Quantitative Chemistry Flashcards
Define relative atomic mass
Relative atomic mass of an atom is the mass of the atom compared with that of the carbon-12 isotope, which has a mass of exactly 12
Define relative formula mass
A weighted mean of the mass numbers of a substance.
What is the mole?
The mole is an amount of a chemical
Calculate the % of an element in a compound
Mass of element in one mole of the compound
——————————————— x 100
Mass of one mole of the compound
Formula for the number of moles in a compound
Mass
——-
RFM
Mole equation
Moles = mass (g)
————-
rfm
How to calculate % yield
- Calculate moles
- Mole x RFM of both elements
- mass (g/kg)of compound provided
——————————————— x 100
Mole x RFM of both elements
Find RFM
Total of all the atomic masses of all the atoms in the formula of the element or compound
Calculate the mass of 3 moles of ammonia
NH3 14 + (3x1) = 17 no. of moles x RFM 3 x 17 = 51g
Calculate the percentage of water of crystallisation in a compound
% water = total RFM of water
————————— x 100
total RFM of compound
List possible reasons why the percentage yield of a product is less than 100% (3)
- In some reactions it may be impossible to separate the product fully out of the reaction mixture leading to less than 100% yield
- As a result of side reaction (e.g producing carbon monoxide inside of carbon dioxide)
- Because the reaction is reversible and may not go to completion
Empirical formula
The simplest whole number ratio of atoms of each element present in a compound
Hydrated definition
Crystalline and containing water molecules
Anhydrous definition
A substance containing no water molecules
Reasons why the percentage yield is not 100% (3)
- Loss by mechanical transfer (from one container to another )
- Loss during a separating technique (filtration or using a separating funnel)
- Reaction is reversible
