Reactivity

1. Reactivity • How do you know a chemical reaction has happened?

2. reactants products +  + carbon oxygen carbon dioxide  What is a chemical reaction? A chemical reaction is a change that takes place when one or more substances (called reactants) form one or more new substances (called products). For example:

3. How can you spot a chemical reaction? Chemical reactions can appear very different. As you observe a chemical reaction, you may detect: • a colour change • precipitate (solid) forming • energy being produced (fizzing, burning) • an odour being produced.

4. Why doesn’t the mass change? In a chemical reaction, no atoms are made or destroyed. The reaction just changes how the atoms are bonded together.

5. Does mass change during a reaction?

6. sulfur dioxide + sulfur oxygen  What is a word equation? A word equation uses the names of the reactants and products to show what happens in a chemical reaction. For example, when a piece of sulfur is burned in oxygen gas it produces a white solid called sulfur dioxide. The word equation for this reaction is:

7. S O2  SO2 + +  What is a symbol equation? A symbol equation uses the formulae of the reactants and products to show what happens in a chemical reaction. A symbol equation must be balanced to give the correct ratio of reactants and products. This equation shows that one atom of sulfur (S) reacts with one molecule of oxygen (O2) to make one molecule of sulfur dioxide (SO2).

8. + S (s) O2 (g) SO2(g)  What do state symbols show? State symbolsare added to a symbol equation to show whether the reactants and products are: • solid – symbol is (s) • liquid – symbol is (l) • gas – symbol is(g) • dissolved in water –symbol is(aq). With state symbols in place, this symbol equation now shows that the sulfur is a solid, the oxygen is a gas and the sulfur dioxide is also a gas.

9. Chemical reactions – true or false?

10. What is thermal decomposition?

11. potassium sodium calcium magnesium aluminium manganese zinc iron copper silver gold increase in reactivity Thermal decomposition – easy or hard? The more reactive a metal, the harder it is to decompose its carbonate by heating. Predict how easy it is to decompose these carbonates: • copper carbonate • calcium carbonate • sodium carbonate • manganese carbonate • zinc carbonate • iron carbonate.

12. Thermal decomposition – activity

13. ironcarbonate ironoxide carbon dioxide +  heat + FeCO3  FeO CO2 Thermal decomposition of carbonates When the metal carbonate is heated, it decomposes to produce a metal oxide and carbon dioxide. What are the word and symbol equations for the thermal decomposition of these carbonates? • copper carbonate • manganese carbonate • zinc carbonate.

14. calciumcarbonate calciumoxide carbon dioxide +  heat + CaCO3  CaO CO2 Heating calcium carbonate When calcium carbonate is heated, it decomposes to produce calcium oxide and carbon dioxide. This reaction is carried out in industry to make calcium oxide (quicklime) from calcium carbonate (limestone): Calcium oxide is used to make concrete and calcium hydroxide (slaked lime).

15. Heating sodium hydrogencarbonate Baking powder and self-raising flour contain sodium hydrogencarbonate (also known as sodium bicarbonate). When sodium hydrogencarbonate is heated, it decomposes to make sodium oxide, carbon dioxide and water. What effect does this reaction have on dough as it is being baked? The carbon dioxide released during the reaction creates tiny bubbles, which help the dough to rise.

16. What is the decomposition equation?

17. What are indicators? Indicators are chemicals that change colour in the presence of an acid or an alkali. There are many different indicators. Lots of them come from plants, like red cabbage. Different indicators turn different colours. Geranium plants grown in acidic soil have red flowers, while geraniums grown in alkali soil have blue flowers. Universal indicator is a mixture of indicators. It is useful because it shows a range of colours from pH 1–14.

18. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 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. What are the pH values of some everyday items?

19. What is the order of pH?

20. What are acids? Acids are substances that: • Have a pH below 7 and turn universal indicator yellow, orange or red. • Turn litmus red. • Form solutions containing hydrogen ions (H+). Hydrochloric acid is a strong acid. Ethanoic acid (vinegar) is a weak acid.

21. What are alkalis? Alkalis are substances that: • Have a pH above 7 and turn universal indicator blue or purple. • Turn litmus blue. • Can neutralize acids • Form solutions containing hydroxide ions (OH-). Sodium hydroxide is a strong alkali. Ammonia is a weak alkali. When ammonia is dissolved in water, it forms ammonium hydroxide (NH4OH), a fertilizer.

