C6 Chemical Synthesis OCR 21st Century W Richards The Weald School 02/12/2018 02/12/2018 C6 Chemical Synthesis OCR 21st Century W Richards The Weald School

C6.1 Chemicals and why we need them 02/12/2018 C6.1 Chemicals and why we need them

Things made by Chemical Synthesis 02/12/2018 Paints and pigments Food additives Perfumes and cosmetics Drugs

Balancing ions Some common ions: 02/12/2018 02/12/2018 Some common ions: Sodium – Na+ Potassium – K+ Magnesium – Mg2+ Ammonium – NH4+ Chloride – Cl- Bromide – Br- Oxide – O2- Sulphate – SO42- Determine the formula of these compounds: Sodium chloride Magnesium oxide Magnesium chloride Ammonium chloride Sodium sulphate Sodium oxide Answers: NaCl MgO MgCl2 NH4Cl Na2SO4 NaO

Simple formulae to learn 02/12/2018 H2O CO2 NH3 H2 O2 N2 SO2 Cl2 KCl Water Carbon dioxide Ammonia Hydrogen Oxygen Nitrogen Sulphur dioxide Chlorine Potassium chloride NaCl CaCl2 MgO HCl NaOH Ca(OH)2 CaCO3 HNO3 H2SO4 Mg(OH)2 Sodium chloride Calcium chloride Magnesium oxide Hydrochloric acid Sodium hydroxide Calcium hydroxide Calcium carbonate Nitric acid Sulphuric acid Magnesium hydroxide

Hazard signs to learn… Acid Corrosive Toxic h i Harmful Irritant 02/12/2018 02/12/2018 Acid Corrosive Toxic h i Harmful Irritant Oxidising

Common acids and alkalis 02/12/2018 Acids Alkalis Hydrochloric acid, HCl Sodium hydroxide, NaOH Nitric acid, HNO3 Potassium hydroxide, KOH Sulphuric acid, H2SO4 Magnesium hydroxide, Mg(OH)2 Citric acid (a solid) Calcium hydroxide, Ca(OH)2 Ethanoic acid (a liquid)

The pH scale Strong acid Strong alkali Neutral 1 2 3 4 5 6 7 8 9 10 11 02/12/2018 The pH scale is a way of showing how strong or weak an acid or alkali is: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Stomach acid Lemon juice Water Soap Baking powder Oven cleaner Strong alkali Strong acid Neutral An acid contains hydrogen ions, H+ An alkali contains hydroxide ions, OH-

Different indicators 02/12/2018 Litmus paper, used to simply indicate if something is acidic or alkaline Universal indicator paper and pH meters, used to detect a pH value

Sodium + water sodium hydroxide + hydrogen Balancing equations 02/12/2018 Consider the following reaction: Sodium + water sodium hydroxide + hydrogen Na O H O H Na + H + This equation doesn’t balance – there are 2 hydrogen atoms on the left hand side (the “reactants” and 3 on the right hand side (the “products”)

Balancing equations We need to balance the equation: 02/12/2018 We need to balance the equation: Sodium + water sodium hydroxide + hydrogen Na O H O H Na O H Na O H + H + Na Now the equation is balanced, and we can write it as: 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)

Some examples 2 2 3 2 3 Mg + O2 Zn + HCl Fe + Cl2 NaOH + HCl CH4 + O2 02/12/2018 2 2 3 2 3 Mg + O2 Zn + HCl Fe + Cl2 NaOH + HCl CH4 + O2 Ca + H2O NaOH + H2SO4 CH3OH + O2 MgO ZnCl2 + H2 FeCl3 NaCl + H2O CO2 + H2O Ca(OH)2 + H2 Na2SO4 + H2O 2 2 4

Words – gold, corroded, fizzes, disappear Adding acids to metals 02/12/2018 If an acid is added to a (fairly reactive) metal the metal will be quickly ________ by the acid. We can see a reaction happening because the mixture _________ and the metal eventually __________. Some metals, like ____, are so unreactive that nothing will happen. Words – gold, corroded, fizzes, disappear

Reactions of metals with acids 02/12/2018 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

