Topic 3 - Equations, Calculations & Electrolysis Flashcards
relative atomic mass (Ar)
average mass of all isotopes of that element
relative formula mass (Mr)
sum of relative atomic masses in a compound
how to find percentage mass of an element within a compound
Ar of element / Mr of compound
Moles equation
Moles = mass / Mr
Avogadro Number
6.02x10^23
conservation of mass
in a chemical reaction, no atoms are created or destroyed, the bonds are just changed
why might the mass of products be less than the reactants?
- reactants could have spilled
- products (if gas) could have floated off
why might the mass of products be greater than the reactants?
- gas from air reacting with reactants
Calculating mass in reactions
- write out balanced equation
- find moles of known substance (moles = mass/mr)
- find moles of unknown substance (using molar ratio)
- find mass of unknown substance (mass = moles x mr)
Volume of gas at RTP equations
Volume = moles x 24 dm^3
Volume = moles x 24,000 cm^3
cm -> dm = /1000
Concentration equation
concentration = mass / volume
molecular formula
actual number of atoms of each element in a compound or molecule
empirical formula
smallest whole number ratio of each element in a compound or molecule
Finding empirical formula
Create a table with all elements separated
- identify mass
- find moles (mass/mr)
- divide by smallest number of moles
- find ratio!
Finding molecular formula
- Divide unknown compound’s Mr by Mr of empirical formula
- multiply all numbers in formula by the result of division