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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: FadyDaniel on July 20, 2009, 06:38:23 pm

Title: pH practical
Post by: FadyDaniel on July 20, 2009, 06:38:23 pm: I completed a prac today on pH. For some odd reason, when I added the methyl violet to .1 M HCl solution, it went green. I thought it was either supposed to go yellow or violet.

Does anyone have any idea why this happened?

Also, when I added 20 drops of HCl and Na2C03(instead of NaOH to produce a neutral solution, which we did not have at school for some reason) in a test tube, the universal indicator added gave me a pH of ten. According to the equation, you get NaCl, C02 and H20- so how is this basic? (keep in mind that they both have the same concentrations- 0.1 M).

Please help!
Title: Re: pH practical
Post by: monokekie on July 20, 2009, 06:50:03 pm: haha, are you in year eleven? i recall times when we get really wiered colours during those pH experiments back in unit 1n2, even though we were 1000% that we did everything correctly. can't really tell why this happened... our teacher didn't bother to explain lol.

hmm.. universal indicator turned to pH of ten? i guess you didn't add enough acid ... because only equal amount of acid and base can produce a neutral solution :) (somethine like that )
Title: Re: pH practical
Post by: FadyDaniel on July 20, 2009, 06:53:55 pm: Yes monokekie, I am in year 11. My teacher did not explain why it happened either!

I know that I need to add equal amounts of acid and base, and I am sure I put 20 drops of each!
Title: Re: pH practical
Post by: FadyDaniel on July 20, 2009, 07:14:16 pm: Um... do it ourselves? I just wanted some advice, not answers!
Title: Re: pH practical
Post by: TrueTears on July 20, 2009, 07:32:59 pm: Quote from: FadyDaniel on July 20, 2009, 06:38:23 pm
I completed a prac today on pH. For some odd reason, when I added the methyl violet to .1 M HCl solution, it went green. I thought it was either supposed to go yellow or violet.

Does anyone have any idea why this happened?

Also, when I added 20 drops of HCl and Na2C03(instead of NaOH to produce a neutral solution, which we did not have at school for some reason) in a test tube, the universal indicator added gave me a pH of ten. According to the equation, you get NaCl, C02 and H20- so how is this basic? (keep in mind that they both have the same concentrations- 0.1 M).

Please help!
One reason could be because all of the $H^+$ reacted to form $H_2O$ but there were still unreacted $OH^-$ ions [in excess] hence it is more basic.