Acids and Bases

Chapter 16

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

In any solution the H3O+ and OH-

concentration is always 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+]

Acid Base Equations

[H3O+] [OH-] = 1 x 10-14

pH = -log [H3O+] [H3O+] = 10^(-pH)

Sig Figs and pH

The number of decimal places in the log value, pH value, is equal to the number of significant figures in the number that we took the logarithm of, concentration.

So [H3O+] = 2.45 x10-4 M 3 sig figs pH = -log 2.45 x10-4 M = 3.611 3 decimal places

Reversing that

Having a pH of 4.32 (2 decimal places) gives you a hydronium concentration of…

[H3O+] = 10^(-4.32) = 4.8 x10-5 M (2 sig figs)

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

Backwards problem

What is the [H3O+] and [OH-] of a solution with a pH of 8.75?

[H3O+] = 10^(-pH) [H3O+] = 10-8.75 [H3O+] = 1.8 x 10-9 M 1.78…x10-9 [OH-] = 1 x 10-14

[OH-] = 5.6 x 10-6 M

Last one

What is the pH and [H3O+] of a solution with a [OH-] conc. of 2.9 x10-4 M?

Homework

What is the pH and [H3O+] of a solution with a [OH-] of 5.92 x10-5

M?

Neutralization of an acid or base.

Mixing acids and bases ~creates water H3O+ + OH- 2 H2O this is called neutralizing the

solution a neutralized solution is no longer

dangerous. The point where neutralization is

complete is called the equivalence point

Salts ~the byproduct of an acid and a

base. NaOH + HCl H2O + NaCl (base) (acid) (water) (salt) there are several more than just

table salt. HNO3 + NH4OH H2O + NH4NO3

Acid Base water salt

Gases can be created this depends on the reactants (not

all will) sodium bicarbonate (baking soda)

will pretty much always release a gas

NaHCO3 + H2SO4 H2O + NaHSO4 +

CO2

GasSalt

Titration ~mixing an acid and base

perfectly to make a neutral solution.

You normally need some kind of indicator for this.

Phenolphthalein- when in solution turns red if basic and is clear if acidic.

You can also use a pH probe

Graph of titration

Volume strong base added

pH equivalence point

Using math To neutralize a solution you will

need to add an equal amount of H3O+ / OH- to what was already present.

so that mol H3O+ = mol OH-

This is used if and only if you are at the equivalence point (completely neutral solution)!

Problem If 94 mL of 4.0 M NaOH neutralizes

6.0 L of an unknown strong acid, what was the H3O+concentration of the unknown?

4 M NaOH x .094 L = .376 mol NaOH

.376 mol H3O+/ 6.0 L = .063 M H3O+

Another problem If 127 mL of 2.0 M NaOH

neutralizes 4.1 L of an unknown acid, what is the initial concentration of the acid?

2.0M(.127 L) = .254 mol NaOH =.254 mol OH- = .254 mol H3O+

4.1 L =.062 M

Equilibrium

Chapter 17

Rates of reaction Different reactions happen at different

speeds. There are ways to speed up or slow

down a reaction. Changing the surface area of the

reactants Powders react more quickly than “chunks”

Changing the amount/concentration of reactants More reactant speeds up the reaction

Changing the temperature Warmer reactions tend to go faster

Amount of rate change depends on the reaction.

Catalysts and Inhibitors Catalyst- something that increases

the rate of a reaction without changing the products of the reaction.

Catalytic converter speeding the reaction of emissions of a car to less dangerous products

Inhibitor- something that slows or stops a reaction

-food preservatives

Catalyst example 2 O3 3 O2

Ozone will decompose into elemental oxygen, however this process is very slow.

Chlorine acts as a catalyst as shown in this two step reaction

2 O3 + 3 Cl2 6 ClO 6 ClO 3 O2 + 3 Cl2 ClO is an intermediate, something

formed in the middle of the reaction that is later consumed.

Chlorine is a catalyst because it is a reactant in the first step, but a product in the last step. So it isn’t used up during the reaction.

Forwards and backwards Most reactions can go forwards or

backwards Neutralization equation H3O+ + OH- 2 H2O Self ionization of water 2 H2O H3O+ + OH-

Equilibrium In water, both of those reactions are

occurring simultaneously. Equilibrium is when the forward and

backward reactions are occurring at the same rate.

This will cause a stable amount of product and reactant to be present. No net change is occurring when it is at equilibrium. (dynamic equilibrium)

The amount of product and reactant do NOT have to be equal!

