FDST 132 - Moisture PH - Lab Activity 2

Rossana Villa Rojas Author

07/23/2020 Added

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Practical Applications in Food Science

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[00:00:03.580]Laboratory activity two,
[00:00:05.940]pH and titratable safety.
[00:00:09.490]In this laboratory session, you will use
[00:00:13.540]pH meter, calibration standards,
[00:00:17.360]sodium hydroxide, buret, one of the following samples,
[00:00:22.410]lemon juice, pop, vinegar solutions,
[00:00:26.130]and Erlenmeyer flask, phenolphthalein solution, pipettes.
[00:00:31.530]You can find a written instructions
[00:00:33.400]for this laboratory activity
[00:00:35.200]in the manual uploaded to Canvas.
[00:00:38.154]The laboratory today has two parts.
[00:00:41.210]We already put our samples in the oven
[00:00:45.330]to measure moisture content.
[00:00:47.680]You've seen my demonstration about the OHAUS balance,
[00:00:53.110]thermal balance, to measure moisture content.
[00:00:56.130]Now we're gonna measure pH and titratable acidity.
[00:01:01.216]You have a bunch of different options
[00:01:04.240]on the samples that you can use.
[00:01:07.030]You can use pure vinegar,
[00:01:09.540]one-on-one dilution with vinegar and water,
[00:01:12.400]one-on-two dilution, one part vinegar for two parts water,
[00:01:17.260]lemon juice, or soda pop.
[00:01:21.030]So in my case, I'm going to use soda pop,
[00:01:24.310]and I chose a transparent one
[00:01:26.080]because the titratable acidity
[00:01:28.600]is gonna depend on the change of color.
[00:01:31.470]So I need to be able to see that.
[00:01:36.630]When your sample is very difficult, has a darker color
[00:01:41.210]so it's very difficult to see
[00:01:42.450]a change in color of phenolphthalein,
[00:01:45.850]then what you do is to measure pH while you're titrating,
[00:01:51.460]and you're looking for neutrality.
[00:01:53.530]So that's a pH of around seven.
[00:01:55.840]pH meter calibration.
[00:01:58.720]Okay, so the first thing you want to do
[00:02:00.440]is to make sure you know how to calibrate it.
[00:02:04.110]This particular model has the instructions here
[00:02:08.030]on how to calibrate your pH meter.
[00:02:11.130]And so the first thing is to
[00:02:15.270]take your probe out of its solution
[00:02:18.430]and then rinse it with just a water.
[00:02:22.100]Now, the first thing I need to do is turn on my pH meter,
[00:02:25.650]which I already did with this button,
[00:02:28.250]and then here it says, so like pH mode,
[00:02:31.900]which I'm already in.
[00:02:34.540]I can see it because there's a pH here,
[00:02:36.870]and then place electrode in the first buffer
[00:02:39.980]and then press calibrate.
[00:02:49.240]So now you can see the display is in calibration mode
[00:02:54.450]and I'm on buffer number one, which is my pH four.
[00:02:59.410]And my pH here is blinking.
[00:03:02.430]Now it stopped blinking,
[00:03:04.470]and I have an arrow here that started blinking.
[00:03:10.560]Calibration one will display.
[00:03:12.160]The pH icon stops flashing.
[00:03:15.050]When this stops flashing,
[00:03:17.040]press calibrate key to accept that measurement.
[00:03:20.310]So I'm at four, 4.01 is good enough.
[00:03:25.910]I take it out.
[00:03:28.980]Rinse it.
[00:03:34.730]Remove excess water.
[00:03:43.880]Put it in my second solution.
[00:03:50.250]Now CAL two will display.
[00:03:54.210]Rinse the electrode and place it in the second buffer
[00:03:57.170]and stir moderately.
[00:03:58.480]I've already done that.
[00:04:00.650]When pH icon stops flashing, press the calibration recurve.
[00:04:10.640]Calibrate, then I press this icon to save it.
[00:04:14.920]So I'm pressing this,
[00:04:18.610]and then I'm pressing this icon to save it.
[00:04:27.820]So you can see on the screen that I no longer have CAL here,
[00:04:32.140]which just means I'm not in calibration mode.
[00:04:35.030]I have this icon here with a probe.
[00:04:37.660]That means that it's measuring.
[00:04:40.933]And I have a four and a seven.
[00:04:43.140]That means that I calibrated using
[00:04:45.620]a four and a seven pH buffer.
[00:04:49.020]pH measurement.
[00:04:51.600]The first thing that I need to do, as your instructions say,
[00:04:55.330]is to take five milliliters
[00:05:02.410]of sample and put it in an Erlenmeyer flask
[00:05:05.910]and then mix it with 25 milliliters of distilled water.
[00:05:12.270]The easiest thing to do, instead of putting it here,
[00:05:17.740]to avoid contaminating my sample
[00:05:21.040]is to pour a little bit of it in a container.
[00:05:32.850]And that way,
[00:05:37.200]I prevent any contamination,
[00:05:38.870]and if I need to reuse my sample, I have it there too.
[00:05:44.830]I'm going to press S.
[00:05:46.340]S means suction.
[00:05:48.130]The S is right here.
[00:05:53.990]This one is a little bit tricky because it's soda
