2.1 Atoms and Reactions Flashcards
Define relative atomic mass
The weighted mean mass compared with 1/12th mass of carbon-12
Define relative molecular mass.
The mass of a molecule is measured as the relative molecular mass by comparison with carbon-12.
Order of scientists that developed knowledge of the atom.
Democritus, John Dalton, Joseph John Thompson, Joseph John Thompson, Ernest Rutherford, Niels Bohr
What did Democritus do?
Developed the idea of ‘atomos’, meaning invisible in Greek. The idea that you would eventually reach a indivisible particle.
What did John Dalton do?
In 1808, he stated that:
- atoms are tiny particles that make up elements
- cannot be divided
- all atoms of a given element are the same
- atoms of one element are different to those of any other element
What did Joseph John Thompson do in 1898?
Discovered that cathode rays were a stream of particles with the following properties:
- negative charge
- deflected by both a magnet and an electric field
- very small mass
- cathode rays were electrons and so split and previous ideas were disproved
What did Joseph John Thompson do in 1904?
Develops idea that atoms are made of electrons scattered unevenly within an elastic sphere surrounded by positive charge - the plum pudding model.
What did Rutherford do?
In 1910, oversaw Geiger and Marsden fire helium nuclei at gold foil. Deflection. In 1911, he proposed that positive charge and most of its mass were at nucleus and negative orbit.
What did Bohr do?
He worked under Rutherford in 1913 and added that electrons are in orbits and that each orbital could have a set number of electrons. Explained spectral lines and different energy with distance from the nucleus.
What do we use mass spectroscopy for?
- to identify an unknown compound
- find the relative abundance of each isotope of an element
- determine structural information about molecules
Define isotope.
Atoms of the same element with different numbers of neutrons and different masses.
Define relative isotopic mass.
Mass compared with 1/12 the mass of carbon-12.
What is the Avogadro constant?
Number of particles per mole. Number of atoms per mole of carbon-12 isotope.
Define empirical formula.
The simplest whole number ratio of atoms of each element present in a compound.
Define molecular formula.
The number and type of atoms of each element in a molecule.
Which atoms do not usually form ions?
Be, B, C and S
How many Pa is 1 atm?
101325 Pa
How many K is 0 degrees Celsius?
273
What is the value of the gas constant?
8.314 Jmol-1K-1
What is n equal to at RTP?
V/24
Percentage yield equation
Actual amount/theoretical amount
Atom economy equation
Molecular mass of desired products/ sum of molecular masses of all products
What are substances called that behave as both acids and bases?
Amphoteric substances
What are amphoteric substances?
Substances that can behave as both acids and bases.
What is water of crystallisation?
Water molecules that form an essential part of the crystalline structure of a compound.
What is the oxidation number of peroxides?
-1
Oxidation number of oxygen?
-2
Oxidation number of hydrogen?
+1
Oxidation number of metal hydrides?
-1
What is a titre?
Final reading minus the initial reading.
What are the main two indicators for acid/alkali reactions?
Methyl orange and phenolphthalein
What does methyl orange do?
Turns yellow to red when adding acid to alkali.
What does phenolphthalein do?
Turns pink to colourless when adding acid to alkali.
Why is universal indicator not good for titrations?
The colour change is too gradual.
What is the unknown solution in a titration known as?
The analyte.
What is reaction stiochiometry?
How many moles of one reactant react with how many moles of another reactant.
What are polyprotic acids?
Acids that donate more than one proton.
Examples of a diprotic acid?
Sulphuric acid,carbonic acid and hydrogen sulfide.
Give example of triprotic acid.
Phosphoric acid.
Formula for carbonic acid?
H2CO3
Formula for hydrogen sulfide?
H2S
What is meant by one mole of substance?
Amount of substance which contains as many particles as there are carbon atoms in 12g of carbon-12
What is used as the standard measurement of relative isotopic mass?
Carbon-12
What happens to the oxidation state if a compound is oxidised?
Increases
What happens to the oxidation state if a compound is reduced?
Decreases
Units of pV=nRT?
p is Pa
V is m^2
T is in K
Conversion from cm^3 to m^3
1 m3 = 1000 dm3 = 1 000 000 cm3
Conversion from bar to Pa
1 bar = 100 kPa = 100000 Pa
Conversion from atm to Pa
1 atmosphere = 101325 Pa
Why does water have a concentration of 56 moldm-3?
1dm3 of water = 1000g
n=1000/18=56 moldm-3
the benefits for sustainability of developing
chemical processes with a high atom economy
fewer natural resources and create less waste
What are concordant titres?
within 0.1cm3
