Question

Calculate the resulting molarity of the solution that is obtained by
adding 5g of Na H to 250 ml of M NaOH solution (density =
1.05 g/cm). The density of the resulting solution is 1.08 g/cm3
a. 0.76 M 'b. 0.86 M c. 7.3 M d. 4.5M​

Answer 1

Answer:

Number of moles of NaOH in given solution = C x V = 1/4 mol L-1 x 250 mL /1000 mL L-1 = 0.0625 mol

Amount of NaOH added = 5g

Moles of NaOH added = 5 g/ Molar mass of NaOH = 5g/40 g mol-1​ = 0.125 mol

Total number of moles in solution = 0.0625 + 0.125 = 0.1875 mol

Total mass of NaOH in solution = number of moles x molar mass

= 0.1875 mol x 40 g mol-1 = 7.5 g

Density = mass/Volume

Volume = Mass/density

            = 7.5 g/1.08 g cm-3

           = 6.94 cm3

          = 6.94 mL

​Molarity of resultant solution = Moles of solute/ solution in L

                                             = 0.1875 mol x 1000 ml L-1/6.94 mL

​                                              = 27.02 mol L-1

​