chem 1-2

• Collecting gas methods:

  • Displacement of water: for insoluble and slightly soluble gases like hydrogen and oxygen carbon dioxide
  • Downward delivery of gas: for gases soluble or very soluble in water, denser than air (mixture) like hydrogen chloride and sulfur dioxide
  • Upward delivery of gas: for gases very soluble and less dense than air, rising to the top like ammonia
• Mixture: two or more substances not chemically combined

  • Pure substance: made up of only one element or compound
  • Substance with impurities: different chemical composition from pure substance
• Steps for separating solid-solid mixtures with a suitable solvent:

  1. Using a suitable solvent that can separate solid-solid mixtures where only one solid is soluble

  2. Filtration to separate insoluble solid from liquid, collecting residue and filtrate

  3. Evaporation to dryness to obtain a soluble solid from a solution by heating until the solvent boils off, ensuring the solvent has a lower boiling point than the solute and the solids do not decompose on heating
• 4. Crystallisation to obtain a soluble solid from a solution by allowing a hot saturated solution to cool, filtering to collect crystals, and drying them between filter paper
• Simple distillation: separates solvent from solute, like water from salt, with the liquid collected called distillate
• Magnet used to separate magnetic from non-magnetic compounds of metal that can be magnetic
• Two liquids that do not dissolve in each other are immiscible liquids
• Fractional distillation: separates miscible liquids using glass beads for larger surface area, with the liquid of lower boiling point collected first, and the temperature in the fractionating column increasing to reach the boiling point of the other liquid
• Evaporation: particles near the surface of a liquid with enough kinetic energy to escape as gas below the boiling point, with oxygen diffusing slower than nitrogen and being denser than air
• Kinetic particle theory:

  • Solid: very strong force of attraction, closely packed and orderly, vibrating at fixed positions with low energy
  • Liquid: strong force of attraction, closely packed and disorderly, sliding over each other with low energy
  • Gas: weak force of attraction, far apart and disorderly, moving at high speeds in all directions
• Changes in state of matter:

  • Heating increases kinetic energy until melting point, where particles vibrate in fixed positions
  • Melting starts when forces of attraction are overcome, with temperature remaining constant
  • Boiling occurs when forces of attraction are overcome, with temperature constant until gaseous state is reached
• Reverse changes:

  • Condensation/boiling, freezing/melting
  • Boiling point of a pure substance is the same as the condensation point
• Sublimation: particles at the surface of a solid having enough energy to escape as gas
• Diffusion: particles moving from higher to lower concentration, with rate increasing as temperature increases and decreasing as particle mass increases
• Room temperature is 25°C
• Curve in liquid is the meniscus, concave for upward and convex for downward
• Chromatography uses a locating agent for colorless substances
• Measuring purity methods:

  • Chromatogram
  • Melting and boiling point of substance, with impurities lowering melting point and raising boiling point
  • Freezing point of a substance in liquid state is the same as the melting point in solid state
• Specific reactions:

  • Hydrogen chloride is very soluble in water
  • Concentrated sulfuric acid dries carbon dioxide and nitrogen, displacing air
  • Ammonia reacts with sulfuric acid
• Quicklime collects ammonia, excluding hydrogen chloride

  • Calcium chloride collects gases hydrogen and nitrogen
• Measurement conversions:

  • 1 dm = 10^-1
  • 1 cm = 10^-2
  • 1 micrometre = 10^-6
• Common measurement tools and their smallest divisions:

  • Metre rule: 0.1 cm to 0.05 cm
  • Electronic balance: 0.01 g
  • Digital stopwatch: 0.01 s nearest second
  • Beaker: common sizes, read water level below the meniscus
  • Measuring cylinder: 0.05 ml for 10 ml, 1.0 ml for 50 ml, 10 cm3, 25 cm3, etc.
  • Pipette filler: for fixed volume liquids
  • Burette: smallest division of 0.01 cm3 or 0.05 cm3
• condensor:Cool the vapour and turn it into a liquid To ensure maximum efficiency in condensing the vapour / to ensure the most amount of distillate is collected