I have a midterm in a fewhours and am still trying to figure out how to solve pr

Question

I have a midterm in a fewhours and am still trying to figure out how to solve problems likethis one. I have the answer key (the answer is 4.75), I justdon't know HOW to do the calculations to get the answer.

"If 15 mL of 0.1 M sodiumhydroxide is added to 30 mL of 0.1 M acetic acid (Ka = 1.84 x10^-5) what is the pH of the resulting solution?"

Can someone help? Also, can you please please be as specific as possible? Iposted the question on Yahoo but only got a very vague andunhelpful answer. Thanks in advance!

Explanation / Answer

                              NaOH + CH 3 COOH   <--------------> CH3 COONa+ H 2 O Initial  moles            15*0.1       30*0.1                                            0                 0                                   1.5             3                                                  0                 0 Atequilibrium              0             3-1.5                                           1.5              1.5          The no. ofmoles of salt formed = 1.5 mole                 The no. of moles of acid which is not reacted =  (3-1.5) mole                                                                                =  1.5 mole According to Henderson's equation          The no. ofmoles of salt formed = 1.5 mole                 The no. of moles of acid which is not reacted =  (3-1.5) mole                                                                                =  1.5 mole According to Henderson's equation      pH = pK a + log {[ salt] / [acid]           = - log( K a ) + log { 1.5 / 1.5 }           = - log(1.84 * 10 -5 )          = 5 - log 1.84           =5 - 0.2648           =4.74  

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