Chemistry C3 Part One

1. Chemistry C3 Part One Revision PowerPoint - Big ideas The Periodic Tableorganising elements into groups

2. Newlands and Mendeleev • Newlands listed the elements in order of atomic weights. He spotted repeating patterns (octaves) in behaviour • Mendeleev arranged elements into groups and periods to fit repeating patterns. He left gaps for undiscovered elements.

3. Modern Periodic Tables • Modern Periodic Tables arrange elements by increasing atomic number. • The number of electrons in the highest energy level (outermost shell) indicates the group number of the element.

4. Group 1 - The Alkali Metals • Elements in Group 1 (The Alkali Metals) are soft, low density metals. • Alkali metals react rapidly with water, forming alkalis & hydrogen. • Alkali metals form ionic compounds with non-metals. • Group 1 ions have the charge +1

5. Reactivity down the group • Group 1 elements become more reactive further down the group. • Large atoms lose electrons from their outer shells more easily because they are further from the positive nuclear charge force and shielded by more inner shells of electrons.

6. Group 7 – The Halogens • Elements in Group 7 (The Halogens) are coloured non-metals. • More reactive halogens displace less reactive halogens from solutions containing halide ions, e.g. Cl2 + 2Br– → Br2 + 2Cl– • Group 7 ions have a charge of –1

7. Chemistry C3 Part Two Revision PowerPoint - Big ideas Hard water

8. Causes of hard water • Hard water is caused by calcium and magnesium ions dissolving when acidic rainwater flows through rocks. • Temporary hard water is caused by calcium hydrogencarbonate, can be removed by boiling the water. • Permanent hardness caused by calcium sulphate isn’t removed by boiling.

9. Softening and desalinating • Washing soda and ion-exchange resins can soften hard water. • Seawater can be desalinated by distillation which needs a lot of energy

10. Tap water treatment • Water is filtered to remove solids and sterilised with chlorine to kill microbes. • Dissolved substances are removed by specialised filters or by ion exchange.

11. Chemistry C3 Part Three Revision PowerPoint - Big ideas Chemical energyand calorimetry experiments

12. Calorimetry • In calorimetry the energy released from a chemical reaction is transferred to water. • The energy transferred, E = m x c x ∆T

13. Calorimetry • Energy level diagrams show the change in chemical energy as reactants change into products. • Energy is released when new chemical bonds form. • Energy is required to break chemical bonds.

14. Chemical energy diagrams • In an exothermic reaction chemical energy in the reactants in transformed into thermal energy • The surroundings become warmer

15. Chemical energy diagrams • In an endothermic reaction thermal energy is taken in from the surroundings and is stored as chemical energy in the products • The surroundings cool down

16. Activation energy • Catalysts reduce the minimum amount of energy needed to start a reaction • This is called the activation energy

17. Hydrogen fuel • Hydrogen releases energy when it reacts with oxygen in combustion or in fuel cells. 2H2 + O2 → 2H2O • Hydrogen burns exothermically

18. Chemistry C3 Part Four Revision PowerPoint - Big ideas Chemical Analysis

19. Flame tests 1 • Colours used in flame tests are used to identify Group 1 ions. • Each salt produces a characteristic flame colour: • Lithium (Li+) – magenta • Sodium (Na+) – golden yellow • Potassium (K+) – lilac

20. Flame tests 2 Other metal ions also produce coloured flames. • Calcium (Ca2+) – brick red • Barium (Ba2+) – apple green • Copper (Cu2+) - green with blue flashes

21. Precipitation reactions Precipitation reactions are used to identify other metal ions. Test the solutions of the salts with sodium hydroxide solution. A coloured precipitate of a metal hydroxide forms. light blue jelly ppt. copper (II) ions, Cu2+ dirty green jelly ppt. iron (II) ions, Fe2+ rusty red- brown jelly ppt. iron (III) ions, Fe3+

22. White hydroxide precipitates? When you test solutions of the salts with sodium hydroxide solution, sometimes the precipitate is white. This is how to distinguish between magnesium, calcium and aluminium ions … Add extra (excess) sodium hydroxide solution to the white precipitate. The precipitate does not dissolve in excess sodium hydroxide= calcium or magnesiumions The precipitate dissolvesin excess sodium hydroxide= aluminium ions

23. Sulphate test • Energy level diagrams show the change in chemical energy as reactants change into products. • Energy is released when new chemical bonds form. • Energy is required to break chemical bonds.

24. Carbonate test • Energy level diagrams show the change in chemical energy as reactants change into products. • Energy is released when new chemical bonds form. • Energy is required to break chemical bonds.

25. Chloride bromide iodide test • Test the solution of the salt with silver nitrate solution, acidified by nitric acid silver iodide ppt. is yellow silver bromide ppt. is cream silver chloride ppt. is white

26. Bases are the chemical opposites of acids. Alkalis are bases that are soluble in water. A = Acid B = Base (alkali) Chemistry C3 Part Five Revision PowerPoint - Big ideas Acid-alkali titrationsvolumetric analysis of acids & alkalis

27. Apparatus • Titrations involve reactions between solutions of acids and solutions of alkalis • Alkalis are delivered using pipettes • Acids are delivered using burettes

28. Solution concentration The concentration of a solution depends on the mass of the solute dissolved in a certain volume of water. Mass is measure in grams, volumes in dm3 Concentration = Mass of solute, in gin g/dm3 Volume of solution, in dm3

29. Molar concentration The concentration of a solution depends on the number of moles of the solute dissolved in a one decimetre cubed of solution. Concentration, c = m ÷ Mrin mol/dm3 V m = mass of solute in gramsMr = molar mass of the solute in g/molV = volume of solution in dm3

30. How many moles are delivered? The number of moles, nA, of acid delivered during the titration depends upon: • the volume of acid, VA added to the flask • the molar concentrationcA of the solution added to the flasknA = cAx VA

31. Titration question 20cm3 The concentration of the acid is unknown 25cm3 0.2mol/dm3 HCl + NaOH→ NaCl + H2O1 mole 1mole

32. Calculation to find acid concentration ACID, A ALKALI (Base), BnA = cAx VA nB= cBxVB1 =cAx 20 1 = 0.25 x 25 20xcA= 0.25 x25 cA = 0.25 x25 20 cA = 0.31 mol/dm3

33. Indicators and colour changes Indicators switch their colours at certain pH’s Match the type of titration with the most suitable indicator using the equivalence point pH.

