Acids and bases

Acids and bases – Part 1

Learning outcomes

�Define acids and bases according to pH

�Describe the characteristic properties of acids as reactions
with metals, bases, metal oxides, metal carbonates and effect
on litmus, methyl orange and phenolphthalein

�Describe the characteristic properties of bases as reactions
with acids and with ammonium salts and

�effect on litmus, methyl orange and phenolphthalein

�Describe the meaning of weak and strong acids and bases
with examples

�Describe neutrality and relative acidity and alkalinity in terms
of pH measured using Universal Indicator paper

�(whole numbers only)

�Describe and explain
�acid rain and its effect

�the importance of controlling acidity in soil

Understanding

Acids and bases

What is an acid?

everyday acids

laboratory acids

Acids are a group of chemicals.

What is a weak acid?

Acids are found in household items such as food, drink
and beauty/skincare products.

It is safe to handle these acids and even taste them, if
they

are for eating! These acids are known weak
acids.

Ethanoic

acid

What is a strong acid?

Some acids, like those found in the laboratory or a car
battery, are very dangerous (too dangerous to taste or
touch).

These acids are said to be corrosive as they can damage
other materials by wearing them away!They are strong
acids.

Why must strong acids always be handled very carefully?

The following are the characteristic properties of acids:

1.Taste - Acids have a sour taste.
This is particularly true of dilute acids. Acids present in
some common substances

What type of acid do these

contain?

Citric acid

Tannic acid

Phosphoric acid
Ethanoic acid

Lactic acid

What is an alkali?

everyday alkalis

laboratory alkalis

Alkalis are another group of chemicals, the opposite of
acids.

What is a weak alkali?

Alkalis are found in soaps and other materials used for
cleaning.

It is safe to handle these alkalis, which can feel
soapy.
These alkalis are known as weak alkalis.

What is a strong alkali?

Some alkalis, like those in the laboratory or in cleaning
materials such as toilet cleaner, are too dangerous to
touch.

These alkalis are said to be caustic because they can
burn skin and damage other materials! They are strong
alkalis.

Why must strong alkalis always be handled very
carefully?

Alkalis

In the science lab you will often find these alkalis. Alkalis are also present
in these objects:

Cleaning
products

Baking soda

Wasp stings

Indigestion
tablets

Soap

Toothpaste

Also
called

Ammonia

Fill in the Blank

If you know that a jelly fish sting is basic, which substance can you use to treat this sting?

What is an indicator?

An indicator is a chemical that turns a different
colour depending on whether it is added to an acid
or an alkali.
Litmus is a commonly used indicator.

Litmus can be blue or red. Blue
litmus turns red under acidic
conditions, and red litmus turns blue
under alkaline conditions.

acid

alkali

neutral

colourles
s

pin
k

re
dre
d

yello
w

methyl
orange
phenolphthalei
n

Litmus

Indicator

Colour in acid

Colour in alkali

blue

What is universal indicator?

Universal indicator has a range of colours that show
how weak or strong the acid or alkali is.

What is the colour for a strong
alkali?

What is the colour for a weak
acid?

Universal indicator is made from a mixture of
indicators.
Why do you think it is more useful than litmus?

weak alkali

weak acid

strong acid

neutral

strong alkali

What is the pH scale?

The strength of an acid or alkali is measured by the pH
scale.
Each universal indicator colour is given a pH
value.
Universal indicator can tell you the pH of a
solution.

What is the pH of a strong
alkali?

What is the pH of a weak
acid?

1

2

3

4

5

6

7

8

9

10

11

12

13

14

strong acid

neutral

strong alkali

What does the pH scale show?
The pH scale runs from 1 to 14. The numbers 1 to 6
represent acidic conditions and 8 to 14 represent alkali
conditions.
A pH value 7 is neutral.

1

2

3

4

5

6

7

8

9

10 11

12 13 14

What are the pH values of some everyday
items?

Popular acids and alkalis

Fill in the Blank

Oven cleaner has a pH of 14, it can be classified as

Fill in the Blank

Soap has a pH of 8, it can be classified as a

Fill in the Blank

Vinegar has a pH of 5, it can be classified as a

Reactions
with acids

Metals

“above

Hydrogen”

Metal

Hydroxide

Metal

Carbonate

Metal
Oxide

Salt + Hydrogen

Salt + Water

Salt + Water

Salt + Carbon Dioxide

+ Water

Ammonia NH3

Ammonium Salt

In aneutralization reaction, an acid reacts with an alkali to
produce a salt and water.

When the acid reacts with the alkali, the acid’s H+ ions
react with the alkali’s OH– ions, forming water.

This process takes place in all neutralization reactions.

