Practical skills assessment video - titration - standard solution

Summary

This video tutorial guides viewers through the process of preparing a 0.1 mol/dm³ sodium carbonate standard solution in a 250 cm³ volumetric flask. It covers the weighing by difference method to accurately measure 2.6 grams of anhydrous sodium carbonate, dissolving it in distilled water, and transferring the solution to the flask. The video emphasizes the importance of thorough rinsing, accurate volume measurement, and gentle mixing to ensure uniform concentration. It concludes with calculating the solution's molar concentration, resulting in a precise 0.0974 mol/dm³ solution.

Takeaways

• 🔍 To prepare a standard solution, you need to create a solution with a known concentration, specifically 0.1 mol/dm3 sodium carbonate in this case.
• 🔬 The process involves accurate measurement of the mass of sodium carbonate using a method called weighing by difference.
• 📏 A spatula is used to measure approximately 2.6 grams of anhydrous sodium carbonate, and the mass is recorded with the weighing boat.
• 🧪 The anhydrous sodium carbonate is then dissolved in distilled water in a 100 cm3 beaker until completely dissolved.
• 🧪 A 250 cm3 volumetric flask and a funnel are essential tools for transferring the solution into the flask.
• 💧 It's crucial to rinse the beaker and funnel with a wash bottle at least three times to ensure all the solution is transferred into the volumetric flask.
• 📏 The volumetric flask should be filled to the 250 cm3 mark with distilled water, observing the meniscus at eye level.
• 🔄 The flask must be gently inverted several times to ensure the concentration of sodium carbonate is uniform throughout the solution.
• 🏷️ The flask should be clearly labeled with the exact concentration of the solution.
• 🧮 The concentration of the standard solution is calculated by dividing the mass of anhydrous sodium carbonate by its molar mass and then by the volume in dm3.

Q & A

What is the purpose of making a standard solution in titration?

A standard solution is required in titration to have a solution of a known concentration, which is essential for accurately determining the concentration of the unknown solution being tested.

What is the concentration of the sodium carbonate solution being prepared in the script?

The concentration of the sodium carbonate solution being prepared is approximately 0.1 mol/dm³.

Why is a 250 cm³ volumetric flask used in this process?

A 250 cm³ volumetric flask is used to ensure the solution is prepared to a precise volume, which is necessary for accurate concentration calculations.

What method is suggested for accurately determining the mass of sodium carbonate?

The method suggested for accurately determining the mass of sodium carbonate is 'weighing by difference'.

How much anhydrous sodium carbonate is initially measured out using a spatula?

Approximately 2.6 grams of anhydrous sodium carbonate is measured out using a spatula.

What is the purpose of dissolving the sodium carbonate in distilled water?

Dissolving the sodium carbonate in distilled water ensures that the solute is completely dissolved, creating a homogeneous solution that can be accurately measured and used in titration.

Why is it important to rinse the beaker and funnel with a wash bottle during the transfer to the volumetric flask?

Rinsing the beaker and funnel with a wash bottle ensures that all of the sodium carbonate solution is transferred to the volumetric flask, preventing loss of solute and ensuring the concentration remains accurate.

How should distilled water be added to the volumetric flask during the preparation?

Distilled water should be added to the volumetric flask up to the 250 cm³ mark, with care taken to observe the meniscus at eye level to ensure accuracy.

What is the purpose of inverting the flask gently after adding water to the mark?

Inverting the flask gently after adding water to the mark ensures thorough mixing and uniform concentration of the sodium carbonate throughout the solution.

Why is it necessary to label the flask with the exact concentration of the solution?

Labeling the flask with the exact concentration of the solution is crucial for traceability and to ensure that the solution can be used correctly in subsequent experiments or analyses.

How is the molar mass of anhydrous sodium carbonate used in the calculation of the solution's concentration?

The molar mass of anhydrous sodium carbonate is used to calculate the amount of substance used by dividing the mass of the anhydrous sodium carbonate by its molar mass, which then allows for the calculation of the solution's concentration.

