# Understanding Titration: A Comprehensive Guide to Determining Solution Concentration

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## Introduction

Titration is an essential procedure in analytical chemistry used to determine the concentration of a solution. Whether you're a novice in the lab or an experienced chemist, understanding the fundamentals of titration is crucial. This article will clarify the titration process, focusing on an example involving hydrochloric acid (HCl) and sodium hydroxide (NaOH). We will explore how to perform titration, interpret results, and calculate the concentration of an acid.

## What is Titration?

Titration involves the gradual addition of a titrant (a solution of known concentration) to a solution with an unknown concentration until a reaction is complete. The point at which the reaction is complete is called the **endpoint** and can be identified using various indicators. In our example, we use phenolphthalein as the acid-base indicator.

## Materials Required

To perform a titration, you will need the following materials:

**Hydrochloric acid (HCl)**- the acid solution with unknown concentration.**Sodium hydroxide (NaOH)**- the standard solution with known concentration (e.g., 0.100 M).**Phenolphthalein**- the acid-base indicator that changes color in response to pH.**Burette**- for dispensing the titrant.**Erlenmeyer flask**- to hold the solution being titrated.**Pipette**- for measuring the volume of HCl accurately.

## Step-by-Step Procedure

### 1. Preparing the Solutions

- Measure
**20.0 mL**of hydrochloric acid using a pipette and transfer it to an Erlenmeyer flask. - Add
**a few drops of phenolphthalein**to the flask. Since the solution is acidic, the indicator will remain colorless.

### 2. Setting Up the Burette

- Fill the burette with the sodium hydroxide solution. Make sure to record its starting volume accurately.
- Carefully note the concentration of the NaOH solution; for our example, this is
**0.100 M**.

### 3. Performing the Titration

- Begin adding NaOH to the HCl solution slowly while swirling the flask to ensure thorough mixing.
- As you add NaOH, watch for a color change. Phenolphthalein will turn light pink when the solution reaches the endpoint, indicating that all HCl has been neutralized.
- Stop adding NaOH once the light pink color persists, indicating a slight excess of NaOH.

### 4. Recording the Volume Used

- Note the final volume of the base in the burette. Let's assume you used
**48.6 mL**of NaOH to reach the endpoint.

## Calculation of Acid Concentration

Once the titration is complete, you can calculate the concentration of the HCl solution using the following steps:

### Step 1: Calculate Moles of NaOH Used

Using the molarity (M) formula: [ M = \frac{\text{moles}}{\text{liters}} ] Converting the volume of NaOH from mL to liters: [ 48.6 \text{ mL} = 0.0486 \text{ L} ] Now, calculate the moles of NaOH used: [ \text{Moles of NaOH} = 0.100 \text{ M} \times 0.0486 \text{ L} = 0.00486 \text{ moles} ]

### Step 2: Determine Moles of HCl

Based on the balanced chemical equation for the reaction:
[ \text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O} ]
This shows a **1:1 molar ratio** between NaOH and HCl. Therefore, the moles of HCl in the solution is also **0.00486 moles**.

### Step 3: Calculate Concentration of HCl

Using the initial volume of HCl in liters: [ 20.0 \text{ mL} = 0.0200 \text{ L} ] Now calculate the concentration of HCl: [ \text{Molarity of HCl} = \frac{\text{moles of HCl}}{\text{liters of HCl}} = \frac{0.00486}{0.0200} = 0.243 \text{ M} ]

## Shortcut Calculation

For a faster calculation, you can use the formula: [ M_a \times V_a = M_b \times V_b ] Where:

- ( M_a ) is the molarity of the acid (what we are solving for).
- ( V_a ) is the volume of the acid (20.0 mL).
- ( M_b ) is the molarity of the base (0.100 M).
- ( V_b ) is the volume of the base used (48.6 mL). Plugging in values and solving gives the same concentration of HCl.

## Conclusion

Titration is a fundamental laboratory technique used to determine the concentration of an unknown solution accurately. In this article, we detailed the titration of hydrochloric acid with sodium hydroxide using phenolphthalein as an indicator. By following the steps outlined and performing calculations, you can effectively determine the concentration of acidic solutions. Mastering titration enhances your analytical skills in chemistry, ensuring accurate and reliable results in your experiments. With practice, you can confidently navigate more complex titrations and further your understanding of acid-base chemistry.

Titration is a procedure for determining the concentration of a solution. And so let's say we're starting with an acidic solution.

So in here let's say we have some hydrochloric acid. So we have come HCl. And we know the volume of HCL,

let's say we're starting with 20.0 milliliters of HCl. But we don't know the concentration right? So question mark here for the concentration of HCl.

We can find out that concentration by doing a titration. Next we need to add a few drops of an acid base indicator. So to this flask we're also going to add

a few drops of an acid base indicator. We're gonna use phenolphthalein. And phenolphthalein is colorless in acid

but turns pink in the presence of base. And since we have our phenolphthalein in acid right now we have a clear solution.

