Question

If you have a 2.14 m aqueous solution of NaHCO₃, what is the mole fraction of NaHCO₃?

Answer 1

Mole fraction

The mole fraction of a compound is a measure of the concentration of the solution. The mole fraction is simply defined as the ratio of the number of moles of one component to the total number of moles of all the components present in the solution. It is expressed as X.

For example,

For a binary solution of two components A&B

X_A =nA/ (nA+nB)         X_B =nB/ (nA+nB)

Molality and molarity

Molarity(M)   : Number of moles of solute dissolved per liter of a solution. Unit=mol/L    Denoted by M

Molarity(m)   : Number of moles of solute dissolved per 1000g of a solution. Unit=mol/kg    Denoted by m

Answer

We have 2.14 m aqueous solution of NaHCO₃

Means, 2.14 moles of NaHCO₃ is dissolved in 1000g of water.

Mole fraction of NaHCO₃ =

X_NaHCO3 = Number of moles of _NaHCO3 / [ Number of moles of _NaHCO3+ Number of moles of _H2O]

X_NaHCO3    = n_NaHCO3 /[n_NaHCO3+n_H2O]

n_NaHCO3 = 2.14 moles

n_H2O      = ?

Number of moles of water in 1000g of water,

Number of moles= Given mass of the substance / Molar mass of the substance

The molar mass of water= H2O =18.01 g/mol

Number of moles of water in1000g = 1000g/18.01 g/mol

                                                   =55.51 moles

X_NaHCO3    = 2.14 /[2.14+55.50]

               =0.037

Mole fraction of NaHCO₃ =0.037