Representing equilibrium It is normally represented with a

double arrow 2 H2O H3O+ + OH-

This reaction comes to equilibrium when [H3O+ ] = 1 x10-7 M and [OH- ] = 1 x10-7 M (assuming the solution is neutral)

you won’t have to calculate this.

Le Châtelier’s Principle ~whenever stress is applied to a

system at equilibrium, a new equilibrium will be obtained to relieve this stress.

stress is a change in temperature, pressure, or concentration of some component.

This will change the rate of reaction of either the forward or backward reaction

So you will see an increase in the concentration of the substances on one side of the equation, and a decrease on the other.

This will “shift” the equation to the right or left.

Examples Endothermic reactions absorb

heat, i.e. they need heat to react. If the solution is heated prior to the

reaction (stress)… It will react more quickly So the equation will be forced to

the right (product side) If the reaction is cooled, it will be

forced to the left (reactant side)

Equilibrium

Equilibrium Systems at equilibrium are still

dynamic (changing). However, no NET CHANGE will be observed.

A system is at equilibrium when the rate of the forward reaction is equal to the rate of the reverse reaction.

Changing concentration 2 H2O H3O+ + OH-

If I add more water It will force the reaction to the right Which means more hydronium and

hydroxide will be produced This is dilution (making the ratio of

hydronium/hydroxide closer)

Equilibrium Add water 2 H2O H3O+ + OH-

Stress + X 0 0 Shift -2y +y +y Final +X - 2y + y +y Since the stress was added to the

left we must take from the left and give to the right to relieve the stress

*where X is the amount of H2O added and larger than 2y

That means… Add water 2 H2O H3O+ + OH-

Final + X - 2y + y +y We increased water because X is

always larger than y (with any coefficent).

We increased H3O+ because +y is an increase

We increased OH- because +y is an increase

The only equilibrium calculation That you will have to do with

numbers is:

[OH-] [H3O+ ] = Kw

Kw is the equilibrium constant for water, it equals 1 x 10-14 M

We have already used the equation

More Le Châtelier’s If I add an acid to the equilibrium… 2 H2O H3O+ + OH-

Stress 0 +X 0 Shift +2y -y -y Final + 2y +X- y -y *Where X is larger than 2y so adding acid will decrease the

[OH-], only slightly increase the[H3O+ ], and increase water.

2 H2O H3O+ + OH-

If I remove hydroxide from the solution…

2 H2O H3O+ + OH-

Stress 0 0 -X Shift -2y +y +y Final - 2y + y -X +y *Where X is larger than 2y So removing hydroxide increases

[H3O+], only slightly decreases [OH-], and decrease the water

Different equation Adding hydrogen to the equilibrium 2 NH3 3 H2 + N2 Stress 0 +X 0 Change +2y -3y -y Final +2y +X-3y -y *where X is larger than 3y Increases the amount of NH3

decreases the amount of N2 and only slightly increases H2

With heat If I cool the following equilibrium Heat+ Co2+ + 4 Cl- CoCl42-

stress -x 0 0 0 Shift +y +4y -y Final +y +4y -y So cooling the solution will cause

more Co2+ & Cl- and less CoCl42- to form

Conjugate acids and bases

Different definitions of acids and bases

Acids are proton donors (Brønsted Lowry definition) they generate H3O+ in water (Arrhenius

definition) Bases are proton acceptors

they generate OH- in water which is an acid/base? HF + H2O H3O+ + F-

NaHCO3 + H2O Na+ +H2O + CO2 + OH-

Follow the proton

HF + H2O H3O+ + F-

NaHCO3 + H2O Na++ H2O+CO2 +OH-

Joining equilibrium to acid base…What about the reverse reaction?

H+

H+

H+

H+

Conjugate acids and bases When you run the reverse reaction you

find the products are also acids and bases. The acids and bases that are formed are called conjugate acids or bases

H2O + HF H3O+ + F-

base acid conjugate acid conjugate base

NaHCO3 + H2O Na+ +H2O + CO2 +OH-

base acid CA CB

Label Acid, Base, Conjugate Acid, Conjugate Base

HClO3 + H2O ClO3- +H3O+

A B CB CA ClO- + H2O HClO + OH-

B A CA CB HSO4

- + H2O SO42- +H3O+

A B CB CA LiOH + H2O Li+ + H2O + OH-

B A CA CB

Conjugate acids and bases … Conjugate acids and bases

determine if an acid or base is strong or weak.

