Title: Why did my experiment kept going wrong? Titration with NaOH Post by: Rinab123 on May 9, 2013 so i added say about 1.025 g of KHP to my flask and about 35 mL of water.
i filled up my buret to 0.00 ml of NaOH. placed flask under buret with 3 drops of pendol.... (it has a long name lol) in the flask now when i was doing the titration the naoh in buret went to say 2.15 ml and my solution already turned pink. my proffesor says thats too little and its wrong . he said it shoulod be around 24 or 27 ml so why my solution turns pink so quick?? what am i doing wrong p.s.i had the worse day in lab and honestly i cried when i left. i hate the people in there and every one is so judmental and mean...including my teacher. he think i dont get stuff because i dress girly..i can tell. i cant stand how they r stereotyping still over how people look.. he gave this older lady credits and not me..anyways...enough of this sorry lol Title: Why did my experiment kept going wrong? Titration with NaOH Post by: nurisar on May 9, 2013 Two things could be wrong. You may have mis-weighed your KHP, like misplacing a decimal point maybe? Your description sounds like it is in the ballpark for a decimal point error. Or, your NaOH is not the right concentration, also by a decimal point, not sure if that was given to you or you had to make it yourself.
BTW, I had crotchety analytic chemistry teacher who rode one guy in my lab pretty hard without helping him, by just asking him the same question he did not know the answer to over and over. Some teachers are like that. If you can just get through this one, a good teacher is likely to be next, don't give up! Title: Why did my experiment kept going wrong? Titration with NaOH Post by: smiley on May 9, 2013 Stop crying and let us try and solve your problem:
KHP is the correct choice of standard to use when standardizing a base such as NaOH The indicator to use is phenolphthalein - which you seem to have used So you started off well The volume of water added to the KHP in the Erlenmeyer is not important . Now let us try and work out what you have done The general titration solution in the laboratory is usually about 0.1M to 0.25M NaOH solution Let us see what the molarity of the NaOH solution is according to your prof: NaOH reacts with KHP in 1:1 molar ratio. Molar mass KHP = 204.22g/mol 1.025g KHP = 1.025/204.22 = 0.00502 mol KHP This will react with 0.00502 mol NaOH If you follow the advice of the Prof: What is the molarity of the NaOH if the titration volume had been 25mL You know that 25mL will contain 0.00502 mol 1000mL will contain 1000/25*0.00502 = 0.200M This seems a reasonable molarity for a lab reagent solution You used approx 1/10th of the volume of NaOH - so the molarity of your NaOH is about 2.0M which does seem high Where can the problems be: 1) What NaOH solution were you using - was it something that you made up yourself , or was it provided by the laboratory ? If you made it up yourself was this done correctly. How did you do this? 2) You say that the solution turned pink after adding only 2.15mL of NaOH: How exactly did you do the titration: During the addition of the NaOH were you constantly shaking the Erlenmeyer flask to mix the NaOH with the KHP. Or did you add the NaOH into the Erlenmeyer which was just standing still beneath the burette. 3) Sorry to ask the obvious question - but are you sure that you weighed out 1.025g KHP and not some lesser amount. I will try and help you with this problem - but you have to provide full details of what you did. If you wish , you can email me directly via Yahoo - but provide all the details of what you have done and how you did it. A final note : Keep up the feminine clothes and appearance. A little bit of good dressing and fashion sense is an asset in all locations. |