What is the concentration of sugar(C12H22O11)in mol/L if its 20 g are dissolved in enugh water to make a final volume upto 2L

Question

This question is from CBSE 11th class portion.It was asked in my Half-Yearly examination..

Answer 1

To the nearest .1, the molecular weights of each element are:

 

C: 12

H: 1

O: 16

 

So the molecular weight of the sugar is 12 x 12 + 22 x 1 + 11 x 16 = 342.  So 20 grams is 20 / 342 = .058 moles.  If the solution contains 2 liters, then the concentration is .058 / 2 = .029 mol / L

 

 

Answer 2

Jon is correct.

 

The easiest way to answer this question is to first figure out the molar mass of the sugar in question.  To do this multiply the number of individual atoms for a given element by its atomic mass.

 

12 X 12.01 g/mol = 144.12 g/mol C

22 X 1.008 g/mol = 22.176 g/mol H

11 X 16.00 g/mol = 176.00 g/mol O

                  Total = 342.296 ~ 342.30 g/mol C₁₂H₂₂O₁₁

 

These numbers can be found using the periodic table

 

The second step is to take the number of grams of sugar you have; in this case 20g and divide it by the molar mass of the sugar 342.30 g/mol.

 

      20g              = 0.058 mol C₁₂H₂₂O₁₁

342.30g/mol

 

The Third step is to take the number of moles and divide it by your total volume of 2L.  Remember that for liquid concentrations, it is always in units of moles/L; this is also the definition of Molarity.

 

0.058 mol = 0.029 mol/L OR 0.029M C₁₂H₂₂O₁₁

    2L

 

I hope this clears up any confusion.