ACIDS, BASES AND SOLUTIONSCHAPTER 7

NOTES 7-1 & 7-2

Solutions

WHAT IS A SOLUTION?

A homogeneous (uniform) mixture that contains a solvent and at least one solute

Solvent = dissolves the other substances (Ex. water)

Solute = dissolved by the solvent (Ex. salt)

*In solutions, there is more solvent than solute.

WATER

Water is the universal solvent It dissolves more solutes than any

other solvents Because its polar (slightly charged) Life depends on water solutions Water is the solvent in blood, saliva,

sweat, tears

BUT WATER IS NOT THE ONLY SOLVENT…

Solutions can be formed from any combination of solids, liquids, and gases.

COLLOIDS AND SUSPENSIONS Not all mixtures are solutions.

Colloids and suspensions are mixtures that have different properties than solutions.

PARTICLES IN A SOLUTION When a solution forms, particles of

the solvent surround and separate the particles of the solute.

Ionic compounds, like salt (NaCl), are separated into individual ions

Covalent compounds (molecular compounds), like sugar, are separated into individual molecules

ELECTRICAL CONDUCTIVITY

Ionic compounds in water conduct electrical current due to the charged ions present

Molecular compounds in water usually do not conduct electrical current

EFFECTS OF SOLUTES ON SOLVENTS

Solutes lower the freezing point of a solvent. This is why salt is added to icy roads; it

melts the ice and keeps it from refreezing thus making the roads less slippery.

Solutes raise the boiling point of a solvent. This is why salt is added to water when

boiling pasta; it makes the water hotter thus cooking the pasta faster.

SOLUTIONS SONG

http://www.youtube.com/watch?v=3G472AA3SEs&feature=related

CONCENTRATION

Concentrated solutions have a lot of solute in the solvent

Dilute solutions have a small amount of solute in the solvent

CALCULATING A CONCENTRATION

To calculate the concentration of a solution, compare the amount of solute to the amount of solution and multiply by 100 percent.

For example, if a solution contains 10 grams of solute dissolved in 100 grams of solution, then its concentration can be reported as 10 percent.

CALCULATING A CONCENTRATION

Practice Problem

A solution contains 12 grams of solute dissolved in 36 grams of solution. What is the concentration of the solution?

33%

SOLUBILITY Solubility is a measure of how much solute can

dissolve in a solvent at a given temperature. If solute continues to dissolve, the solution is

unsaturated. If no more solute will dissolve, the solution is

saturated.

Which compound is the most soluble?

TEMPERATURE AND SOLUBILITY The solubility of

the compound potassium nitrate (KNO3) varies in water at different temperatures.

TEMPERATURE AND SOLUBILITY Reading Graphs:

At which temperature shown in the graph is KNO3 least soluble in water?

KNO3 is least soluble at 0ºC.

TEMPERATURE AND SOLUBILITY Reading Graphs:

At which temperature shown in the graph is KNO3 least soluble in water?

KNO3 is least soluble at 0ºC.

TEMPERATURE AND SOLUBILITY Calculating:

About how much more soluble is KNO3 at 40ºC than at 20ºC?

KNO3 is about twice as soluble at 40ºC as it is at 20ºC.

TEMPERATURE AND SOLUBILITY Interpreting Data:

Does solubility increase at the same rate with every 20ºC increase in temperature? Explain.

No; the curve shows that solubility increases more with each 20ºC increase in temperature.

FACTORS THAT AFFECT SOLUBILITY:

Pressure- increases solubility (soda can)

Solvent- some solvents and solutes are not compatible (oil and water), “like dissolves like”

Temperature- increases solubility (high temps when cooking)

NOTES 7-3 AND 7-4: ACIDS AND BASES

ACIDS Properties: Sour Taste, Corrosive

(reacts with metals), Reacts with carbonates to make CO2 gas, Turns blue litmus paper red

BASES

Properties: Bitter taste, Slippery Feel, Turns red litmus paper blue (“Bases turn Blue”)

Acids: Examples: Juice, Vitamin C,

Vinegar, HCl

Bases: Examples: Ammonia

(cleaners), baking soda, soap

Acids in Solutions

An acid produces Hydrogen ions (H+) in water

Acids in water solution separate into hydrogen ions (H+) and negative ions. In the case of hydrochloric acid, for example, hydrogen ions and chloride ions form:

High in Hydrogen Ions (H+), Low in Hydroxide Ions (OH-)

Low on the pH scale (pH0-pH7) *pH7= neutral

Bases in

Solutions

A base produces hydroxide ions (OH-) in water

When bases dissolve in water, the positive ions and hydroxide ions separate. Look at what happens to sodium hydroxide in water:

Not all bases contain hydroxide ions. For example, the gas ammonia (NH3) does not. But in solution, ammonia is a base that reacts with water to form hydroxide ions.

Low in Hydrogen ions (H+), High in Hydroxide Ions (OH-)

High on pH scale (ph7-pH14)

ACIDS AND BASES IN SOLUTIONS

http://www.youtube.com/watch?v=J9zxjz0bctI