Science 20FH Chemistry in Action

Acids and Bases

Acid comes from the Latin word “acidus” meaning “sour”

Acid - substance that produces hydrogen ions, H+ when dissolved in water.

Example: HCl ➡ H+ + Cl-

Common acids:

Name Formula Uses

Hydrochloric acid HCl Stomach acid, in the lab

Sulphuric acid H2SO4 Car batteries, acid

rain

Citric Acid C6H8O7 Citrus fruits

Base - substance that produces hydroxide ions, OH- when dissolved in

water.

Example: NaOH ➡ Na+ + OH-

Common bases:

Name Formula Uses

Sodium bicarbonate NaHCO3 Baking powder

Magnesium hydroxide Mg(OH)2 Indigestion tablets

Potassium Hydroxide KOH Soap

Properties of Acids - Acids have a sour taste

- Produces hydrogen gas upon reaction with

metals

- Conductors of electricity

- React with carbonates to produce carbon dioxide

- [H+] concentration greater than [OH-] concentration

- Identified by colour change with indicators

- Acid corrodes metals

Properties of Bases - Bases have a bitter taste

- Feels slimy or slippery

- Conductors of electricity

- Produce ammonia (NH3) when reacted with

ammonium chloride

- Identified by colour change with indicators

- [OH-] concentration greater than [H+] concentration

pH Scale

pH means Power of Hydrogen

● The pH scale measures the concentration of H+ ions, the acidity of a

solution.

● pH ranges from 0-14

● A solution with a pH of 7 is neutral

● Acidic solutions have a pH less than 7

● Basic solutions have a pH greater than 7

● The pH scale is a base ten logarithmic scale

o pH = - log [H+]

o Each whole pH value below 7 is ten times more acidic than the

next higher value

o Using the concept of money, let’s say pH 7 is 1 cent, pH 6 (or 8) is

ten times stronger so worth 10 cents. A pH of 5 (or 9) is ten times

stronger than that so it’s worth 100 cents ($1). A pH of 4 (or 10) is

10 times stronger than that, so worth $10.

Determine pH from concentration of H+ ions:

Solution of 0.00001M = 1 x 10-5 pH = - log[1 x 10-5] = 5

Example 1: Determine the concentration of H+ ions from pH:

pH = 3

1 x 10-3 = 0.001 Moles per liter -Acid

pH = 7

1 x 10-7 = 0.0000001 Moles per liter - Neutral

pH= 10

1 x 10-10 = 0.0000000001 Moles per liter -Base

Example 2: Classify each of the following solutions as acid, basic, or neutral.

Then arrange the solutions in order of increasing acidity.

a) Human blood – 7.4 (base)

b) Tomatoes – 4.5 (Acid)

c) Liquid drain cleaner – 14.0 (Base)

d) Battery acid – 1.0 (Acid)

e) Pure water – 7.0 (Neutral)

f) Sea water – 8.0 (base)

Liquid drain cleaner < seawater < Human blood < Pure water < Tomatoes <

Batter acid

Indicators A chemical indicator is a substance that changes color in the presence of H+

and OH-. Indicators are used as a safe way to determine if the substance is an

acid or a base.

Litmus Paper

Litmus paper is filter paper stained with litmus (dye from lichens) used to

indicate is a substance is an acid or a base.

Litmus paper can be red or blue and changes colour accordingly:

Red Litmus Blue Litmus

Acid Stays Red Turns red

Neutral Stays red Stays blue

Base Turns blue Stays blue

Phenolphthalein

Phenolphthalein is an organic compound that changes

colour in a basic solution (C20H14O4)

Colourless in solution that is below 8 (acid)

Pink in a solution that is above 10 (base)

Bromothymol Blue

Bromothymol Blue is a chemical indicator for weak acids

and bases, substances that are close to neutral.

● Below pH 6 it turns the solution yellow

● pH of 7 the solution is green

● Above pH 8 the solution is blue

Universal Indicator

Universal indicator is a solution that changes a variety of colours over a range

of pH’s. Universal indicators are usually mixtures of several indicators. An

example of a universal indicator is red cabbage juice that contains the pigment

anthocyanin that changes colour in various pH.

pH Indicator Activity

1) In groups of two (one person needs to have a device)

you are assigned an “unknown substance” that you will

test using the cabbage indicator.

2) Go to Padlet to post:

a. What you think your substance is

b. A picture of video of the colour change

c. Why might it be important for us to be able to

identify acids and bases?

d. Sign both names

https://padlet.com/katlyn_paslawski/AcidBase