H++ OH–

H2O

The chemical reaction between an acid and an alkali can be
written as:

+

→

acid

alkali

salt + water

2. Reaction of acid with base - neutralization

The name of the salt depends on the type of

acid used and the metal in the base

Naming salts

● When an alkali reacts with hydrochloric acid, the salt

produced is a chloride.

● When an alkali reacts with sulfuric acid, the salt

produced is a sulfate.

● When an alkali reacts with nitric acid, the salt

produced is a nitrate.

Which acid would be needed to make these

salts?

1.

copper nitrate

2.

magnesium chloride

3.

sodium sulfate

Multiple Choice

Copper Chloride can be produced from which of the following?

• Copper chloride and nitric acid

• Copper hydroxide and nitric acid

• Copper hydroxide and hydrochloric acid

• Copper hydroxide and sulfuric acid

Multiple Choice

The reaction between Sodium hydroxide and Nitric acid produces

• Calcium nitrate

• Sodium nitrate

• Sodium chloride

• Sodium sulfate

Reactions
with acids

Metals

“above

Hydrogen”

Metal

Hydroxide

Metal

Carbonate

Metal
Oxide

Salt + Hydrogen

Salt + Water

Salt + Water

Salt + Carbon Dioxide

+ Water

Ammonia NH3

Ammonium Salt

Open Ended

Write the balanced equation for the reaction between Sodium Hydroxide and Sulfuric acid H2SO4

Reactions
with acids

Metals

“above

Hydrogen”

Metal

Hydroxide

Metal

Carbonate

Metal
Oxide

Salt + Hydrogen

Salt + Water

Salt + Water

Salt + Carbon Dioxide

+ Water

Ammonia NH3

Ammonium Salt

​Reaction of metal oxides with acids

Acids react with metal oxides to produce a salt and water

Na₂O + 2HCl -----> 2NaCl + H₂O

Complete the following reactions

Hydrochloric acid + sodium oxide →Sodium chloride + Water

HCl + Na2O →NaCl + H2O

Sulfuric acid + calcium oxide →calcium sulfate + Water

H2SO4 + CaO →CaSO4 + H2O

Nitric acid + copper oxide →copper nitrate + Water

HNO3 + CuO →Cu(NO3)2 + H2O

Multiple Choice

The following is the balance equation for the reaction between Calcium Oxide and Nitric acid

• CaO + HNO₃ --> CaNO_{3 +} H₂O

• CaO + 2HNO₃ --> Ca(NO₃)_{2 +} H₂O

• CaO + HNO₃ --> Ca(NO₃)2 + H₂O

• Ca₂O₂ + HNO₃ --> CaNO_{3 +} H₂O

Reactions
with acids

Metals

“above

Hydrogen”

Metal

Hydroxide

Metal

Carbonate

Metal
Oxide

Salt + Hydrogen

Salt + Water

Salt + Water

Salt + Carbon Dioxide

+ Water

Ammonia NH3

Ammonium Salt

4. Reaction of acid and metal carbonate

When a carbonate reacts
with an acid, it gives off
carbon dioxide gas.

To confirm that it is
carbon dioxide, the gas
is passed through lime
water solution.

Lime water turns milky

carbon dioxide

limewater

Open Ended

Write the word equation for the reaction between Sodium carbonate and sulfuric acid

Reactions
with acids

Metals

“above

Hydrogen”

Metal

Hydroxide

Metal

Carbonate

Metal
Oxide

Salt + Hydrogen

Salt + Water

Salt + Water

Salt + Carbon Dioxide

+ Water

Ammonia NH3

Ammonium Salt

magnesium + hydrochloric acid → magnesium chloride + hydrogen

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2 (g)

Zinc + sulphuric acid → Zinc sulphate + hydrogen

Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)

Potassium + Nitric acid → Potassium nitrate + hydrogen

K(s) + HNO3(aq) → KNO3(aq)+H2(g)

Complete the following reactions

reaction of ammonia (weak base) NH3 and
acids

NH3 + HCl → NH4Cl

NH3 + H2SO4 → (NH4)2SO4

NH3 + HNO3 → NH4NO3

Reaction of bases

❖ Bases often have a bitter taste and are found in

foods less frequently than acids.

❖ Many bases, like soaps, are slippery to the touch.

❖ Bases also change the color of indicators.

❖ Litmus turns blue in the presence of a base while

phenolphthalein turns pink

❖ Bases do not react with metals in the way that acids

do.

In aneutralization reaction, an acid reacts with an alkali to
produce a salt and water.

