NCERT Class-9 Science Solutions: Chapter 3-Atoms and Molecules Part 7

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Question 27:

The difference in the mass of each of sodium atoms and sodium ions is . Compute the mass of an electron.

Answer:

A sodium atom and ion, differ by one electron. For 100 moles each of sodium atoms and ions there would be a difference of 100 moles of electrons.

Question 28:

Cinnabar is a prominent ore of mercury. How many grams of mercury are present in of pure ? Molar mass of respectively.

Answer:

Question 29:

The mass of one steel screw is . Find the mass of one mole of these steel screws. Compare this value with the mass of the Earth ( ). Which one of the two is heavier and by how many times?

Answer:

Question 30:

A sample of is known to contain oxygen atoms. How many moles of oxygen atoms are present in the sample?

Answer:

Question 31:

Raunak took 5 moles of carbon atoms in a container and Krish also took 5 moles of sodium atoms in another container of same weight.

  1. Whose container is heavier?

  2. Whose container has more number of atoms?

Answer:

  1. Mass of sodium atoms carried by

    While mass of carbon atom carried by

    Thus, Krish’s container is heavy

  2. Both the bags have same number of atoms as they have same number of moles of atoms