A sample of 9.4 grams of NaOH is dissolved into 693 mL of aqueous 0.250 M NaOH (assume no volume change). This solution is then poured into 2.37 gallons of water. (You may assume that the two volumes can be added.) What is the concentration of NaOH in the final solution?

Question

A sample of 9.4 grams of NaOH is dissolved into 693 mL of aqueous 0.250 M NaOH (assume no volume change). This solution is then poured into 2.37 gallons of water. (You may assume that the two volumes can be added.) What is the concentration of NaOH in the final solution?
Answer in units of M.

Okay heres my work:

9.4/40(MM)= .235
.250x .693=.17325

added togehter= .40825

2.37 gallons= 8971.4259 mL

.40825/8971.4259= .000045506 but my answers wrong.

DrBob222 · Answer

Okay heres my work:

9.4/40(MM)= .235
The 0.235 mole is correct.

.250x .693=.17325
This is OK.

added togehter= .40825
This is OK (except for the typo on together :-)).

2.37 gallons= 8971.4259 mL
This is OK.
.40825/8971.4259= .000045506 but my answers wrong.
Two things wrong here. First you didn't add the 693 mL to the 8971 mL AND you didn't convert mL to L. M = moles/L, not moles/mL. Making those two corrections should take care of it.