Adding acid to carbonates 02/12/2018 Carbonates are compounds containing carbon and oxygen. When an acid is added to a carbonate the carbonate starts to _______. A gas called ______ _______ is produced. Carbonates used to be used as building materials but aren’t any more because acid rain would eventually ________ the building. Words – dissolve, fizz, carbon dioxide, oxygen

Reactions of metals carbonates with acid 02/12/2018 A metal carbonate is a compound containing a metal, carbon and oxygen. METAL CARBONATE + ACID SALT + CARBON DIOXIDE + WATER Mg H Cl C O Copy and complete the following reactions: Magnesium carbonate + hydrochloric acid Calcium carbonate + hydrochloric acid Sodium carbonate + sulphuric acid

Reactions of metal oxides with acid 02/12/2018 A metal oxide is a compound containing a metal and oxide. They are sometimes called BASES. 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

Neutralisation reactions 02/12/2018 A neutralisation reaction occurs when an acid reacts with an alkali. An alkali is a metal oxide or metal hydroxide dissolved in water. ACID + ALKALI SALT + WATER Na Cl H O Copy and complete the following reactions: Sodium hydroxide + hydrochloric acid Calcium hydroxide + hydrochloric acid Sodium hydroxide + sulphuric acid Magnesium hydroxide + sulphuric acid

Acids and Alkalis 02/12/2018 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acids produce hydrogen ions when they dissolve in water: H Cl + - Alkalis produce hydroxide ions: H O Na - +

Neutralisation reactions 02/12/2018 When acids and alkalis react together they will NEUTRALISE each other: Sodium hydroxide Hydrochloric acid Na H OH Cl The sodium “replaces” the hydrogen from HCl Cl Na Sodium chloride H2O Water General equation: H+(aq) + OH-(aq) H2O(l)

Neutralisation experiment 02/12/2018 For example, in a neutralisation experiment we can mix sodium hydroxide (an _____) and hydrochloric acid together and they will ________ each other. The equation for this reaction is… Sodium hydroxide + hydrochloric acid sodium chloride + water A ____ was formed during the reaction, and we could have separated this by __________ the solution. 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 – nitrate, neutralise, alkali, sulphate, salt, evaporating

Neutralisation reactions 02/12/2018 The basic equation for any neutralisation reaction is: H+(aq) + OH-(aq) H2O(l) Write word and chemical equations for the following reactions: Hydrochloric acid + sodium hydroxide Hydrochloric acid + potassium hydroxide Nitric acid + potassium hydroxide Sulphuric acid + calcium hydroxide Nitric acid + copper oxide, CuO Sulphuric acid + calcium carbonate, Ca(CO)3

Making salts 02/12/2018 Whenever an acid and alkali neutralise each other we are left with a salt, like a chloride or a sulphate. Complete the following table: Hydrochloric acid Sulphuric acid Nitric acid Sodium hydroxide Sodium chloride (NaCl) + water Potassium hydroxide Potassium sulphate (K2SO4) + water Calcium hydroxide Calcium nitrate (Ca(NO3)2) + water

Endothermic and exothermic reactions 02/12/2018 02/12/2018 Step 1: Energy must be SUPPLIED to break bonds: Energy Step 2: Energy is RELEASED when new bonds are made: Energy A reaction is EXOTHERMIC if more energy is RELEASED then SUPPLIED. If more energy is SUPPLIED then is RELEASED then the reaction is ENDOTHERMIC

Common examples of these reactions 02/12/2018 Photosynthesis Are these reactions exothermic or endothermic? Burning Hand warmer packs Cooling packs

Example reactions Reaction Temp. after mixing/OC 02/12/2018 02/12/2018 Reaction Temp. after mixing/OC Exothermic or endothermic? Sodium hydroxide + dilute hydrochloric acid Sodium hydrogencarbonate + citric acid Copper sulphate + magnesium powder Sulphuric acid + magnesium ribbon

Energy level diagrams Energy level 02/12/2018 02/12/2018 Energy level Energy required to break bonds (endothermic) Energy given out making bonds (exothermic) Reaction progress

Exothermic vs endothermic: 02/12/2018 02/12/2018 What sort of things would industrial chemists need to consider when carrying out large scale exothermic and endothermic reactions? EXOTHERMIC – more energy is given out than is taken in (e.g. burning, respiration) ENDOTHERMIC – energy is taken in but not necessarily given out (e.g. photosynthesis)

