12.6 – How can we use ions in solutions?

1. 12.6 – How can we use ions in solutions? • Ionic compounds have many uses and can provide other substances. • Electrolysis is used to produce alkalis and elements such as chlorine and hydrogen. • Oxidation-reduction reactions do not just involve oxygen. • Soluble salts can be made from acids and insoluble salts can be made solutions of ions.

2. Metal ions Calcium is in group 2 and has two electrons in its outer shell, so it will form a Ca2+ ion. Chlorine is in group 7 so a chloride ion will be Cl- Metal compounds in a solution contain metal ions. For example, consider calcium chloride: Calcium chloride has the formula CaCl2

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4. Sodium atom Chlorine atom Electron transfer Click Again

5. Sodium Chloride + - Positive and negative ions attract

6. Electrolysis Molecule of solid copper chloride CuCl2 (s) Molecule of solid copper chloride after being dissolved CuCl2 (aq) Copper ion chloride ion If you melt or dissolve an ionic compound (such as NaCl or CuCl2), then the ions become free to move around – and carry electrical current.

7. Electrolysis = chloride ion = copper ion Electrolysis is used to separate a metal from its compound. When we electrolysed copper chloride the _____ chloride ions moved to the ______ electrode and the ______ copper ions moved to the ______ electrode – OPPOSITES ATTRACT!!!

8. Purifying Copper ++++ ---- Impure copper Pure copper Cu2+ Cu2+ Cu2+ At the anode: Cu(s) Cu2+(aq) + 2e- At the cathode: Cu2+(aq) + 2e- Cu(s) Solution containing copper ions

9. Electrolysis equations At the negative electrode the positive ions GAIN electrons to become neutral copper ATOMS. The half equation is: Cu2+ + e- Cu At the positive electrode the negative ions LOSE electrons to become neutral chlorine MOLECULES. The half equation is: Cl- - e- Cl2 We need to be able to write “half equations” to show what happens during electrolysis (e.g. for copper chloride): 2 2 2

10. Oxidation and Reduction in Electrolysis At the positive electrode the negative ions LOSE electrons –This is called Oxidation. The half equation is: 2Cl-- 2e-Cl2 At the negative electrode the positive ions GAIN electrons – this is called Reduction. The half equation is: Cu2+ +2e-Cu Oxidation Is Loss, Reduction Is Gain (of electrons) O I L R I G

11. Electrolysis of brine Chlorine gas (Cl2) – used to kill bacteria and to make acids, bleach and plastics Hydrogen gas (H2) – used to manufacture ammonia and margarine Sodium chloride (brine) NaCl(aq) Positive electrode Negative electrode Sodium hydroxide (NaOH(aq)). Used to make soap, paper and ceramics Sodium chloride (salt) is made of an alkali metal and a halogen. When it’s dissolved we call the solution “brine”, and we can electrolyse it to produce 3 things…

12. Electrolysis - summary When an ionic substance is melted or dissolved in water, the _____ are free to _______ about in the solution. Passing an ________ __________through these _________ or dissolved ionic substances, breaks them down into __________. This is called ___________. During electrolysis, ___________ charged ions move towards the negative electrode and ___________ charged ions move towards the positive ___________. Move molten ions electric current elements positively electrolysis electrode negatively

13. Making Soluble Salts METAL HYDROXIDE (Alkali) +ACID SALT + WATER METAL+ACIDSALT+HYDROGEN e.g. magnesium + hydrochloric acid magnesium chloride + hydrogen METAL OXIDE + ACID SALT + WATER There are 3 types of reaction that can be used to make soluble salts. All 3 involve: • An Acid • A metal or metal compound Method 1 Method 2 Method 3

14. Making salts To form the name of a salt, you just combine the name of the metal involved, with the salt type associated with the acid. Hydrochloric acid makes chlorides, Sulfuric makes sulfates, Nitric makes nitrates. Complete the table as practice

15. Reactions of metals with acids METAL + ACID SALT + HYDROGEN e.g. magnesium + hydrochloric acid magnesium chloride + hydrogen • Copy and complete the following reactions: • Calcium + hydrochloric acid • Zinc + hydrochloric acid • Iron + hydrochloric acid • Lithium + sulphuric acid When a metal reacts with an acid it gives off hydrogen (which can be “popped” using a lit splint). The other product is a salt.

16. Quiz on acids and alkalis Acid, alkali or both??? • This a pH of less than 7 • This could kill cells • A metal hydroxide (e.g. sodium hydroxide) would be an _____ • When this reacts with a metal hydrogen is released • A metal carbonate (e.g. calcium carbonate) would be an _____ • This would feel soapy on your skin • This could be a corrosive • This will turn universal indicator purple • This would taste sour • This means “a base that can be dissolved”

17. Neutralisation reactions Sodium hydroxide Hydrochloric acid Na H OH Cl The sodium DISPLACES the hydrogen from HCl Na Cl H2O Sodium chloride Water When acids and alkalis react together they will NEUTRALISE each other. Neutralisation is an example of a displacement reaction:

18. + - H ions and OH ions + - • H ions make acids acidic. • OH ions make alkalis alkaline. • The pH scale measures the alkalinity or acidity of a solution. + During neutralisation reactions the H ions react with the OH ions to form H2O (water). - + - H (aq) + OH (aq) → H2O(l)

19. Neutralisation experiment • Sodium hydroxide + hydrochloric acid  sodium chloride + water • A ____ was formed during the reaction, and we could have separated this by __________ the solution, allowing the salt to Crystallise. The salt that we formed depended on the acid: • Hydrochloric acid will make a CHLORIDE • Nitric acid will make a _________ • Sulphuric acid will make a _________ Words to use – nitrate, neutralised, alkali, sulphate, salt, evaporating

20. Reactions of metal oxides with acid Al Na Mg Na Al Magnesium oxide Sodium oxide Aluminium oxide METAL OXIDE + ACID SALT + WATER O O O O O O O H Cl Mg H H Mg Cl Cl Cl H • Copy and complete the following reactions: • Magnesium oxide + hydrochloric acid • Calcium oxide + hydrochloric acid • Sodium oxide + sulphuric acid A metal oxide is a compound containing a metal and oxide. They are sometimes called BASES. A BASE is simply an insoluble alkali – it neutralises acids, but does not dissolve in water. For example:

21. Using Bases to Make Salts Because Bases are insoluble the procedure for making a salt is very slightly different… …Instead of simply evaporating off the water, you have to first remove any remaining (or excess) Base by filtration. 1) Drop the base into the acid… 2) Filter it to remove any leftover base 3) Evaporate it to get the salt

22. Ammonium Salts Ammonia + Nitric acid Ammonium Nitrate NH3(g) + HNO3(aq) NH4NO3(aq) • Ammonia (NH3) is a gas that dissolves in water to make an alkali (Ammonium hydroxide). • This can then be used to make Ammonium salts by reacting it with an acid. • Notice how NO water is made in this neutralisation reaction. • Ammonium salts make good fertilisers because plants need nitrogen to make proteins (to grow). Ammonium Nitrate is the best for this purpose – can you see why??

23. Making Insoluble Salts Barium chloride + Sodium sulfate Barium sulfate + Sodium chloride BaCl2(aq) + Na2SO4(aq) BaSO4(s) + 2NaCl(aq) • Doesn’t usually require an acid. • Insoluble salts can be made by mixing appropriate solutions of ions (soluble salts), so that a precipitate is formed. Precipitation can be used to remove unwanted ions from solutions, for example in treating water for drinking or in treating effluent. – The filter is covered in ions, which form precipitates with ions in the water.

24. An example question on reactivityWhich metal is most reactive?