Mass spec.

Question 1

What does it measure?

Answer 1

relative atomic mass pf the different isotopes and their relative abundance win the sample

Question 2

Four main stages plus 1

Answer 2

vaporisation, ionisation, acceleration, deflection, detection

Question 3

Describe vapourisation

Answer 3

sample is vaporised so it can be injected into the machine and ionised

Question 4

Ionisation

Answer 4

electron gun produces a stream of HIGH energy electrons, these bombard the vaporised sample and knocks off an electron from the atom, so it becomes a unipositive ion

Question 5

Acceleration

Answer 5

positive ions attracted to negatively charged plates and accelerate at high speed.

Question 6

What does the speed at which the electrons accelerate depend on

Answer 6

mass of ion therefore the lighter the ion the faster it accelerates

Question 7

Deflection

Answer 7

beam moves into the magnetic field at right angles to its direction of travel. Field deflects ions

Question 8

What does deflection depend on

Answer 8

ratio of mass to charge of ion. charge is usually 1+. 2+ ions deflected twice as much. Heavier ions deflected less. Also depends on magnetic field strength.

Question 9

Detection

Answer 9

ions strikes the detector and accepts an electron, so it returns to an atoms, losing their charge. this creates a current proportional to the abundance of each isotope.

Question 10

In a mass spectrometer, the relative abundance of each isotope is proportional to the current generated by that isotope at the detector.Explain how this current is generated.

Answer 10

Electron(s) transferred / flow (at the detector) (From detector / plate) to the (+) ion

Question 11

X and Zn are different elements.Explain why the chemical properties of 70X and 70Zn are different

Answer 11

They do not have the same electron configuration / they have different number of electrons (in the outer shell)

Question 12

In a mass spectrometer, the isotopes of an element are separated.Two measurements for each isotope are recorded on the mass spectrum.State the two measurements that are recorded for each isotope.

Answer 12

m/z(relative) abundance / (relative) intensity

Question 13

State why isotopes of an element have the same chemical properties.

Answer 13

Same number of electrons (in outer shell) / same electronic configuration

Question 14

Explain how the gaseous atoms of rubidium are ionised in a mass spectrometer.

Answer 14

Electron gun / high speed/high energy electrons Knock out electron(s)

Question 15

In terms of fundamental particles, state the difference between isotopes of an element.

Answer 15

Different number / amount of neutrons

Question 16

State why isotopes of an element have the same chemical properties.

Answer 16

Same electron configuration / same number of electrons (in the outer shell)

Question 17

Give the meaning of the term relative atomic mass.

Answer 17

Average mass of an atom/isotope compared to C-12 on a scale in which an atom of C-12 has a mass of 12

Question 18

Suggest one reason why particles with the same mass and velocity can be deflected by different amounts in the same magnetic field.

Answer 18

Size of the charge (on the ion) / different charges / differentm/z

Question 19

Explain how the detector in a mass spectrometer enables the abundance of an isotope to be measured.

Answer 19

(ions hit detector and) cause current/(ions) accept electrons/cause electron flow/electric pulse causedbigger current = more of that isotope/current proportional to abundance

Question 20

A sample of indium must be ionised before it can be analysed in a mass spectrometer. State what is used to ionise a sample of indium in a mass spectrometer.

Answer 20

Using an electron gun -> fast moving beam of high energy electrons

Question 21

Write an equation, including state symbols, for the ionisation of indium that requires the minimum energy.

Answer 21

In(g) + e —-> In+(g) + 2e

Question 22

State why more than the minimum energy is not used to ionise the sample of indium.

Answer 22

So no more than 1 electron is knocked out/ so only one electron is knocked out/ prevent further ionisation

Question 23

Give two reasons why the sample of indium must be ionised.

Answer 23

so it can be:Accelerated (owtte)Deflected (owtte) Detected (owtte)

Question 24

In a mass spectrometer, under the same conditions, 14N+ and 15N+ ions follow different paths. State the property of these ions that causes them to follow different paths.State one change in the operation of the mass spectrometer that will change the path of an ion.

Answer 24

15N is heavier / 15N has a bigger m/z / different m/z valuesElectromagnet/ electric field/ magnet /accelerating potential or voltage / electric current

Question 25

Explain briefly how the relative abundance of an ion is measured in a mass spectrometer.

Answer 25

(ions hit detector and) cause current/(ions) accept electrons/cause electron flowbigger current = more of that isotope/current proportional to abundance