Chemistry 1

Unit 6 Notes - Polarity, Solubility, Acids and Bases

Polar or Nonpolar

It is important to know if substances are polar or nonpolar Because it tells you whether or not they will

dissolve in each other The rule is that “like dissolves like”

Polar substances dissolve polar substances

Nonpolar substances dissolve non-polar substances

Polar or Non-Polar (cont.)

Polar means… A substance has a positive and negative

end Therefore, all ionic compounds are polar!

Non-polar means… A substance does not have a positive and

negative end

Polar or Non-Polar (cont.)

An easy way to check for polarity is to check for symmetry If a molecule is symmetric…

It is non-polar If a molecule is not symmetric…

It is polar

Let’s see some

examples on the next

slide.

Polar or Non-Polar (cont.)

Is this molecule symmetric? CH4

It is symmetric, therefore it is… Non-polar

Polar or Non-Polar (cont.)

Is this molecule symmetric? H2O

It is not symmetric, therefore it is… Polar

Practice Problem #2

Are the following molecules polar or non-polar? MgCl2 CCl4 NH3

Polar

Non-polar

Polar

Solutions When one substance dissolves into

another, that is called a SOLUTION Example: sugar water

There are two main parts of a solution: SOLUTE= the dissolved material

Example: sugar SOLVENT= the substance that is doing the

dissolving (usually a liquid) Example: Water

Solutions

Saturated solution Add a crystal and it will fall to the bottom

Unsaturated solution Add a crystal and it will dissolve

Supersaturated solution Add a crystal and it fills the container with crystals

Solubility Curves

The solubility of substances changes with temperature For example, is it easier to dissolve sugar

in hot or cold coffee? Solids become more soluble at higher

temperatures Gases become less soluble at higher

temperatures

Solubility Curves (cont.)

Scientist have studied many substances solubility at different temperatures They created graphs

which show this data

Solubility Curves (cont.)

Let’s simplify the graph with all the substances down to just one substance

Solubility of KCl in 100 g of water

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

Temperature (degrees Celcius)

Grams of solute dissolved in 100 g of

water

Solubility Curves (cont.)

What does this graph tell you about KCl at 80°C? 52g of KCl dissolve in 100g of water

Solubility of KCl in 100 g of water

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120

Temperature (degrees Celcius)

Grams of solute dissolved in 100 g of

water

Is KCl a solid or gas in this

graph?

Solubility Curves (cont.)

How many grams of KCl will dissolve in 500g of water at 80°C? 260g of KCl

Solubility of KCl in 100 g of water

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120

Temperature (degrees Celcius)

Grams of solute dissolved in 100 g of

water

Solubility Curves (cont.)

How many grams of water will it take to dissolve 29 g of KCl at 80°C? 56g of H2O

Solubility of KCl in 100 g of water

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120

Temperature (degrees Celcius)

Grams of solute dissolved in 100 g of

water

Solubility Curves (cont.)

If one dissolves 95 grams of KCl in 250 grams of water at 80°C, what kind of solution will they have? Unsaturated

Solubility of KCl in 100 g of water

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120

Temperature (degrees Celcius)

Grams of solute dissolved in 100 g of

water

Practice Problem #1

How many grams of NH4Cl will dissolve in 300 grams of water at 70°C?

If one dissolves 127.5 grams of NaNO3 in 125 grams of water at 45°C, what kind of solution will they have?

186g NH4Cl

Unsaturated

Unit 6

Acid and Base Chemistry

Section 1

What are acids and bases?

Acid

Substance that can give an H+ ion HCl hydrochloric acid H2SO4 sulfuric acid

HNO3 nitric acid

Base

Substance that can give an OH- ion NaOH sodium hydroxide Mg(OH)2 magnesium hydroxide

Al(OH)3 aluminum hydroxide

Acid/Base

Properties of acids: Taste sour Burn human skin Neutralize bases Corrode metals

Properties of bases: Taste bitter Break down human

skin (denature proteins)

Neutralize acids

Acid/Base (cont.)

How can one recognize an acid by the chemical formula? Starts with an H

How can one recognize a base by the chemical formula? Ends with an OH

pH scale

pH means the potential for hydrogen The ability of the solution to give of H+ ions

Indicates intensity of acid or base 0-14, 7 is considered neutral (in the

middle) The closer you get to 0, the more acidic The closer you get to 14, the more basic

pH Scale

Acidic

H+ Ions

Sour taste

Alkaline

OH- Ions

Bitter taste

CLEAR PINK

Acid/Base (cont.)

pH scale

0 7 14

Which end of the

spectrum is for acids and which end is for bases?

acidic basic

RED BLUE

There are two indicators that you should know

Phenolphthalein (clear or pink) Litmus (red or blue)

Section 2

Indicators

Indicators

Turn color to “indicate” the pH of the solution

Litmus Paper

Great acid / base indicator Acids = blue litmus turns RED Bases = red litmus turns BLUE

Phenolphthalein

Another great acid / base indicator Clear colored as an acid Pink colored as a base

Section 3

Acid / Base Reactions

Acid / Base Reactions

Called “Neutralization” Reactions Double Replacement Reactions Acid + Base Salt + Water

Example

Acid + Base Salt + Water

+1 -1 +2 -1 +2 -1 +1 -1

H(NO3) + Mg(OH)2 Mg(NO3)2 + H(OH)