c5

• concentration

  the amount or mass of a substance in a given volume of solution
• units of concentration

  • mol/dm^3
  • g/dm^3
• calculations for concentration

  • conc (mol/dm^3) = moles / volume (dm^3)
  • conc (g/dm^3) = mass (g) / volume (dm^3)
• how could you increase the concentration of a solution of hydrochloric acid?

  • increase the number of moles of hydrochloric acid
  • decrease the volume of the solution
• what equipment is required for a standard titration?

  • burette
  • conical flask
  • pipette and pipette filler
  • white tile
  • funnel
  • clamp and stand
• describe how to carry out a standard acid/alkali titration to find the concentration of the alkali

  1. add acid to burette
  2. use pipette to add 25cm^3 of alkali to a conical flask
  3. add a few drops of indicator to the conical flask
  4. record initial burette reading
  5. slowly add the acid to the conical flask, swirling the flask constantly
  6. when the solution in the conical flask changes colour, stop adding the acid and record the final volume in the burette
  7. calculate the total volume of acid added from the burette
• why must the conical flask be swirled during a titration?

  to ensure all the particles react
• why is a white tile used when carrying out a titration?

  the white tile is placed under the conical flask so that the colour change of the indicator is easier to see
• after an acid/alkali titration how can you calculate the concentration of the alkali if you know the concentration of the acid?

  1. multiply the concentration of acid by the volume from the burette to calculate the number of moles of acid
  2. use the balanced equation to work out the molar ratio of acid:alkali then calculate the number of moles of alkali that reacted using this ratio
  3. calculate the concentration of alkali by dividing the number of moles of alkali by the initial volume of alkali in the conical flask
• what is 1 cm^3 in dm^3?

  • 1 / 1000
  • = 0.001 dm^3
• define the molar volume of a gas

  the volume occupied by one mole of any gas at room temperature and pressure
• what is the molar volume of gas at room temperature and pressure?

  24 dm^3 / 24000 cm^3
• what is rtp?

  • room temperature and pressure
  • 20 degrees celcius
  • 1 atmosphere
• how can the volume of gas be calculated at rtp?

  volume at rtp (dm^3) = moles x 24
• how many moles of oxygen are there in 72 dm^3 of oxygen at rtp?

  • moles = volume / 24
  • = 72 / 24
  • = 3 moles
• why can the theoretical mass of a product be calculated if you know the masses of all the other reactants and products?

  the law of conservation of mass means that the total mass of the reactants must equal the total mass of the products
• 11 g of calcium carbonate is heated to produce 4.7g of carbon dioxide.

  what mass of calcium oxide is theoretically produced?

  • mass calcium carbonate = mass of carbon dioxide + mass of calcium oxide
  • mass of calcium oxide = 11 - 4.7
  • = 6.3g
• how can the theoretical mass of a product be calculated using the mass of one reactant only?

  • divide the mass of the reactant by its molecular mass to find the number of moles of this reactant
  • work out the molar ratio of reactant to product and use this to find the number of moles of the product (e.g. a 1:2 ratio means you would double the number moles of the reactant)
  • multiply the moles by molecular mass to find the theoretical mass of the product