What is the final calculated concentration of the sodium carbonate solution as per the script?

The final calculated concentration of the sodium carbonate solution is 0.0974 mol/dm³.

Outlines

00:00

🧪 Preparing a Standard Solution

This paragraph outlines the process of preparing a standard solution of sodium carbonate with a known concentration of 0.1 mol/dm3. The process begins with accurately measuring the mass of anhydrous sodium carbonate using a method called weighing by difference. Approximately 2.6 grams of the compound is measured and then transferred to a 100 cm3 beaker. After dissolving the sodium carbonate in distilled water, the solution is transferred to a 250 cm3 volumetric flask using a funnel and glass rod. The beaker and funnel are rinsed with distilled water to ensure all of the solution is transferred. The volumetric flask is then filled to the 250 cm3 mark with distilled water, and the solution is mixed by inverting the flask. The concentration of the solution is calculated by dividing the mass of sodium carbonate by its molar mass and the volume of the solution in dm3, resulting in a concentration of 0.0974 mol/dm3.

Keywords

💡Titration

Titration is a common laboratory method used to find the concentration of an unknown solution by gradually adding a solution of known concentration until the reaction is complete. In the video, the preparation of a standard solution is discussed as a prerequisite for performing a titration, emphasizing the importance of accurate concentration measurements for successful titration.

💡Standard Solution

A standard solution is a solution with a precisely known concentration, which is essential for calibration and comparison in various chemical analyses, including titration. The video focuses on creating a 0.1 mol/dm3 sodium carbonate standard solution, highlighting the meticulous process required to ensure the solution's exact concentration.

💡Molar Concentration

Molar concentration, often expressed in mol/dm3, is a measure of the amount of a substance (in moles) per unit volume of solution. The video script describes the calculation of molar concentration for the sodium carbonate solution, which is crucial for determining the solution's strength and its use in titration.

💡Anhydrous Sodium Carbonate

Anhydrous sodium carbonate is a chemical compound without water of crystallization. It is used in the script to prepare the standard solution. The video emphasizes the importance of using anhydrous sodium carbonate to avoid errors in concentration due to the presence of water molecules.

💡Weighing by Difference

Weighing by difference is a method used to determine the mass of a substance by weighing the container before and after adding the substance. The video script describes using this method to accurately measure the mass of anhydrous sodium carbonate, which is critical for preparing a solution with the correct molar concentration.

💡Volumetric Flask

A volumetric flask is a piece of laboratory glassware used to prepare solutions of precise volume and concentration. In the video, a 250 cm3 volumetric flask is used to ensure that the final volume of the sodium carbonate solution is accurate, which is essential for titration.

💡Meniscus

The meniscus is the curved surface of a liquid in a container, which is used as a reference point when making volume measurements. The video script instructs viewers to observe the meniscus at eye level when filling the volumetric flask to ensure accurate volume measurements, which is vital for the correct concentration of the solution.

💡Molar Mass

Molar mass is the mass of one mole of a substance and is used to convert mass to the amount of substance (in moles). The video script includes a step to calculate the molar mass of anhydrous sodium carbonate, which is necessary to determine the amount of substance in the prepared solution.

💡Distilled Water

Distilled water is water that has been purified through distillation, removing impurities and minerals. In the video, distilled water is used to dissolve the anhydrous sodium carbonate because it is free from contaminants that could affect the solution's concentration or quality.

💡Rinse

Rinsing is the process of washing out a container with a solvent to ensure that all of the solute is transferred to the final solution. The video script mentions rinsing the beaker and funnel with a wash bottle to transfer all of the sodium carbonate solution to the volumetric flask, which is important for achieving the correct concentration.

💡Labeling

Labeling in a laboratory context refers to marking containers with information such as the contents, concentration, and date prepared. The video script emphasizes the importance of labeling the volumetric flask with the exact concentration of the sodium carbonate solution, which is crucial for accurate record-keeping and usage in titration.

