Chemical Analysis

• A pure substance in chemistry contains a single element or compound that is not mixed with any other substance
• Pure substances melt and boil at specific temperatures
• An impure substance contains more than one type of element or compound in a mixture
• Impure substances melt and boil at a range of temperatures
• Formulations are mixtures with many different components in specific proportions
• Scientists aim to get the right components in the right proportions to make useful products
• Examples of formulations include fuels, cleaning agents, paints, alloys, fertilisers, and foods
• Common gases can be identified through specific tests:

  • Hydrogen: hear a squeaky pop when a lighted splint is held near the gas
  • Oxygen: splint re-lights when a glowing splint is held near the gas
  • Carbon dioxide: limewater turns milky when the gas is bubbled through it
  • Chlorine: bleaches damp litmus paper when a piece of damp litmus is held near the gas
• Flame tests can identify metal ions by the colour they produce in a flame:

  • Lithium: crimson
  • Sodium: yellow
  • Potassium: lilac
  • Calcium: orange-red
  • Copper: green
• Instrumental analysis involves using complex scientific equipment to test substances
• Instrumental methods are rapid, accurate, and sensitive
• Flame emission spectroscopy is a type of instrumental analysis that identifies substances by the wavelength of light emitted in a flame
• Chromatography is a method to separate components in a mixture:

  • Rf value is calculated as the distance moved by the substance divided by the distance moved by the solvent (always between 0 and 1)
  • Different substances have different Rf values, which can be used to identify them
• Metal ions have a positive charge and can be identified using sodium hydroxide solution:

  • Aluminium ions form a white precipitate that dissolves with excess sodium hydroxide
  • Calcium and magnesium ions form white precipitates that do not dissolve
  • Copper(II) ions form a blue precipitate
  • Iron(II) ions form a green precipitate
  • Iron(III) ions form a brown precipitate
• Anions can be identified through specific tests:

  • Carbonate: forms carbon dioxide gas with dilute acid
  • Chloride: forms a white precipitate with silver nitrate and nitric acid
  • Bromide: forms a cream precipitate with silver nitrate and nitric acid
  • Iodide: forms a yellow precipitate with silver nitrate and nitric acid
  • Sulfate: forms a white precipitate with barium chloride and hydrochloric acid
• A solution with a pH value of 7 is neutral (neither acidic nor basic).
• The pH scale is logarithmic, meaning that the difference between two adjacent values on the scale represents a tenfold change.
• Acidic solutions have lower pH values than neutral ones, while alkaline or basic solutions have higher pH values.
• The pH scale ranges from 0-14.
• Acids are proton donors, while bases are proton acceptors.
• Strong acids completely ionize in water, while weak acids only partially ionize.
• Indicators are compounds that change color at a particular pH range, indicating whether a solution is acidic, neutral, or alkaline.
• Bases have a pH greater than 7.
• Universal indicator changes color from red to purple to blue to green depending on its concentration and the pH of the solution it's added to.
• Strong acids completely ionize in water to produce H+ ions.
• Phenolphthalein turns pink when added to an alkaline solution but remains colorless in acidic solutions.
• Weak acids only partially ionize in water to produce H+ ions.
• Strong acids completely dissociate into their component ions when dissolved in water, while weak acids only partially dissociate.
• Weak acids can be titrated using strong bases to determine their concentration.
• Titrations involve adding a known volume of one substance to another until they react completely.