ACIDS & BASESACIDS & BASES

Last section!Last section!

Lesson OutlineLesson Outline

What are acids & bases?What are acids & bases?Properties of acids and basesProperties of acids and basesFormulas for acids and basesFormulas for acids and basesThe pH scaleThe pH scale

What are Acids & Bases?What are Acids & Bases?

Chemists use classification systems to Chemists use classification systems to make sense of mattermake sense of matter

Acids and bases are types of Acids and bases are types of compounds that have characteristic compounds that have characteristic formulas & similar chemical behavioursformulas & similar chemical behaviours

E.g. lemon juice; baking sodaE.g. lemon juice; baking soda

Properties of AcidsProperties of Acids

Acids are sour-tasting, water-soluble substancesAcids are sour-tasting, water-soluble substances They are very reactive and combine with many They are very reactive and combine with many

other substancesother substances (e.g. Mg(e.g. Mg(s)(s) + 2 HCl + 2 HCl(aq)(aq) MgCl MgCl22 + H + H2(g)2(g)))

Acids react with compounds containing Acids react with compounds containing carbonate and hydrogen carbonate groupscarbonate and hydrogen carbonate groups (e.g. 2 HCl(e.g. 2 HCl(aq)(aq) + CaCO + CaCO3(s)3(s) CO CO2(g)2(g) + H + H22OO(l) (l) + CaCl+ CaCl2(aq)2(aq)

Properties of AcidsProperties of Acids

Acids are good conductors of electricity Acids are good conductors of electricity (think of BATTERY ACID) because…(think of BATTERY ACID) because…

When acids dissolve in water, they release When acids dissolve in water, they release hydrogen ions (Hhydrogen ions (H++))HClHCl(aq)(aq) H H++

(aq)(aq) + Cl + Cl--(aq)(aq)

Properties of BasesProperties of Bases

Bases are bitter-tasting, water-soluble Bases are bitter-tasting, water-soluble substancessubstances

They feel slippery in aqueous solutionsThey feel slippery in aqueous solutionsThink of soap!!Think of soap!!

Bases are good conductors of electricity Bases are good conductors of electricity because…because…

Properties of BasesProperties of Bases

When bases dissolve in water, they When bases dissolve in water, they release release hydroxide ions (OHhydroxide ions (OH--))E.g. NaOHE.g. NaOH(aq)(aq) Na Na++

(aq)(aq) + OH + OH--(aq)(aq)

Substances described as basic may also Substances described as basic may also be described as be described as alkalinealkaline

What does this remind you of?What does this remind you of?

Formulas for Acids & BasesFormulas for Acids & Bases

Acid formulas begin with a hydrogenAcid formulas begin with a hydrogenE.g. HCl, HE.g. HCl, H22SOSO44, H, H33POPO44

Base formulas are trickier…most contain Base formulas are trickier…most contain the hydroxide ion (e.g. sodium hydroxide the hydroxide ion (e.g. sodium hydroxide is NaOH) – some contain the bicarbonate is NaOH) – some contain the bicarbonate or hydrogen carbonate group (e.g. sodium or hydrogen carbonate group (e.g. sodium hydrogen bicarbonate is NaHCOhydrogen bicarbonate is NaHCO33))

The pH ScaleThe pH Scale

Chemists use the Chemists use the pH scalepH scale to represent to represent how acidic or basic a solution ishow acidic or basic a solution is

A very acidic solution has a A very acidic solution has a very lowvery low pH pH valuevalue

A very basic solution has a A very basic solution has a very highvery high pH pH valuevalue

Water (neutral) has a pH of 7Water (neutral) has a pH of 7

The pH ScaleThe pH Scale

The pH scale is LOGARITHMICThe pH scale is LOGARITHMIC Means that a change of one unit on the scale represents Means that a change of one unit on the scale represents

a tenfold effect on the concentration of the solutiona tenfold effect on the concentration of the solution

For example, a solution with pH of 3 is 10 times For example, a solution with pH of 3 is 10 times more acidic than a solution with a pH of 4more acidic than a solution with a pH of 4

pH = -logpH = -log1010[H[H++]] “concentration of “concentration of

hydrogen ions in solution”hydrogen ions in solution”

[H+] pH Example

Acids

1 X 100 0 HCl 

1 x 10-1 1 Stomach acid

1 x 10-2 2  Lemon juice

1 x 10-3 3  Vinegar

1 x 10-4 4 Soda

1 x 10-5 5 Rainwater

1 x 10-6 6 Milk

Neutral 1 x 10-7 7 Pure water

Bases

1 x 10-8 8 Egg whites

1 x 10-9 9 Baking Soda

1 x 10-10 10 Tums® antacid

1 x 10-11 11 Ammonia

1 x 10-12 12 Mineral Lime - Ca(OH)2

1 x 10-13 13  Drano®

1 x 10-14 14 NaOH