Chemical Calculations Flashcards
What is the definition of relative atomic mass (Ar)?
The mean mass of an atom from an element relative to the mean mass of the carbon-12 isotope.
What is the definition of relative molecular mass (Mr)?
The mean mass of an atom from a molecule from a compound relative to the mean mass of the carbon-12 isotope.
What is the definition of relative isotopic mass?
The mean mass of an atom from an isotope relative to the mean mass of the carbon-12 isotope.
What is mass spectrometry?
An analytical technique that measures mass to charge ratio that can used to find the relative atomic mass and identify isotopes.
Describe the first stage of mass spectrometry
Ionisation- a sample of an element is vaporised and injected into a mass spectometer where a high voltage is passed over the chamber. This causes electrons to be removes from the atoms creating positively charged ions.
Describe the second stage of mass spectrometry
Acceleration- The +1 ions are accelerated towards a negatively charged detection plate.
Describe the third stage of mass spectrometry
Ion Deflection- THese ions are then deflected by a magnetic field into a curved path. The radius of their paths are dependent on the charge and mass of the ion.
The greater the charge, the smaller the radius.
Describe the fourth stage of mass spectrometry
Detection- When the + ions hit the negatively charged plate, they gain an electron producing a flow of charge.
The greater the abundance, the greater the current produced
Describe the fifth stage of mass spectrometry
Analysis- These current values are than used in combination with flight times to produce a spectra with the relative abundance of eachisotope displayed.
What is the formula to find the relative atomic mass of ions from a mass spectrometry graph?
Ar=(m/z x abundance)/Total abundance
Define empirical formula
The simplest whole number ratio of atoms in a compound. It is found using molar ratios of each element.
Define molecular formula
The true number of atoms in a compound.
What is avogadros constant?
6.02x10^23
What is the equation linking avogadros constant to moles?
No. of particles= moles x avogadros number
Define molar mass
The mass per mole of an substance. Measures in gmol^-1
What is the equation that links moles to mass?
Moles=Mass/Mr
Define concentration
The amount of moles per unit volume
What is the equation that links moles to concentration?
Moles=Concentration x Volume
What is the equation that links concentration to mass?
Concentration=Mass(g)/Volume(dm^3)
What is the molar volume of any gas at room temperature and pressure?
24.5 dm^3
What equation links molar volume at RTP to moles?
Volume of gas at RTP= Moles x 24.5dm^3
How is the molar volume at a given pressure affected if the temperature is increased?
At a constant pressure, the molar volume of a gas increases as temperature increases. Volume is directly proportional to temperature.
How is the molar volume at a given temperature affected if the pressure is increased?
At a constant temperature, the molar volume of a gas decreases as the pressure increases. Volume is inversely proportional to pressure.
What is the ideal gas equation?
pV=nRT
p= pressure (pascals)
V= volume (m^3)
n= No. of moles
R= gas constant (8.31 JK^-1 mol^-1)
T= temperature (kelvin)
