3) Amount of Substance

• What is the equation that links number of moles, number of particles, and the Avogadro's constant?

  Number of moles = Number of particles / Avogadro's constant
• What is the equation that links number of moles, mass, and molar mass?

  number of moles = mass/ molar mass
• What is the unit of mass, when it is used to calculate the number of moles of a substance.

  Grams (g)
• What is Avogadro's constant:

  • Avogadro's constant is the number of particles in 1 mole of a substance.
  • The value of the constant is 6.02 x 10^23
• What is a mole? (mol)

  A mole is a unit of measure the allows us to count extremely large number of particles.
• What is the unit for molar mass?

  g mol^-1
• What is the equation that links concentration, number of moles, and volume?

  Number of moles = concentration x volume
• What is the unit for concentration?

  mol dm^-3

  g dm^-3
• What is the equation the links concentration, mass, and volume?

  Mass (g) = concentration (g dm^-3) x volume
• How do you convert between units of dm^3 and cm^3

  dm^3 ----> cm^3 (x1000)

  cm^3 ----> dm^3 (/1000)
• What is the equation that links number of moles, gas volume, and molar gas volume?

  Volume of gas (dm^3) = moles x molar gas volume
• • 1 mole of any gas, at room temperature and pressure, is 24.0 dm^3
  • The volume is dependant on the amount of particles, not the size of the particles.
• What is room temperature (in K) and pressure in (kPa)

  • Temperature: 293K
  • Pressure: 101kPa
• What is the ideal gas equation?

  pV = nRT

  • p = Pressure (Pa)
  • V = Volume (m^3)
  • n = number of moles (mol)
  • R = Molar Gas Constant (8.314)
  • T = Temperature (K)
• Main reason real gases do not follow ideal gas predictions perfectly?

  1. Intermolecular attractions/ forces exist between particles
• • 1 atm = 101 000 Pa
  • 1 KPa = 1000 Pa
  • 1m^3 = 1000dm^3 = 1000 000cm^3
  • 1m^3 = 1000L
  • Temp(K) = Temp(°C) + 273
  • Molar Gas Constant = 8.314
• Difference between a hydrated salt and an anhydrous salt:

  • A hydrated salt is one in which the solid crystals contain water of crystallisation.
  • An anhydrous salt is one in which the solid crystals do not contain water of crystallisation.
• What is the empirical formula?

  Simplest whole number ratio of atoms of each element in a compound.
• What is the molecular formula?

  The molecular formula is a formula that shows the number of atoms of each element within a compound.
• In the compound CuSO4.5H2O, how many water molecules are there per copper sulphate molecule?

  5
• What is water of crystallisation?

  Water of crystallisation refers to water molecules that are chemically bound to the substance, such as a salt, forming an integral part of its crystal structure.
• Experimental procedure: Hydrated Copper Sulphate ----> Anhydrous Copper Sulphate + H2O

  1. Put CuSO4.xH2O into crucible
  2. Measure the mass of crucible and crucible and salt
  3. Heat until the colour change pale blue
  4. Measure mass again
  5. Repeat until mass stays constant
• What does it mean if a reactant is in excess?

  Excessive amount, some left over at the end of the reaction.
• What is a limiting reactant?

  • A reactant that all gets used up.
  • So limits how much product can be made (as there is no more that can react)
• What do we mean by molar ratio?

  Stoichiometry - the ratio of the amount (moles) of each substance in a balanced equation.
• What is the formula for percentage yield?

  Actual yield/ theoretical yield x 100
• Percentage yield of a reaction:

  • Percentage yield is a measure of how efficient a reaction is.
• 3 reasons why the percentage yield of a chemical reaction may be less than 100%

  1. They reactant may not all react (e.g. because the reaction is very slow or reaches reaches equilibrium)
  2. Some products may be lost by practical losses
  3. There may be unwanted side reaction, meaning that other product are produced as well.
• What is atom economy?

  Atom economy is a measure of the percentage of reactant atoms end up in the final desired product (not in by-products).
• Equation of Atom Economy

  Formula mass of desired product / Sum formula mass of all reactants x 100
• • High atom economy = greater proportion of products become useful products
• Problem with low atom economy:

  1. Less sustainable as it uses more raw materials/ reactants used ---> more expensive to operate.
  2. Produces more waste products which has to be disposed of, which could be expensive and/or harm the environment.
  3. (≈) Increased costs associated with separating the desired products from the increased amount of waste products
• • All reaction with a single product will have an atom economy of 100%