There's no color to it. Up here we're gonna have our standard solution right? We're gonna have a known concentration of sodium hydroxide.

So let's say we have a solution of sodium hydroxide and the concentration is zero point one zero zero molar. And we're ready to start our titration.

So we allow the sodium hydroxide to drip into our flask containing our HCl and our indicator. And the acid in the base will react, right?

So we get an acid base neutralization reaction. HCl plus NaOH right? If we think about the products, this would be OH minus,

this would be H plus, H plus and OH minus give us H2O. And our other product we would have Na plus and Cl minus,

which give us NaCl, or sodium chloride. So let's say we add a certain volume of base right? So now this would be higher,

and we see our solution turn light pink. Alright so let's say we see our solution turn light pink and it stays light pink.

That means that all of the acid has been neutralized by the base. And we have a tiny amount of excess base present,

and that's causing the acid base indicator to remain pink. So a tiny excess of base means we've neutralized all of the acid present.

And where the indicator changes color, this is called the end point of a titration, alright? So when our solution changes color,

that's the end point of our titration. And here we stop and we check and see the volume of base that we used in our titration.

So if we started right here, if we started with that much base, let's say we ended down here, alright?

So we still have a little bit of base left. And this would be the volume of base that we used in the titration.

Alright so we have a change in volume here, and let's say that it's 48.6 milliliters. So it took 48.6 milliliters of our base

to completely neutralize the acid that we had present. And so we can now calculate the concentration of the HCl. Alright so let's go ahead and do that,

and let's start with the concentration of sodium hydroxide. Alright we know that we started with point one zero zero molar solution of sodium hydroxide.

So point one zero zero molar. And molarity is equal to mols over liters. Alright so this is equal to mols over liters.

And our goal is to figure out how many mols of base that we used to neutralize the acid that was present. Alright so we can take our volume here, 48.6 mililiters

and we can convert that into liters. Alright so just move your decimal place three places to the left.

So one, two, three. So that's point zero four eight six liters. So this is equal to mols over

zero point zero four eight six liters. And so let's get some more space. Alright let me just rewrite this really quickly.

Zero point one zero zero is equal to X over zero point zero four eight six. So we're just solving for X, and X represents

the mols of sodium hydroxide that were necessary to neutralize the acid that we had present. Alright so when you solve for X,

you get zero point zero zero four eight six mols of sodium hydroxide used in our titration. Next you look at the balanced equation for what happened .

So if I look at my balanced equation alright there's a one here and there's a one here.

So we have a one to one mol ratio. And the equivalence point is where just enough of your standard solution has been added

to completely react with the solution that's being titrated. And at the equivalence point, all of the acid has been neutralized.

Right? So it's completely reacted. And since we have a one to one mol ratio, if I used this many mols of sodium hydroxide,

that must be how many mols of HCl that we had present in our original solution. So therefore, I can go ahead and write that I must have had

zero point zero zero four eight six mols of HCl present in the flask before we started our titration. Right and I knew that because of the one to one mol ratio.

Remember our goal was to find the concentration of HCl. The original concentration. And concentration,

molarity is equal to mols over liters. So now I know how many mols of HCl I had, and my original volume of HCl

was 20 milliliters right? So right up here we had 20 milliliters. So I need to convert that into liters.

So I move my decimal place one two three. So I get point zero two liters. So now our final step here to calculate

the concentration of HCl, right so the concentration of HCl is equal to how many mols of HCl we have,

which is zero point zero zero four eight six mols, over liters of solution. And we had 20 milliliters which is equal to

zero point zero two zero zero liters. Alright so now we can take out our calculator and do this calculation to find

the concentration of HCl that we started with. Point zero zero four eight six, all right and we're gonna divide that by

point zero two zero zero. And we get zero point two four three for our answer. So the concentration of HCl is equal to

zero point two four three molar. So we've solved for the original concentration of HCl. There's a shortcut way to do this problem,

and the shortcut way would be to do the molarity times the volume of the acid is equal to the molarity times the volume of the base used.

So MV is equal to MV. So let's say we have the acid over here on the left, and the base over here on the right.

So the molarity of the acid is what we're trying to find. So I'll just make that X. The volume of the acid that we started with,

you can just leave this in milliliters if you want, 20 point zero milliliters is how much of the acid we started with.

And for the base, we knew the concentration of the base that we used in our titration right? It was zero point one zero zero molar.

And we also knew the volume of base that we used to completely neutralize the acid. We used 48.6 milliliters.

And notice how the mLs would cancel out here. Right and we can just go ahead and do the math and solve for X.

So we get out the calculator, and we need to multiply 48.6 times point one zero zero. Alright and so we get four point eight six obviously.

And then if we divide by 20 we will get our answer of zero point two four three. So X is equal to zero point two four three molar.

And this shortcut way works pretty well when you're dealing with a strong acid and a strong base and a one to one molar relationship.

Alright in the next video we'll do a problem where the mol ratio is no longer one to one.