Presentation on theme: "12.6 – How can we use ions in solutions?"— Presentation transcript:
1 12.6 – How can we use ions in solutions? 22/04/201712.6 – 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 Calcium chloride has the formula CaCl2 Metal ionsMetal 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
4 Sodium atomChlorine atomElectron transferClick Again
5 Positive and negative ions attract Sodium Chloride+-Positive and negative ions attract
6 Electrolysis22/04/2017If 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 chlorideCuCl2 (s)Molecule of solid copper chloride after being dissolvedCuCl2 (aq)chloride ionCopper ion
7 Electrolysis22/04/2017Electrolysis is used to separate a metal from its compound.= chloride ion= copper ionWhen we electrolysed copper chloride the _____ chloride ions moved to the ______ electrode and the ______ copper ions moved to the ______ electrode – OPPOSITES ATTRACT!!!
8 Solution containing copper ions Purifying Copper22/04/2017++++----Impure copperPure copperCu2+Solution containing copper ionsAt the anode:Cu(s) Cu2+(aq) + 2e-At the cathode:Cu2+(aq) + 2e Cu(s)
9 Electrolysis equations 22/04/2017We 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:Cu e Cu2At the positive electrode the negative ions LOSE electrons to become neutral chlorine MOLECULES. The half equation is:Cl e Cl222
10 Oxidation and Reduction in Electrolysis 22/04/2017At the positive electrode the negative ions LOSE electrons –This is called Oxidation.The half equation is:2Cl e Cl2At the negative electrode the positive ions GAIN electrons – this is called Reduction. The half equation is:Cu e CuOxidation Is Loss, Reduction Is Gain(of electrons)O I L R I G
11 Electrolysis of brine22/04/2017Sodium 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 plasticsHydrogen gas (H2) – used to manufacture ammonia and margarinePositive electrodeNegative electrodeSodium chloride (brine)NaCl(aq)Sodium hydroxide (NaOH(aq)). Used to make soap, paper and ceramics
12 Electrolysis - summary 22/04/2017When 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 Salts22/04/2017There are 3 types of reaction that can be used to make soluble salts. All 3 involve:An AcidA metal or metal compoundMethod 1METAL + ACID SALT + HYDROGENe.g. magnesium + hydrochloric acid magnesium chloride + hydrogenMethod 2METAL OXIDE ACID SALT WATERMethod 3METAL HYDROXIDE (Alkali) + ACID SALT WATER
14 Making saltsTo 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 practiceHydrochloric acidSulphuric acidNitric acidSodium hydroxideSodium chloride + waterPotassium oxidePotassium sulfate + waterCalciumCalcium nitrate + water
15 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 + HYDROGENe.g. magnesium + hydrochloric acid magnesium chloride + hydrogenCopy and complete the following reactions:Calcium + hydrochloric acidZinc + hydrochloric acidIron + hydrochloric acidLithium + sulphuric acid
16 Quiz on acids and alkalis Acid, alkali or both???This a pH of less than 7This could kill cellsA metal hydroxide (e.g. sodium hydroxide) would be an _____When this reacts with a metal hydrogen is releasedA metal carbonate (e.g. calcium carbonate) would be an _____This would feel soapy on your skinThis could be a corrosiveThis will turn universal indicator purpleThis would taste sourThis means “a base that can be dissolved”
17 Neutralisation reactions When acids and alkalis react together they will NEUTRALISE each other. Neutralisation is an example of a displacement reaction:OHNaSodium hydroxideClHHydrochloric acidThe sodium DISPLACES the hydrogen from HClClNaSodium chlorideH2OWater
18 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)
19 Neutralisation experiment Sodium hydroxide + hydrochloric acid sodium chloride + waterA ____ 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 CHLORIDENitric 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 22/04/2017A 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:MgONaAlMagnesium oxideSodium oxideAluminium oxideMETAL OXIDE ACID SALT WATERMgOHClCopy and complete the following reactions:Magnesium oxide + hydrochloric acidCalcium oxide + hydrochloric acidSodium oxide + sulphuric acid
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 base3) Evaporate it to get the salt
22 Ammonium Salts22/04/2017Ammonia (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 NitrateNH3(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??
23 Making Insoluble Salts 22/04/2017Doesn’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 chlorideBaCl2(aq) Na2SO4(aq) BaSO4(s) NaCl(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.
24 An example question on reactivity Which metal is most reactive? Reaction with dilute acidReaction with waterReaction with oxygenASome reactionSlow reactionBurns brightlyBNo reactionReacts slowlyCDViolent reactionEReasonable reactionReacts with steam only