Chemistry Objective 4:

Water, Solutions and pH

Structure (& Properties) of Water

I. Polar Vs. Nonpolar a. Water is a polar molecule. It has dipoles

(meaning a positive end and a negative

end). Look at the figure below. ( Think:

Mickey mouse ears !!)

Polar Vs Nonpolar

b. Because of its polar nature, water can dissolve any otherpolar molecule or any IONIC

compound.Ex. NaCl- salt ; Na is (+) and Cl (-) • The oxygen (-) from water

will bond with Na(+), • The hydrogen (+) will bond

with the Cl (-).

Polar Vs. Nonpolar

c. Like dissolves like - polar dissolves polar; nonpolar dissolves nonpolar.

Ex. (Polar) Water can clean paintbrushes that were used to paint with watercolors, BUT (Nonpolar) gasoline or

mineral spirits must be used to clean paintbrushes that have been used with oil paints. Water cannot clean oil based

paints!

Solubility

I. A solution contains 2 parts:a. solvent - does the dissolving (or the one in

the greater amount)ex. Water

b. solute - gets dissolved (or the one in the lesser amount)

ex. SaltII. Solubility- the maximum amount of a solute that

can be dissolved in a given amount solvent at a given temperature.

Factors Affecting Solubility

3 factors affect how fast a solute will dissolve:1. Surface area (particle size)- that larger the surface area the faster it will dissolve

Ex. Sugar cube vs. crushed sugar (crushed dissolves faster due to the increased surface area)

Vs

2. Stirring and shaking (gets those particles moving)

3. Temperature - increasing the temperature allows more particles of a liquid or solid solute to dissolve. (However, increasing temperature has the opposite effect on a gas)

– Pressure has little effect on solids in liquids, but greatly affects gases because gases are compressible.

This is a solubility graph. Notice as temperature increases, the solubility of the different solutes also increase. Except for NH3 because it is a gas. The solubility of a gas decreases as temperature increases. That is why cokes go “flat” really quickly when they are hot. The CO2 escapes!

Acids and Bases

1. acids contain a hydrogen ion (H+1) – have a sour tasteex. HNO3 - nitric acid

HC2H3O2 – Vinegar (acid)

H2SO4 – sulfuric acid

HCl--- hydrochloric acid2. On the pH scale, acids range from 0-6; 0 is the

strongest, 6 is weakest

3. Bases contain the hydroxide ion (OH-1) ---have a bitter taste.

Ex: NaOH sodium hydroxide, soap, and shampoo are bases4. On the pH scale, bases range from 8-14; 8 being

the weakest, 14 being the strongest.

5. As you can see, the closer you are to 7, the weaker the acid or base because 7 is neutral.

Ex. Pure water has a pH of 7

To balance an equation take an “atom inventory” on both sides of the equation:

___K + ___H2O ___KOH + ___H2

Reactants Products

K: 1 K: 1

H: 2 H: 3

O: 1 O: 1

Sodium +   Chlorine   Sodium Chloride (metal (non-metal (NaC)

group IA) group VIIA)

Density

Density compares the mass of an object to its volume

D = mass = g or g

volume mL cm3

Note: 1 mL = 1 cm3