2.3 Quantitative Chemistry And Analysis Flashcards
Define relative atomic mass (Ar)
The average mass of the atoms in an element, relative to the mass of 12C. It is an average value for the isotopes of the element.
Define relative molecular mass
The sum of the relative atomic masses of the atoms in the numbers shown in the formula.
What is the definition of empirical formula?
Simplest whole number ratio of atoms in a compound
What is paper chromatography used for?
Paper chromatography is used to analyse coloured substances, such as the coloured pigments in plants and artificial colours used as food additives.
Why does paper chromatography work?
some of the coloured substances are better at dissolving in the liquid than they are at bonding with the paper, so they travel further up the paper.
How does paper chromatography allow for the detection of similar substances?
Substances are the same if they have the same colour and they travel the same distance up the paper.
What are some of the benefits of using machines for instrumental analysis?
Fast
Accurate (they identify elements and compounds)
Sensitive (they can detect very small amounts of a substance in a small amount of sample)
In paper chromatography what does a longer distance traveled show?
The substances are more soluble
What is an isotope?
An atom of the same element which contains the same numbers of protons (and electrons) but different numbers of neutrons.
How do you calculate the amount of moles in a substance?
Mass (g) divided by relative formula mass.
Mass (g) / Mr
How do you calculate the percentage by mass of particular elements in a compound?
Percentage by mass of the particular element in a compound = 100 X (relative mass of all the atoms in the compound / Mr)
Calculate the percentage of O in H2O:
O - 16
H - 1
Mr - 18
100 X (16/18) = 88.9%
