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PCAT Chemical Processes – Dilution Equation

  • by Sam
  • Oct 25, 2017
  • PCAT Question of the Day

A student prepares a ten liter solution of 0.01M NaOH by starting with 25mL of a stock solution. What is the concentration of the stock solution?

 

A) 0.1 M

B) 0.4 M

C) 2.5 M

D) 4.0 M

Explanation

The student is only adding water when doing the dilution. Thus moles i = moles f. Because M = mol / volume, you can substitute M x V for moles. Thus the dilution equation is:

 

M1V1 = M2V2

 

Plugging in the values given, we get:

 

(0.01M)(10L) = (0.025L) x M2

 

0.1 moles = 0.025 L x M2

 

0.1 / 0.025 = M2

 

100 / 25 = M2

 

4 = M2

 

Therefore, (D) is the answer.

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