Relative Masses Flashcards
(11 cards)
What is the concept of relative masses used for?
To compare the mass of atoms, elements, and compounds
Relative masses are used because atoms are very small, making direct comparison difficult.
Define relative atomic mass.
Mean mass of atoms of the element compared with 12th of the mass of a carbon-12 atom
Relative atomic mass accounts for the slight variations in atomic mass among isotopes.
Where can relative atomic mass values be found?
On the periodic table in your exam paper
These values can be looked up when required during exams.
What is relative molecular mass?
The sum of the relative atomic masses of all the atoms present in a molecule
This term is used for molecules with simple covalent structures.
What is relative formula mass?
The sum of the relative atomic masses of all the atoms in the formula of a substance
This term is applied to substances with giant structures.
How is relative molecular mass calculated for ethanol (C2H5OH)?
C: 24.0, H: 6.0, O: 16.0, total = 46.0
Ethanol has 2 carbon atoms, 6 hydrogen atoms, and 1 oxygen atom.
What is the relative molecular mass of hydrated copper sulfate (CuSO4·5H2O)?
249.6
Calculation includes contributions from copper, sulfur, oxygen, and water molecules.
What does the notation ‘·5H2O’ indicate in a chemical formula?
5 water molecules are attached to the copper sulfate crystals
Such crystals are referred to as hydrated crystals.
Do relative masses have units?
No
Relative masses are ratios compared to the mass of an atom of carbon-12.
What is the precise relative atomic mass of sulfur?
32.1
This is more accurate than the commonly recalled value of 32.
Calculate the relative formula mass of Mohr’s salt, (NH4)2Fe(SO4)2·6H2O.
Calculate based on the sum of the relative atomic masses of each component
This includes nitrogen, hydrogen, iron, sulfur, oxygen, and water molecules.
