure affects solubility. The higher the pressure, the more gas is soluble in a solvent.

•What is an example of this?

Reading Solubility Charts

Concentration• Concentration-the amount of

solute that is dissolved into a solvent

• Concentrated-when a solution has a high concentration of solute

• Dilute-when a solution has a low concentration of solute

Concentration…•Concentration can be

described in terms of “weak” or “strong”, “concentrated” or “dilute”, but these are both relative terms and can be subjective.

So how do we measure

concentration objectively? There are lots of ways!

Molarity• Molarity is one way to measure

concentration; it is the number of moles of solute per liter of solution. Notice, this is volume of the entire solution, not just of the solvent.

• The unit of molarity is mol/L, which can be abbreviated with an uppercase M.

Molarity (M) =

• When reading a solutions molarity, its numerical value is read as “molar”.

• So a solution with a molarity of 1.5 would be called a “1.5 molar” solution.

moles of soluteliters of solution

Practice Problem #1•What is the molarity of a

solution that contains 0.15mol of MgCl2 in a 1.13L solution?

Practice Problem #2•A saline solution contains

0.020mol of NaCl in exactly 100mL of water. What is the molarity of this solution?

Practice Problem #3•How many moles of solute

are present in a 1.5L sample of 0.24M Na2SO4?

Practice Problem #4•A saline solution contains 0.75g of NaCl in exactly 100mL of water. What is the molarity of this solution?

Practice Problem #5•What would the molarity of a

solution be if you took 1.5L of 0.5M NaOH and added enough water to make the total volume 4.2L?

Molality•Another way to measure

concentration is in terms of molality, which is the number of moles of solute per kilogram (or 1000g) of solvent.

•The unit of molality is mol/kg, or you can abbreviate with a lowercase m (also usually in italics)

Practice Problem #1•What is the molality of a

solution made by adding 35.3g of NaCl to 1.34kg of water?

Practice Problem #2•What is the molality of a

solution made by adding 128.0g MgBr2 to 895g of water?

Practice Problem #3•How many grams of KI must

be dissolved in 500.0g of water to make a 0.060m solution?

Practice Problem #4•How many grams of CaCl2

must be dissolved in 350.0g of water to make a 0.905m solution?

% Solution•You can also talk about

solution in terms of a percent of solution.

•% by volume•% by mass•% by mass/volume

% = part X 100 total

Practice Problem #6•What is the percent by volume of ethanol in the final solution when 85mL of ethanol is diluted with water to a total volume of 200mL?

Practice Problem #7

•What is the percent mass of a solution made by adding 15.5g of sugar to 58.2g of water?

Making Dilutions•Because only certain molarities

are available for purchase, scientists need to be able to dilute a stock solution to get other molarities.

•To calculate, use:

M1V1=M2V2

Practice Problem #1

•How many milliliters of 6.0M HCl would you need to make 550mL of 1.5M HCl?

Practice Problem #2•What would the molarity of a

solution be if you took 1.5L of 0.5M NaOH and added enough water to make the total volume 4.2L?

Mole Fraction•The final way to measure concentration is with mole fraction, or the ratio of moles of one component to total moles in solution.

• In any solution, there are two mole fractions, the symbols of which are XA and XB. They do not have a unit.

Practice Problem #7•What is the mole fraction of

each component in a solution that contains 1.25 moles of ethylene glycol in 4.00 moles of water?

Practice Problem #8•What is the mole fraction of

each substance in a solution made with 7.8 moles ethanol and 6.2 moles water?