What Is a Solution?

• Solutions can be made from any combinations of solids, liquids, and gases.

Particles in a Solution • When a solution forms, particles of the solute leave each other and become surrounded by particles of the solvent.

Colloids and Suspensions • Colloids and suspensions are mixtures that have properties different from those of solutions.

Effects of Solutes on Solvents • At 0ºC, pure water freezes, but water mixed with a solute does not. Solutes lower the freezing point of a solvent.

Solid (frozen) water Liquid water solution

Assessment

1. What is a solution?

2. Suppose you mix food coloring in water to make it blue. Have you made a solution or a suspension? Explain.

3. How are solutions different from colloids and suspensions?

Assessment

1. What happens to the solute particles when a solution forms?

2.

What affects do solutes have on a solvent’s freezing and boiling points?

3. Why is the temperature needed to freeze ocean water lower than the temperature needed to freeze the surface of a freshwater lake?

4. Why does salt sprinkled on icy roads cause the ice to melt?

CONCENTRATION Definition:

The amount of a substance per defined space. Concentration usually is expressed in terms of mass per unit volume .

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.

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

Solubility • Solubility is a measure of how much solute can dissolve in a solvent at a given temperature.

Key Terms

: unsaturated solution supersaturated solution

Examples:

An

unsaturated solution

more solute.

can continue to dissolve A

supersaturated solution

has more dissolved solute than is predicted by its solubility at the given temperature.

dilute solution concentrated solution solubility saturated solution A

dilute solution

is a mixture that has only a little solute dissolved in a certain amount of solvent.

A

concentrated solution

is one that has a lot of solute dissolved in the same amount of solvent.

Solubility

is a measure of how much solute can dissolve in a solvent at a given temperature.

A

saturated solution

more dissolves.

contains so much solute that no

Assessment

1. What is concentration?

2. What quantities are compared when the concentration of a solution is measured?

3. Solution A contains 50 g of sugar. Solution B contains 100g of sugar. Can you tell which solution has a higher sugar concentration? Explain.

Assessment

1. What is solubility?

2. How can solubility help identify a substance?

3. What are the three factors that affect solubility?

Acid:

A substance that releases H+ ions in an aqueous solution

“aqueous” means: water

Characteristics of Acids:

 

Acids have a sour taste Acids react with metals

 

Acids contain Hydrogen Many are poisonous and corrosive to skin H

Strong Acids (break down completely to give off many H+ ions)

Weak Acids (only partially breaks down, gives less H+)

Common Acids: Strong Acids The Formula

Sulphuric acid Hydrochloric acid Hybrobromic acid Hydroiodic acid Nitric acid Perchloric acid H 2 SO 4 HCl HBr HI HNO 3 HClO 4

All others considered Weak (examples) Weak Acid The Formula Acetic acid (vinegar) Carbonic acid HC 2 H 3 O 2 HCO 3

Base: A substance that releases OH- ions in an aqueous solution

Characteristics of Bases:



Bases usually taste bitter

  

Bases feel slippery Bases contain hydroxide ions STRONG bases are also poisonous and corrosive to skin

OH

-

Common Bases: Strong Bases The Formulae

Lithium hydroxide Sodium hydroxide Potassium hydroxide Rubidium hydroxide Caesium hydroxide Barium hydroxide Calcium hydroxide Strontium hydroxide LiOH NaOH KOH RbOH CsOH Ba(OH) 2 Ca(OH) 2 Sr(OH) 2

(Hydroxides of Group 1 and Group 2 Metals are STRONG) All others are WEAK

Some bases (VERY FEW) don’t have OH Most commonly: ammonia NH3

Section 3 Assessment

1. What are four properties of acids? Of bases?

2. How can you use litmus paper to distinguish and acid from a base?

3. How might you tell if a food contains an acid as one of its ingredients?

Section 3 Assessment

1. What are three practical uses of an acid? Of a base?

2. Where are you most likely to find acids and bases in your own home? Explain.

3. Why is it wise to wear gloves when spreading fertilizer in a garden?

Salts

Reactions between acids and bases

When and acid and a base react with each other, the characteristic properties of both are destroyed. This is called neutralization .

Reactions between acids and bases

General formula for acid base reaction:

Acid + Base → H

2

O + Salt

“Salt” means any ionic compound formed from an acid/base reaction NOT JUST NaCl !!

Neutralization

HCl + NaOH → H

2

O + NaCl

acid base water salt

Neutralization

Another Example

HNO

3

+ KOH → H

2

O + KNO

3

H NO

3

K OH

acid base water salt

pH pH stands for “potential hydrogen” and is a measure of how many H+ ions there are in solution.

The MORE H+ there are, the LOWER the pH will be.

Indicators

An indicator is a compound that will change color in the presence of an acid or base



Red Litmus-Turns blue in base



Blue Litmus-Turns red in acid



Universal indicator (pH paper) Used for the full pH range



Phenolphthalein-Turns pink in base

pH Scale

Shows the range of H+ concentrations High H+ concentration Low H+ concentration

Section 4 Assessment

1.

What does a substance’s pH tell you?

2. If a solution has a pH of 6, would the solution contain more or fewer hydrogen ions (H + ) than an equal volume of solution with a pH of 3?

Digestion and pH