Any advice on chemistry??

Leftist
Thu, 02 Dec 2004 16:17:41 +0000

pH questions on the SAT 2 chemistry are really simple. B/c you can’t use a calculater, none of the questions actually require caculating logarithims. All of the questions are going to involve lower than 1 M concentrations. In the 3 practice tests I’ve taken (one from college board, 2 from barrons) they were all able to be solved like this: If there is one H in the acid formula (HCl, HI, HBr) you just count how many numbers are after the decimal place. So .01 M HCl has a pH of 2 (apparently…it seems high to me but that was the listed answer) and .001 would be a pH of 3. For acids like H2S04 you multiply the molarity by the number of H in the formula. So .005 M H2S04 would be calculated the same as .01 M HCl and would have a pH of 2. This also works with bases. Except instead of adding the number of digits after the decimal to 0 your subtract it from 14. So .01 M NaOH would have a pH of 12. I don’t kno why this works, but it has for me so far. I did a quick search and found this chart (http://scidiv.bcc.ctc.edu/wv/acid_base/000-ph-number-line.htm) which seems to confirm my theory on calculating pH this way. I’m taking the Chem. test this saturday as well so I hope both of us have good luck on it.