Daltons Atomic Theory - UNSOLVED PRACTICE SET

Q7. State any two postulates of Dalton's atomic theory.

Q8. Which postulate of Dalton's atomic theory explains the law of definite proportions? Explain how.

Q9. Name the two fundamental particles discovered after Dalton's theory that proved atoms are divisible.

Q10. How did the discovery of isotopes challenge Dalton's atomic theory?

Q11. Your history teacher explains that ancient Indian philosophers like Kanada proposed the concept of "paramanu" (indivisible particles) thousands of years before Dalton. While Kanada's idea was philosophical, Dalton's was scientific. What is the difference between a philosophical idea and a scientific theory in terms of experimental evidence?

Q12. Why is Dalton's atomic theory considered a milestone in chemistry, even though some of its postulates have been modified?

Q13. State the main postulates of Dalton's atomic theory. Explain how each postulate accounts for the laws of chemical combination. Which postulates have been modified by later discoveries, and what were those discoveries?

Q14. Compare Dalton's atomic theory with modern atomic theory on the following points:

(a) Divisibility of atoms

(b) Identity of atoms of the same element

(c) Nature of chemical combination

(d) Creation and destruction of atoms

Why is Dalton's theory still taught in schools despite its limitations?

Q15. Imagine you are John Dalton in 1808, presenting your atomic theory to the Manchester Literary and Philosophical Society.

(a) What experimental evidence would you present to support your claim that matter consists of tiny, indivisible particles?

(b) How would you explain why hydrogen and oxygen always combine in a fixed 1:8 ratio by mass to form water?

(c) A sceptic asks: "If atoms are indivisible, how do you explain the discovery of electrons by J.J. Thomson a century later?" How would a modern scientist answer this, while still respecting Dalton's contribution?

(d) Why did Dalton use symbols for atoms, and how did this help in representing chemical reactions?

Q16. According to Dalton's atomic theory, 1 atom of hydrogen combines with 1 atom of chlorine to form 1 molecule of hydrogen chloride (HCl).

(a) If the mass of 1 atom of hydrogen is 1 u and the mass of 1 atom of chlorine is 35.5 u, what is the mass of 1 molecule of HCl?

(b) If 100 atoms of hydrogen combine with 100 atoms of chlorine, how many molecules of HCl are formed? What is the total mass?

(c) Dalton assumed atoms combine in 1:1 ratio. We now know HCl contains 1 H and 1 Cl. Does this mean Dalton was always correct about combining ratios? Explain with the example of water (H₂O).

Q17. Dalton assigned relative atomic masses based on hydrogen = 1. Later, oxygen = 16 became the standard, and now carbon-12 = 12 u is used.

(a) If an element X has an atomic mass of 24 on the hydrogen scale, what would be its atomic mass on the carbon-12 scale? (Hint: H = 1.008 u on C-12 scale)

(b) Why did scientists change from hydrogen to oxygen, and then to carbon-12 as the standard?

(c) If Dalton had used oxygen = 1 as his standard, what would be the atomic mass of carbon on his scale? (Atomic mass of C = 12 u, O = 16 u on modern scale)

Q18. A student is analysing Dalton's symbols for elements. Dalton used circular symbols with different patterns to represent different elements.

(a) If Dalton's symbol for hydrogen is a circle with one dot, and for oxygen a circle with a cross, how would he represent water (assuming his incorrect formula HO)?

(b) Given that water is actually H₂O, explain why Dalton's assumption of 1:1 ratio for all compounds was incorrect.

(c) If Dalton had known about Avogadro's hypothesis, how might his symbols and formulae have been different?