tom.greato8362 wrote:Re calculation of -log (4.18 x 10^-4)= 3.38. Does anyone have any advice on how to hand calculate this? most ways i have found do not come close to getting a answer as precise as the one documented.

There is no way to "hand calculate" 3.38. Perhaps we should have made it more clear: We tried to explain in 6.6.1 (page CHM-149, Masters Series) that a question based on that calculation would have, as an example, 4 multiple-choice answers sufficiently far apart such that your calculation only needs to determine if the pH is between 2 and 3, or between 3 and 4, or between 4 and 5, etc.

The key is to use log rules to reduce:

-log (4.18 x 10^-4)

to

4 - log 4.18

...which must result in a number between 3 and 4 (as shown at the end of CHM 6.6.1).

Suggestions: The practice questions at the end of the chapter (especially questions 20, 21, 22, 23, 26) and, of course, the Spoiler Alert section which also has a few similar calculations using ACER's materials.

FYI, our next free webinar will be next weekend:

https://www.gamsat-prep.com/GAMSAT-free-online-seminar/