Presentation on theme: "The Periodic Table organising elements into groups"— Presentation transcript:
1The Periodic Table organising elements into groups Chemistry C3 Part OneRevision PowerPoint - Big ideasThe Periodic Table organising elements into groups
2Newlands and Mendeleev Newlands listed the elements in order of atomic weights. He spotted repeating patterns (octaves) in behaviourMendeleev arranged elements into groups and periods to fit repeating patterns. He left gaps for undiscovered elements.
3Modern 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.
4Group 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
5Reactivity 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.
6Group 7 – The HalogensElements in Group 7 (The Halogens) are coloured non-metals.More reactive halogens displace less reactive halogens from solutions containing halide ions, e.g. Cl Br– → Br Cl–Group 7 ions have a charge of –1
7Revision PowerPoint - Big ideas Hard water Chemistry C3 Part TwoRevision PowerPoint - Big ideasHard water
8Causes of hard waterHard 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.
9Softening and desalinating Washing soda and ion-exchange resins can soften hard water.Seawater can be desalinated by distillation which needs a lot of energy
10Tap water treatmentWater is filtered to remove solids and sterilised with chlorine to kill microbes.Dissolved substances are removed by specialised filters or by ion exchange.
11Chemical energy and calorimetry experiments Chemistry C3 Part ThreeRevision PowerPoint - Big ideasChemical energy and calorimetry experiments
12CalorimetryIn calorimetry the energy released from a chemical reaction is transferred to water.The energy transferred, E = m x c x ∆T
13CalorimetryEnergy 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.
14Chemical energy diagrams In an exothermic reaction chemical energy in the reactants in transformed into thermal energyThe surroundings become warmer
15Chemical energy diagrams In an endothermic reaction thermal energy is taken in from the surroundings and is stored as chemical energy in the productsThe surroundings cool down
16Activation energyCatalysts reduce the minimum amount of energy needed to start a reactionThis is called the activation energy
17Hydrogen fuelHydrogen releases energy when it reacts with oxygen in combustion or in fuel cells.2H2 + O2 → 2H2OHydrogen burns exothermically
18Revision PowerPoint - Big ideas Chemical Analysis Chemistry C3 Part FourRevision PowerPoint - Big ideasChemical Analysis
19Flame tests 1Colours used in flame tests are used to identify Group 1 ions.Each salt produces a characteristic flame colour:Lithium (Li+) – magentaSodium (Na+) – golden yellowPotassium (K+) – lilac
20Flame tests 2 Other metal ions also produce coloured flames. Calcium (Ca2+) – brick redBarium (Ba2+) – apple greenCopper (Cu2+) - green with blue flashes
21Precipitation 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+
22White 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 magnesium ionsThe precipitate dissolves in excess sodium hydroxide = aluminium ions
23Sulphate testEnergy 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.
24Carbonate testEnergy 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.
25Chloride bromide iodide test Test the solution of the salt with silver nitrate solution, acidified by nitric acidsilver iodide ppt. is yellowsilver bromide ppt. is creamsilver chloride ppt. is white
26Acid-alkali titrations volumetric analysis of acids & alkalis Titrations RevisionChemistry C3 Part FiveBases are the chemical opposites of acids. Alkalis are bases that are soluble in water.A = AcidB = Base (alkali)Revision PowerPoint - Big ideasAcid-alkali titrations volumetric analysis of acids & alkalis
27ApparatusTitrations involve reactions between solutions of acids and solutions of alkalisAlkalis are delivered using pipettesAcids are delivered using burettes
28Solution 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 g in g/dm3 Volume of solution, in dm3
29Molar concentrationThe concentration of a solution depends on the number of moles of the solute dissolved in a one decimetre cubed of solution.Concentration, c = m ÷ Mr in mol/dm Vm = mass of solute in grams Mr = molar mass of the solute in g/mol V = volume of solution in dm3
30How 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 flaskthe molar concentration cA of the solution added to the flask nA = cA x VA
31Titration question HCl + NaOH → NaCl + H2O 1 mole 1mole 20cm3 The concentration of the acid is unknown25cm30.2mol/dm3HCl + NaOH → NaCl + H2O 1 mole mole
32Calculation to find acid concentration ACID, A ALKALI (Base), B nA = cA x VA nB = cB x VB 1 = cA x 20 1 = 0.25 x x cA = 0.25 x 25 cA = 0.25 x cA = 0.31 mol/dm3
33Indicators and colour changes Indicators switch their colours at certain pH’sMatch the type of titration with the most suitable indicator using the equivalence point pH.
