Presentation on theme: "Chemistry C3 Part One Revision PowerPoint - Big ideas The Periodic Table organising elements into groups."— Presentation transcript:
Chemistry C3 Part One Revision PowerPoint - Big ideas The Periodic Table organising elements into groups
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.
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.
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
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.
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. Cl 2 + 2Br – → Br 2 + 2Cl – Group 7 ions have a charge of –1
Chemistry C3 Part Two Revision PowerPoint - Big ideas Hard water
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.
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
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.
Chemistry C3 Part Three Revision PowerPoint - Big ideas Chemical energy and calorimetry experiments
Calorimetry In calorimetry the energy released from a chemical reaction is transferred to water. The energy transferred, E = m x c x ∆T
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.
Chemical energy diagrams exothermic reaction In an exothermic reaction chemical energy in the reactants in transformed into thermal energy surroundings warmer The surroundings become warmer
Chemical energy diagrams endothermic reaction In an endothermic reaction thermal energy is taken in from the surroundings and is stored as chemical energy in the products surroundings cool The surroundings cool down
Activation energy start a reaction Catalysts reduce the minimum amount of energy needed to start a reaction activation energy This is called the activation energy
Hydrogen fuel Hydrogen releases energy when it reacts with oxygen in combustion or in fuel cells. 22 2H 2 + O 2 → 2H 2 O Hydrogen burns exothermically
Chemistry C3 Part Four Revision PowerPoint - Big ideas Chemical Analysis
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
Flame tests 2 Other metal ions also produce coloured flames. Calcium (Ca 2+ ) – brick red Barium (Ba 2+ ) – apple green Copper (Cu 2+ ) - green with blue flashes
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, Cu 2+ dirty green jelly ppt. iron (II) ions, Fe 2+ rusty red- brown jelly ppt. iron (III) ions, Fe 3+
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 dissolves in excess sodium hydroxide = aluminium ions The precipitate does not dissolve in excess sodium hydroxide = calcium or magnesium ions
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.
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.
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
Chemistry C3 Part Five Revision PowerPoint - Big ideas Acid-alkali titrations volumetric analysis of acids & alkalis Bases are the chemical opposites of acids. Alkalis are bases that are soluble in water. A = Acid B = Base (alkali)
Apparatus Titrations involve reactions between solutions of acids and solutions of alkalis Alkalis are delivered using pipettes Acids are delivered using burettes
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 dm 3 Concentration = Mass of solute, in g in g/dm 3 Volume of solution, in dm 3
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 ÷ M r in mol/dm 3 V m = mass of solute in grams M r = molar mass of the solute in g/mol V = volume of solution in dm 3
How many moles are delivered? The number of moles, n A, of acid delivered during the titration depends upon: the volume of acid, V A added to the flask the molar concentration c A of the solution added to the flask n A = c A x V A
Titration question HCl + NaOH → NaCl + H 2 O 1 mole 1mole 25cm 3 0.2mol/dm 3 20cm 3 The concentration of the acid is unknown
Calculation to find acid concentration ACID, A ALKALI (Base), B n A = c A x V A n B = c B x V B 1 = c A x 20 1 = 0.25 x x c A = 0.25 x 25 c A = 0.25 x c A = 0.31 mol/dm 3
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.
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
Chemistry C3 Part Six Revision PowerPoint - Big ideas The Haber Process making ammonia from its elements
Ammonia NH 3 Ammonia is manufactured when nitrogen gas reacts with hydrogen gas – the Haber Process Nitrogen - N 2 is obtained from air Hydrogen is obtained from natural gas (methane) reacting with steam CH 4 + H 2 O → CO + 3H 2
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 reversible exothermic reaction takes place N 2 + 3H 2 ↔ 2NH 3 + heat ∆H = –92 kJ/mole
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
Temperature considerations 1 N 2 + 3H 2 ↔ 2NH 3 + 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.
Temperature considerations 2 N 2 + 3H 2 ↔ 2NH 3 + heat ∆H = –92 kJ/mole Temperature in ℃ Yield of ammonia Rate of the ammonia reaction High yield Low yield Fast rate Slow rate 450 ℃ is the optimum temperature for a reasonable rate and a reasonable yield. You can’t have a fast rate and a high yield. 450 ℃ Use the Goldilocks principle … not too hot … not too cold … but just right! 450 ℃ 450 ℃
Pressure considerations 1 1N 2 + 3H 2 ↔ 2NH 3 + 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
Pressure considerations 2 1N 2 + 3H 2 ↔ 2NH 3 + 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 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)
Chemistry C3 Part Seven Revision PowerPoint - Big ideas Reversible reactions
Reversible reactions 1 These are chemical reactions which can proceed in two directions the forward reaction changes the reactants into product e.g. NH 3 (g) + HCl (g) → NH 4 Cl (s) the product can break down to re- create the original reactants e.g. NH 4 Cl (s) → NH 3 (g) + HCl (g)
Reversible reactions 2 The equations for reversible reactions contains the two-way arrow reaction sign e.g. NH 3 (g) + HCl (g) ↔ NH 4 Cl (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: CaCO 3 (s) ↔ CaO (s) + CO 2 (g)
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.
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. X Y At X the heated ammonium chloride solid decomposes. NH 4 Cl (s) → NH 3 (g) + HCl (g) At Y the cooled gases combine together to form solid ammonium chloride. NH 3 (g) + HCl (g) → NH 4 Cl (s)
Chemistry C3 Part Eight Revision PowerPoint - Big ideas Organic Chemistry alcohols, carboxylic acids and esters
Alcohols C n H 2n+1 OH 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)
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
Carboxylic acids are weak acids The vinegar = pH3 to 4 Vinegar is a weak, partially ionised acid Hydrochloric acid = pH0 to 1 HCl is 100% dissociated into ions and it is a strong acid
Carboxylic acid reactions 1 Carboxylic acids react with carbonates like marble chips to form carbon dioxide. CaCO 3 + 2H + → CO 2 + H 2 O + Ca 2+ The reaction is slow because they are weak acids.
Carboxylic acid reactions 2 Carboxylic acids react with alcohols in the presence of an acid catalyst to form esters Esters are sweet-smelling liquids found in perfumes and fruits like oranges and strawberries Esters also give some fruits a special flavour
Esters – nice niffs & flavours The ester ethyl ethanoate has the smell of pears It is made when ethanol reacts with ethanoic acid in the presence of an acid catalyst Esters contain the –COO- functional group.