A sample in vitamin C is known to contain 2 . 58 × 10 24 oxygen atoms. How many moles of oxygen atoms are present in the sample?

We know that, 6 . 023 × 10 23 oxygen atoms = 1 mole of oxygen atoms 1 oxygen atom = 1 6 . 023 × 10 23 mole of oxygen atoms 2 . 58 × 10 24 Oxygen atoms = 2 . 58 × 10 24 × 1 6 . 023 × 10 23 mole of oxygen atoms = 0 . 428 × 10 = 4 . 28 moles.

Calcium chloride, when dissolved in water, dissociates into its ions according to the following equation CaCl 2 aq → Ca ( 2 + ) aq + 2 Cl - aq Calculate the number of ions obtained from CaCl 2 when 222 g of it is dissolved in water.

1 mole of calcium chloride =111g 222g of CaCl 2 is equivalent to 2 moles of CaCl 2 Since 1 formula unit CaCl 2 gives 3 ions, therefore, 1 mole of CaCl 2 would give 3 moles of ions 2 moles of CaCl 2 would give 3 × 2 = 6 moles of ions. Number of ions = Number of moles of ions × Avogadro number . = 6 × 6 . 022 × 10 23 = 36 . 132 × 10 23 = 3 . 6132 × 10 24 ions.

E M B I B E

Core science chemistry>Chapter 3 - Atoms and Molecules>EXERCISE 3C>Q 2

HARD

9th CBSE

IMPORTANT

Earn 100

Which has more number of atoms?
$100$ g of $N_{2}$ or $100$ g of ${NH}_{3} .$

$[Atomic weight of N =14; H =1]$

Important Questions on Atoms and Molecules

HARD

9th CBSE

IMPORTANT

Core science chemistry>Chapter 3 - Atoms and Molecules>EXERCISE 3C>Q 3

Compute the number of ions present in $5.85$ g of sodium chloride.

$[Atomic weight of Na = 23, Cl = 35.5]$

HARD

9th CBSE

IMPORTANT

Core science chemistry>Chapter 3 - Atoms and Molecules>EXERCISE 3C>Q 4

A gold sample contains

90 %

of gold and the rest copper. How many atoms of gold are present in one gram of this sample of gold?

MEDIUM

9th CBSE

IMPORTANT

Core science chemistry>Chapter 3 - Atoms and Molecules>EXERCISE 3C>Q 5

What are ionic and molecular compounds? Give examples.

HARD

9th CBSE

IMPORTANT

Core science chemistry>Chapter 3 - Atoms and Molecules>EXERCISE 3C>Q 6

In photosynthesis, 6 molecules of carbon dioxide combine with an equal number of water molecules through a complex series of reactions to give a molecule of glucose having a molecular formula