Mass number and isotopes Flashcards

1
Q

What is mass number?

A

Number of protons and neutrons

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2
Q

What is atomic number?

A

Number of protons

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3
Q

Define isotopes

A

The same number of protons but different number of neutrons.

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4
Q

What are the similarities and differences of isotopes?

A

Similarities: They have the same chemical properties (they have the same number of electrons in their outer shell)

Differences: They have different physical properties (they have different masses)

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5
Q

Explain why mass spectrometry is kept under a vacuum?

A

To prevent the ions that are produced colliding with molecules from the air

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6
Q

State the 4 stages in the mass spectrometer

A

Ionisation
Acceleration
Ion drift
Detector

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7
Q

What is the mass spectrometer used for?

A

To identify unknown purified compounds by composing mass spectrum obtained in data space.

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8
Q

What are the two types of ionisation for a mass spectrometer?

A

Electron impact
Electron spray ionisation

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9
Q

Describe the stage of electron impact.

A

The sample being analysed is vaporised and then high energy electrons are fired at it which comes from an electron gun which is hot filament wire with a current running through it that emits electrons. This usually knocks off one electron from each particle forming +1 ion

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10
Q

Describe the stages of electrospray ionisation.

A
  1. The sample is dissolved in a volatile solvent (e.g. methanol or water) and injected through a fine hypodermic needle as a spray into the ionisation chamber.
  2. The needle is attached to the positive terminal of a high voltage power supply.
  3. As the spray emerges from the end of the needle, the particles gain a proton from the positive charge of the supply.
  4. The solvent evaporates, leaving the 1+ ions.
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11
Q

Explain how ions are accelrated in mass psectrometer

A

The positive ions are accelerated using an electrical field so that they all have the same kinetic energy.
Lighter particles have a faster velocity and heavier particles have a lower velocity

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12
Q

Describe the flight tube

A

The positive ions travel through a hole in the negatively charged plate into a tube. The time of flight tube depends on its velocity which then also depends on the mass.

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13
Q

Describe the detective ion stage

A

The positive ions hit a negatively charged electric plate. Then the positive ions discharged by gaining electrons from the plate. This generates a movement of electrons so the electric current is measured.

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14
Q

Why do some ions travel faster?

A
  1. lighter in mass
  2. more highly charged
    This means they have a higher velocity
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15
Q

What does the size of the current give to the plate?

A

Number of ions hitting the plate

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