Acids and alkalis How many examples of acids and alkalis can you spot?
Mixing an acid and an alkali What happens when an acid and an alkali are mixed? + acid alkali Mixing an acid and an alkali causes a chemical reaction. How could you check that a chemical reaction has taken place?
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? + acid alkali salt + water The mixture of salt and water is neutral, so its pH is 7. The chemical reaction between an acid and an alkali can be written as: + acid alkali salt + water
Neutralizing stings Bee stings are acidic. Wasp stings are alkaline. Which safe household substances could you use to treat a bee sting? Which safe household substances could you use to treat a wasp sting?
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. hydrochloric acid sodium hydroxide sodium chloride + + water Which acid and which alkali would be needed to make the salt potassium chloride? hydrochloric acid potassium hydroxide potassiumchloride + + 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? • copper nitrate • magnesium chloride • sodium sulfate
Making salts: word equations Complete these word equations: hydrochloric acid potassium hydroxide potassium chloride + + water sodium hydroxide sodium sulfate + + sulfuric acid water potassium hydroxide potassiumnitrate + + nitric acid water
hydrochloric acid potassium hydroxide potassium chloride + + water Making salts: symbol equations Complete these symbol equations: + + HCl KOH KCl H2O potassium hydroxide potassiumnitrate + + nitric acid water + + HNO3 KOH KNO3 H2O magnesium hydroxide magnesium sulfate + + sulfuric acid water + + H2SO4 Mg(OH)2 Na2SO4 2H2O
Balancing equations When a chemical reaction occurs, it can be described by a a symbol equation. The balanced symbol equation for a chemical reaction shows the ratio of reactants and products involved. For example: sodium hydroxide sodium sulfate + + sulfuric acid water + + 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.
+ + H2SO4 NaOH Na2SO4 H2O 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: + + H2SO4 2NaOH Na2SO4 H2O 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 2NaOH Na2SO4 2H2O
Indigestion remedies The acid in your stomach that helps you break down your food is called hydrochloric acid. It has a pH of between 1 and2. 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?
Metal oxide Metal oxides are compounds made from a metal and oxygen. For example, burning magnesium in oxygen produces magnesium oxide. + magnesium oxygen magnesium oxide 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 + + sulfuric acid water
Base or alkali? Bases are substances that react with acids, which include metals oxides, hydroxides and carbonates. bases: react with acids alkalis: soluble in water 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.
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?
combining power non-metal atom combining power metal atom Na Cl K F Mg O Cu N Formulae and combining powers Here are the combining powers of some metal and non-metal atoms: 1 1 1 1 2 2 2 3
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 The products of the reaction between a carbonate and an acid are a salt, carbon dioxide and water. 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? hydrochloric acid calcium carbonate calcium chloride carbon dioxide + + + water
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? hydrochloric acid calcium chloride + + calcium 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. sulfuric acid sodium sulfate sodium carbonate carbon dioxide + + + water Could you safely use sodium hydroxide to make sodium sulfate? What about sodium oxide?
What is acid rain? Rainwater has a pH of about 5.6, which means that it is naturally slightly acidic. This natural acidity is due to carbon dioxide in the air dissolving into the rain, forming a weak acid called carbonic acid. 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. These gases dissolve in rainwater to make sulfuric acid and nitric acid, which are strong acids, so also form acid rain. Why is acid rain a serious environmental problem?
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. • Rivers, lakes and streams become more acidic so that animals and plants cannot live in them. • 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. What can be done to reduce acid rain and its effects?
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. • 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. How do these changes help to reduce acid rain?
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. This happens because air pollution can be carried high up into the sky, where it is pushed by strong winds towards other countries. Is it right that a country can directly cause pollution in another?