% composition and dilution GC question

[Contach]

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Can som1 explain how to do this question step by step? thanks a ton.


An aqueous sulfuric acid solution is 39.2% H2SO4 by mass and has a specific gravity of 1.25. How many milliliters of this solution are required to make 100 mL of a 0.20 M sulfuric acid solution?

A. 1.6

B. 3.0

C. 4.0

D. 5.0

E. 6.25

 

[Neil45]

I hope I'm right.

The answer is "C".

Here's why:

*REMEMBER THAT SPECIFIC GRAVITY IS THE SAME NUMBER AS DENSITY EXCEPT WITHOUT UNITS!

Formula for mass percentage is: % mass= (mass solute)(100)/ (mass solution)

First, find the mole of solute of H2SO4. (0.20mol/L)(1L/1000mL)(100 mL of H2SO4 solution)= 0.02 mole H2SO4.

Next, convert moles of sulfuric acid into grams. (0.02 mole H2SO4)( 98g/mol H2SO4)= 1.96 grams

Rearrange the mass percentage formula so that you are solving for mass of solution-----> "mass solution= (mass solute) (100)/ (mass percentage).

Plug in numbers and you get 5 grams of H2SO4 solution. mass solution= (1.96g)(100)/ (39.2)

Now, multiply this by the specific gravity (remember density!) to get the answer: (5 g of H2SO4)( mL/ 1.25g)= 4 mL.

Is this the answer in the book?

 

[Contach]

yup! 4.0 is correct

Thanks a lot. helped me a great deal.