If the conjugate acid/base readily reacts to run the reverse reaction it is a weak acid/base.

If it does not react in the reverse reaction the acid or base is strong.

Strong acids

Acid formula

Nitric Acid HNO3

Sulfuric Acid

H2SO4

Hydrochloric acid

HCl

Strong Bases

Name Formula Name Formula

Sodium Hydroxide

NaOH Calcium Hydroxide

Ca(OH)2

Potassium Hydroxide

KOH Strontium Hydroxide

Sr(OH)2

Barium Hydroxide

Ba(OH)2

these make a lightning bolton the periodic table!

More with conjugate acids/bases

H2SO4 + H2O H3O+ + HSO4-

Sulfuric acid is a strong acid so its conjugate base, HSO4

-, will not run the reverse reaction.

HSO4 - is actually an acid in water.

HSO4 - + H2O H3O+ + SO4

2-

SO42- will run the reverse reaction, so

it is a weak acid

Other weak acids and bases

Weak Acids Acetic Acid (vinegar) Citric Acid Ascorbic Acid (vitamin C) Boric Acid Carbonic Acid

Weak Bases Sodium Bicarbonate Ammonia Sodium Hypochlorite (bleach)

Danger!!! Strong and Weak acids and bases do

NOT necessarily tell you how dangerous they are.

Concentration is the most important factor for determining danger.

Ammonia is a weak base, if it is highly concentrated it can burn you.

Dilute hydrochloric acid (less than 1 M) is not particularly dangerous

What is water

Water is either an acid or base depending on the situation.

Anything that is either an acid or a base is called amphoteric.

Several things are amphoteric, like parts of you.

Donating Protons

Hydrochloric acid (HCl) can donate 1 proton, so it is called a monoprotic acid.

Sulfuric acid (H2SO4) can donate 2 protons, so it is called a diprotic acid.

Phosphoric acid (H3PO4) can donate 3 protons, so it is called a triprotic acid.

Indicators

Weak acids and bases can act as an indicator

can be forced the other way So ammonia… NH3 + H2O NH4

++OH-

Ammonia is a gas with a distinct odor

Ammonium and hydroxide are both odorless.

If base is added to the solution you will smell ammonia, if hydroxide is removed you won’t.

Pet Stain Problem Urine has ammonia in it. Most cleansers are basic NH3 + H2O ⇌ NH4

++OH-

If I stress this equilibrium by adding a base…

It shifts to the left causing more ammonia to form. Animals sense of smell is better so they fine the same spot and mark it again.

That is why there are special cleansers (acidic) for pet stains

Indicators Indicators are a substance that

change color in the presence of (whatever they check for)

They do this because of Le Châtelier’s principle. All you need an equilibrium reaction with different colored products and reactants.

The pen used to check for counterfeit money is a starch indicator

How an acid base indicator works

A generic indicator will follow this reaction, HId is the reactant indicator, and Id- is its product

HId + H2O  H3O+  + Id-

The color differences are important in an acidic solution (high H3O+) you

see reactant

HId + H2O   H3O+  + Id-

in a basic solution (low H3O+) you see product

HId + H2O  H3O+  + Id-

Acid Base indicators

Acid base indicators change color at certain pH levels

They don’t have to change at 7 (most don’t)

Universal indicator solution (phenolphthalein, bromthymol blue and methyl red dissolved in

ethanol and water) changes color at each integral pH value

Other pH indicators Litmus and

phenolphthalein are indicators

Red cabbage has a pigment that changes colors at different pH values

Buffers Buffers are solutions that don’t

change in pH when acids or bases are added.

They use weak acids/bases and Le Châtelier’s principle.

WA = weak acid HWA + H2O H3O+ + WA-

How? pH is determined by the

concentration of H3O+

Concentration is measured by mol /L

Moles of H3O+ / L (primarily of) H2O

What it does adding H3O+ should increase [H3O+] However, this forces the equation to the

left, decreasing H3O+ and increasing H2O so the [H3O+] remains constant Removing H3O+ (adding a base) should

decrease [H3O+] However, this forces the equation to the

right, increasing H3O+ and decreasing H2O

So again, there is no change to [H3O+] There is a breaking point where the pH

will change.

What does this have to do with my life? Your blood is a buffered solution The pH must remain between 7.35-

7.45 Outside of that range can kill you below this range is called acidosis above is called alkalosis

Buffered Products medications (Bufferin) Shampoos, body soaps All are buffered to be near your

body pH so they won’t cause a major disruption.