Intro to Acid-Base Titration Curves - Video Tutorials & Practice Problems
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Acid-Base Titration Curve
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Now, when it comes to an acid base titration, realize that it is a neutralization reaction used in determining the concentration of an acid and a base. Here, we have some terms to remember when it comes to an acid base titration. The first one being a tit trin, a tit trt is a strong acid or base solution with a known concentration that is added to the titrate. Now, what's a titrate? Well, a titrate is an acidic or basic solution with an unknown concentration being neutralized by the tight trend. The titration curve results from their interacting with one another. Here, we're going to say the titration curve is a graph of the ph of the titrate during the titration with a T trend, right? So these are terms that you need to remember. So if we were to visualize this, we would say that in an acid base titration, we have our set in our set up, we have our flask within this flask, we have our titrate above it. We have our burette and drop by drop. We're adding our T Trent here. We're saying that our tran is in the form of potassium hydroxide. A known strong base here, we're showing the ph before any of our strong base has been added. So before any strong base has been added, we have here a ph of one. And what we're seeing here is the gradual addition of various volumes of potassium hydroxide. When we've gotten to 10 MLS of potassium hydroxide added, the PH has increased to 4.15. When we got to 50 MLS of potassium hydroxide, the PH is around 8.76. And then once we got to 100 mls of potassium hydroxide, we can see that our PH is 12.95 here. If we take each one of these basic volumes and PHS, we can put them on a graph and create our titration curve here. Our PH is on the Y axis and the various volumes of our titrate being added are on our X axis here. This is how our curve is actually form. So this curve is the result of adding our potassium hydroxide tran to our titrate within this uh flask here. Now, the titrate itself, all we said is that it's an acidic or basic solution. It doesn't necessarily have to be a strong acid or a strong base. All that's important is that it's acidic or basic in nature. OK. So it could be strong or weak. The tran on, on the other hand, has to be a strong species when doing these typical types of acid base titrations. Later on, we'll go into greater detail and talk about the various parts of a titration curve that results from the interaction between a titrate and a tight trend.
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The Equivalence Point
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Now, when it comes to acid base titration curves, you'll hear the term equivalence point. Now, the equivalence point is just the point of complete neutralization where the moles of acid equal the moles a base. Here, we're going to say the equivalent point volume equation represents a simplified approach to solution stoichiometry calculations. So in the past, we've talked about doing stoichiometry and incorporating calculations dealing with molarity, we can bypass that by using this simplified version of the equivalent point volume formula. Here, it represents ma times va equals MB times VB. Here ma equals the molarity of the acid. That's why it's a va equals the volume of the acid. So MB would be the molarity of the base because of B and VB would be the molarity of the base or the volume of the base. Now, what's important in terms of this equation is it helps to simplify solution to geometric calculations, but you still need to pay close attention to the type of acid and base that you have. Here, we're going to say for di protic, which means you have two acidic hydrogens and for polyp protic acids when you have more than two, the number of H plus ions will affect the overall concentration. So for example, let's say we had 0.40 molar of sulfuric acid, sulfuric acid in itself has a total of two acidic H plus ions. Yes, I know that the first one is strong, but the second one is very weak. But here we're looking at the totality of, of the number of H plus ions within sulfuric acid. That being two, that would mean that the true concentration when it comes to equivalence point would be H plus equals the concentration of the whole compound times the number of H plus ions, which is two. So that gives us a true concentration of 0.80 molar. Now, for strong bases, we've done what we've always done. We've looked at the number of oh minus H minus 02 minus and NH two minus ions be, this gives us the true concentration of our strong base. So for example, we have 0.10 molar of be hydroxide. It has two oh minus ions within it. So the true concentration of oh minus would be 0.10 which is the concentration of the entire compound times two, the number of oh minus ions. So this would be 0.20 molar, right. So keep in mind if you're going to utilize this equivalence point volume formula to keep an eye out for the number of H plus ions in our acid. And also the number of our basic anions for the base. So that would be in the form of, oh minus H minus +02 minus and NH two minus respectively.
