1.2 Amount of substance

• What are these conversions?

  1ml = 1 cm³

  1m³ = 1000 dm³

  1m³ = 1000000 cm³

  1dm³ = 1000 cm³
• What is the ideal gas equation formula?

  PV = nRT
• How do you convert from Celsius to Kelvin?

  +273
• Why do we use carbon¹² in the formula to work out relative atomic/molecular mass?

  Carbon is very common and we use isotope 12 as it's stable
• What is avagradro's constant?

  6.022x10²³
• What is the formula for mass and moles?

  Amount, n = mass, g / Mr
• 4x + y -> 2z.

  1. How many moles of x and y do we need to get 1 mole of z?

  2. If we react 2moles of x with excess y what is the maximum of z we can get?

  1. 2 moles of x and 0.5 moles of y.

  2. We can get a maximum of 1 mole of z.
• What's the equation for moles of solution, linking; n, concentration and volume?

  n = concentration, mol dm^-3 x volume, dm^3
• Why are back titrations carried out?

  To analyse a base (or acid) that does not react easily or quickly with an acid (or base)
• How does a back titration work?

  A base (or acid) is treated with excess acid (or base), then the left over acid (or base) is titrated. You can then work back to find out the original base (or acid).
• What is the empirical formula?

  The simplest whole number ratio of atoms of each element in a compound e.g. C₂H₆ = CH₃, SO₂ = SO₂, P₂O₃ = P₂O₃.
• What is a molecular formula? (definition)

  The actual number of atoms of each element in a molecule or compound.
• Convert these empirical formula ratios into whole number ratios

  1:1.98:1.

  1:1.48:1.

  1:1.28:1.

  1:1.75:1.

  1:1.98:1 --> 1:2:1 Close enough to round to 2.

  1:1.48:1 --> 1:1.5:1 --> 2:3:2 Have to round to 1.5 then times by 2.

  1:1.28:1 --> 1:1.25:1 --> 4:5:4 Have to round to 1.25 then times by 4.

  1:1.73:1 --> 1:1.75:1 --> 4:5:4 Have to round to 1.75 then times by 4.
• What is the formula for atom economy?

  % atom economy = (mass of desired product x 100) / total mass of reactants
• What is the equation for percentage yield?

  Percentage yield = (actual mass of product x 100) / theoretical mass of product
• Give three reasons why percentage yield may decrease.

  Losses during reaction (state the reaction type if provided).

  Human error (inaccurate measurement).

  A side reaction may have occurred.
• x.5H₂O How many waters of crystalisation does x contain?

  5
• What does it mean if a compound is hydrated?

  It contains water of crystalisation x.H₂O
• What does it mean if a compound is anyhydrous?

  It does not contain any water of crystalisation
• A student heated a solid sample of Na2CO3. xH2O for 1 minute to remove water.

  Why might the water they calculated to have removed in the experiment not match the theoretical value? What can they do to fix this?

  They may not have heated it for long enough. To fix this they can just heat it for longer.
• Barium hydroxide is dissolved in a beaker containing 150cm3 of distilled water, how could this solution be used to make 250cm3 of a 0.1mol dm-3 barium hydroxide solution.

  Transfer the solution into a volumetric flask then add washings using distilled water up to 250cm3. Shake the solution to mix it.
• Why is it good practice to rinse the pipette with the solution to be used before a titration?

  This will remove any water or contaminants so that the solution is not diluted.
• In the ideal gas equation, PV=nRT:

  P = pressure of gas and has the units Pa

  V = volume of gas and has the units m ^3

  n = moles of gas

  R = gas constant

  T = temperature and has the units K
• How would you work out which of these have a different number of atoms to the rest?

  • 2 moles of nitrogen.
  • 2 moles of water.
  • 4 moles of argon.
  • 2 moles of oxygen.

  Times the number of moles by the number of atoms present in the molecule then times that by Avogadro's constant.

  E.g. 2 moles of water, H2O: 2 x 3 x 6.022x10^23 = 3.612x10^24

  E.g. 2 moles of nitrogen, N2: 2 x 2 x 6.022x10^23 = 2.408x10^24