♡ Topic 9_ Separate chemistry II ♡

• An ion is a charged atom, molecule, or particle
• A test for a specific ion must be unique to give an easily observed result specific to the ion present
• To carry out a flame test to test for ions:

  • Clean a nichrome wire using hydrochloric acid
  • Turn the Bunsen burner onto the blue flame
  • Dip the wire in a solution of the substance being tested
  • Place the wire in the flame and record the colour
• Results of flame tests on ions:

  • Lithium ions result in a crimson flame
  • Sodium ions result in a yellow flame
  • Potassium ions result in a lilac flame
  • Calcium ions result in an orange-red flame
  • Copper ions result in a blue-green flame
• The wire must be cleaned before a flame test to remove unwanted ions that might obscure the flame colour
• A flame test cannot be used for compounds containing a mixture of metal ions because the flame colours will blend together, making it impossible to identify individual ions
• To test for aqueous metal ions without a flame test:

  • Add sodium hydroxide solution to the metal ions
  • Observe the colour of the precipitate
• A precipitate is an insoluble solid suspended in a liquid
• Results of precipitates with sodium hydroxide:

  • Calcium ions form a white precipitate
  • Copper(II) ions form a blue precipitate
  • Iron(II) ions form a green precipitate
  • Iron(III) ions form a brown precipitate
  • Aluminium ions initially form a white precipitate, which re-dissolves with excess NaOH
• When sodium hydroxide reacts with ammonium ions, a pungent smelling gas (NH3) is produced, turning damp red litmus paper blue
• To distinguish between solutions containing aluminium ions and calcium ions:

  • Add excess sodium hydroxide
  • Both will form white precipitates initially, but the aluminium ion precipitate will re-dissolve to form a colourless solution
• To test for carbonate ions:

  • Add HCl to the sample in a test tube
  • Connect the test tube to a test tube of limewater
  • Carbonate ions will react with the acid to produce carbon dioxide, turning the limewater cloudy
• To test for sulfate ions:

  • Add HCl to remove any carbonate ions
  • Add barium chloride
  • If sulfate ions are present, a white precipitate of barium sulfate will form
• To test for halide ions:

  • Add nitric acid to react with any carbonate ions
  • Add silver nitrate
  • Observe the colour of the precipitate
• Results of precipitates with silver nitrate:

  • Chloride solution forms a white precipitate of silver chloride
  • Bromide solution forms a cream precipitate of silver bromide
  • Iodide solution forms a yellow precipitate of silver iodide
• Instrumental methods of analysis involve using machinery like mass spectrometry and gas chromatography
• Benefits of using instrumental methods for analysis:

  • Accurate
  • Sensitive
  • Quick to carry out
• A flame photometer is a device used in inorganic analysis to identify or determine the concentration of metal ions
• Flame photometry can be used to identify metal ions by producing an emission spectrum where each metal ion has a unique spectrum
• Flame photometry can determine the concentration of metal ions by plotting a calibration curve and comparing readings of unknown samples
• The major advantage of flame photometry over simple flame testing is that it can analyze mixtures of ions, whereas flame tests can only identify one ion at a time
• The general formula for alkanes is CnH2n+2
• General formula for alkanes: CnH2n+2
• First four alkanes and their molecular formulae:

  • Methane: CH4
  • Ethane: C2H6
  • Propane: C3H8
  • Butane: C4H10
• Type of bond formed between carbon and hydrogen atoms in alkanes: Covalent bonds
• Displayed formula of ethane: C2H6
• Why alkanes are saturated hydrocarbons:

  • Saturated because all C-C bonds are single bonds
  • Hydrocarbons because they only contain carbon and hydrogen atoms
• General formula for alkenes: CnH2n
• First four alkenes and their molecular formulae:

  • Ethene: C2H4
  • Propene: C3H6
  • Butene: C4H8
  • Pentene: C5H10
• Why alkenes are unsaturated hydrocarbons:

  • Compounds made of only carbon and hydrogen atoms
  • Contain double carbon bonds, C=C
• Functional group in alkenes: C=C double bond
• Difference between but-1-ene and but-2-ene:

  • Both alkenes with 4 carbons
  • C=C bond found between different carbons in the chain
  • But-1-ene: double bond between first and second carbon
  • But-2-ene: double bond between second and third carbon
• Word and balanced symbol equation for addition reaction between ethene and bromine:

  • Ethene + Bromine → 1,2-dibromoethane
  • C2H4 + Br2 → C2H2Br2
• Displayed formula of 1,2-dibromoethane: C2H2Br2
• How bromine water distinguishes between alkanes and alkenes:

  • Alkanes: solution remains orange
  • Alkenes: solution changes from orange to colorless
• Why alkenes decolourise bromine water:

  • Alkenes are unsaturated
  • Double bond allows alkenes to react with bromine to form a bromoalkane
• Product of complete combustion of hydrocarbons:

  • Water and carbon dioxide produced
  • Carbon and hydrogen oxidised
• Balanced symbol equation for complete combustion of propane:

  • C3H8 + 5O2 → 3CO2 + 4H2O
• Type of reaction when energy is released during hydrocarbon combustion: Exothermic reaction
• Definition of a polymer:

  • Substance of high average relative molecular mass made of small repeating units