C3.1 INTRO

• formula of ammonium

  NH4+
• formula of hydroxide

  OH-
• formula of nitrate

  NO3-
• formula of sulphate

  SO4(2-)
• formula of carbonate

  CO3(2-)
• formula of phosphate

  PO4 (3-)
• how do you balance equations?

  same number of atoms of each element on either side of the equation in accordance with the Law of Conservation of Mass
• in a half equation, what does the left side show?

  gain of electrons

  e.g. Cl2 + 2e- = 2Cl-
• in a half equation, what does the right side show?

  loss of electrons

  e.g. Na = Na+ + e-
• what is the Avogadro constant?

  6.022 x 10^23 (number of particles in one mole of a substance)
• how many atoms are in one mole of sodium?

  6.022 x 10^23
• • The mass of 1 mole of a substance is known as the molar mass
  • For an element, it is the same as the relative atomic mass written in grams
  • For a compound it is the same as the relative formula mass or relative molecular mass in grams
• mass = moles x molar mass
• mass of 1 atom or molecule = molar mass / Avogadro constant
• what is the law of conservation of mass?

  no matter is lost or gained during a chemical reaction

  • total mass of reactants is equal to the total mass of the products
• why can the mass change?

  the presence of a gaseous reactant/product

  in a non-enclosed system, if the gas is allowed to escape, then the total mass will decrease
• • The reagent that is used up first is the limiting reactant, as it limits the duration of the reaction and hence the amount of product that a reaction can produce
  • The one that is remaining is the excess reactant
  • The limiting reagent is the reactant which is not present in excess in a reaction
  • The amount of product obtainable is therefore directly proportional to the amount of the limiting reagent added at the beginning of a reaction