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chemistry a level > Atoms, molecules and stoichiometry > Flashcards

Atoms, molecules and stoichiometry Flashcards

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1
Q

Unified Atomic Mass

Masses of atoms and molecules

A

one twelfth of the mass of a carbon-12 atom

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2
Q

Relative Atomic Mass

Masses of atoms and molecules

A

the weighted average mass of atoms in a given sample of an element compared to the value of the unified atomic mass unit

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3
Q

Define

Isotopes

Masses of atoms and molecules

A

atoms of the same element having
* same atomic number
* different mass number
* same proton number
* different neutron number

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4
Q

Relative Isotopic Mass

Masses of atoms and molecules

A

the mass of a particular atom of an element compared to the value of the unified atomic mass

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5
Q

Relative Molecular Mass

Masses of atoms and molecules

A

the weighted average mass of a molecule in a given sample of that molecule compared to the value of the unified atomic mass unit

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6
Q

Relative Formula Mass

Masses of atoms and molecules

A

the weighted average mass of one formula unit compared to the value of the unified atomic mass unit

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7
Q

What are Hydrated Compounds ?

A

compounds which contain a definite number of moles of water in their structure

e.g : CuSO4.H2O

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8
Q

Define ‘anhydrous’

A

containing no water of crystallisation

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9
Q

Mass Spectrometry

Accurate relative isotopic masses

A

the use of a mass spectrometer to measure the mass of each isotope present in an element

also compares how much of each isotope is present

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10
Q

Relative Isotopic Abundance

Accurate relative isotopic masses

A

the proportion of one particular isotope in a mixture of isotopes, usually expressed as a percentage

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11
Q

Molecular ion, M+

Accurate relative isotopic masses

A

the ion that is formed by the loss of an electron from the original complete molecule during mass spectrometry

this gives us the relative formula mass of an unnown compound

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12
Q

Fragmentation

Accurate relative isotopic masses

A

the breaking up of a covalent compound during mass spectrometry into smaller positively charged species

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13
Q

How does fragmentation take place ?

Accurate relative isotopic masses

A

it takes place when the single bonds of a covalent compound break up due to an electron bombardment, giving fragments

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14
Q

What is the most common cause of fragmentation ?

Accurate relative isotopic masses

A

the breaking of single bonds
* C-C
* C-H
* C-N

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15
Q

What does the molecular ion peak represent ?

Accurate relative isotopic masses

A
  • the heaviest ion
  • has the highest m/e ratio
  • not necessarily the most abundant ion
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16
Q

What does the base peak represent ?

Accurate relative isotopic masses

A
  • always the tallest peak
  • most common and abundant ion
17
Q

How are fragmentation patterns useful ?

Accurate relative isotopic masses

A

to determine the molar weight and structural formula of unknown molecules

18
Q

What is the importance of high resolution spectra ?

Accurate relative isotopic masses

A

allows us to distinguish between ions that appear to have the same mass on a low-resolution spectrum

19
Q

Molecular Formula

Accurate relative isotopic masses

A

shows the number and type of each atom in a molecule

20
Q

What is the [ M+1 ] peak ?

Accurate relative isotopic masses

A

a very small peak just beyond the molecular ion peak, caused by molecules in which one of the carbon atoms is the 13C isotope

21
Q

What is the [ M +2 ] peak ?

Accurate relative isotopic masses

A

helps us identify whether chlorine or bromine is present in an organic compound by comparing the relative heights of the peaks

22
Q

When is it one chlorine atom ?

[ M+2 ] peak

Accurate relative isotopic masses

A

if the [ M+2 ] peak is 1/3 of the M peak

23
Q

When is it one bromine atom ?

[ M+2 ] peak

Accurate relative isotopic masses

A

if the [ M+2 ] peak is equal to the height of the M peak

24
Q

Avogadro Constant

Amount of substance

A

the number of specified particles equivalent to the relative atomic mass or the relative molecular mass of a substance in grams

25
Q

Symbol of Avogadro Constant

Amount of substance

A

L

26
Q

Numerical Value of Avogadro Constant

Amount of substance

A

6.02 x 10^23

27
Q

Define the ‘mole’

Amount of substance

A

the amount of substance which contains 6.02 x 10^23 specified particles

28
Q

Specified particles

mole

A
  • atoms
  • molecules
  • ions
  • electrons
29
Q

Define ‘molar mass’

Amount of substance

A

the mass of a mole of substance in grams

30
Q

Stoichiometry

Mole calculations

A

The mole ratios of reactants and products shown in a balanced equation

31
Q

Empirical Formula

Mole calculations

A

The simplest whole number ratio of the elements present in one molecule or formula unit of a compound

32
Q

Molecular Formula

A
  • shows the actual number of each of the different atoms present in a molecule
  • used to write balanced equations and to calculate molar masses
  • it is always a multiple of the empirical formula
33
Q

Oxidation number ( oxidation state )

A

a number given to an ion/atom in a compound to represent how oxidised/reduced it is

34
Q

Compound ion

A

ions that contain more than one type of atom

35
Q

Spectator ions

A

Ions present in a reaction mixture which do not take part in the reaction

36
Q

Ionic equation

A

A balanced equation showing only those ions, atoms or molecules taking part in the reaction

- often written for reactions involving a change in oxidation state

37
Q

Titre

A

final reading - initial reading

burette

38
Q

Solution concentration

A

the amount of solute ( in moles ) dissolved in a stated volume of solution ( usually 1.00 dm3 )

39
Q

Molar gas volume

A

The volume occupied by one mole of any gas at r.t.p

chemistry a level (32 decks)

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