C6.2 Planning and Carrying out Chemical Synthesis 02/12/2018 C6.2 Planning and Carrying out Chemical Synthesis

Chemical Synthesis 02/12/2018 In the manufacture of an inorganic compound the following stages can be used: Work out the reactions that need to be done Carry out a risk assessment Calculate the quantities of reactants to use Do the reaction Separate the product from the mixture Purify it Measure the yield Check its purity

Different Techniques What would you use these techniques for? 02/12/2018 What would you use these techniques for? Filtration Dissolving Drying in an oven Evaporation/crystallisation

Mass and atomic number revision 02/12/2018 02/12/2018 Particle Relative Mass Relative Charge Proton 1 +1 Neutron Electron Very small -1 MASS NUMBER = number of protons + number of neutrons He 2 4 SYMBOL PROTON NUMBER = number of protons (obviously)

Relative formula mass, Mr 02/12/2018 The relative formula mass of a compound is the relative atomic masses of all the elements in the compound added together. Relative atomic mass of O = 16 E.g. water H2O: Relative atomic mass of H = 1 Therefore Mr for water = 16 + (2x1) = 18 Work out Mr for the following compounds: HCl NaOH MgCl2 H2SO4 K2CO3 H=1, Cl=35 so Mr = 36 Na=23, O=16, H=1 so Mr = 40 Mg=24, Cl=35 so Mr = 24+(2x35) = 94 H=1, S=32, O=16 so Mr = (2x1)+32+(4x16) = 98 K=39, C=12, O=16 so Mr = (2x39)+12+(3x16) = 138

Calculating the mass of a product 02/12/2018 E.g. what mass of magnesium oxide is produced when 60g of magnesium is burned in air? IGNORE the oxygen in step 2 – the question doesn’t ask for it Step 1: READ the equation: 2Mg + O2 2MgO Step 2: WORK OUT the relative formula masses (Mr): 2Mg = 2 x 24 = 48 2MgO = 2 x (24+16) = 80 Step 3: LEARN and APPLY the following 3 points: 48g of Mg makes 80g of MgO 1g of Mg makes 80/48 = 1.66g of MgO 60g of Mg makes 1.66 x 60 = 100g of MgO

Mr: 2Al2O3 = 2x((2x27)+(3x16)) = 204 4Al = 4x27 = 108 When water is electrolysed it breaks down into hydrogen and oxygen: 2H2O 2H2 + O2 What mass of hydrogen is produced by the electrolysis of 6g of water? 02/12/2018 Work out Mr: 2H2O = 2 x ((2x1)+16) = 36 2H2 = 2x2 = 4 36g of water produces 4g of hydrogen So 1g of water produces 4/36 = 0.11g of hydrogen 6g of water will produce (4/36) x 6 = 0.66g of hydrogen 2) What mass of calcium oxide is produced when 10g of calcium burns? 2Ca + O2 2CaO Mr: 2Ca = 2x40 = 80 2CaO = 2 x (40+16) = 112 80g produces 112g so 10g produces (112/80) x 10 = 14g of CaO 3) What mass of aluminium is produced from 100g of aluminium oxide? 2Al2O3 4Al + 3O2 Mr: 2Al2O3 = 2x((2x27)+(3x16)) = 204 4Al = 4x27 = 108 204g produces 108g so 100g produces (108/204) x 100 = 52.9g of Al2O3

So mass of product = (4/36) x 6g = 0.66g of hydrogen Another method 02/12/2018 Try using this equation: Mass of product IN GRAMMES Mass of reactant IN GRAMMES Mr of product Mr of reactant Q. When water is electrolysed it breaks down into hydrogen and oxygen: 2H2O 2H2 + O2 What mass of hydrogen is produced by the electrolysis of 6g of water? Mass of product IN GRAMMES 4 6g 36 So mass of product = (4/36) x 6g = 0.66g of hydrogen

