Acids and Bases

Chapter 17

A special solution Acids and bases are ALWAYS in a

water solution. Your body has water in it so they are

always dangerous to living things. Bases are just as dangerous as acids. In low concentrations they are not

that dangerous and found all over your house.

Acids and Bases

Aci Re less than 7 sour metals and

bases

ase lue more than 7 bitter and feel

slippery oils and acids

• Although they can be dangerous, acids and base do not react with or “eat”everything.• Neither has an effect on glass for example.

turn litmus paperhave a pHtastereact with

D B

Common places to find acids and bases

Acids Vinegar- acetic

acid citrus fruits-

citric acid carbonated

drinks- carbonic acid

Your stomach- hydrochloric acid

Bases Antacid tablets

(calcium hydroxide)

Windex- ammonia

Oven cleaner- sodium hydroxide

Draino – sodium hydroxide

Homework Using the litmus paper provided in class

check to see if two common items found in your house are acidic or basic.

Report your findings on a piece of paper, and staple the litmus paper with it.

You need to report what the items are and if they are acidic or basic.

Please exercise caution and common sense. Do NOT test anything dangerous!

Definitions Acid- a proton (H+) donor [force

feeder] Acids produce H3O+ (hydronium) in

water Base- a proton (H+) acceptor [thief] Bases produce OH- (hydroxide) in

water

Heat of solution Normally dissolving a substance is

an exothermic process. You are normally increasing the

state of entropy (measure of disorder)

Which normally means you will release heat.

There are exceptions, dissolving ammonium nitrate is an endothermic process

Always do what you oughta … Always add acid to water Dissolving the acid in water

releases heat If you have a lot of acid and a little

water on top, the water typically boils quickly causing the hot acid to spray out.

A lot of water on the bottom typically doesn’t boil if the acid is added slowly enough.

Self dissociation of water.

Some water will dissociate itself H2O +H2O H3O+ +OH-

in “pure” water you will find H3O+ has concentration of 1 x 10-7 M OH- has concentration of 1 x 10-7 M The product of the conc. of H3O+ and

OH- is always 1 x 10-14 [ ]-conc. [H3O+] [OH-] = 1 x 10-14

pH

The H3O+ and OH- concentration is normally very small.

pH- method of representing the H3O+ concentration in a solution.

pH = -log [H3O+] So the pH of water is… pH = - log 1 x10-7

pH = 7

What is a log log stands for logarithm ~we can use them to solve for an

exponent. log xy = y log x For example log 1 x10-7 = -7 the log key on your calculator is log10

meaning it will cancel out a 10^. To reverse a log10 raise the whole thing

to the 10th power (10^), this is an antilog

The reversed pH equation is [H3O+] = 10^(-pH)

pH values

pH of 7 is neutral- equal [H3O+] and [OH-]

below 7 is acidic, higher [H3O+] than [OH-]

above 7 is basic or alkaline, higher [OH-] than [H3O+]

pOH pOH = -log [OH-] pH + pOH = 14 pOH is the reverse of pH Above 7 is acidic, below 7 is basic

pH problems What is the pH of a 2.4 x 10-4 M H3O+? pH = - log 2.4 x 10-4 pH = 3.62 What is the OH- concentration? [H3O+] [OH-] = 1 x 10-14

2.4 x10-4 [OH-] = 1 x 10-14

[OH-] = 4.2 x10-11 M What is the pOH? pOH = - log 4.16666x10-11

pOH = 10.38

Backwards problem

What is the pOH, [H3O+] and [OH-] of a solution with a pH of 8.72?

[H3O+] = 10^(-pH) [H3O+] = 10-8.72 [H3O+] = 1.9 x 10-9 M 1.905…x10-9 [OH-] = 1 x 10-14

[OH-] = 5.2 x 10-6 M pOH + pH = 14 pOH = 5.28