1.3 Chemical calculations Flashcards
What is the definition of relative atomic mass?
the average mass of one atom of the element relative to one twelfth the mass of one atom of carbon-12
What is the definition of relative isotopic mass?
The mass of an atom of an isotope relative to one twelfth of the mass of carbon 12
What is the mass spectrometer used for?
To find the relative atomic mass of an element by measuring the mass of each different isotope of the element and the relative abundance of each isotope of the element.
What are the 4 stages of the mass spectrometer?
- Ionisation
- Acceleration
- Deflection
- Detection
what happens during ionisation in a mass spectrometer?
The particles in the sample are bombarded with a stream of electrons and some are sufficiently energetic enough to knock one or more electrons out of the particles to make positive ions.
What happens in the acceleration stage in the mass spectrometer?
An electric field accelerates the positive ions to a high speed.
What happens in the deflection stage in the mass spectrometer?
Different ions are deflected by the electrical field by different amounts depending on:
- The mass of the ion. Lighter ions are deflected more than heavier ones.
- The charge on the ion. Ions with two (or more) positive charges are deflected more than ones with only positive charge.
What happens in the detection stage of the mass spec?
Detected electrically and then amplified and recorded. A vacuum pump is needed inside the apparatus as the ions that are deflected by the magnetic field will collide with the wall and pick up electrons thus becoming neutralised thus they are removed via the vacuum pump.
How do you work out the relative atomic mass in an isotopic mixture?
relative abundance x mass/charge ratio
divided by 100
what is the ratio of ions in Cl+ and Cl2+?
Cl+ is 3:1
Cl2+ is 9:6:1
what is the ratio of ions in bromine?
1:2:1
what is a mole?
the amount of any substance that contains the same number of particles as there are atoms in exactly 12 g of carbon-12
What is the equation to work out molar mass?
molar mass = mass/moles
what is the equation that connnects number of moles and mass?
no of moles = mass/Mr
How do you work out concentration in mol dm-3
No moles/volume (dm3)
How do you work out concentration in g dm-3
Mass in g/volume dm3
How do you work out the number of moles of a gas?
Volume of gas/ volume of 1 mole of gas (22.43 at stp)
What is the STP (temp,pressure etc)
1 atm pressure and either 0 or 25 degrees celcius
What is the empirical formula?
The simplest formula showing the simplest whole number ratio of the number of atoms of each element present.
What is the molecular formula?
Shows the actual number of atoms of each element present in the molecule. It is a simple multiple of the empirical formula. Usually the relative formula mass is needed to determine the molecular formula.
