Worksheet: Isotopes

In this worksheet, we will practice defining and identifying isotopes of an element, listing some of their properties and uses, and calculating the relative atomic mass of an element from isotopic abundances.

Q1:

The “iso” in “isotope” is derived from the Greek word for “equal”. In what way are isotopes equal?

  • AThey have the same number of protons in their nuclei.
  • BThey have the same atomic radius.
  • CThey have the same mass number.
  • DThey have the same number of neutrons in their nuclei.
  • ETheir common ions have the same charge.

Q2:

Fill in the blank. Isotopes are atoms with the same number of protons but a different number of .

  • Aions
  • Bnuclei
  • Catoms
  • Dneutrons
  • Eelectrons

Q3:

An atom has 3 protons and 5 neutrons in its nucleus. Which of the following is an isotope of this atom?

  • AAn atom with 3 protons and 5 neutrons in its nucleus
  • BAn atom with no protons and 5 neutrons in its nucleus
  • CAn atom with 4 protons and 4 neutrons in its nucleus
  • DAn atom with 3 protons and 4 neutrons in its nucleus
  • EAn atom with 5 protons and 3 neutrons in its nucleus

Q4:

Which of the following is an isotope of magnesium-25?

  • AMagnesium-24
  • BMagnesium-25
  • CSodium-25
  • DTitanium-50
  • ESodium-23

Q5:

Which of the following isotopes is the heaviest?

  • ANeon-22
  • BBoron-11
  • CHydrogen-3
  • DSodium-21
  • EFluorine-17

Q6:

What does it mean if two atoms are described as isotopes?

  • AThey are different elements with the same atomic mass.
  • BThey have the same number of neutrons but different numbers of protons in their nuclei.
  • CThey have the same number of protons but different numbers of neutrons in their nuclei.
  • DThey are equally unstable.
  • EThey are chemically bonded together.

Q7:

Which of the following isotopes is the heaviest?

  • A4018Ar
  • B4418Ar
  • C3919K
  • D4020Ca
  • E4119K

Q8:

Which of the following isotopes is the heaviest?

  • ACarbon-12
  • BOxygen-16
  • CNitrogen-15
  • DBoron-11
  • EFluorine-15

Q9:

Which of the following is an isotope of carbon-12?

  • ABoron-11
  • BCarbon-14
  • CNitrogen-15
  • DOxygen-12
  • EOxygen-16

Q10:

An atom has 2 protons and 2 neutrons in its nucleus. Which of the following is an isotope of this atom?

  • AAn atom with no protons and 2 neutrons in its nucleus
  • BAn atom with 2 protons and 3 neutrons in its nucleus
  • CAn atom with 1 proton and 2 neutrons in its nucleus
  • DAn atom with 2 protons and 2 neutrons in its nucleus
  • EAn atom with 1 proton and 3 neutrons in its nucleus

Q11:

Which of the following is an isotope of 32S?

  • ASilicon-32
  • BScandium-30
  • CSulfur-30
  • DSilicon-30
  • ESulfur-32

Q12:

An atom has 1 proton and 2 neutrons in its nucleus. Which of the following is an isotope of this atom?

  • AAn atom with 2 protons and 1 neutron in its nucleus
  • BAn atom with 1 proton and 1 neutron in its nucleus
  • CAn atom with 2 protons and no neutrons in its nucleus
  • DAn atom with 1 proton and 2 neutrons in its nucleus
  • EAn atom with 2 protons and 2 neutrons in its nucleus

Q13:

Chlorine exists as two isotopes: chlorine-35 and chlorine-37. Their isotopic abundances are 75% and 25% respectively. What is the atomic mass of chlorine to 1 decimal place?

Q14:

Magnesium exists as three isotopes: magnesium-24, magnesium-25, and magnesium-26. Their isotopic abundances are 79%, 10%, and 11%, respectively. What is the relative atomic mass of magnesium to 1 decimal place?

Q15:

Silicon exists as three isotopes: silicon-28, silicon-29, and silicon-30. Their isotopic abundances are 92%, 5%, and 3%, respectively. What is the relative atomic mass of silicon to 1 decimal place?

Q16:

Phosphorus-33 has an atomic number of 15. How many neutrons are there in an atom of phosphorus-33?

Q17:

The atomic mass unit (u) is defined as 112th of the mass of an atom of carbon-12. What is the mass of a carbon-13 atom in atomic mass units, to 2 significant figures?

Q18:

Relative isotopic mass is the mass of an isotope of an element on a scale .

  • Awhere the most common isotope of the element has a mass of 100
  • Bfrom 0–100, where 0 is the mass of hydrogen and 100 is the mass of the heaviest element
  • Cwhere carbon-12 has a mass of 12
  • Dwhere hydrogen-1 has a mass of 1

Q19:

Chlorine has two stable isotopes, chlorine-35 and chlorine-37. A sample of chlorine was analyzed using a mass spectrometer, and the following isotopic abundances were calculated.

IsotopeChlorine-35Chlorine-37
Abundance (mol %)75.8%24.2%

What is the relative atomic mass of chlorine in the sample?

Q20:

Silicon exists as three isotopes: silicon-28, silicon-29, and silicon-30. Their isotopic abundances are 92%, 5%, and 3% respectively. What is the relative atomic mass of silicon to 1 decimal place?

Q21:

Which of the following is not a medical use of radioactive isotopes?

  • ATracer studies
  • BLocating tumors
  • CChecking thyroid function
  • DTreating cancer
  • EMeasuring the thickness of paper

Q22:

Magnesium exists as three isotopes: magnesium-24, magnesium-25, and magnesium-26. Their isotopic abundances are 79%, 10%, and 11% respectively. What is the relative atomic mass of magnesium to 1 decimal place?

Q23:

Chlorine exists as two isotopes: chlorine-35 and chlorine-37. Their isotopic abundances are 75% and 25% respectively. What is the atomic mass of chlorine to 1 decimal place?

Q24:

Which of the following is not an industrial use of radioactive isotopes?

  • ASterilizing food
  • BMeasuring the thickness of metals
  • CRadiotherapy
  • DA nuclear fuel used to generate electricity
  • EDetecting leaks

Q25:

Which of the following is not a medical use of radioactive isotopes?

  • AMeasuring the thickness of paper
  • BTreating cancer
  • CLocating tumors
  • DChecking thyroid function
  • ETracer studies

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