Chemical Calculations Flashcards
What is the relative atomic mass (Ar) of an element?
The average mass of one atom relative to one-twelfth of the mass of one atom of carbon-12.
What is the relative isotopic mass of an isotope?
The average mass of an isotope relative to one-twelfth of the mass of one atom of carbon-12.
How is relative atomic mass calculated?
Relative atomic mass = sum of (isotopic mass x abundance) / total relative abundance.
What does the relative formula or molecular mass (Mr) represent?
The average mass of one molecule relative to one-twelfth of the mass of one atom of carbon-12.
How is percentage by mass calculated?
Percentage by mass = ((molar mass of element x number of that element) / molar mass of compound) × 100.
What are the steps involved in the mass spectrometry process?
- Vaporisation
- Ionisation
- Acceleration
- Deflection
- Detection
What occurs during the vaporisation step of mass spectrometry?
The sample is heated and turned into a gas before it enters the spectrometer.
What happens during the ionisation step in mass spectrometry?
The gaseous sample is bombarded with high energy electrons, knocking electrons off the particles to form positive ions.
What is the purpose of the acceleration step in mass spectrometry?
The positive ions are accelerated using an electric field and a vacuum pump.
What is the role of the deflection step in mass spectrometry?
The ions are deflected by a magnetic field, with the amount of deflection depending on the mass and charge of the ion.
What is detected in the detection step of mass spectrometry?
The abundance and mass/charge (m/z) ratio of the ions, producing a mass spectrum graph.
How is the ratio of peaks on mass spectrometers explained?
Do (abundance of isotope 1 as fraction) * (abundance of isotope 2 as fraction) for all combinations.
How do you find the empirical formula?
Find the number of moles of each and divide both by the smallest value to get a ratio.
What is the formula for percentage yield?
Percentage yield = mass obtained / theoretical mass.
How is atom economy calculated?
Atom Economy = (mass of useful / mass of total) x 100.
What is the formula for percentage error?
Percentage Error = (uncertainty / measured value) x 100.
