allery - acids

• Acids

  proton donors
• bases

  proton acceptor
• when acids and bases react

  they form a reversible reaction

  acids >>>> HA +H2O<>H3O+ +A-

  bases >>>> B + H2O<> BH+ + OH-
• alkali

  is a soluble base

  produce OH- ions when added to water
• acids produce

  acids produce H3O+ when they react with water

  aka H+
• Weak acid

  backwards reaction is favoured so not many H+ protons are produced

  example - CH3COOH(Ethanoic acid ) and other carboxylic acids

  CH3COOH <> CH3COO- + H+backward
• Strong acid

  forwards reaction favoured strongly

  lots of H+ produced

  example - HCl (hydrochloric acid )

  H2SO4- (sulfuric acid )

  HNO3(nitric acid )

  equation -- HCl<> H+ + Cl-
• Strong base

  forward reaction favoured strongly

  lots of OH- ions produced

  example - NaOH (sodium hydroxide )

  KOH-potassium hydroxide

  equation NaOH<> Na+ + OH-
• Weak base

  backwards reaction favoured so not many OH- ions produced

  example - NH3 ammonia

  equation- NH3 + H2O <> NH4+ + OH-
• Polyprotic acids

  acids that can donate more than one proton
• monoprotic acid

  example nitric acid HNO3

  1 mole of NHO3 will produce one mole of H+ ions
• diprotic acid

  example sulfuric acid is diprotic

  1 mole of H2SO4 will produce 2 moles of H+ ions
• Triprotic acid

  example 1 mole of phosphoric acid(H3PO4) will produce 3 moles of H+ ions
• Acids and bases

  acids react with bases to form salts which are pH-neutral

  H+ ions produced from acids react with OH- ions produced from alkalis we make water which is neutral

  H+ (aq) + OH (aq) <> H2O(l)

  salts are made from the metal from the base and the non metal from the acid

  be careful with ammonia bc it doesn't produce OH- ions directly it reacts with water first and accepts a proton to produce ammonium ions (NH4+) and OH- ions

  Ammonia reacts with acid to form ammonium salts but no water
• Metals reacting with acids

  metal + acid >>> salt +hydrogen

  remove spectator ions from aqueous compounds
• Metal oxides reacting with acids

  metal oxide + acid -> salt + water

  remove spectator ions from aqueous compounds
• metal hydroxides reacting with acids

  metal hydroxide + acid -> salt + water
• metal carbonate reacting with acids


  metal carbonate + acid >>>>>>>> salt + carbon dioxide + water
• The mole solutions

  concentration (moldm-3) x volume (dm3)
• Titrations

  can be used to work out the concentration of an acid or an alkali

  1) have acid or alkali in burette with known concentration

  2) have an acid or alkali with unknown concentration but known volume in conical flask add a few drops of indicator too

  3) add the chemical in the burette to the conical flask until the indicator changes colour -aka end point add few drops near end point

  4) read how much chemical was added from the burette to neutralise the chemical in the conical flask - read bottom of meniscus - always read at eye level

  5) record result to 2 dp and repeat until you get 2 results that are concordant ( within 0.10 cm3 of each other)
• Indicators for titration

  phenolphthalein

  acid - colourless

  alkali - pink
• indicators for titration - methyl orange

  acid - red

  alkali - yellow
• Making standard solutions

  used on titrations

  have a known concentration

  can titrate standard solution against the unknown concentration in the conical flask

  made from solids with a known mass dissolved in water to fixed volume in volumetric flask - we can work out concentration of this too
• method in making standard solution

  1) weigh out amount of solid precisely using a balance and plastic /glass weighing boat

  2) transfer the solid from weighing boat to a beaker wash any solid left behind into the beaker using deionised water

  3) dissolve solid fully using deionised water stir to ensure the solid is dissolved fully

  4) transfer solution to volumetric flask use a funnel to avoid spillage and rinse the beaker and glass rod into the flask to make sure most of the solution is transferred

  5) fill use more deionised water to fill to the graduation line be careful not to go above the line use a pipette to fill to the line when you get near

  6) mix invert the flask a few times make sure you put a lid on it first this ensures the solution is thoroughly mixed and ready to use
• standard solution calculations

  1- work out the number of moles of solution you want to make - conc x volume

  2- calculate the mass - moles x relative formula mass (gmo-1)

  if you want it to be stronger add larger mass
• titration calculations - conc

  can be used to work out conc of an acid or an alkali

  1- balance out equation

  2- calc number of moles - conc x volume

  3- use the equation to find out molar ratio in order to work out moles

  4- calculate conc = moles /volume
• titration calculations - volume

  1- write out equation and balance

  2 - work out moles conc x volume

  3- use equation to find molar ratio in order to work out moles (stoichiometry)

  4- calculate volume using moles /conc divided by 1000 to get cm3
• Calculating volumes

  Volume(cm cubed) = Number of moles x1000

  . ———————————-

  . Concentration
• theoretical yield

  mass of product that should be formed in a chemical reaction
• theoretical yield assumes

  no chemicals are lost in the process
• calculating theoretical yield

  use masses of reactants and a balanced equation to calculate theoretical yield for a reaction

  1) work out how many moles of the limiting reagent you have

  2) use the equation to work out how many moles of the product you would expect that much reactants to make

  3) calculate the mass of that many moles of product and thats the theoretical yield
• calculating percentage yield 


  actual yield

  zxzxzxzxzxzxxzxzx x100

  theoretical yield