461770
Description
Flashcards by Nina hallwood, updated more than 1 year ago
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Created by Nina hallwood
over 10 years ago
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| Question | Answer |
| What does mass spectrometry determine? | Relative atomic masses. |
| Relative atomic masses are measured on a scale on which Carbon 12 is defined as exactly 12. | This means the protons and neutrons have relative masses of exactly 1. |
| Generalise what happens in mass spectrometry. | Atoms are converted to ions Accelerated Deflected Detected |
| What is the instrument kept under so ions do not collide with air molecules? | High vacuum. |
| The sample is investigated in a gaseous state, if the sample is solid what happens to it? | It is vaporised first by heating. |
| Ionisation is the first past of mass spectrometry. What happens at this step? | A beam of electrons from an electron gun knock out electrons from atoms or molecules. |
| Why are electrons knocked off atoms or molecules? | To form positive ions. |
| Positive ions are attracted to negatively charged plates. What step is this? | Acceleration, negatively charged plates attract positive ions accelerating them. |
| There is a slit in the plates, what does this do to the ions? | It forms a beam. |
| Deflection is the next step, what do ions move into? | A magnetic field. |
| The magnetic field deflects the beam of ions into a what? | Arc of a circle. (The beam of ions moves into the magnetic field at right angles to its direction of travel) |
| What does the deflection depend on? HINT m/z | Mass to charge ratio. Z is the charge on the ion. |
| Are heavier ions deflected more of less than lighter ones? | Less than lighter ones |
| What happens in detection? | The magnetic field is gradually increased, so ions of increasing mass enter the detector one after another. |
| Ions strike the detector, lose their charged and create a what? | Current, whichever is proportional to the abundance of each ions. |
| The computer works out the value of the mass to charge ratio by the strength of what? | The magnetic field |
| Four key stages are. | Ionisation, acceleration, deflection and detection. |
| High resolution mass spectrometry is to what decimal place? | Five decimal places of an atomic mass. |
| Most work is done to the nearest whole number, this is called... | Low resolution mass spectrometry. |
| If you had two mass numbers of 20 and 22. With abundances of 90% and 10% how do you work it out? | (90x20) + (10x22) /100 =20.2 |
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