Volumetric Analysis

Volumetric analysis is a standard method for determining an unknown concentration. With this method, a measured volume of a standard solution is mixed with a measured volume of the solution with an unknown concentration. Another name for volumetric analysis is titration. The element whose concentration needs to be calculated is referred to as titrate. The component whose solution is used to calculate the concentration of an unknown solution is known as the titrant. Volumetric analysis is additionally known as titrimetric analysis.

Table of Content

• Aim of the Experiment

• Material Required

• Theory

• Procedure

• Precautions

• Observation

• Result

• Lab Manual Questions

• Practical based Questions

• Viva Questions

• Summary

Aim of the Experiment

To determine the concentration of an unknown component in a solution by volumetric analysis technique.

Material Required

• A 100 mL conical flask

• A Graduated-burette

• A Graduated-Pipette

• Weighing tube

• Watch glass

• Measuring flask

• Measuring Cylinder

• Beaker (250 ml)

• Glass rod

• Tile

• Chemical balance

• Wash bottle

• Funnel

• Funnel stand

• Distilled water

Theory

Titration

Titration, also referred to as titrimetry, is a method used to determine the concentration of a specific analyte in a mixture that is used in chemical qualitative analysis. Titration, which is also sometimes referred to as volumetric analysis, is a crucial analytical chemistry technique.

Types of Titration:

Titration can take three different forms:

1. Simple Titration

When a concentration of one standard solution is known, it is possible to apply simple titration to determine the concentration of an unknown solution.

2. Back Titration

Back titration is also known as Indirect titration. It uses a known volume of an excess reagent to determine an analyte's concentration, whereas a direct titration looks directly at the concentration of an unknown analyte. When conducting back titrations, more reagents are not introduced.

3. Double Titration

To compare the concentration of a substance present in a solution with another solution, a double titration is conducted. Double titration is another name for Gilson's titration technique, which determines how much organometallic substance is present in a hydrocarbon solvent. 

Principle of Titrations

The following are some of the volumetric analysis's guiding principles:

• The solution, which needs to be investigated, must contain an unspecified amount of compounds.

• When an indicator is present, the reaction between an unknown chemical and a reagent at an unknown concentration demonstrates the end-point (usually phenolphthalein). The reaction has completed its course at the end-point.

• Titration is used to measure the volumes once the reaction between the solution and the reagent is complete.

• Titration is used to measure the volumes once the reaction between the solution and the reagent is complete.

• The volume and concentration of the reagent used in the titration indicate the amount of reagent and solution.

• The amount of an unknown chemical in the specified volume of solution is determined by the mole fraction of the equation.

When the reaction reaches its endpoint, the volume of reactant consumed is measured and used to calculate the analyte's volumetric analysis using the formula below.

$C_{a}=C_{t}\times V_{t}\times \frac{M}{V_{a}}$

Where,

The analyte concentration, usually expressed in molarity, is Ca.

The titrant concentration is usually expressed in molarity Ct.

V is the used titrant's volume, usually expressed in litres.

M is the analyte and reactant's mole ratio according to the balanced equation.

Terms Related To Volumetric Titrations

1. Standard Solution: Solutions containing a known concentration of a chemical are known as standard solutions. They are used to determine or calculate the amounts of unknown substances. Standard solutions are prepared using primary standards.

2. Indicator: Indicators are weak acids or bases that change colour as hydrogen ion concentration in a solution or pH varies.  Litmus, turmeric and phenolphthalein are examples of indicators.

3. Endpoint: The point in a titration when an indicator indicates that a solution has obtained the required amount of reactant to complete a reaction.

4. Molarity: Molarity, or molar concentration, is the ratio of a substance's moles per litre of solution.

5. Normality: The number of grams of solute present per unit of solution volume is referred to as normality.

Preparation of Standard Solution

1. Calculating the required amount of the substance is the first step in creating a standard solution.

For example, if we want to make 250.0 mL of a 0.0500 mol/L solution of sodium carbonate: 

$\\n = c \times V \\ \\n(Na_2CO_3) = 0.0500 \times 0.250 = 0.0125 \hspace{0.1cm} mol \\ \\m = n \times MM \\ \\m(Na_2CO_3) = 0.0125 \times (2 \times 22.99 + 12.01 + 3 \times 16.00) \\ \\m(Na_2CO_3) = 1.33 \hspace{0.1cm} g \hspace{0.1cm}$

So, to make this solution, 1.33 g of sodium carbonate is needed.

2. Now, 1.33 g of sodium carbonate from step 1 is dissolved in a small amount of distilled water in an appropriate-sized beaker. To assist the solid dissolve fully, use a stirring stick.

3. Using a funnel, transfer the mixture to a 250.0 mL volumetric flask. Prior to use, make sure the volumetric flask has been washed with distilled water. The volumetric flask should be cleaned with water since distilled water will eventually be added to the flask to create the standard solution.

4. Make sure all of the sodium carbonate has been transferred completely by thoroughly cleaning the volumetric flask, stirring rod, and beaker with distilled water.

5. Add distilled water to the volumetric flask once the solution has been placed there until the level is 1 cm below the graduation mark of the flask.

6. Drop by drop, add distilled water using a plastic pipette until the meniscus's bottom reaches the graduation point.

7. Invert the flask up to 10 times after stopping it.

Procedure

• Beginning with a calibrated burette or pipette containing the titrant, a beaker containing a measured volume of the analyte and a small amount of indicator is placed beneath it.

• The amount of substance to be evaluated in the solution must be accurately weighed in the sample to within +/- 0.0001g.

