C4. Stoichiometry
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Define Relative atomic mass
average mass of isotopes of an element compared to 1/12th of the mass of an atom ¹²C
Define the Molecular formula
the number and type of different atoms in one molecule
Define relative molecular mass
sum of the relative atomic masses (Mᵣ)
Relative formula mass
Mᵣ, is used for ionic compounds
Define Mole
Symbol ‘Mole’ is the unit of amount of substances, 1 mole contains 6.02 x 10²³ particles, e.g. Atoms, Ions, molecules. This number is called the Avogadro constant
Mole of atoms [2]
=6.02 x 10²³ this is called Avagadro’s number
Steps to reacting masses [4]
n=m/Mr 1) identify 2 substances 2) n,m,Mᵣ 3) Calculate n. of moles + consider ratios (1:1) 4) calculate missing mass
define Molar mass Mᵣ
Mass of 1 mole of a substance is a molar mass - Relative formula mass in grams
Describe what a limiting reactant is
The reactant that is used up the fastest
Explain why particular reactants are added in excess
Worked example of limiting reactant
2Ca + O₂ –> 2CaO n 2.0 n 2.0 m 80g m 64g M
ratio of 3:2 is
ratio of 3:2 is ÷2, x3
state the equations [2]
n = m/Mᵣ n = V/Vm
state conversion of cm³ and dm³
1000cm³ = dm³ cm to dm –>
state conversion of cm³ and dm³
1000cm³ = dm³ cm³ to dm³ –> ÷ by 1000 dm³ to cm³ –> x by 1000
define Molar mass volume
volume occupied by one mole of any gas, at room temperature and pressure The molar volume is equal to 24 dm³ (24,000 cm 3) (24,000 cm 3)
(Mole Equation) Example: determine the number of moles in 95g of MnO₂
Example 1: Determine the number of moles in 95g of MnO₂. Solution: Mass of MnO2 = 95g Mass of one mole MnO2 = 86.94g Number of moles formula is n = m/Mr Number of moles = 95 / 86.94 Number of moles = 1.092 mol
(Reacting masses simple ratios e.g. 1:2) Example: 4.8g of magnesium ribbon reacts in a solution f hydrochloride acid containing 7.3g of HCL
Example: 4.8g of magnesium ribbon reacts in a solution f hydrochloride acid containing 7.3g of HCL Mg (s) + 2HCL (g) ⟶ 2 MgCL₂ + H₂ Step 1. calculate the moles of magnesium used in the reaction n = m/Mr Mg 2HCL n = 0.2 ml n = 0.2 m; m = 4.8 m = 7.3 Mᵣ = 24 Mᵣ = 36.5 step 2. find the ratio of Mg to MgO using the molar ratio from the balanced equation 2Mg : 2MgO 1 : 2 0.2 : 0.4 Mg is in excess HCL is the limiting reactant
Metal ions are ____ most non-metals ions are
positve, negative
ionic compounds are formed when _____ react with ______
ionic compounds are formed when metals react with non-metals