The theoretical yield is 136g (using Cl = 35.5) so the % yield is 75% Percentage Yield 02/12/2018 Theoretical yield = the amount of product that should be made as calculated from the masses of atoms Actual yield = what was actually produced in a reaction Percentage yield = actual yield (in g) theoretical yield Example question: 65g of zinc reacts with 73g of hydrochloric acid and produces 102g of zinc chloride. What is the percentage yield? Zn + 2HCl ZnCl2 + H2 The theoretical yield is 136g (using Cl = 35.5) so the % yield is 75%

Percentage yield Percentage yield = Actual yield Predicted yield 02/12/2018 Percentage yield = Actual yield Predicted yield X 100% Some example questions: The predicted yield of an experiment to make salt was 10g. If 7g was made what is the percentage yield? Dave is trying to make water. If he predicts to make 15g but only makes 2g what is the percentage yield? Sarah performs an experiment and has a percentage yield of 33%. If she made 50g what was she predicted to make? 70% 13% 150g

Titration 02/12/2018 1) Fill a burette with sodium hydroxide solution of known concentration 2) Accurately measure out 25cm3 of acid and place it in the conical flask 3) Add phenolphthalein indicator to the flask 4) Slowly add the alkali until the mixture in the flask turns pink 5) Repeat until you get similar results

No. of moles = concentration x volume Titration Equations 02/12/2018 Q. 0.05dm3 of HCl neutralises 0.1dm3 of NaOH of concentration 0.5mol dm-3. What is the concentration of the acid? The key steps: 1) Look at the equation to compare the numbers of moles: HCl + NaOH NaCl + H2O Notice that 1 mole of HCl neutralises 1 mole of NaOH 2) Use this equation: No. of moles = concentration x volume So, the number of moles of NaOH is (0.5 x 0.1) = 0.05mol According to the equation, this will neutralise 0.05mol of HCl Therefore we have (0.05mol/0.05dm3) = 1mol dm-3 HCl

Titration Equations 02/12/2018 0.2dm3 of HCl neutralises 0.1dm3 of NaOH of concentration 0.5mol dm-3. What is the concentration of the acid? H2SO4 of concentration 0.4mol dm-3 neutralises 0.1dm3 of NaOH of concentration 0.2mol dm-3. How much acid was used? HCl + NaOH NaCl + H2O H2SO4 + 2NaOH Na2SO4 + 2H2O

Measuring the Rate of Reaction 02/12/2018 Three common methods:

Measuring the Rate of Reaction 02/12/2018 Three common methods:

Rate of reaction graph Amount of product formed/ reactant used up 02/12/2018 Amount of product formed/ reactant used up Slower rate of reaction here due to reactants being used up Fast rate of reaction here Slower reaction Time

Q. What if less reactants were used? Rate of reaction graph 02/12/2018 Q. What if less reactants were used? Amount of product formed/ reactant used up Time

Rates of Reaction 02/12/2018 Oh no! Here comes another one and it’s got more energy… Here comes another one. Look at how slow it’s going… No effect! It didn’t have enough energy! Hi. I’m Mike Marble. I’m about to have some acid poured onto me. Let’s see what happens… It missed! Here comes an acid particle…

Words – energy, quicker, catalyst, temperature, collide Rates of Reaction 02/12/2018 Chemical reactions occur when different atoms or molecules _____ with each other but they HAVE to collide with enough _______. Basically, the more collisions we get and the more energetic they are the _______ the reaction goes. The rate at which the reaction happens depends on four things: The _______ of the reactants, Their concentration Their surface area Whether or not a _______ has been used Words – energy, quicker, catalyst, temperature, collide

Words – different, speed up, used up, cheaper Catalyst Summary 02/12/2018 Catalysts are used to ____ __ a reaction to increase the rate at which a product is made or to make a process ________. They are not normally ___ __ in a reaction and they are reaction-specific (i.e. different reactions need _________ catalysts). Words – different, speed up, used up, cheaper

Chemical Economics 02/12/2018 Hi. We’re industrial scientists and we want to make lots of chemicals and sell them to make money. What problems would we face? Possible problems with making chemicals: Reactions often produce chemicals that aren’t commercially useful or that can’t be sold Reactions also need to be fast to be economical but not so fast that they’re dangerous! Therefore we need reactions and processes that give us a pure, high percentage yield where all of the products are useful and the reactions happen quickly.