[00:05:56.110]so it has a lot of carbonation and gas.
[00:05:59.040]Remember your chemistry classes.
[00:06:01.590]You're supposed to watch the aliquot at a eye level
[00:06:05.520]to make sure that you're taking the correct measurement.
[00:06:14.500]And that's it.
[00:06:15.620]I have five millimeters,
[00:06:18.824]and by pressing empty, I'm going to pour my sample
[00:06:23.200]into my Erlenmeyer flask until all the drops are out.
[00:06:30.870]To measure water I'm going to use a probette.
[00:06:37.224]And I want to gently slide the liquid through the side.
[00:06:44.780]Now I'm going to pour this into my Erlenmeyer flask
[00:06:54.330]and gently swirl.
[00:06:58.050]To measure the pH of my sample,
[00:06:59.940]I need to take the probe and rinse it out,
[00:07:03.230]get out the excess water, which I've done.
[00:07:09.320]I'm going to take it out of its stand
[00:07:10.930]because it's a little bit difficult for it
[00:07:12.950]to go to be covered by my sample,
[00:07:15.120]and tilt this flask so I'm sure my electrode is covered.
[00:07:21.070]Hit the measure button
[00:07:24.500]and wait for the probe to equilibrate properly.
[00:07:32.042]Okay, now that's stopped blinking,
[00:07:34.940]and the pH of my sample is 3.45.
[00:07:39.280]Remember to always rinse and pat dry your probe.
[00:07:43.570]Titratable acidity.
[00:07:46.530]Now that we've measured pH, let's measure the acidity,
[00:07:50.130]the percentage of acid in our sample.
[00:07:53.580]For this, we're gonna do a titration with sodium hydroxide.
[00:07:58.410]So this, this is a buret.
[00:08:01.676]I want to make sure that it's closed
[00:08:05.050]by putting this little lever in the closed position,
[00:08:10.230]so transversal to my tube, and then I'm going to use
[00:08:17.460]this funnel to pour my hydroxide,
[00:08:23.370]sodium hydroxide solution into my buret.
[00:08:29.270]And the reason why I'm going above
[00:08:32.380]the capacity of my buret is
[00:08:38.830]to make sure that the full volume is covered.
[00:08:45.470]What does that mean?
[00:08:46.850]This also takes into account this little part
[00:08:52.270]where the drops of sodium hydroxide are dripping.
[00:08:58.240]So I need to make sure that this is at eye level with me
[00:09:03.930]over here, and now I'm gonna open my valve
[00:09:11.150]and let it drain.
[00:09:13.400]That is covering everything here.
[00:09:15.270]Let it drain
[00:09:17.600]to zero.
[00:09:20.560]We're instruction number three on your manual.
[00:09:23.460]We need to add five drops of phenolphthalein solution,
[00:09:26.690]which will be our indicator, to the flask
[00:09:29.790]and titrate with sodium hydroxide solution
[00:09:34.590]until the pink end point,
[00:09:37.330]which is a pink color last for about 20 seconds,
[00:09:41.690]and then record how much volume we've used.
[00:09:46.248](sped up squeaking)
[00:09:52.900]And make sure I swirl it to mix it pretty well.
[00:10:00.650]And now I can start titrating.
[00:10:06.800]So if you remember your chemistry classes,
[00:10:10.128]you should start, since we don't know
[00:10:12.570]where is the start point or the end point,
[00:10:15.707]we can start by dropping a few drops at a time,
[00:10:21.840]and you can control the speed of the drops
[00:10:28.010]by opening the valve more or closing it a little bit more.
[00:10:37.490]Okay, so now you can see that it's been dropped.
[00:10:42.530]And as soon as I dropped in,
[00:10:44.790]I'm going to put it a little bit moved up
[00:10:47.020]so it's easier for you to see, there was a pink color
[00:10:50.240]but the pink color didn't stay.
[00:10:57.160]So the pink color has to stay for about 20 seconds.
[00:11:03.717](sped up squeaking)
[00:11:22.244]So now I have a very pink color in my solution
[00:11:27.800]and I can measure,
[00:11:29.870]but it was, in my case, about 1.1 milliliters
[00:11:37.617]of sodium hydroxide at .1 normal.
[00:11:42.210]Now I can use this volume to calculate
[00:11:46.110]the amount of acid that is in my sample.
[00:11:50.420]How much was in yours?
[00:11:54.000]Watch the post-lab video to take a look at the calculations
[00:11:58.320]that we can use, and you can also find them in your manual.
[00:12:02.630]This is it for today's lab on moisture content,
[00:12:06.680]pH, and acidity.
[00:12:09.850]I'll see you next time.
[00:12:12.440]This concludes the instructional video
[00:12:14.640]and discussion for this laboratory session.
[00:12:18.070]The written instructions for your laboratory activity
[00:12:21.350]and further instructions for your lab report
[00:12:23.870]can be found posted on Canvas.
[00:12:26.260]Thank you for watching this video.
[00:12:28.720]Have a lovely day, and I'll see you on the next session.

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FDST 132 - Moisture PH - Lab Activity 2

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