Acids and Bases

Solutions can be sorted by whether they are: acid, basic (alkali) or neutral.

When a substance dissolves in water it makes a solution.

Acids & Bases• Acids

– Taste sour– Turns litmus red– Neutralizes bases– Acids are made of one

or more H atoms and one negative ion

– Ex. HCl– Produces H+ ions when

dissolved in water– Are corrosive

• Bases– Taste bitter– Turns litmus blue– Neutralizes acids– Bases are made of

metals combined with hydroxide ions (OH-)

– Ex. NaOH– Produces OH- when

dissolved in water– Feel slippery or

“soapy”

– Are corrosive

Acids & Bases STRONG vs WEAKSTRONG vs WEAK_ _ completely ionizedcompletely ionized _ partially ionized_ partially ionized_ strong electrolyte_ strong electrolyte _ weak electrolyte_ weak electrolyte_ ionic/very polar bonds_ ionic/very polar bonds _ some covalent _ some covalent

bondsbonds

Strong AcidsStrong Acids:: Strong Bases:Strong Bases:HClOHClO44 LiOHLiOHHH22SOSO44 NaOHNaOHHIHI KOHKOHHBrHBr Ca(OH)Ca(OH)22

HClHCl Sr(OH)Sr(OH)22

HNOHNO33 Ba(OH)Ba(OH)22

Acids

Lemon juice contains citric acid, and vinegar contains acetic acid (also known as ethanoic acid).

Some strong acids are hydrochloric acid, sulphuric acid and nitric acid.

Some weak acids are ethanoic acid, citric acid and carbonic acid.

There are many acids present in our everyday lives.

Bases

Alkalis are present in many cleaning substances used in our homes.

Kitchen cleaners are alkaline because they contain ammonia or sodium hydroxide, which attack grease.

Calcium hydroxide and sodium hydroxide are strong alkalis. The most recognizable and common weak alkali is ammonia.

Neutralization

• Acids and bases (alkalis) react with each other. The alkali cancels out the acid in the reaction. This is called neutralization.

A salt is made.

Salts

• The salt made depends on the acid and alkali used.

• The salt contains the metal atom from the alkali, and the non-metal of the acid molecule.

The salts of sulphuric acid are known as sulphates. The salts of hydrochloric acid are known as chlorides. The salts of nitric acid are known as nitrates.

Applications of Neutralization

• Indigestion: Our stomach carries around hydrochloric acid. Too much of this leads to indigestion. To cure indigestion, you can neutralize the

excess acid with baking soda or specialized indigestion tablets.

• Insect Stings Bee stings are acidic and can be neutralized with baking soda (bicarbonate of soda). Wasp stings are alkaline and can be neutralized with vinegar.

Factory Waste: Liquid waste from factories is often acidic. If it reaches a river it will destroy and kill sea life of many forms. Neutralizing the waste with slaked lime can prevent this.

Soil Treatment: When soils are too acidic (often as a result of acid rain) they can be treated

with slaked lime, chalk or quicklime, all alkalis. Plants

and crops grow best in neutral soils.

Indicators

They change color in acid or alkaline solutions. Different indicators change to different colors.

Indicators help you find out whether a solution is acidic or not.

Universal Indicator• Universal indicator changes color in

acids and alkalis.

Its color shows the strength of an acid or alkali.

ACIDS ALKALIS

Neutral

LitmusTest

• Litmus is an indicator. It changes color in acid and alkaline solutions.

• Litmus is red in an acid. • Litmus is blue in an alkali.

The pH scale

1 – 6 8 - 14 Alkalis 7N

eutral

Acids

• Potential of Hydrogen (or power of Hydrogen)• Concentration (measure) of hydrogen ions• 0-14

– Less than 7 acidic– More than 7 basic

• [ ]= Molarity/ConcentrationpH= -log [H+] [H+]= 10-pH

• Potential of Hydroxide (power of hydroxide)• Concentration of hydroxide ions

pOH = -log [OH-]

pH + pOH = 14

[OH-] = 10-pOH

pH Calculations

pH

pOH

[H+]

[OH-]

pH + pOH = 14

pH = -log[H+]

[H+] = 10-pH

pOH = -log[OH-]

[OH-] = 10-pOH

[H+] [OH-] = 1.0 x10-14

Example

• What is the pH of a solution if its Molarity is [H+]= 3.0 x 10-5?

• What is the hydrogen ion concentration [H+] in a solution with a pH of 3.12?

pH= -log [H+]

[H+] = 10pH

Example

• What is the pOH of a solution that has a .0658 moles of NaOH in 0.156 L of solution?

• What is the [OH-] of a solution if the pH is 9?

pOH = -log [OH-]

pH + pOH = 14

[OH-] = 10pOH

M = moles/ L = [ ]

•[ ]= Molarity/Concentration

Your turn….What is the pH of a solution if the [H+] is 2.8 x 10-3?What is the [H+] of a solution if the pH is 3.5?What is the pOH of LiOH if you have 0.45 moles in 0.65 L?What is the [OH-] of a solution if the pH is 5.6?What is the pH if the [OH-] is 4.5x 10-2?

pH= -log [H+] [H+]= 10pH

M = moles/ L = [ ]

pOH = -log [OH-] [OH-] = 10pOH

pH + pOH = 14

“How to” guide to calculateFinding [H+] and [OH-][H+] x [OH-] = 1 x 10-14 M2

[H+] = 1 x 10-14 M2 or [OH-] = 1 x 10-14 M2

[OH-] [H+]

Finding pHpH = -log [H+]Ex: find pH if [H+] = 6.70 x 10-7 MIn the calculator, enter :- Log 6.70 exp – 7 = ans pH = 6.17

continuedHow to find pOHpOH = -log [OH-]Example: What is the pOH of a solution that has a [H+] = 3.0 x 10-5M

First find [OH-]: [OH-] = 1 x 10-14 M2 [OH-] = 3.33 x 10-10 M 3.0 x 10-5 M

In the calculator, enter:- Log 3.33 exp - 5 = ans. pOH = 4.48

continuedHow to calculate [H+] from pHTake the antilog of the negative pHExample: What is the [H+] of a solution with a pH of 5.25?In the calculator, enter:Shift log - 5.25 = ans.[H+] = 5.62 x 10-6 M

Last but not least, remember:pH + pOH = 14