C2.3 Atomic structure, analysis and quantitative chemistry Flashcards
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
very small
What is the mass number of an atom?
The total number of protons and neutrons
What is an isotope?
Atoms of the same element that have a different number of neutrons.
What does the relative atomic mass of an element compare the mass of atoms with?
with the carbon 12 isotope
What is the relative formula mass of a compound?
the sum of the relative atomic masses in a compound
What is the relative mass of a proton?
1
What is one mole of a substance?
The relative formula mass of a substance in grams
How do you find the number of moles of a substance?
number of moles= mass (g) divided by relative formula mass
moles, mass, ram
How can elements and compounds be detected and identified by?
using instrumental methods
What are some advantages of using instrumental methods to detect and identify elements and compounds?
- accurate
- sensitive
- rapid
- useful when the sample is very small
Describe paper chromatography
can be used to identify additives and colourings in foods.
extract colour from food by placing it on a pencil baseline on filter paper in a beaker with solvent
keep the baseline above the level of solvent.
the solvent will seep up the paper, taking dyes with it. Different dyes form spots at different places.
In paper chromatography, why do we use pencil to draw a base line not pen?
pen will dissolve in the solvent and confuse the experiment
In paper chromatography, why might you put a lid on the beaker?
to prevent evaporation of solvent
What does GC-MS stand for?
gas chromatography linked to mass spectroscopy
Describe how a GC-MS works
- different substances, carried by a gas, travel through a column packed with solid material, at different speeds so that they become separated.
- The number of peaks on the output of a gas chromatograph shows the number of compounds present.
- the position of the peaks on the output indicates the retention time
- the output from the gas chromatography column can be linked to a mass spectrometer, which can be used to identify the substances leaving the end of the column
- the mass spectrometer can identify substances very quickly and accurately and can detect very small quantities. It also gives the relative molecular mass of each substance separated in the column.
in GC-MS, what shows the number of compounds present?
the number of peaks on the output of a gas chromatograph
in GC-MS, what indicates the retention time?
the position of the peaks on the gas chromatograph
In GC-MS, how can you tell the molecular mass?
by reading off the molecular ion peak
In GC-MS, what is the retention time?
the time taken for a substance to travel through the column
How can you work out the percentage of an element in a compound?
% of element = relative mass of element divided by relative formula mass of compound
x100
What is a reversible reaction?
a reaction where the products of the reaction can themselves react to produce the original reactants.
Why is it not always possible to obtain the calculated amount of product? (3 reasons)
- The reaction may not go to completion because it is reversible
- some of the product may be lost when it is separated from the reaction mixture
- Some of the reactants may react in ways different from expected
The amount of product obtained from a reaction is know as…
the yield
