C2.3.1-2 Atomic structure and analysis Flashcards
What is an isotope?
An atom of the same element with a different number of neutrons
What does the relative atomic mass (Ar) compare the mass of atoms to? What is Ar an average value for?
- Ar compares the mass of atoms with the ^12Carbon isotope
- An average value for the isotopes of the element
What is the relative formula mass (Mr) of a compound?
The sum of the relative atomic masses of the atoms shown in the formula
What is the relative formula mass of a substance also known as?
One mole of that substance
Give three advantages to using instrumental methods of analysis. Can you name a method?
- Accurate
- Sensitive
- Useful when sample is v. small
What can chemical analysis be used to identify? What method could be used?
- Additives in food
- Paper chromatography to find artificial colours
3points about GC-MS, about: (a) What it allows (b) What the time tells us (c) What the GC output can be linked to
(a) The separation of a mixture of compounds
(b) The time taken for a substance to pass through the column can help identify it
(c) The GC column output can be linked to an MS
What two things can a mass spectrometer identify?
- The SUBSTANCES LEAVING column
- The Mr of each substance
How does a GC-MS work? (5 marks/points to make)
- Sample dissolved in solvent,
- carried by unreactive gas (e.g. N/He)
- through column packed with a solid material
- different substances=come out different speeds
- so they become separated
What is an ‘inert’ gas?
An unreactive gas, such as helium or nitrogen
What is the ‘retention time’?
Time taken for the substance to pass through the column
On a gas chromatography graph what can we tell from:
(a) the shortest peak (b) the first peak (c) The number of peaks
(a) The substance is present in the smallest quantity
(b) The substance has the shortest retention time
(c) Number of compounds present
The molecular mass is given by…
…the molecular ion peak
