Question

find the number of molecules of CH2O in 0.55 L of a 1.25 M CH2O solution

Answer 1

Molarity (M)= moles of solute / liters of solution

1.25M CH2O solution = (Wt taken in g / molecular weight) / 0.55 L

(Wt taken in g / molecular weight) = 1.25 M x 0.55 L

(Wt taken in g / 30) = 1.25 M x 0.55 L

Wt taken in g = 0.6875 x 30 = 20.625 g

30 g of CH2O is 1 mole of substance

so, 20.625 g is 0.6875 moles

1 mole contains 6.023x 10²³ numbers of molecules (Avagadro's no)

hence,  0.6875 mole will have 4.1408 x 10^₂₃ numbers of molecules

4.1408 x 10^₂₃ numbers of molecules of CH2O is present in 0.55 L in 1.25 M CH2O solution.