pKA Calculations

[Alpha Centauri]

Hey guys quick question. Say we are given ph, moles of acid, and asked to find pKA. I know how to do this equation and plug it into my calculator say, but when written out, these problems take SOOO much time to do manually. On the DAT do they expect us to have a final answer or would they have the equation in the answer and we have to select the already formatted correct equation? Thanks

 

[DAT Destroyer]

Hey guys quick question. Say we are given ph, moles of acid, and asked to find pKA. I know how to do this equation and plug it into my calculator say, but when written out, these problems take SOOO much time to do manually. On the DAT do they expect us to have a final answer or would they have the equation in the answer and we have to select the already formatted correct equation? Thanks

Indeed so. You must be able to find the log of simple numbers. For example, the - log of 1 x 10 exp -5 is 5........if we had to do it for - log 2 x 10 exp -5 it would be a bit under 5.....it would be around 4.8. You also need to use the Henderson Hasselbach equation when doing buffer problems. Perhaps you would have to just set it up, but do NOT count on that. Also be prepared to do a limiting reagent calculation, as well as balancing a redox reaction. Hope this helps.

 

[rak173]

Hey guys quick question. Say we are given ph, moles of acid, and asked to find pKA. I know how to do this equation and plug it into my calculator say, but when written out, these problems take SOOO much time to do manually. On the DAT do they expect us to have a final answer or would they have the equation in the answer and we have to select the already formatted correct equation? Thanks

Chad has a video on how to round logs. It's excellent.

 

[Alpha Centauri]

Indeed so. You must be able to find the log of simple numbers. For example, the - log of 1 x 10 exp -5 is 5........if we had to do it for - log 2 x 10 exp -5 it would be a bit under 5.....it would be around 4.8. You also need to use the Henderson Hasselbach equation when doing buffer problems. Perhaps you would have to just set it up, but do NOT count on that. Also be prepared to do a limiting reagent calculation, as well as balancing a redox reaction. Hope this helps.

Thanks orgoman! I definitely am good at estimating -logs, that is no problem. Come to think of it, practice problems have me dividing my exponents by denominators such as .55, .25, .89 etc. I just get confused easily when I see things like this though. Although I can approximate, the answer choices from some old test banks are very close and obviously were designed for people who would use a calculator. Would the answer choices be a bit more unique and distant from each other?

 

[DAT Destroyer]

Thanks orgoman! I definitely am good at estimating -logs, that is no problem. Come to think of it, practice problems have me dividing my exponents by denominators such as .55, .25, .89 etc. I just get confused easily when I see things like this though. Although I can approximate, the answer choices from some old test banks are very close and obviously were designed for people who would use a calculator. Would the answer choices be a bit more unique and distant from each other?

All the answers on the DAT will be far apart, you should have no worries.

Dr. Romano