3.42g of sucrose are dissolved in 18g of water in a beaker. The number of oxygen atoms in the solution are
(a) 6.68 X 1023
(b) 6.09 X 1022
(c) 6.022 X 1023
(d) 6.022 X 1021

AcademicChemistryNCERTClass 9

Correct Answer: (a) 6.68 X 1023

Explanation: Molar mass of sucrose

C12H22O11 = 12× 12 + 1× 22 + 16 × 11

= 342g/mol

Number of moles =  Mass of glucose/ Molar mass of sucrose 

Number of moles =  3.42 g /342 (g/mol) 3.42g/342 (g/mol)

⇒Number of moles = 0.01

Sucrose(C12H22O11) contains 11 oxygen atoms ⇒11 x 6.022 x 1023

For 0.01 moles of sucrose ⇒ 0.01 x 11 x 6.022 x 1023 Now, Molar mass of water = H2O = 2 × 1 + 16 = 18g/mol

⇒ Number of moles = 1 Sucrose (H2O) contains 1 oxygen atom = 6.022 × 1023

For 1 mole of water = 6.022 × 1023

On adding both values 6.6 × 1022 + 6.022 × 1023

=6.68 × 1023 atoms.

Hence, (a) is correct. 

raja
Updated on 10-Oct-2022 13:30:05

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