Reactions of acids

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Acids and alkalis

How many examples of acids and alkalis can you spot?


Acids: true or false?


Alkalis: true or false?


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 reaction.

How could you check that a chemical reaction has taken place?

+

acid alkali


Mixing acids and alkalis


What is neutralization?

The chemical reaction between an acid and an alkali is called

neutralization.

What is the pH value of the mixture of salt and water?

The chemical reaction between an acid and an alkali can be

written as:

+ acid alkali salt + water

+

acid alkali salt + water

The mixture of salt and water is neutral, so its pH is 7.


Neutralizing stings

Bee stings are acidic.

Which safe household

substances could you

use to treat a bee sting?

Wasp stings are alkaline.

Which safe household

substances could you

use to treat a wasp sting?


Separating a salt


Making salts

The salt produced by a neutralization reaction depends on

the acid and the alkali used.

Sodium chloride is produced by the reaction between

hydrochloric acid and sodium hydroxide.

Which acid and which alkali would be needed to make the

salt potassium chloride?

potassium

hydroxide

hydrochloric

acid+

potassium

chloridewater+

+ +sodium

hydroxide

sodium

chloride

hydrochloric

acidwater


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


Making salts: word equations

potassium

hydroxide

hydrochloric

acid+

potassium

chloridewater+

sodium

hydroxidesulfuric acid +

sodium

sulfatewater+

potassium

hydroxidenitric acid +

potassium

nitratewater+

Complete these word equations:


Making salts: completing equations


Making salts: symbol equations

potassium

hydroxide

potassium

chloride

hydrochloric

acidwater+ +

HCl KOH KCl H2O+ +

Complete these symbol equations:

magnesium

hydroxide

magnesium

sulfatesulfuric acid water+ +

+H2SO4 Mg(OH)2 Na2SO4 2H2O +

potassium

hydroxide

potassium

nitratenitric acid water+ +

HNO3 KOH KNO3 H2O+ +


Balancing equations

The balanced symbol equation for a chemical reaction shows

the ratio of reactants and products involved. For example:

When a chemical reaction occurs, it can be described by a

a symbol equation.

+

sodium

hydroxide

sodium


H2SO4 2NaOH Na2SO4 2H2O +

An ‘unbalanced’ equation can be balanced by multiplying

the different atoms and molecules on each side by different

amounts, so that they match.


Balancing equations

If you count the number of atoms of each type on each side

of this equation, you will see that they do not match.

So, multiply the sodium atoms on the left by 2:

Now that the number of sodium atoms on each side is equal

the number of hydrogen atoms on the left side has increased.

So multiply the number of hydrogen atoms on the right by 2.

+H2SO4 NaOH Na2SO4 H2O +

+H2SO4 2NaOH Na2SO4 H2O +

+H2SO4 2NaOH Na2SO4 2H2O +


Balancing equations for making salts


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.

What do you think antacids do

to the acid in your stomach?

The acid in your stomach that helps you break down your food

is called hydrochloric acid. It has a pH of between 1 and 2.



Metal oxide

Metal oxides are compounds made from a metal and oxygen.

For example, burning magnesium in oxygen produces

magnesium oxide.

magnesium magnesium oxideoxygen+

Acids react with metal oxides to make a salt and water.

For example, sulfuric acid reacts with copper oxide to make

copper sulfate and water.

copper

oxide

copper



Base or alkali?

Bases are substances that

react with acids, which include

metals oxides, hydroxides and

carbonates.

Alkalis are substances that

react with acids and which

are soluble in water.

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.

bases: react

with acids

alkalis:

soluble in

water


Acids and metal oxides


Making copper sulfate


Metal oxides + acids


What is the formula?


Formulae

How do we know that the formula of sodium chloride is NaCl,

while the formula of copper chloride is CuCl2?

It is because of the combining power of the atoms.

Sodium has a combining power of 1, so it bonds with one

other atom.

Chlorine also has a combining power of 1, so it bonds

with one other atom.

