Solutions

What is a solution? A homogeneous mixture (made up of two or more substances)

A solution contains a solute and a solvent. Solutes are substances like salt or sugar that dissolves in water Solvents are usually liquids

Solutes (ex. Sugar) dissolve faster in water when you stir or shake the solution, or when you raise the temperature/crush the sugar. The more sugar in a solution, the more concentrated it is. When there is very little sugar in a solution it is called dilute

Solubility Shows the most sugar the water can hold, or the most sugar that can dissolve in the water at a specific temperature.

What affects Solubility? 1. Temperature 2. Pressure 3. Nature of Solute * graph

When temperature increases… Solubility of a gas decreases Solubility of a solid increases

Types of Solutions Saturated: it contains the most solute that can dissolve at a given temperature Unsaturated: it contains less solute than a saturated solution Supersaturated: only a temporary situation, caused by slowly cooling a saturated solution. it has more solute than a saturated solution

Solubility of KNO3 in H2O Grams of Solute/100 mL water Temperature, °C Supersaturated 200 Grams of Solute/100 mL water 160 Saturated 120 80 Unsaturated 60 20 Temperature, °C

Pressure Makes gas more soluble  ex. Soda can Has almost no effect on liquids and solids High pressure forces carbon dioxide into water to make soda. - When you open the cap, there is less pressure on the soda b/c the soda fizzes and gas escapes.

Nature of Solute “Like Dissolves Like” A polar solute molecule (alcohol) dissolves in a polar solvent (water). A nonpolar solute (oil paint) dissolves in a nonpolar solvent (turpentine) “Like Dissolves Like”

Table F

Questions Is NaCl soluble? Yes! Is AgBr soluble? No!

Determining Electrical Conductivity When a solution is soluble, it has ions that can conduct electricity (electrolytes) Ex. NaCl When a solution is insoluble, it cannot conduct electricity (non-electrolytes or poor electrolytes) Ex. AgBr

Entropy When a solid dissolves in water, entropy increases. NaCl(s) (H2O) Na+ + Cl- NaCl dissolves in water Entropy increases

Review

Concentration of Solution You can describe the concentration of the solution by molarity, percent by volume, percent by mass or parts per million.

Molarity = moles of solute / liters of solution Molarity of a solution is the number of moles of solute in one liter of solution. Molarity = moles of solute / liters of solution

Example If you have 50 moles (mol) of solute (salt) in 25 liters (L) of solution and you want to know the molarity (concentration), look at Table T for the molarity formula. Molarity = moles of solute / liters of solution 50 moles / 25 liters = 2M

Percent By Volume Percent by volume can be used to describe the concentration of a solid or a liquid in a solution. For a solid solute the formula is: percent by volume = grams of solute / mL of solution x 100

Example: 10% salt solution = 10 grams of salt / 100 mL of solution x 100

The liquid solute formula is: percent by volume = mL of solute / mL of solution x 100

Example Orange drink has 10% orange juice (solute) 10% orange juice in orange drink = 10 mL orange juice / 100 mL of solution x 100

Percent By Mass Percent by mass also describes the concentration of a solution Percent by mass = grams of solute / grams of solution

Example 1 2% salt solution = 2 grams of salt / 100 grams of solution x 100 Recap: 2% of a salt solution means that you have 2 grams of salt. Add water to the 2 grams of salt until the solution weighs 100 grams.

Concentration (Parts per million / PPM) grams of solute / grams of solution x 1000000 Example: ppm = .050 g CuSO4 / 1000 grams x 1000000 = 50 parts per million

Now you try….. A solution has 300 parts per million of KOH. Find the number of grams of KOH in 1000 grams of this solution.

Answer 300 = x grams / 1000 x 1000000 = Cross multiply, you can even cancel out the 1000, you should get x to be 0.3 grams.

Concentration of Ions Affects how Well Solutions Conduct Electricity The higher the concentration of ions the better the solution conducts electricity. A low concentration of ions, is a poor conductor of electricity. A high concentration of ions, is a good conductor of electricity.

Boiling Point Elevation The presence of sugar (solute) in water raises the boiling point of the water (solvent). Rule: The presence of a (nonvolatile) solute (salt or sugar) raises the boiling point of the solvent. The greater the concentration of solute or the more sugar it contains, the more it raises the boiling point.

Freezing Point Depression The presence of sugar (solute) in water lowers the freezing point of water (solvent) Rule: The presence of any solute (salt or sugar) lowers the freezing point of the solvent. The greater the concentration of a solute, and or the more sugar it contains the more it lowers the freezing point.

Once Again… The addition of a nonvolatile solute (sugar, salt) raises the boiling point and lowers the freezing point of the solvent The more solute (salt, sugar) added, the higher the boiling point and the lower the freezing point.

Review