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Homework Help: Working on my lab report

  1. Oct 6, 2013 #1
    1. The problem statement, all variables and given/known data

    Hi, I was working on my lab report and I got stuck. I was trying to get some input please. So my experiment was to put 2ml of cornstarch, 2ml saliva, 2ml HCl. I vary the HCl concentration in 3 test tubes. I have one test tube that is just 2mL HOH. I added iodine in and I watched as the blue color disappeared. Oh I had a 40 minute time cap on my experiment. I'm just having issue with my discussion because I feel like my data was bunk. In terms of fastest time for the blue color to disappear I had 2mL HOH, .025 N HCl. The solutions of .0125 N HCl and .05 N HCl were past the time cap. With this being said I will post what I have written so far. Please help me see if my statements are logical and not out of wack.

    2. Relevant equations

    The bold is what I'm most concerned about. This is just my slop copy.

    3. The attempt at a solution

    The hypothesis that Ph affects enzyme activity was supported. We observed that by changing HCl concentrations we could alter the time it took for the iodine indicator to disappear. Our general trend in terms of least time was 2mL HOH, .025 N HCl. The solutions of .0125 N HCl and .05 N HCl were past the time cap. Seeing as the optimum pH for amylase is 6.7-7.0 (Princeton). It would make more sense to see a trend in which the more acidic the solution the longer the time. For instance the trend in terms of increasing time would be more likely to follow , HOH, .0125 N HCl, .025 N HCl, .05 N HCl. A possible explanation for the trend in our data might be due to the collection and mixing process. Although each of the samples were shook regularly during the timing period the original collection of saliva may have had settling occur. Test tubes containing .0125 N HCl and .05 N HCl may have been mixed first where the
  2. jcsd
  3. Oct 7, 2013 #2


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    Staff: Mentor

    Sorry, but it is a word salad to me. There are patches that make sense, but overall I have no idea what you really did and what data you collected.
  4. Oct 7, 2013 #3
    Well, it seems good to me...grammar's a bit out of whack but the logic looks good.
    greater deviation from the optimum pH results in more time needed by the enzyme to digest the starch.
  5. Oct 7, 2013 #4


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    Homework Helper
    Gold Member

    Well you have to read several times and then you can guess.

    Result of apparently some hydrolysis in the intermediate acid concentration 0.025 N is odd, was thre a big difference between that and the water solution? if others did the experiment see the repeatability.

    Reasonable reasoning.
  6. Oct 7, 2013 #5
    A pH close to the optimum range (6.7-7) for salivary amylase should result in faster hydrolysis of starch, that was probably the point of 0.025N HCl.
    (I did this experiment in high school- lots of spitting was involved.:yuck:)
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