Question

calculate the number of moles and molecules of urea present in 5.6 g of urea​

Answer 1

Molar mass of urea = 60g

No of moles = given mass/molar mass

                   = 5.6/60

                    =0.09 moles

 No of molecules = Avogadro no * moles

                             = 6.022 * 10^23 * 0.09

                            = 0.56 *10^23 molecules are present

Answer 2

Given: 5.6 g of urea is present.

To find: Number of moles and molecules of urea present in the sample

Solution: Let the given mass of urea be m.

m = 5.6 g

The molecular formula of urea is CH4N2O.

Molecular mass of urea

= 1×Molar mass of carbon + 4 × molar mass of hydrogen+ 2 × molar mass of nitrogen+ 1×molar mass of oxygen

= 1×12 + 4×1 + 2×14 + 1×16

= 12+4+28+16

= 60 g/mol

Number of moles

= Given mass/Molar mass

= m/Molar mass

= 5.6/60

= 0.093 moles

Number of molecules of urea

= Number of moles of urea × Avogadro's number

$= 0.093 \times 6.022 \times {10}^{23}$

$= 0.56 \times {10}^{23}$

Therefore, the number of moles of urea is 0.093 and the number of molecules of urea is $0.56 \times {10}^{23} .$