The chemical reaction between an acid and an alkali can be
written as:

+

→

acid

alkali

salt + water

1. Reaction of base with acid - neutralization

magnesium
hydroxide

magnesium

sulfate
sulfuric acid

water

+

→

+

+

H2SO4
Mg(OH)2
Na2SO4
2H2O

→

+

potassium
hydroxide

potassium

nitrate
nitric acid

water

+

→

+

HNO3
KOH

KNO3
H2O

+

→

+

Reactions of Ammonia (NH3) weak base with Acids

When a mixture of an alkali and ammonium salt is heated,
ammonia gas is given off.
Heat
Alkali + ammonium salt → Salt + ammonia + water

NaOH(s) + NH4Cl(s) → NaCl(s) + NH3(g) + H2O(l)

Ca(OH2)(s) + (NH4)2SO4(s) →CaSO4(s) + 2NH3(g) + 2H2O(l)

2. Reaction of base with ammonium salts

Ammonia is a basic gas
It turn damp (wet) litmus paper blue

What neutralizes soil acidity?

Calcium Carbonate CaCO3
CaO
Ca(OH)2

Remember some identification tests!!

Carbon dioxide produced by reaction of carbonates with acids is tested by turning limewater into
white.
https://www.youtube.com/watch?v=Gz5KeGJF1CM

Hydrogen gas produced by reaction of acids with metals is tested by using a lighted splint.
https://www.youtube.com/watch?v=0VonvhSzhR4

Ammonia gas is produced in the reaction of ammonium salts with base.

This ammonia gas is then identified by turning litmus paper into blue!
https://www.youtube.com/watch?v=5F88xqmpzWg

Glossary

acid – A substance which donates H+ ions.
alkali – A soluble base, which releases OH– ions in solution.
base – A substance which accepts H+ ions.
strong – An acid or alkali that dissociates fully in solution.
weak – An acid or alkali which does not dissociate fully in
solution.
Monoprotic – An acid that releases one H+ ions per molecule.
diprotic – An acid that releases two H+ ions per molecule.
dissociate – The process of forming ions from a compound
when it dissolves.
indicator – A substance that changes colour according to the
pH of a solution.
neutralization – A reaction between an acid and an alkali.

21 of 36

© Boardworks Ltd 2009

Let’s take a deeper look

What are acids?

Acids can be defined as substances that release H+ ions
when they dissolve in water.

When hydrogen chloride dissolves in water, it releases
H+ ions and Cl– ions:

HCl

H++

Cl–

Let’s take a look at hydrogen ions

• Hydrogen atom contains one proton and one electron.
• When it loses this electron forming hydrogen ion, it will

only contain a proton.

• That’s why we call hydrogen ion a proton

Acids are proton donors

A H+ ion is a hydrogen atom that has
lost its single electron. This leaves a
lone, positively charged proton.

Because acids donate protons, they are sometimes called
proton donors.

What is base and alkali?

everyday bases

laboratory bases

Base are another group of chemicals, the opposite of acids.

What are bases and alkalis?

Bases are substances that react with acids .

The oxides, hydroxides and carbonates of metals are
bases. For example, NaOH, CaO, Mg(OH)2, MgO etc.

What are bases and alkalis?

Some bases are

soluble in water: these

bases are called

alkalis.

Alkalis release hydroxide ions (OH–) in solution.

Sodium hydroxide is an alkali. It dissolves in water to release
Na+ ions and OH– ions:

NaOH

Na++ OH–

Base or alkali?

alkalis:

Water soluble

bases

bases:

react with acids
All alkalis are bases, but not all

bases are alkalis.

Copper oxide is a base, but not an
alkali, because it reacts with acids,
but does not dissolve in water.

Sodium hydroxide is an alkali (and a base), because it
reacts with acids and it is soluble in water.

Mixing an acid and an alkali

What happens when an acid and an alkali are mixed?

Mixing an acid and an alkali causes
a chemical change.

This chemical change is called a
chemical reaction.

How do you know this chemical
reaction has taken place?

?

What is neutralization?

The chemical reaction betweenan acidandan alkali
is calledneutralization.

What happens to the pH value of the
reaction mixture during neutralization?

acid

alkali

a salt

water

The pH value of the reaction mixture
becomes closer to 7.

32 of 36

© Boardworks Ltd 2009

What is neutralization?

The chemical reaction between anan acidandan
alkalican be written as:

What are the two new substances produced by a
neutralization reaction?

a salt

acid

alkali

water

33 of 36

© Boardworks Ltd 2009

Real life application: Neutralizing stings

A beesting

isacidic.

A wasp sting

isalkaline.

Why can bicarbonate
of soda (pH 9) be used

to treat a bee sting?

Why can vinegar (pH 3)

be used to treat
a wasp sting?

Indigestion remedies

Indigestion and heartburn are caused by
an excess of acid in your stomach.

Indigestion remedies such as Milk of
Magnesia contain antacids, like
magnesium oxide and calcium carbonate.

