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Boardworks KS3 Science 2008 Reactions of Acids

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Presentation on theme: "Boardworks KS3 Science 2008 Reactions of Acids"— Presentation transcript:

1 Boardworks KS3 Science 2008 Reactions of Acids

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Acids and alkalis Boardworks KS3 Science 2008 Reactions of Acids How many examples of acids and alkalis can you spot? Teacher notes This illustration contains several discussion points relating to acids and alkalis, including: Foods (lemons, oranges etc.): examples of some foods that are acidic or alkali Flowers (hydrangeas): hydrangeas grow blue flowers in an acidic soil, but pink flowers in an alkaline soil Acid rain: power stations and factories produce polluting gases such as sulphur dioxide, which react with water in clouds to form acid rain. Putting lime on soil: Lime raises soil pH, and is used to neutralize the acidic effects of acid rain and certain fertilizers. Brushing teeth: Depending on the brand and formulation, toothpaste is usually neutral or slightly alkaline. Toothpastes that contain fluorine tend to have a lower pH than toothpastes that contain baking soda however. Washing the tractor/cleaning products : Most cleaning products tend to be alkaline Stung by a bee: Bee stings are acidic. Wasp stings are alkaline.

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Acids: true or false? Boardworks KS3 Science 2008 Reactions of Acids

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Alkalis: true or false? Boardworks KS3 Science 2008 Reactions of Acids

6 Mixing an acid and an alkali
Boardworks KS3 Science 2008 Reactions of Acids 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?

7 Mixing acids and alkalis
Boardworks KS3 Science 2008 Reactions of Acids

8 What is neutralization?
Boardworks KS3 Science 2008 Reactions of Acids 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

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Neutralizing stings Boardworks KS3 Science 2008 Reactions of Acids Bee stings are acidic. Wasp stings are alkaline. Photo credit (left and right): © 2008 Jupiterimages Corporation Which safe household substances could you use to treat a bee sting? Which safe household substances could you use to treat a wasp sting?

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Separating a salt Boardworks KS3 Science 2008 Reactions of Acids

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Making salts Boardworks KS3 Science 2008 Reactions of Acids 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 potassium chloride + + water

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Naming salts Boardworks KS3 Science 2008 Reactions of Acids 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

13 Making salts: word equations
Boardworks KS3 Science 2008 Reactions of Acids Complete these word equations: hydrochloric acid potassium hydroxide potassium chloride + + water sodium hydroxide sodium sulfate sulfuric acid + + water potassium hydroxide potassiumnitrate nitric acid + + water

14 Making salts: completing equations
Boardworks KS3 Science 2008 Reactions of Acids

15 Making salts: symbol equations
Boardworks KS3 Science 2008 Reactions of Acids Complete these symbol equations: potassium hydroxide potassium chloride hydrochloric acid water + 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

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Balancing equations Boardworks KS3 Science 2008 Reactions of Acids 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.

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Balancing equations Boardworks KS3 Science 2008 Reactions of Acids If you count the number of atoms of each type on each side of this equation, you will see that they do not match. + H2SO4 NaOH Na2SO4 H2O 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

18 Balancing equations for making salts
Boardworks KS3 Science 2008 Reactions of Acids

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Indigestion remedies Boardworks KS3 Science 2008 Reactions of Acids 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. 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. Photo credit: © 2008 Jupiterimages Corporation What do you think antacids do to the acid in your stomach?

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Metal oxide Boardworks KS3 Science 2008 Reactions of Acids 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

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Base or alkali? Boardworks KS3 Science 2008 Reactions of Acids 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.

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Acids and metal oxides Boardworks KS3 Science 2008 Reactions of Acids

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Making copper sulfate Boardworks KS3 Science 2008 Reactions of Acids

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Metal oxides + acids Boardworks KS3 Science 2008 Reactions of Acids

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What is the formula? Boardworks KS3 Science 2008 Reactions of Acids

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Formulae Boardworks KS3 Science 2008 Reactions of Acids 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?

28 Formulae and combining powers
Boardworks KS3 Science 2008 Reactions of Acids Here are the combining powers of some metal and non-metal atoms: Na K Mg Cu metal atom combining power non-metal atom Cl F O N 1 1 1 1 2 2 2 3

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Acid and carbonate Boardworks KS3 Science 2008 Reactions of Acids 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

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Acid and carbonate Boardworks KS3 Science 2008 Reactions of Acids 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? Photo credit: © 2008 Jupiterimages Corporation hydrochloric acid calcium carbonate calcium chloride carbon dioxide + + + water

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Boardworks KS3 Science 2008 Reactions of Acids

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Acid and metal Boardworks KS3 Science 2008 Reactions of Acids 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? Reactions of Acids Worksheet 1 accompanies this slide. Teacher notes The gas produced during the react between an acid and a metal is hydrogen. hydrochloric acid calcium chloride + calcium + hydrogen

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Choose your reaction Boardworks KS3 Science 2008 Reactions of Acids 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 carbonate sodium sulfate carbon dioxide + + + water Could you safely use sodium hydroxide to make sodium sulfate? What about sodium oxide?

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Choose your reaction Boardworks KS3 Science 2008 Reactions of Acids

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What is acid rain? Boardworks KS3 Science 2008 Reactions of Acids 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. Photo credit: © 2008 Jupiterimages Corporation 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?

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How does acid rain work? Boardworks KS3 Science 2008 Reactions of Acids

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Effects of acid rain Boardworks KS3 Science 2008 Reactions of Acids 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?

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Reducing acid rain Boardworks KS3 Science 2008 Reactions of Acids 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. Photo credit: Vince Petaccio How do these changes help to reduce acid rain?

41 Acid rain – a global problem
Boardworks KS3 Science 2008 Reactions of Acids 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. Photo credit: Eva Jurenikova Is it right that a country can directly cause pollution in another?

42 Should pollution be contained?
Boardworks KS3 Science 2008 Reactions of Acids

43 Limiting the effects of acid rain: opinions
Boardworks KS3 Science 2008 Reactions of Acids

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Glossary Boardworks KS3 Science 2008 Reactions of Acids Glossary acid – A chemical that has a pH less than 7. acid rain – Rain that has a pH lower than about 5.6. alkali – A chemical that has a pH greater than 7 and that dissolves in water. antacid – A medicine used to cure indigestion by neutralizing excess stomach acid. base – A substance that reacts with an acid. neutralization – The chemical reaction between an acid and an alkali. salt – A substance formed by the reaction of an acid with a base.

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Anagrams Boardworks KS3 Science 2008 Reactions of Acids

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Multiple-choice quiz Boardworks KS3 Science 2008 Reactions of Acids


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