Leaving Cert Chemistry Atomic structure: In 1922, Francis Aston, pictured

In 1922, Francis Aston, pictured right, was awarded the Nobel Prize in chemistry for detecting the existence of isotopes using the first mass spectrometer: (i) What are isotopes? (ii) What is the principle of the mass spectrometer? (iii) Calculate, to two decimal places, the relative atomic mass of a sample of neon shown by mass spectrometer to be composed of 90.50% of neon-20 and 9.50% of neon-22. - Leaving Cert Chemistry - Question c - 2009

Question c

In 1922, Francis Aston, pictured right, was awarded the Nobel Prize in chemistry for detecting the existence of isotopes using the first mass spectrometer: (i) What... show full transcript

Worked Solution & Example Answer:In 1922, Francis Aston, pictured right, was awarded the Nobel Prize in chemistry for detecting the existence of isotopes using the first mass spectrometer: (i) What are isotopes? (ii) What is the principle of the mass spectrometer? (iii) Calculate, to two decimal places, the relative atomic mass of a sample of neon shown by mass spectrometer to be composed of 90.50% of neon-20 and 9.50% of neon-22. - Leaving Cert Chemistry - Question c - 2009

Step 1

What are isotopes?

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Answer

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This means they have the same atomic number but different mass numbers. For instance, isotopes of carbon (like Carbon-12 and Carbon-14) have 6 protons, but the number of neutrons varies, resulting in different atomic masses.

Step 2

What is the principle of the mass spectrometer?

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Answer

The principle of the mass spectrometer is based on the manipulation of charged particles (ions) in a magnetic field. When ions are produced from a sample and are accelerated, they are separated based on their mass-to-charge ratio. Lighter ions deflect more than heavier ions, allowing measurements of relative masses.

Step 3

Calculate, to two decimal places, the relative atomic mass of a sample of neon shown by mass spectrometer to be composed of 90.50% of neon-20 and 9.50% of neon-22.

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Answer

To calculate the relative atomic mass of neon:

Determine the contributions based on the percentage composition:
- Neon-20:
  
  $90.5 \% \times 20 = 1810$
- Neon-22:
  
  $9.5 \% \times 22 = 209$
Total mass contribution:

$1810 + 209 = 2019$
Calculate the average relative atomic mass:

$\text{Relative Atomic Mass} = \frac{2019}{100} = 20.19$

Thus, the relative atomic mass of the sample of neon is approximately 20.19.

What are isotopes?

What is the principle of the mass spectrometer?

Calculate, to two decimal places, the relative atomic mass of a sample of neon shown by mass spectrometer to be composed of 90.50% of neon-20 and 9.50% of neon-22.

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