Highlights

Introduction to creating a standard solution with a known concentration.

Preparation of a 0.1 mol/dm3 sodium carbonate solution in a 250 cm3 volumetric flask.

Emphasis on the importance of accurate measurements and calculations for precise concentration.

Method of weighing by difference to determine the exact mass of sodium carbonate.

Use of a spatula to measure approximately 2.6 grams of anhydrous sodium carbonate.

Recording the mass of sodium carbonate with the weighing boat.

Transfer of the solid to a 100 cm3 beaker and re-weighing the boat for mass calculation.

Dissolving the anhydrous sodium carbonate in distilled water and stirring until completely dissolved.

Utilization of a 250 cm3 volumetric flask and a funnel for solution transfer.

Technique of pouring the solution down a glass rod into the flask for smooth drainage.

Rinsing the beaker with a wash bottle and transferring the rinse to the volumetric flask.

Careful addition of distilled water up to the 250 cm3 mark without exceeding it.

Observing the meniscus at eye level for accurate volume measurement.

Inversion of the flask to ensure uniform concentration of sodium carbonate.

Clear labeling of the flask with the exact concentration of the solution.

Calculation of the molar mass of anhydrous sodium carbonate.

Determination of the amount of substance used by dividing mass by molar mass.

Conversion of volume units from cm3 to dm3 for concentration calculation.

Final known accurate concentration of the sodium carbonate solution is 0.0974 mol/dm3.

Transcripts

Before you carry out your titration you'll need to make up a standard solution,

that's the solution of a known concentration.

In this case we'll be

making up a solution that's about 0.1 mol/dm3 sodium carbonate

in a 250 cm3 volumetric flask.

In this video we'll run through the steps required to make up your standard solution,

including all of the measurements and calculations you'll need

to carry out to get the exact concentration of your sodium carbonate solution.

To make up the standard solution, it's necessary to know accurately the exact

mass of sodium carbonate, which will be dissolved in a known volume of water.

The best way to do that is by a method called weighing by difference.

Using a spatula, measure out approximately 2.6 grams of anhydrous sodium carbonate.

Record the mass of the sodium carbonate with the weighing boat.

Transfer this solid to 100 cm3 cubed beaker.

Re-weigh and record the mass of the used boat.

Using these measurements, you can calculate the exact mass of anhydrous sodium carbonate.

Next, take this anhydrous sodium carbonate

and dissolve in distilled water from a wash bottle.

Stir this solution thoroughly until the solid is completely dissolved.

For the next step, you'll need a 250 cm3 volumetric flask,

and a funnel.

Pour your solution down a glass rod and

through the funnel into the flask.

Make sure to raise the funnel, so that it drains smoothly.

To make sure all of your sodium carbonate solution is transferred

to the volumetric flask, you should use a wash bottle to rinse the beaker.

Make sure to add this rinse to the volumetric flask each time,

and do this at least three times.

Take care as well to only use a small amount of water,

so as to not go higher than the 250 cm3 mark

on the volumetric flask.

The same should also be done with the funnel.

Add distilled water to the 250 cm3 mark.

Take care to observe the meniscus at eye level,

rather than from above or below.

To make sure the concentration of anhydrous sodium carbonate is the same

throughout your solution, stopper the flask

and gently invert it several times.

Finally, you will need to label the flask clearly

including the exact concentration of your solution.

To calculate the concentration of your standard solution,

you first have to work out the molar mass of anhydrous sodium carbonate

as shown here.

To calculate the amount of substance used, you will then have to divide the

mass of the anhydrous sodium carbonate used by its molar mass.

As we know the volume of the solution in the volumetric flask is

250 cm3, we can calculate the concentration.

Remember to divide by a thousand to convert the units of volume

from cm3 into dm3.

So, the known accurate concentration of your sodium carbonate solution is

therefore 0.0974 mol/dm3.