Isotopes and Isobars - UNSOLVED PRACTICE SET

Q7. Define isotopes and isobars. Give one example of each.

Q8. Why do isotopes of an element have different physical properties (like density, boiling point) but similar chemical properties? Explain in terms of subatomic particles.

Q9. Your science textbook mentions that carbon-14 is used for carbon dating to determine the age of ancient objects. Explain why carbon-14 and carbon-12 are both called "carbon" even though they have different numbers of neutrons.

Q10. Write the isotopes of carbon and oxygen. For each isotope, write the number of protons, neutrons, and electrons.

Q11. Differentiate between isotopes and isobars using a table with at least four points of difference.

Q12. The average atomic mass of chlorine is 35.5 u. Explain why it is not a whole number, even though individual isotopes have whole number mass numbers.

Q13. Define isotopes and isobars with examples. Explain why isotopes have the same chemical properties but different physical properties. Describe two applications of isotopes: (i) in medicine, and (ii) in archaeology. Give specific examples like carbon-14 dating and cobalt-60 therapy.

Q14. A student is confused about the difference between isotopes, isobars, and isotones. Create a clear comparison table for the student that includes:

(a) Definitions of isotopes, isobars, and isotones.

(b) Two examples of each.

(c) The relationship between protons, neutrons, and mass number for each.

(d) One practical application or significance of each.

Q15. "Isotopes are nature's way of showing that the identity of an element is determined by its protons, not its neutrons." Discuss this statement by explaining: (i) how isotopes prove that atomic number determines chemical identity, (ii) why isotopes have different physical properties, (iii) the applications of radioactive isotopes in medicine and industry, and (iv) the role of isotopes in understanding nuclear stability and the evolution of elements in stars.

Q16. Chlorine has two naturally occurring isotopes: ³⁵Cl (abundance = 75%) and ³⁷Cl (abundance = 25%).

(a) Calculate the average atomic mass of chlorine.

(b) Verify whether your answer matches the value given in the periodic table (35.5 u).

(c) If a sample contains 1000 atoms of chlorine, how many atoms of each isotope are present?

(d) Calculate the total mass of these 1000 atoms in atomic mass units.

(e) Why is the average atomic mass important in chemical calculations rather than the mass of individual isotopes?

Q17. Boron has two isotopes: ¹⁰B (mass = 10 u, abundance = 20%) and ¹¹B (mass = 11 u, abundance = 80%).

(a) Calculate the average atomic mass of boron.

(b) If a chemist needs 10.8 g of boron for an experiment, how many moles of boron does she need?

(c) How many atoms of boron are present in 10.8 g?

(d) In this sample, how many atoms of ¹⁰B and ¹¹B are present?

(e) Boron is used in nuclear control rods. Why is the isotopic composition of boron important for this application?

Q18. In India, radioisotopes are used extensively in medicine, agriculture, and industry.

(a) Cobalt-60 is used in cancer therapy. If a hospital has a 5 g sample of Co-60, calculate the number of atoms present. (Atomic mass of Co-60 ≈ 60 u)

(b) Iodine-131 is used to treat thyroid disorders. A patient is given 100 micrograms of I-131. Calculate the number of atoms administered.

(c) Carbon-14 has a half-life of 5730 years. An archaeological sample from the Indus Valley civilization shows 25% of the original C-14 activity. Calculate the age of the sample.

(d) Uranium-235 is used as fuel in nuclear reactors. If India needs 100 tonnes of natural uranium to extract enough U-235 for a reactor, and natural uranium contains only 0.7% U-235, calculate the mass of U-235 obtained.

(e) Why is it important for India to develop expertise in isotope technology?