22. bases (react with acids) alkalis (soluble bases) What are bases? All alkalis are bases. Bases are substances that react with acids by absorbing hydrogen ions (H+). The oxides, hydroxides and carbonates of metals, such as sodium hydroxide, are bases. Ammonia is a base that does not contain a metal. Some bases are soluble in water – these are called alkalis. All alkalis contain hydroxide ions (OH–). The more OH– ions in the solution, the stronger the alkali.

23. Acids and bases – true or false?

24. + acid base  a salt • The first part of the salt’s name comes from the base: e.g. sodium hydroxide sodium…  • The second part of the salt’s name comes from the acid: e.g. sulfuric acid sulfate…  How are salts made and named? When an acid reacts with a base, a neutralization reaction occurs and produces a chemical called a salt. The name of the salt depends on the names of the reactants. For example, if sodium hydroxide neutralizes sulfuric acid, the product is a salt called sodium sulfate.

25. lead nitrate sodium chloride lead chloride sodium nitrate + +  + + Pb(NO3)2(aq) 2NaCl (aq)  PbCl2 (s) 2NaNO3 (aq) What is a precipitation reaction? Sometimes when two solutions are mixed, they react to form an insoluble solid product. The insoluble solid product is called a precipitate. You can spot a precipitate because the mixture goes cloudy. For example, mixing solutions of lead nitrate and sodium chloride produces a yellow precipitate of lead chloride.

26. Identifying metals

27. What is the name of the salt?

28. What are salts used for? The colours of fireworks are formed when certain salts burn. Calcium chloride, for example, burns a bright red colour. Table salt is sodium chloride. This is the salt used to flavour and preserve food. Indigestion remedies often contain magnesium salts. Salts can also be used as coloured pigments in paints, and to help fuels burn better.

29. + + acid alkali  salt water hydrochloricacid sodiumhydroxide sodiumchloride + +  water + + NaCl (aq) HCl (aq) H2O (aq)  NaOH(aq) Making salts 1: acid + alkali When an acid reacts with an alkali, the products are a salt and water. Water is formed because OH– ions from the alkali react with H+ ions from the acid to produce molecules of water (H2O). For example:

30. hydrochloricacid sodiumhydroxide sodiumchloride + +  water + + NaCl (aq) HCl (aq) H2O (aq)  NaOH(aq) When is the reaction complete? The reaction between sodium hydroxide and hydrochloric acid produces sodium chloride, which is soluble in water. There is no obvious sign when this reaction is complete, so an indicator is used to show when the solution is neutral. This process is called titration.

31. What is a titration?

32. + + acid metal  a salt hydrogen hydrochloricacid zincchloride + + zinc  hydrogen + + ZnCl2(aq) 2HCl (aq) H2 (aq)  Zn (aq) Making salts 2: acid + metal When a metal is added to an acid, the products are a salt and hydrogen gas. For example: This method of making salts only works with some metals. What would happen if potassium was used? Or copper?

33. Which metal will react the most?

34. + + acid metal oxide  salt water calciumchloride hydrochloricacid calciumoxide + +  water + + CaCl2 (aq) 2HCl (aq) CaO(aq)  H2O (aq) Making salts 3: acid + metal oxide When a metal oxide is mixed with an acid, the products are a salt and water. Water forms because oxygen ions from the oxide join up with H+ ions from the acid to produce molecules of water (H2O). For example:

35. sulfuricacid copper oxide copper sulfate + +  water H2SO4 (aq) CuO (s) CuSO4 (aq) H2O (aq) Obtaining salts from metal oxides When a metal oxide is added to an acid, it dissolves as it reacts. You know when you have added enough of the metal oxide because it stops dissolving. How could the solid copper sulfate salt be separatedfrom the water?

36. Obtaining salts from copper oxide

37. carbon dioxide + + + acid carbonate  salt water coppernitrate carbondioxide nitricacid coppercarbonate + + +  water + + + Cu(NO3)2(aq) 2HNO3(aq) CuCO3(s)  H2O(aq) CO2(g) Making salts 4: acid + carbonate When a carbonateis mixed with an acid, the products are a salt, carbon dioxide and water. Water and carbon dioxide are formed because the carbonate ions (CO32-) react with H+ ions from the acid. For example: What would you expect to observe in this reaction?

38. acid + alkali a salt + water • acid + metal a salt + hydrogen • acid + metal oxide a salt + water • acid + carbonate a salt + carbon dioxide + water     Making salts – summary Salts can be made by reacting acids with bases. There are four ways of making salts from acids:

39. Matching reactants and salts

40. Complete the neutralization reaction