Copper, though, has a combining power of 2, so it needs

to bond to two chlorine atoms.

The formula of magnesium chloride is MgCl2, so what do you

think is the combining power of magnesium?


Formulae and combining powers

Here are the combining powers of some metal and non-metal

atoms:

1

1

2

2

Na

K

Mg

Cu

metal atomcombining

power

non-metal

atom

combining

power

Cl

F

O

N

1

1

2

3


Formulae and combining powers



Acid and carbonate

When a carbonate reacts

with an acid, it gives off

carbon dioxide gas.

How could you test the

gas given off, to confirm

that it is carbon dioxide?

What would you

observe in this test?

carbon dioxide

limewater


Acid and carbonate

Calcium carbonate is a substance

that is naturally found in the shells

of sea creatures and snails.

What salt do you think will be produced by the reaction of

hydrochloric acid and calcium carbonate?

calcium

carbonate

calcium

chloride

hydrochloric

acidwater+ +

carbon

dioxide+

The products of the reaction between a carbonate and an

acid are a salt, carbon dioxide and water.


Reaction of carbonates


Acid and metal

Acids also react with metals to make a gas.

When an acid reacts with a metal, the gas

produced makes a lighted splint go pop.

What is this gas?

A salt is also produced during the

reaction. What is the name of the salt

that will be produced by the reaction

of hydrochloric acid with calcium?

calciumcalcium

chloride

hydrochloric

acid+ hydrogen+


Choose your reaction

Some metals react violently with acids, so it wouldn’t be safe

to use them to make a salt in the classroom.

However, if you still wanted to make that salt, you could use

the metal carbonate instead.

Sodium reacts very violently with sulfuric acid, so should not

be uses to make sodium sulfate. However, you could safely

use sodium carbonate.

Could you safely use sodium hydroxide to make sodium

sulfate? What about sodium oxide?

sodium

carbonate

sodium

sulfate

sulfuric

acid+

carbon

dioxide+ water+


Choose your reaction


What is acid rain?

Rainwater has a pH of about 5.6, which

means that it is naturally slightly acidic.

Rainwater with a lower pH than normal

is called acid rain.

Burning of fossil fuels in power stations and cars forms

pollutants such as sulfur dioxide and nitrogen oxides.

Why is acid rain a serious environmental problem?

These gases dissolve in rainwater to make sulfuric acid and

nitric acid, which are strong acids, so also form acid rain.

This natural acidity is due to carbon

dioxide in the air dissolving into the rain,

forming a weak acid called carbonic acid.


How does acid rain work?


Effects of acid rain

Acid rain has many damaging effects on the environment:

The acids in acid rain speed

up the chemical weathering

of rocks and buildings.

What can be done to reduce acid rain and its effects?

Soil that becomes more acidic has fewer nutrients so trees

and other plants cannot grow. Acid rain also damages

trees by breaking down the waxy coating of leaves.

Rivers, lakes and streams

become more acidic so

that animals and plants

cannot live in them.


Reducing acid rain

Governments are working to reduce the emissions of the

acidic pollutants produced by burning fossil fuels.

Sulfur dioxide is formed when coal containing sulfur is

burned in power stations. This acidic pollutant can be

removed from the gases before they are released into

the atmosphere.

How do these changes help to reduce acid rain?

Nitrogen oxides are formed

when petrol burns in a car’s

engine. Exhaust systems

can be fitted with a catalytic

converter which turns harmful

gases into harmless gases.


Acid rain – a global problem

Forests in Scandinavian countries such as Sweden have

suffered greatly from the damaging effects of acid rain.

However, scientists have shown that

the acid rain that falls in Sweden is

not produced there. The source of the

acidic pollutants is in fact more likely

to be UK factories and power stations.

Is it right that a country can directly cause pollution in another?

This happens because air pollution

can be carried high up into the sky,

where it is pushed by strong winds

towards other countries.


Should pollution be contained?


Limiting the effects of acid rain: opinions



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Reactions of acids