Atoms, Isotopes and Relative Atomic Masses

Question 1

How is an atom of 151Eu different from an atom of 153Eu? (1)

Answer 1

153Eu has 2 more neutrons

Question 2

How is an atom of 151Eu similar to an atom of 153Eu? (1)

Answer 2

They have the same number of protons AND electrons

Question 3

Define: relative isotopic mass

Answer 3

Mass of the isotope compared to 1/12th of the mass of an atom of carbon-12

Question 4

Define: relative atomic mass

Answer 4

The weighted mean mass of an atom compared to 1/12th of the mass of an atom of carbon-12

Question 5

Define: relative molecular mass (Mr)

Answer 5

The mean mass of a molecule compared to 1/12th of the mass of an atom of carbon-12

Question 6

Define: isotopes

Answer 6

Atoms of the same element with different numbers of neutrons

Question 7

Isotopes of carbon have the same chemical properties.
Explain why. (1)

Answer 7

They have the same electron configuration

Question 8

Which isotope is used as the standard against which the masses of elements are measures? (1)

Answer 8

Carbon-12

Question 9

A sample of carbon was found to contain 95% of Carbon-12 and 5% of Carbon-13.
How could this information be obtained experimentally?

Answer 9

Mass spectrometry

Question 10

State the block in the periodic table in which silicon is placed and explain your answer (2)

Answer 10

• p-block
• outermost electron in a p-orbital

Question 11

Suggest why the relative atomic mass on the Periodic Table might be different to the relative atomic mass of a sample analysed using a mass spectrometer

Answer 11

• other isotopes may be present

Question 12

Suggest why the molecular formula: C7H54O is possible. (1)

Answer 12

• the relative atomic masses add up to the correct molecular mass

Question 13

Suggest why the molecular formula: C7H54O is NOT possible. (1)

Answer 13

• the number of hydrogen atoms is not possible with 7 carbon atoms and 1 oxygen atom

Question 14

State why mA and nA have identical chemical properties, but mA and pB have different chemical properties. (3)

Answer 14

• mA and nA are isotopes
• isotopes have the same electron configuration
• mA and pB have different numbers of outer electrons

Question 15

Name an instrument which would be used to measure the relative abundance of isotopes of an element.

Answer 15

Mass spectrometer

Question 16

A graph can be produced when measuring the relative abundances of isotopes in an element.
Describe how the graph and data obtained can be used to calculate the relative atomic mass of the element in question. (5)

Answer 16

• mass spectrum produced gives abundance of each isotope present
• and a m/z value for each isotope
• multiply each m/z value by its abundance
• add together all values
• divide by total abundance

Question 17

A student stated that isotopes of silicon will have different chemical properties due to different mass numbers.
Is the student correct? (2)

Answer 17

• no, isotopes have the same chemical properties
• because they have the same number of electrons

Question 18

metal + acid –>

Answer 18

salt + hydrogen

Question 19

metal oxide + acid –>

Answer 19

salt + water

Question 20

metal hydroxide + acid –>

Answer 20

salt + water

Question 21

metal carbonate + acid –>

Answer 21

salt + carbon dioxide + water