Unit 6: Acids, Bases & the pH Scale

A World of Liquids With Interesting Properties!

What is an Acid?• A substance that has an increased

number of dissolved Hydronium ions, (H3O+)

• When a Hydrogen ion (H+) bonds with a water molecule (H2O)

• Hydronium is simply a water molecule with an extra hydrogen atom making it an ion+

• Acid comes from a Latin term acere, which means “sour”

What are the Properties of Acids?

• Sour taste• React with metals

to produce hydrogen gas

• Change color of an indicator

• Change blue litmus paper to red

• Conduct electricity

What is a Base?

• A substance that has an increased number of dissolved Hydroxide ions (OH-)

• A substance that has less than 49% of Hydronium dissolved in it

What are the Properties of a Base?

• Bitter taste • Slippery feel to them• Does NOT react

with metals• Change color of an

indicator• Change red litmus

paper blue• Conducts electricity

What is a Strong Acid?

• A substance that has ALL of the Hydronium ions dissolved in water

• Note - – Strong acids don’t

always mean the most corrosive

What is a Weak Acid?

• A substance that only has a few molecules of Hydronium dissolved in water

• Note - – Can be very corrosive,

but not always

What is a Strong Base?

• A substance that has ALL of the Hydroxide ions dissolved in water

• Used mostly as household cleaners

What is a Weak Base?

• A substance that only has a few molecules of Hydroxide dissolved in water

• Most common in detergents/soaps.

What is a Neutralization Reaction?

• When the H+ ions of an acid react with the OH- ions of a base to form water, which is neutral

• 2 substances form from this reaction– Salt and Water

What is the pH scale?• A scale showing the

concentration of Hydronium ions dissolved in water.

• Each number represents a power of 10

• pH2 is 100 times more acidic than pH4

What are pH Indicators?

• A substance that changes color in the presences of either an acid or a base.

• Examples– pH paper– Litmus papers– Bromthymol blue

What are Salts?

• Not necessarily table salt

• An ionic compound formed from the neutralization of an acid and a base

• Used for many products in society