chem

• bond become polar bc of large differences in electronegativity
• polar bonds are attracted to water molecules, making them soluble
• non-polar substances have no polarity so they don't dissolve in water
• water has high surface tension due to strong intermolecular forces between H2O molecules
• what is avogrado's constant?

  the number of C-12 atoms in 12g of carbon-12
• why do lone pairs repel more than bonding paris?

  bc the electrons in a lone pair are not involved in bonding and are thus free, the repulsion is higher
• the greater the difference in size of two atoms, the stronger the ionic bond formed
• red light (900nm) has a longer wavelength than purple light (200nm)
• lower pH values signify an increase in the concentration of H+ ions
• why is the true/actual value greater than the calculated value?

  bc insoluble salt is present

  not all water is lost (heat to constant mass)
• how to prepare a soluble salt?

  • heat solution in evaporating basin
  • don't evaporate all water bc crystals must form
  • leave to crystallise
• how to prepare an insoluble salt?

  • precipitation
  • filter
  • wash ppt. to remove physical impurities
  • leave to dry in oven
• outline 3 methods to measure the rate of a reaction?

  measure the change in volume of gas produced against a timer

  measure the change in pressure over time

  measure the concentration of substance at intervals
• preparing a (standard) solution?

  weigh mass of salt

  dissolve in small volume of deionised water

  transfer to a 250cm^3 volumetric flask using a funnel

  wash funnel and beaker

  transfer washing to flask

  add deionised water up to the 250cm^3 mark

  shake solution/invert flask to mix
• state the effect of a catalyst on a reaction in equilibrium?


  inc. rate of reaction (forward=backward)

  offers an alt. pathway w/ lower activation energy
• increase in temperature favours...?

  endothermic side (+ve 🔺H)
• decrease in temperature favours...?

  exothermic side (-ve 🔺H)
• increase in pressure favours...?

  side with fewer moles of gas (releases build up of pressure)
• decrease in pressure favours...?

  side with more moles of gas (bc pressure has been lost)
• increase in the concentration of the reactants favours...?

  the forward reaction to inc. the yield of products
• increase in the concentration of the products favours...?

  the backward reaction to reform the reactants
• endothermic sign?


  +ve 🔺H
• exothermic sign?


  -ve 🔺H
• 4 characteristics of a reaction at dynamic equilibrium?

  reversible

  rate of forward = backward

  conc. of products and reactants = constant

  closed system
• strong acid?

  acid that completely dissociates in water to produce hydrogen ions.
• weak acid?


  acid that only partially dissociates in water and has a low concentration of hydrogen ions.
• acid?

  proton donor (H+ ions)
• base?

  proton acceptor (H+ ions)
• alkali?


  base that dissolves/soluble in water.
• what is the test for halide ions?

  silver nitrate + nitric acid (to remove impurities {carbonates/hydroxides})

  Chloride: white ppt.

  Bromide: cream ppt.

  Iodide: yellow ppt.
• what is a further test to distinguish the halide ions after silver nitrate test?

  Chloride: add dilute ammonia = dissolve

  Bromide: add concentrated ammonia = dissolves

  Iodide: doesn't dissolve
• group 7 characteristics?

  down the group:

  • less reactive
  • MP + BP increases
  • oxidation ability decreases
• halide ion characteristics?

  Fluoride: gain electrons easily = easily reduced = best oxidising agent

  Iodide: easily oxidised = best reducing agent
• strontium flame test?

  crimson
• calcium flame test?


  orangey-red
• barium flame test?


  apple green
• group 2 solubility of carbonates?

  insoluble
• group 2 solubility of nitrates?

  soluble
• group 2 solubility of hydroxides?

  more soluble down the group
• group 2 solubility of sulfates?

  more insoluble down the group