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example
Intro to Acid-Base Titration Curves Example
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He is considered the titration of 40 mls of 0.0550 molar of carbonic acid with 0.1 60 molar aluminum hydroxide. How many milliliters of 0.160 molar aluminum hydroxide are required to reach the equivalence point. So here we're talking about the complete neutralization between our acid and our base. So here we're gonna say m acid times V acid equals M base times V base. Here we have to take in consideration how many H plus ions our acid has carbonic acid has two H plus ions. So we'd have to multiply this concentration by two. So it's real concentration will be 0.110 molar, the volume of our acid is 40 MLS. Then here we have to figure out the molarity of our base aluminum hydroxide has three hydroxides in it. So we multiply the concentration times three. So it'd be 0.480 more. And we're looking for the volume of our base. That's what's missing. Divide out the 0.480 molar here molarity cancel out and we'll have our answer in Millers. When we plug that in, we're gonna have 9.17 mL of our alumin hydroxide pits.
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Shape of a Titration Curve
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In our further discussion of acid base titration curves, we can say that the parts and overall shape of the titration curve depends on the type of titrate and titrate used, whether they're both strong or a combination of weak and strong can have a vast effect on the overall shape of our titration curve. Here, we're going to say sigmoid, this is the shape of the titration curve when both the titrate and tight trend are strong, kind of like an s almost like an uh a more straightened out shape. Now here, this is an example of a strong, strong titrate, strong titrate curve. It gives us a sigmoidal shape. And when it comes to this typical type of acid base titration curve, there are some key features you need to keep in mind. So here we're gonna say are pure tit trait. So this is just the beginning of the titration before any tran has been added. So here we have zero MLS of our tran that has been added. So this is our starting point and that's what we have just the pure titrate by itself. Then we have what's called the equivalence point, the equivalence point is just the middle region of the curve that has the steepest incline. So we see that it sharply increases. Once we hit around 60 mls, it kind of like shoots up the middle of that, that's our equivalence point. And then finally, we're gonna have after the equivalence point, this is just a region where excess tight trt is being added. So once we've gone beyond this equivalence point, this is where we have access tran that's continuously added. And then we reach a plateau over time, right? So keep in mind when we're dealing with the ST strong tight rate, strong tight rate curve. These are the three key features. You should keep in mind when looking at a typical curve.
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example
Intro to Acid-Base Titration Curves Example
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Based on the image of the titration curve provided below. What is the potential identity of the titrate? All right. So if we take a look here at this curve, we have a sigmoidal shape just in the opposite direction. So it's still between a strong titrate and strong tight trend. Remember if we want to find the identity of the titrate, look at the beginning of the titration curve, we're gonna say the beginning starts before we've added any tight. So we're starting right here. Now, what can we say about this starting point? Well, we can say that this starting point has a ph of 12. So it's a ph that's greater than seven, meaning that our tight trait is a basic compound. Remember basis have PHS greater than seven. So if we take a look here, which one of these will represent a base. The first one is nitric acid, it is an oxy acid. So it wouldn't count, then we have Hydrofluoric acid. A binary acid that doesn't count either potassium hydroxide. This is an example of a strong base. So this could be our answer. Next, we have acetic acid doesn't work. And then finally, that we have a positively charged amine, remember, positively charged amines are acidic. So they would have PHS less than seven. So out of all the options, option C is the correct choice. Potassium hydroxide represent a strong base and it would represent the identity of my tit rate.
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Problem
Problem
Consider the titration of 100.0 mL of 0.40 M HCl with 0.40 M NaOH. If sodium hydroxide is the titrant, which volume would place it in excess?
a) 70.0 mL b) 25.0 mL c) 100.0 mL d) 110.0 mL e) 9.0 mL
A
70.0 mL
B
25.0 mL
C
100.0 mL
D
110.0 mL
E
9.0 mL
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