# Dilution problem

#### SilvrGrey330

##### SilvrGrey330
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5+ Year Member
100ml of H20 is added to 300ml of .4M soln of NaOH. WHat is the molarity of the NaOH after dilution.

I understand the whole M1V1 = M2V2....but cant seem to make it work for this problem. The answer is .1 NaOH, can someone please show me their work.

This is what i have so far:

(300ml)(.4) = (M2)(300ml + 100ml).........solve for M2, but this isnt correct

#### Prophecies

##### ...I bleed orange...
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5+ Year Member
You are doing the problem the right way...the answer is 0.3 M, not 0.1 M. The answer key is probably incorrect...for example, if you added 300 mL water to 300 mL 0.4 M solution, then you would get 0.2 M (it's a half dilution). Therefore, adding 100 mL of water would make a solution stronger than 0.2 (you are diluting it less than half). There is no way the answer can be 0.1 M...it is 0.3 M.

OP
S

#### SilvrGrey330

##### SilvrGrey330
10+ Year Member
5+ Year Member
cool...ya, dont u hate it when the keys are incorrect. it makes u doubt yourself..thanks for confirming.

#### Prophecies

##### ...I bleed orange...
10+ Year Member
5+ Year Member
Not a problem...never doubt your answers Especially on the real MCAT