Question

In the lab, you grind up 2.205 g of an unknown compound and dissolve it in 250 mL of water. You take 5 mL of this solution and dilute it to a volume of 125 mL. Using a titration, you measure the concentration of the resulting solution to be 1.96*10-3 M. Determine which of the following could be the formula of the compound. Show your work. You will need to work backwards and remember that the molar mass is equal to the mass of a sample over the number of moles in it. N2O4 P4O10 C6H12O6 MnO2 UF6

Answer 1

Given:

M2 = 1.96*10^-3 M

V1 = 5 mL

V2 = 125 mL

use:

M1*V1 = M2*V2

M1 = (M2 * V2) / V1

M1 = (1.96*10^-3*125)/5

M1 = 0.049 M

This is the concentration of original solution

volume , V = 2.5*10^2 mL

= 0.25 L

use:

number of mol,

n = Molarity * Volume

= 4.9*10^-2*0.25

= 1.225*10^-2 mol

mass(solute)= 2.205 g

use:

number of mol = mass / molar mass

1.225*10^-2 mol = (2.205 g)/molar mass

molar mass = 180 g/mol

This is molar mass of compound

which is same as molar mass of C6H12O6

So, the compound is C6H12O6

Answer: C6H12O6