34Equivalence 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
35The Haber Process making ammonia from its elements Chemistry C3 Part SixRevision PowerPoint - Big ideasThe Haber Process making ammonia from its elements
36Ammonia NH3Ammonia is manufactured when nitrogen gas reacts with hydrogen gas – the Haber ProcessNitrogen - N2 is obtained from airHydrogen is obtained from natural gas (methane) reacting with steam CH4 + H2O → CO + 3H2
37Faster reactionNitrogen and hydrogen gases are mixed and passed over a catalyst of iron filingsThe catalyst speeds up this slow reactionIron filings have a larger surface area (better than a block of iron)A reversible exothermic reaction takes place N H2 ↔ 2NH3 + heat ∆H = –92 kJ/mole
38Conditions for the reaction Ammonia is being produced by the forward reactionAmmonia is broken down by the backward reaction into nitrogen and hydrogenConditions are chosen to produce a reasonable yield of ammonia as quickly as possible
39Temperature considerations 1 N H2 ↔ 2NH3 + heat ∆H = –92 kJ/moleRaise 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.
40Temperature considerations 2 N H2 ↔ 2NH3 + heat ∆H = –92 kJ/mole450℃ 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 rateHigh yieldYield of ammoniaRate of the ammonia reactionLow yield450℃Slow rate350450550Temperature in ℃
41Pressure considerations 1 1N H2 ↔ 2NH3 + heat ∆H = –92 kJ/moleNotice 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
42Pressure considerations 2 1N H2 ↔ 2NH3 + heat ∆H = –92 kJ/moleSo, an increase in the pressure shifts the equilibrium to the right and increases the yield of ammoniaA high pressure of atmospheres is chosen for the Haber processUsing higher pressures adds to building costs (walls for reaction chambers will be thicker) and running costs (faster electric pumps)
43Revision PowerPoint - Big ideas Reversible reactions Chemistry C3 Part SevenRevision PowerPoint - Big ideasReversible reactions
44Reversible reactions 1These are chemical reactions which can proceed in two directionsthe forward reaction changes the reactants into product e.g. NH3 (g) + HCl (g) → NH4Cl (s)the product can break down to re-create the original reactants e.g. NH4Cl (s) → NH3 (g) + HCl (g)
45Reversible reactions 2The equations for reversible reactions contains the two-way arrow reaction sign e.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)
46Dynamic 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.
47Dynamic 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.YXAt 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)
48Organic Chemistry alcohols, carboxylic acids and esters Chemistry C3 Part EightRevision PowerPoint - Big ideasOrganic Chemistry alcohols, carboxylic acids and esters
49Alcohols CnH2n+1OHAlcohols, such as ethanol, are a family (homologous series) of compounds containing the –OH functional groupThey make excellent fuels (e.g. bioethanol is a petrol substitute)They are used as solvents and fuelsThey mix with water easily (whisky)
50Carboxylic 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 groupCarboxylic acids are weak acids. Acid molecules are partially ionise. They release small quantities of H+ ions into the water, pH = 4
51Carboxylic acids are weak acids The vinegar = pH3 to 4 Vinegar is a weak, partially ionised acidHydrochloric acid = pH0 to 1 HCl is 100% dissociated into ions and it is a strong acid
52Carboxylic acid reactions 1 Carboxylic acids react with carbonates like marble chips to form carbon dioxide. CaCO3 + 2H+ → CO2 + H2O + Ca2+The reaction is slow because they are weak acids.
53Carboxylic acid reactions 2 Carboxylic acids react with alcohols in the presence of an acid catalyst to form estersEsters are sweet-smelling liquids found in perfumes and fruits like oranges and strawberriesEsters also give some fruits a special flavour
54Esters – nice niffs & flavours The ester ethyl ethanoate has the smell of pearsIt is made when ethanol reacts with ethanoic acid in the presence of an acid catalystEsters contain the –COO- functional group.