The acid in your stomach that helps you break down your
food is called hydrochloric acid.

35 of 36

© Boardworks Ltd 2009

Real life application: Neutralizing soil

Soils in different places
can be acidic, alkaline or
neutral.

Many plants do not grow
well in acidic soil.

Why do farmers test soil
to check the pH?

Farmers often add an alkali to acidic soil to make their
plants grow better.

How does the alkali help to treat the acidic soil?

36 of 36

© Boardworks Ltd 2009

Real life application: Neutralizing acid rain

Gases emitted by cars, power
stations and factories mix
with rainwater in the
atmosphere.

This rainwater has a pH <5.5.

Why is it called acid rain?

Acid rain can have a
harmful effect on the
environment killing trees,
polluting lakes and
damaging buildings.

How can the effects of
acid rain be prevented?

Understanding

Acids and bases

What do you notice ??

Strong acids

Strong acids dissociate fully into solution, so that all their
H+ ions are released into the mixture.

Hydrochloric acid is a typical strong acid, so the dissociation
reaction is complete:

HCl

H+

+

Cl–

HA

H+

+

A–

Other strong acids are Sulphuric acid (H2SO4) and Nitric
acid (HNO3)
These acids are said to be corrosive as they can damage
other materials

In the general equation above “HA” represents the general
formula for an acid, “H” representing the hydrogen, “A” the
accompanying negative ion.

Difference between strong and weak acids

When ethanoic acid (vinegar) dissolves in water, it releases
H+ ions and CH3COO–ions:

CH3COOH

H++CH3COO–

Weak acids do not dissociate fully, some of their H+ ions stay
attached to the acid molecule.

Other examples of weak acids are citric acid, found in oranges
and lemons, carbonic acid, found in soft drinks and ascorbic acid
(vitamin C).

Acid – monoprotic

Monoprotic acids are acids that can release only one proton
per molecule

For example hydrochloric acid HCl
.

Other example include Nitric acid HNO3

HNO3
H++

NO3

–

HCl

H+

+

Cl–

CH3COOH ⇌
H++

CH3COO–

Ethanoic acid (acetic acid or vinegar )

Diprotic acids are acids that can release two proton per
molecule

H2SO4
2H++

SO4

2–

Carbonic acid (H2CO3) , a weak acid, is another example

H2CO3 ⇌

2H+ + CO3

2-

Sulfuric acid (H2SO4) contains two hydrogen ions per
sulphate ion. Both hydrogen ions can dissociate in solution.

Acid – Diprotic

What is a strong alkali?

Some alkalis, like those used
in laboratories, or in cleaning
materials such as bleach, are
too dangerous to touch.

These alkalis are said to be
caustic because they can
burn skin, and damage other
materials.

These are strong alkalis.

What is a strong alkali?

Alkali which dissociates fully into its ions are called strong
alkalis

For example Sodium hydroxide is a strong alkali because
it completely dissociates in water to produce ions.

NaOH(aq) → Na+(aq) + OH−(aq)

Strong alkalis produce large quantities of hydroxide ions.
Other examples are Group 1 and 2 metal hydroxides

Ba(OH)2(aq) → Ba2+(aq) + 2OH−(aq)

What is a weak alkali?

Alkalis are found in soaps and other materials used for
cleaning.

It is safe to handle these alkalis, which can feel soapy.
These alkalis are known as weak alkalis.

What is a weak alkali?

Weak alkali is a substance which partly ionizes in water to
give hydroxide ions (OH- ions.)

A good example of a weak alkali is ammonium hydroxide
(NH4OH).

In water, it does not completely dissociate into its respective
ions. The concentration of OH- ions in a solution containing a
weak alkali will be much lower.

NH4OH(aq) ⇌

NH4

+ + OH–

Glossary

acid – A substance which donates H+ ions.
alkali – A soluble base, which releases OH– ions in solution.
base – A substance which accepts H+ ions.
strong – An acid or alkali that dissociates fully in solution.
weak – An acid or alkali which does not dissociate fully in
solution.
Monoprotic – An acid that releases one H+ ions per molecule.
diprotic – An acid that releases two H+ ions per molecule.
dissociate – The process of forming ions from a compound
when it dissolves.
neutralization – A reaction between an acid and an alkali.

Glossary

● acid –A chemical that has a pH less than 7.
● alkali –A chemical that has a pH greater than 7 and

dissolves in water.

● indicator –A special chemical that changes into

different colours in acid and alkali solutions.

● neutral –A chemical with a pH of 7 that is not an acid or

an alkali.

● neutralization –The chemical reaction between an acid

and an alkali.

● pH scale – The range of values that shows how strong

or weak an acid or alkali is.

● universal indicator – The indicator that shows the pH

value of a chemical.