Acids, Bases and pH

What is an Acid? An acid is an ionic compound that contains a hydrogen ion. Hydrogen ion = H+ Hydrogen ion is basically just a proton An acid is a compound that donates (gives up) a proton (H+)

Acids – what do you notice?

What is a Base? A base is an ionic compound that contains a hydroxide ion. Hydroxide ion = OH- A base is a compound that accepts (takes on) a proton (H+)

Bases – what do you notice?

What about water? Water is a special chemical for lots of reasons Water can act as an ACID and a BASE

HCl + H2O --> Cl- + H3O+ water acts as a base it accepts a proton to become H3O+ H3O+ is called a HYDRONIUM ion (created when water gets an extra proton)

H2O + NH3 --> OH- + NH4+ Water acts as an acid loses a proton to become OH-

Water is really H(OH): a hydrogen ion bonded with a hydroxide ion.

How do we know if something is an acid or a base? Look at the chemical formulas, look for H (acid) or OH (base) Look at a chemical reaction, does the compound accept a proton (base) or lose one (acid) Determine the pH (power of Hydrogen?) of the substance

What is pH? pH is a number that tells us how acidic or basic a substance is.

Acid The pH scale starts at 0 and goes to 14 If the pH is from 0-6.9, the substance is an acid

Base If the pH is from 7.1 – 14, the substance is a base

A pH of 7 is a neutral substance (neither an acid nor a base): WATER, lots of everyday substances

There are other ways to determine if something is an acid or a base? Indicators these are chemicals that change colors based on their environment

Phenolphthalein (Pth) Below a pH level of 7, Pth stays clear. Above a pH level of 7, Pth turns pink/purple.

Litmus paper (red/blue). Red litmus paper turns blue when placed in a base. Blue Litmus paper turns red when placed in an acid.

Neutralization

We can mix acids & bases together! Example: Hydrochloric acid is combined with sodium hydroxide. HCl + Na(OH)  H2O + NaCl

Anytime you mix an acid and a base, one product will be water In the reaction, H+ (from the acid) and OH- (from the base) combine to form HOH or H2O or water molecules.

Anytime you mix an acid and a base, the other product will be a salt After the H and OH form water, the leftover ions form a bond and create the salt.

Another Example: Explain why lakes with limestone or calcium carbonate beds experience less adverse effects from acid rain than lakes with granite beds.

Limestone = CaCO3 (acts as a BASE) Acid Rain = H2SO4 (sulfuric acid) or HNO3 (nitric acid)

What reaction occurs when they combine? CaCO3 + H2SO4  H2O + CaSO4 + CO2 We now have water, a salt (CaSO4), and a gas (just carbon dioxide). None of these are harmful.

Granite does not act like a base and the acid will simply hang out in the water, which affects the fish and plants in the area.