Practical skills assessment video - titration procedure

Royal Society Of Chemistry
21 Sept 201504:45
EducationalLearning
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TLDRThis video script outlines a meticulous procedure for an acid-base titration using a standard solution of sodium carbonate to determine the concentration of a dilute hydrochloric acid solution. The process involves using methyl orange as an indicator, which changes color from red to yellow at the endpoint of the titration. The video demonstrates the importance of rinsing equipment, accurately measuring solutions, and observing color changes to determine when the endpoint is reached. It emphasizes the need for precision, such as ensuring no air bubbles in the burette and recording the burette's level to the nearest 0.05 cm3. The script also guides viewers through a rough titration to approximate the endpoint before conducting a more accurate titration, where the endpoint is approached drop by drop. The final step involves repeating the titration until two titers agree within a 0.1 cm3 margin, providing the data necessary to calculate the concentration of the hydrochloric acid.

Takeaways
  • 🧪 The experiment involves an acid-base titration using a standard solution of sodium carbonate to determine the concentration of a dilute hydrochloric acid solution.
  • 📏 Methyl orange is the indicator used, which changes color from red to yellow to signify the endpoint of the titration.
  • 💧 The sodium carbonate solution is poured into a beaker, and the burette is rinsed with distilled water to avoid dilution.
  • 🔍 The burette is filled with sodium carbonate solution above the zero mark and checked for air bubbles to ensure accurate readings.
  • 👀 The initial burette reading is taken by observing the meniscus against a white background for clarity.
  • 🔬 The pipette is rinsed with distilled water and then with hydrochloric acid to prepare for transferring the acid solution.
  • ⚗️ Exactly 25 cm³ of hydrochloric acid is transferred into a conical flask using a pipette, ensuring no liquid is forced from the pipette tip.
  • 🎨 Two to three drops of methyl orange are added to the flask, and the initial color is noted for comparison with the endpoint color change.
  • 🔄 A rough titration is performed first to estimate the amount of sodium carbonate needed to neutralize the acid and approximate the endpoint.
  • 📝 The endpoint is reached by adjusting the flow of sodium carbonate solution, starting with larger volumes and then adding drop by drop.
  • 🔍 The permanent color change indicates the endpoint, and the burette reading is noted to calculate the concentration of hydrochloric acid.
  • 🔁 The titration process is repeated until two titers agree within 0.1 cm³, ensuring accuracy in the results.
Q & A

  • What is the purpose of the titration described in the script?

    -The purpose of the titration is to determine the exact concentration of a dilute solution of hydrochloric acid using a standard solution of sodium carbonate.

  • Which indicator is used in this titration and what is its color change?

    -Methyl orange is used as the indicator in this titration, and it changes color from red to yellow to indicate the endpoint.

  • Why is it necessary to rinse the burette with distilled water and the sodium carbonate solution?

    -Rinsing the burette with distilled water and then with the sodium carbonate solution ensures that there is no dilution of the sodium carbonate solution when it is filled into the burette.

  • How should the burette be filled with the sodium carbonate solution?

    -The burette should be filled with sodium carbonate solution above the zero mark, and then the funnel should be removed. The solution should be allowed to flow until the level is at or slightly below the zero mark, ensuring no air bubbles are present in the nozzle.

  • What is the significance of recording the initial burette reading?

    -Recording the initial burette reading is crucial for determining the volume of sodium carbonate solution used during the titration, which is necessary for calculating the concentration of the hydrochloric acid.

  • Why is it important to rinse the pipette with distilled water and then with the dilute hydrochloric acid solution?

    -Rinsing the pipette with distilled water and then with the dilute hydrochloric acid solution ensures that the pipette is clean and free of any contaminants that could affect the accuracy of the volume transferred.

  • What volume of hydrochloric acid solution is transferred into the conical flask using the pipette?

    -Exactly 25 cm3 of the hydrochloric acid solution is transferred into the clean conical flask using the pipette.

  • What is the purpose of adding methyl orange indicator to the flask containing hydrochloric acid?

    -Methyl orange indicator is added to the flask to visually signal the endpoint of the titration by changing color, aiding in the accurate determination of when the reaction is complete.

  • Why is a rough titration performed before the main experiment?

    -A rough titration is performed to estimate the amount of alkaline solution needed to neutralize the acid, providing an approximate value of the endpoint before the precise titration.

  • How should the endpoint of the titration be approached during the accurate titration?

    -During the accurate titration, the endpoint should be approached by gently swirling the conical flask and adding the sodium carbonate solution drop by drop from the burette, noting when a permanent color change occurs.

  • What is the final step in the titration process to ensure accuracy?

    -The final step is to repeat the titration until two titers agree within 0.1 cm3, ensuring the accuracy of the results used to calculate the concentration of the hydrochloric acid.

Outlines
00:00
🧪 Acid-Base Titration Setup

This paragraph describes the setup for an acid-base titration experiment using a standard solution of sodium carbonate to determine the concentration of a dilute hydrochloric acid solution. The process involves using the indicator methyl orange, which changes color from red to yellow at the endpoint of the titration. The participant is guided through the preparation of the beaker, burette, and conical flask, including rinsing and filling procedures to ensure accuracy. The importance of observing the meniscus for accurate burette readings is highlighted, as is the initial setup for the titration, such as the transfer of hydrochloric acid into the conical flask and the addition of the indicator.

🔬 Initial Steps in Titration Process

The paragraph details the initial steps of the titration process, including rinsing the pipette with distilled water and hydrochloric acid solution, and transferring exactly 25 cm3 of hydrochloric acid into a clean conical flask. It also describes the addition of methyl orange indicator to the flask and the observation of the solution's color against a white tile. The paragraph further explains the purpose of a rough titration to estimate the amount of alkaline solution needed to neutralize the acid and provides instructions on how to perform this preliminary titration, including the observation of color changes and the gradual addition of sodium carbonate solution.

