Question

calculate the number of molecules in (i) 5.6 g of calcium oxide (ii) 1.5 mole of nitric acid​

Answer 1

Given - (i) 5.6 g of calcium oxide (ii) 1.5 mole of nitric acid

Find - Number of molecules

Solution - The number of molecules (I) 6.02*10²² and (ii) 9.03*10²³.

The number of molecules in 1 mole of any substance is equal to Avogadro's number.

(I) Molar mass of calcium oxide is 56 grams/mole.

Number of moles of calcium oxide = 5.6/56

Number of moles of calcium oxide = 0.1

As 1 mole has a number of molecules = 6.02*10²³

0.1 moles will have a number of molecules = 6.02*10²³*0.1

The number of molecules = 6.02*10²².

(II) As 1 mole has a number of molecules = 6.02*10²³

1.5 moles will have a number of molecules = 6.02*10²³*1.5

The number of molecules = 9.03*10²³.

Thus, the number of molecules (I) 6.02*10²² and (ii) 9.03*10²³.

Answer 2

Given :

(i) 5.6 g of CaO

(ii) 1.5 mole of HNO₃

To Find :

Number of molecules in (i) 5.6 g of calcium oxide (ii) 1.5 mole of nitric acid​

Solution :

(i) Molecular mass of calcium oxide (CaO) = 40 + 16 = 56 gm

56 gm of CaO = 1 mole

We know 1 mole of any substance contains 6.022 × 10²³ molecules. Thus,

56 gm of CaO contains 6.022 × 10²³ molecules

1 gm of CaO contains $\frac{6.022 * 10^2^3}{56}$ molecules

5.6 gm of CaO will contain $\frac{6.022 * 10^2^3}{56}$ × 5.6 molecules

                                          = 6.022 × 10²² molecules

Therefore, 5.6 g of calcium oxide contains 6.022 × 10²² molecules.

(ii) 1 mole of nitric acid contains 6.022 × 10²³ molecules

So,

1.5 mole of nitric acid will contain 6.022 × 10²³× 1.5 molecules

                                                     = 9.033 × 10²³ molecules.

Therefore, the number of molecules in 1.5 mole of nitic acid is 9.033 × 10²³.