34. Equivalence points and pH This titration graph shows what happens to the pH when a strong alkali is slowly added to a strong acid. Use methyl orange. This titration graph shows what happens to the pH when a strong alkali is slowly added to a weak acid. Best indicator = phenolphthalein

35. Chemistry C3 Part Six Revision PowerPoint - Big ideas The Haber Processmaking ammonia from its elements

36. Ammonia NH3 • Ammonia is manufactured when nitrogen gas reacts with hydrogen gas – the Haber Process • Nitrogen - N2 is obtained from air • Hydrogen is obtained from natural gas (methane) reacting with steam CH4 + H2O → CO + 3H2

37. Faster reaction • Nitrogen and hydrogen gases are mixed and passed over a catalyst of iron filings • The catalyst speeds up this slow reaction • Iron filings have a larger surface area (better than a block of iron) • A reversibleexothermic reaction takes placeN2 + 3H2 ↔2NH3 + heat ∆H = –92 kJ/mole

38. Conditions for the reaction • Ammonia is being produced by the forward reaction • Ammonia is broken down by the backward reaction into nitrogen and hydrogen • Conditions are chosen to produce a reasonable yield of ammonia as quickly as possible

39. Temperature considerations 1 N2+ 3H2 ↔2NH3 + heat ∆H = –92 kJ/mole • Raise the temperature of the reaction and molecules of gas will have more kinetic energy, move faster and collide more violently. • Violent collisions lead to old chemical bonds breaking – but be careful, ammonia molecules may decompose faster too!! • 450℃ is a good compromise for this exothermic reaction – you get a reasonable yield of ammonia at a reasonable rate.

40. Temperature considerations 2 N2+ 3H2 ↔2NH3 + heat ∆H = –92 kJ/mole 450℃ is the optimum temperature for a reasonable rate and a reasonable yield. You can’t have a fast rate and a high yield. Use the Goldilocks principle … not too hot … not too cold … but just right! 450℃ Fast rate High yield Yield of ammonia Rate of the ammonia reaction Low yield 450℃ Slow rate 350 550 450 Temperature in ℃

41. Pressure considerations 1 1N2+ 3H2 ↔2NH3 + heat ∆H = –92 kJ/mole • Notice that the number of molecules on the left hand side of the equation is 3+1 = 4 and there are 2 molecules of ammonia on the right. • For all reversible reactions involving gases an increase in pressure effects the equilibrium position favouring the reaction that produces fewer molecules

42. Pressure considerations 2 1N2+ 3H2 ↔2NH3 + heat ∆H = –92 kJ/mole • So, an increase in the pressure shifts the equilibrium to the right and increases the yield of ammonia • A high pressure of 100 - 200 atmospheres is chosen for the Haber process • Using higher pressures adds to building costs (walls for reaction chambers will be thicker) and running costs (faster electric pumps)

43. Chemistry C3 Part Seven Revision PowerPoint - Big ideas Reversible reactions

44. Reversible reactions 1 These are chemical reactions which can proceed in two directions • the forward reaction changes the reactants into producte.g. NH3 (g) + HCl(g)→ NH4Cl (s) • the product can break down to re-create the original reactantse.g. NH4Cl (s) → NH3 (g) + HCl(g)

45. Reversible reactions 2 The equations for reversible reactions contains the two-way arrow reaction signe.g. NH3 (g) + HCl(g)↔ NH4Cl (s) By changing the reaction conditions we can favour either the forward reaction or the reverse reaction. Other reversible chemical reactions include the decomposition of limestone: CaCO3(s)↔ CaO(s) + CO2 (g)

46. Dynamic chemical equilibrium 1 Ammonia and hydrogen chloride gases can react in a closed system such as the beaker in the diagram. Nothing can get in & nothing can escape. Over time the reaction reaches dynamic chemical equilibrium. The forward and backward reactions are both happening.

47. Dynamic chemical equilibrium 2 At this point of dynamic chemical equilibrium, the rate of the forward reaction and the rate of the backward reaction are exactly equal. The amount of each substance remains constant and the forward and backward reactions continue to proceed. Y X At X the heated ammonium chloride solid decomposes. NH4Cl (s) → NH3(g) + HCl(g) At Y the cooled gases combine together to form solid ammonium chloride. NH3(g) + HCl(g) → NH4Cl (s)

48. Chemistry C3 Part Eight Revision PowerPoint - Big ideas Organic Chemistryalcohols, carboxylic acids and esters

49. Alcohols CnH2n+1OH • Alcohols, such as ethanol, are a family (homologous series) of compounds containing the –OH functional group • They make excellent fuels (e.g. bioethanol is a petrol substitute) • They are used as solvents and fuels • They mix with water easily (whisky)

50. Carboxylic acids (e.g. vinegar) • Ethanol is oxidised to ethanoic acid. This happens when we leave wine open to the air. • Carboxylic acids have a –COOH functional group • Carboxylic acids are weak acids. Acid molecules are partially ionise. They release small quantities of H+ ions into the water, pH = 4