📝 Conducting the Accurate Titration

This section outlines the procedure for conducting an accurate titration after the rough titration has been completed. It instructs on how to prepare for the titration by washing and drying the conical flask, adding a second 25 cm3 sample of hydrochloric acid, and the methyl orange indicator. The participant is then guided through the process of adding sodium carbonate solution from the burette drop by drop, while continuously swirling the flask, until a permanent color change is observed. The importance of rinsing the burette tip and the flask's side with distilled water after each addition is emphasized to ensure accuracy. The paragraph concludes with the instruction to repeat the titration until two titers agree within 0.1 cm3, which is crucial for obtaining reliable data to calculate the concentration of the hydrochloric acid.

Mindmap
Keywords
💡Acid-Base Titration
Acid-base titration is a quantitative analytical technique used to determine the concentration of an unknown acid or base solution by neutralizing it with a solution of known concentration. In the video's context, it involves using a standard solution of sodium carbonate to find the exact concentration of a dilute hydrochloric acid solution. The process is central to the video's theme as it demonstrates the steps involved in performing a titration.
💡Sodium Carbonate
Sodium carbonate, also known as washing soda or soda ash, is a chemical compound with the formula Na2CO3. It is used in the script as the standard solution for the titration process. The role of sodium carbonate is crucial as it reacts with hydrochloric acid to determine the acid's concentration, illustrating the script's focus on chemical reactions in titration.
💡Indicator Solution
An indicator solution is a substance that changes color in response to changes in pH, which helps to visually identify the endpoint of a titration. In the video, methyl orange is the indicator used, and it changes from red to yellow to signify the endpoint. The indicator solution is key to understanding the titration process as it provides a visual cue for the experiment's conclusion.
💡Methyl Orange
Methyl orange is a specific type of indicator solution used in the script for the titration process. It is an azo dye that changes color at a certain pH range, which is crucial for identifying the endpoint of the titration. The script mentions adding methyl orange to the flask to observe the color change, which is a direct example of its use in the experiment.
💡Beaker
A beaker is a cylindrical container used in laboratories for mixing, stirring, and heating chemicals. In the script, a beaker is used to hold the sodium carbonate solution during the titration process. It is an essential piece of laboratory equipment that facilitates the mixing and observation of the reaction.
💡Burette
A burette is a piece of laboratory equipment used to dispense precise volumes of liquid. In the video, the burette is filled with the sodium carbonate solution and used to add it to the hydrochloric acid in the conical flask. The burette's role is vital as it allows for the controlled addition of the titrant, which is central to the accuracy of the titration.
💡Meniscus
The meniscus refers to the curved surface of a liquid in a container, which can make it difficult to read the volume accurately. In the script, it is mentioned to take readings from the bottom of the meniscus to ensure an accurate volume measurement. Understanding the meniscus is important for the precision required in titration.
💡Pipette
A pipette is a laboratory tool used to transfer or dispense measured volumes of liquid. In the video, a pipette is used to accurately transfer 25 cm3 of hydrochloric acid into the conical flask. The pipette's use is crucial for ensuring that the correct volume of the unknown solution is used in the titration.
💡Conical Flask
A conical flask is a type of laboratory flask with a conical shape, often used for titration and mixing. In the script, the conical flask is where the hydrochloric acid solution is placed, and the titration with sodium carbonate occurs. It is a key container in the video's demonstration of the titration process.
💡Endpoint
The endpoint of a titration is the point at which the reaction between the acid and base is complete, and the indicator changes color. In the video, the endpoint is identified by the color change of the methyl orange indicator. The concept of the endpoint is central to the video's theme as it represents the completion of the titration.
💡Rough Titration
A rough titration is a preliminary step performed to estimate the amount of titrant needed to neutralize the analyte. In the script, a rough titration is carried out to determine approximately how much sodium carbonate is needed to neutralize the hydrochloric acid. This step is important for planning the main titration and ensuring accuracy.
Highlights

Acid-base titration using sodium carbonate to determine the concentration of dilute hydrochloric acid.

Methyl orange as an indicator for the endpoint of the titration, changing from red to yellow.

Pouring 50 cm3 of sodium carbonate solution into a beaker and rinsing the burette with distilled water.

Rinsing the burette with sodium carbonate solution to prevent dilution.

Filling the burette with sodium carbonate solution and ensuring no air bubbles in the nozzle.

Recording the initial burette reading to the nearest 0.05 cm3.

Rinsing the pipette with distilled water and hydrochloric acid solution.

Transferring exactly 25 cm3 of hydrochloric acid into a conical flask.

Adding methyl orange indicator to the flask and noting the color change.

Performing a rough titration to estimate the endpoint and amount of alkaline solution needed.

Slowing down the flow of sodium carbonate as the indicator color change becomes persistent.

Recording the burette reading at the endpoint of the rough titration.

Preparing for the accurate titration with a second 25 cm3 sample of hydrochloric acid.

Rapidly adding sodium carbonate solution until approximately 2 cm3 from the endpoint.

Adding sodium carbonate drop by drop and rinsing the burette tip after each addition.

Swirling the conical flask and rinsing its side with distilled water after each addition.

Noting the permanent color change and recording the final burette reading.

Repeating the titration until two titers agree within 0.1 cm3 for accuracy.

Using the recorded data to calculate the concentration of hydrochloric acid.

Transcripts

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Related Tags
Acid-Base TitrationChemical AnalysisConcentration DeterminationSodium CarbonateHydrochloric AcidMethyl OrangeLaboratory ProtocolIndicator Color ChangeTitration TechniqueChemistry Education