© Boardworks Ltd 20081 of 47. © Boardworks Ltd 20082 of 47

© Boardworks Ltd 20081 of 47



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 chloride

water+

+ +sodium

hydroxidesodium chloride

hydrochloric acid

water


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 chloride

water+

sodium hydroxide

sulfuric acid + sodium sulfate

water+

potassium hydroxide

nitric acid + potassium

nitratewater+

Complete these word equations:


Making salts: completing equations


Making salts: symbol equations

potassium hydroxide

potassium chloride

hydrochloric acid

water+ +

HCl KOH KCl H2O+ +

Complete these symbol equations:

magnesium hydroxide

magnesium sulfate

sulfuric acid water+ +

+H2SO4 Mg(OH)2 Na2SO4 2H2O +

potassium hydroxide

potassiumnitrate

nitric 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 sulfate


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 sulfate



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

powernon-metal

atomcombining

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 acid

water+ +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

sulfuricacid +

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



Glossary


Anagrams


Multiple-choice quiz

Documents

© Boardworks Ltd 20081 of 47. © Boardworks Ltd 20082 of 47