12.6 – How can we use ions in solutions? 22/04/2017 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.

Calcium chloride has the formula CaCl2 Metal ions Metal compounds in a solution contain metal ions. For example, consider calcium chloride: 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- Calcium chloride has the formula CaCl2

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Sodium atom Chlorine atom Electron transfer Click Again

Positive and negative ions attract Sodium Chloride + - Positive and negative ions attract

Electrolysis 22/04/2017 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. Molecule of solid copper chloride CuCl2 (s) Molecule of solid copper chloride after being dissolved CuCl2 (aq) chloride ion Copper ion

Electrolysis 22/04/2017 Electrolysis is used to separate a metal from its compound. = chloride ion = copper ion When we electrolysed copper chloride the _____ chloride ions moved to the ______ electrode and the ______ copper ions moved to the ______ electrode – OPPOSITES ATTRACT!!!

Solution containing copper ions Purifying Copper 22/04/2017 ++++ ---- Impure copper Pure copper Cu2+ Solution containing copper ions At the anode: Cu(s) Cu2+(aq) + 2e- At the cathode: Cu2+(aq) + 2e- Cu(s)

Electrolysis equations 22/04/2017 We need to be able to write “half equations” to show what happens during electrolysis (e.g. for copper chloride): At the negative electrode the positive ions GAIN electrons to become neutral copper ATOMS. The half equation is: Cu2+ + e- Cu 2 At the positive electrode the negative ions LOSE electrons to become neutral chlorine MOLECULES. The half equation is: Cl- - e- Cl2 2 2

Oxidation and Reduction in Electrolysis 22/04/2017 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

Electrolysis of brine 22/04/2017 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… Chlorine gas (Cl2) – used to kill bacteria and to make acids, bleach and plastics Hydrogen gas (H2) – used to manufacture ammonia and margarine Positive electrode Negative electrode Sodium chloride (brine) NaCl(aq) Sodium hydroxide (NaOH(aq)). Used to make soap, paper and ceramics

Electrolysis - summary 22/04/2017 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

Making Soluble Salts 22/04/2017 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 METAL + ACID SALT + HYDROGEN e.g. magnesium + hydrochloric acid magnesium chloride + hydrogen Method 2 METAL OXIDE + ACID SALT + WATER Method 3 METAL HYDROXIDE (Alkali) + ACID SALT + WATER

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 Hydrochloric acid Sulphuric acid Nitric acid Sodium hydroxide Sodium chloride + water Potassium oxide Potassium sulfate + water Calcium Calcium nitrate + water

Reactions of metals with acids 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. 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

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”

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

H ions and OH ions + - H ions make acids acidic. 22/04/2017 + 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)

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

Reactions of metal oxides with acid 22/04/2017 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: Mg O Na Al Magnesium oxide Sodium oxide Aluminium oxide METAL OXIDE + ACID SALT + WATER Mg O H Cl Copy and complete the following reactions: Magnesium oxide + hydrochloric acid Calcium oxide + hydrochloric acid Sodium oxide + sulphuric acid

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

Ammonium Salts 22/04/2017 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. Ammonia + Nitric acid Ammonium Nitrate NH3(g) + HNO3(aq) NH4NO3(aq) 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??

Making Insoluble Salts 22/04/2017 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. Barium chloride + Sodium sulfate Barium sulfate + Sodium chloride BaCl2(aq) + Na2SO4(aq) BaSO4(s) + 2NaCl(aq) 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.

An example question on reactivity Which metal is most reactive? Reaction with dilute acid Reaction with water Reaction with oxygen A Some reaction Slow reaction Burns brightly B No reaction Reacts slowly C D Violent reaction E Reasonable reaction Reacts with steam only