Weak Acid strong Base Titration
Weak Acid with strong Base Titration
All right, here I’m gonna teach you how to do weak acid strong base titration. I’m doing a titration of acetic acid in here, which is a weak acid with 2 molar of sodium hydroxide. I’m going to say I don’t know the concentration of acetic acid, but you could use titrations to figure that out.
So in my burette I actually have it upstairs 0 Mark to make my measurements easier. I have 2 molar sodium hydroxide. I took the initial pH of the acetic acid and it was to a lot higher than the initial pH reading of hydrochloric acid, which means that this is definitely a weak acid.
Higher pH means less acidic, more basic. All right. Now before we do the titration, we got to add some phenolphthalein acid-base indicator. I did a couple of drop, and i’m going to throw that in there swirl 3x, and now I’m going to drop a couple of mL of the sodium hydroxide and record changes in pH.
I’m going to do two at a time. So I got 2ml swirl 5x, 2ml and I saw a lot of pink color. All right, I have it exactly at the 2ml mark, Now. I’m going to quickly record the pH. Looks like the peaches 3.0 my Jumping 3x. My knee keeps on going on. Looks like the pH is about 3.96. Right. So 3.96 is the pH since it jump so much. I’m going to do another .5Ml, right, so I got another .5ml in there. So it’s 2.5 milliliters.
And if I were quickly record the pH, pH is about 4.13, just a quickly do it 4.13. I’m going to add another .5 in, they’re not even looking at the bottom here.
Right? And the technique is better if you had a drop slowly, slowly, So I have 3ml in here. Now that pH then looks like it’s 4.23 Okay Let’s drop another .5x. So this is worth a 4Ml. Now I have 4ml in here. And it looks like my pH is 4.41, kind of hang it onto a constant pH. There’s a reason for that.
All right. I’m going to drop another ml I got 25ml, got a dark color, I got 5ml. And my pH is looking like 4.57, I’ll just wait for it to stop. So 4.57 found a steady pH here, all right, we’re going to call this the buffer region, I’m going to drop another ml in there.
I got 6ml and my pH is about 4.83, got a steady climb here. Another ml again, got 7ml in here, in the pink color. We got 5.06 after dropping up until 7ml.
Let me do another .5 actually. I got 7.5 was getting darker. Once you notice that big pink color is coming around, that means you’re getting very close to your end point. I got 5.28 is my PH, got slutty. It’s a steady Increase, 5.28 I got 7.5ml approximately and there’s two decimal places for the burette. So I’ve been recording them at 7.50, let’s do another .5, let’s go to 8ml.
when you look at that pink you will realize that is getting really dark, taking a pH I got 5.47, 5.47 is my pH I have 8ml in there, drop another .5 actually drop a ml. I got 9ml in here. And I went way past the end point. I’m at 9ml, 9ml was way too much for that.
Well, actually, no, it’s going away swirl 3x. That’s why you swirl. I add a little bit of water. I didn’t do that before adding a little bit of water swirl 3x.
Not as dark as the other one taking the pH. And I’ve climbed to about look in the think that the colors kind of Disappearing a little bit, after throwing a little bit more. But now I have a pH of about let’s say it’s slowly increasing, and the colors going away.
I got a pH of about 7.0800 and the color is fading even more. All right. So there’s some equilibrium reaction happening in here where the base is reacting and it’s going back and forth and I’m making acid using up acid, making acid using up acid, and the color is fading, that’s a nice pink color and if you can see it in the result you’ve got right, and now my pH is about 8.05 after 9ml.
I did jump a bit, right? now it’s faint pink, a little bit more. Let’s add maybe up to 9.5ml, I got a dark color swirl 3x and now I’ve definitely past the end point. All right, pH is about, we jumped way high. Now, we’re at 11ml
Let’s see. And the readings are very finicky. It doesn’t read it automatically. It’s stuck. It’s keeps on moving. That’s why there’s like a lag and and a jet air time sometimes because I’m waiting for the measurement. So I got 12.08 is my pH it jumped way up there. So 12.08 after having dropped a 9.5ml and put 50ml. I’m going to add a up until 10ml now. I’m going to record measurements beyond the dark pink, all right. I got 10mL in there and my pH is about 12.33ml.
12.33ml And I got 10ml. I’m going to add another ml in there. Now. I’m at like 11ml, and my pH should be higher, I got 12 point. Let’s see what we got and again, it’s a bit finicky, but this is way past the end point. So a lot going on there 12.59, you want to record the pH after the end point. So you get like the rest of your curve.
You don’t want to have the curve just automatically stop, you want to see where the curve could keep on going? So you could find kind of like a midpoint. I’m going to do another 2 or 3ml. So first, let’s do 12ml.
I’m at 12ml, and my pH is very finicky. Again pH is about 12.58 So we’re kind of getting flat now. Peaches and changing 12.58. Let’s do maybe 1 or 2 more. I’m going to go to 13ml, Swirl 5x. pH is about 12.72ml and that’s after adding 13ml.
Let’s go to 14ml See if the pH changes anymore or at about 14ml, record that pH. We got about 12.8ml. All right, so let’s get still staying kind of flat 14ml, let’s do 1 more, 15 by the way, this is way past the end point, but we’re still getting the state, that means all of the assets gone by now, if they were still acid in there.
It’d be a bit colorless like this, but there’s no acid in here. I have all faced and how do I know that I have mostly roll-base. The pH is really high, pH is greater than 7. So it’s mostly basic. All right, and so now I have 12.84ml, so I’m going to say I’m done recording measurements up to 15ml, and it went to 12.84ml.
For the 12.84 Okay. So if I wanted to plot this graph, now, I’m going to plot this graph and get that shape or the titration curve. Remember the pH started higher initially before dropping anything It was higher than my HCL.
I mean my hgf peach was like .4ml, which means that this acetic acid is definitely weaker than hydrochloric acid, because it has a higher pH, higher oH means less acidic. Alright, so after After dropping 2ml in, 1 up to about a pH of 4ml Someone up here. All right, after the 2.5ml and went to like 4.13ml so like I had a little bit more and it went away 4.13ml.
And then I added a bit more and for like a couple of readings that stayed in the four to five region. So like over here, all of these points kind of stayed a bit flat and you can kind of see them as soon as and it’s still kind of over here as soon as I got to like 8 and 9 and started climbing up a little bit more to a pH of 5 or 6. So right here 9 I got 5 and then 6, right? So slowly climbing. And then after 9, it went to 8 up here.
And then after 9.5 and went all the way up to 12, so the shorter curve and then after 10 kind of stayed up here. I have a very short curved but I only did it up to 15ml basically, my curve looks something like this.
Titration Curve Graph
A much shorter curve. That’s because I required less sodium hydroxide and so it looks like my with 1’s point will look at this. And this is true for a titration of a strong base with a weak acid. Looks like my equivalence point, the pH is about 9 at the equivalence point, it’s higher.
If I titrate a strong base with a weak acid, the pH at the equivalence point is going to be basic because I have the strong, strong base if I had the opposite, if I titrated a strong acid with a weak base, my pH is going to be lower. And so now that I know this is kind of like my Alan’s point, I could go on down and see that it took approximately 10ml of 2 molar NaOH to titrate this.
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