• Making the proper material selection for analysis is crucial, as using the incorrect titrant will produce inaccurate results. A chemical is chosen that interacts quickly and thoroughly to create a full solution.

• As the indicator's colour changes in response to the titrant saturation threshold, indicating the titration's endpoint, small amounts of titrant are gradually added to the analyte and the indicator.

• The titration must be continued until the reaction is finished, and the amount of reactant added must match the amount required to finish the reaction perfectly.

• Since molarity is a common metric for calculating the number of moles in a solution, measuring the correct volume of the standard solution is another crucial step.

• Single drops or less of the titrant determine whether the indication changes permanently or only temporarily, depending on the desired endpoint.

• Weighing and dissolving the reagent into a solution will give it a specific volume within a volumetric flask if the reagent or reactant we employ is to be put into a standard solution.

Observation Table

Result

1. Molarity of the given KMnO4 solution is _________ moles/litre.

2. The strength of the given  solution is _______ g/L.

Precautions

• There should not be any solution hanging at the burette's tip or endpoint.

• Check to make sure the stopcock is not leaking.

• As soon as the burette is filled, remove the funnel.

• Always situate the eye precisely at the level of the meniscus and use an anti-parallax card.

Lab Manual Questions

1. Why should a pipette be never held from its bulbs?

Ans. Holding the pipette close to or below the bulb is not advised. This is because holding it will allow stress to be applied to the bulb, which is the pipette's weakest component. Sharp glass fragments sometimes embed themselves in a student's one or both hands if the pipette breaks while being placed into the filler.

2. Why is the last drop of solution not blown out the pipette?

Ans. This is because volumetric pipets are calibrated to account for the solution that settles at the tip owing to surface tension, they should not be "blown out" to eject all liquid at the tip.

3. Why does a burette with rubber pinch cork should not be in acidic titrations like KMnO4? 

Ans. Because permanganate attacks rubber, a burette with a pinch cork regulator is not utilised for the titration of permanganate.

4. Why is the front door of chemical balance closed while measuring the weight of the sample?

Ans. While weighing something, shut the balance door to prevent air currents from affecting the reading. To stop dirt and dust from getting into the balance after finishing, the operator should shut the balance door.

Viva Questions

1. Name the apparatus used in a volumetric titration.

Ans. The pipette, the graduated cylinder, and the burette are the three most often used instruments used in a volumetric analysis.

2. Why shouldn't a titration flask be rinsed before use?

Ans. Since some liquid will stay stuck in the titration flask after rinsing, it is necessary to rinse the flask. This will increase the pipetted volume used in the titration flask.

3. Why are burettes and pipettes required to be rinsed with the solution they are filled with?

Ans. In order to avoid water from clinging to the sides of the burettes and pipettes, which would otherwise lower the volume of the solution taken into it, they are cleaned with the solution with which they are filled.

4. What is the other name for double titration?

Ans. The other name for double titration is Gilson's titration which establishes the concentration of an organometallic compound in a hydrocarbon solvent.

5. What various kinds of volumetric methods are there?

Ans. There are three different categories for volumetric analysis:

Simple titration, Back titration, and double titrations.

6. What is the purpose of preparing a standard solution for volumetric analysis?

Ans. To calculate the analyte concentration during titration, a standard solution is employed. The number of moles in the reaction's solution is determined using this method. For this purpose, the volumetric flask is provided with the scale marks. 

7. What impact does temperature show in volumetric titrations?

Ans. When the temperature changes, the equilibrium constant also changes, which can have an impact on titrations by moving equilibria in one way or another and adding sources of error to the titration process.

Practical Based Questions

1. A strong acid and a weak base are titrated using which of the following as an indicator?

1. Methyl orange

2. Phenolphthalein

3. Thymol blue

4. Fluorescein

Answer: a)

2)  The ideal indicator should fall between the pH range of _____ when used to titrate strong acids and weak bases.

a) 3-5

b) 4-6

c) 6-8

d) 7-9

Answer: b)

3. Which titration will have the equivalence point at a pH greater than 8?

a) NaOH and CH3COOH

b) NaOH and HCl

c) NH3 and CH3COOH

d) NH3 and HCl

Answer: c)

4. If 25 ml of the barium hydroxide solution is titrated with 35 ml of 0.1 M HCl, what is the molarity of the barium hydroxide solution?

a) 0.28

b) 0.21

c) 0.14

d) 0.07

Answer: d)

5. When titrating a weak acid and a strong base, which of the following is employed as an indicator?

a) Methyl orange (3 to 4.6)

b) Bromothymol blue (6 to 7.5)

c) Phenolphthalein (8 to 9.6)

d) Methyl red (5 to 6.9)

Answer : c) 

6. If 50 ml of 0.5 M Ba(OH)2 solution is used to neutralise 100 ml of sulphuric acid solution, what is the concentration of the resulting solution?

a) 0.25 M

b) 0.5 M

c) 25 M

d) 50 m

Answer : a) 

7. A process called a titration is used to

1. determine the identity of an unknown substance

2. determine the volume of an unknown substance

3. determine the molarity of an unknown substance

4. determine if an unknown substance is a solid, liquid, or gas

Answer:  c)

8. Phenolphthalein changes its colour in

1. Acidic medium

2. Basic medium

3. Neutral medium

4. All of the above

Answer: b)

Summary

Volumetric analysis is a method of quantitative analysis. It is a technique where the volume of a substance is measured along with the volume of another substance that mixes with the first in a specific ratio to determine how much of the substance is present. This is sometimes referred to as titration or titrimetric analysis.