Lab: Back titration to determine the % CaCO3 in eggshell DATA COLLECTION [IB CHEMISTRY]

Summary

The video explains an experiment involving the reaction between hydrochloric acid and eggshells. The speaker adds excess acid to ensure full reaction and then uses sodium hydroxide (lye) to neutralize the extra acid. Through titration, the remaining acid is measured using phenolphthalein as an indicator. The speaker emphasizes careful handling of the chemicals, especially sodium hydroxide, and demonstrates the process, discussing systematic errors and overshooting in titration. They highlight the importance of repeating the experiment to obtain accurate results and provide insights into achieving a precise color change in the solution.

Takeaways

• 🧪 The speaker added excess hydrochloric acid to ensure complete reaction with the eggshell, instead of adding it drop by drop, which would take too long.
• ⚗️ To calculate how much calcium carbonate reacted with the acid, the speaker plans to neutralize the extra acid using sodium hydroxide (NaOH).
• ⚠️ The speaker warns that sodium hydroxide is highly dangerous and can cause serious harm, like turning eye proteins into soap, so safety precautions like goggles are necessary.
• 📏 A systematic error in the experiment involves clearing air gaps in the burette, which must be corrected for accurate measurements.
• 🧮 The experiment involves titration, where an indicator (phenolphthalein) is used to detect the endpoint of the acid-base reaction by changing color.
• 🎨 Adding too much phenolphthalein could skew the results because it is acidic, but adding too little would make the color change less visible.
• ⚖️ The first titration is treated as a trial run, with a rough estimate of 32 milliliters of titrant used, and this value is noted as a starting point for further precision.
• 💧 During the second titration, the speaker aims for more precision, adding the sodium hydroxide drop by drop to avoid overshooting the endpoint.
• 📊 The speaker records the data from multiple titrations, acknowledging that systematic errors, such as overshooting, are inevitable in titration experiments.
• 🔬 Ideally, the experiment should be repeated until two titration results are within 0.1 milliliters of each other for accuracy, but the speaker opts to use one particular result for the final calculation.

Q & A

Why did the speaker add excess hydrochloric acid to the eggshell?

The speaker added excess hydrochloric acid to ensure that all of the eggshell reacted, as adding it drop by drop would slow down the reaction and take much longer.

Why didn't the speaker add hydrochloric acid drop by drop to determine the exact amount of calcium carbonate?

Although adding acid drop by drop would work and help measure the exact amount of calcium carbonate, the reaction slows down as the reactants become less, making the process take too long.

What is the purpose of adding sodium hydroxide in the experiment?

The sodium hydroxide is added to neutralize the excess hydrochloric acid that was added initially to ensure the reaction with the eggshell was complete.

What safety precautions did the speaker mention when handling sodium hydroxide?

The speaker advised using goggles and caution when handling sodium hydroxide (also known as lye) because it is dangerous and can turn proteins in the eyes into soap.

What indicator is used in the titration process, and why?

Phenolphthalein is used as the indicator in this titration because it changes color at the endpoint of the acid-base reaction, signaling when the reaction is complete.

What happens if too much phenolphthalein is added?

If too much phenolphthalein is added, it could mess up the titration because phenolphthalein is acidic, which could affect the balance of the acid-base reaction.

Why is the first titration considered a trial?

The first titration is considered a trial to get a rough estimate of when the color change happens. This allows for better accuracy in subsequent titrations by knowing when to slow down the addition of sodium hydroxide.

What systematic error is mentioned in the titration process?

A systematic error occurs because the volume of titrant added is always a little more than necessary to see the color change, meaning the endpoint of the reaction is slightly overshot.

Why does the speaker suggest repeating the experiment multiple times?

The speaker suggests repeating the experiment to achieve more accurate results, aiming for two values within 0.1 milliliters of each other, which increases the reliability of the data.

How does the speaker plan to use the trial data in the final calculation?

The speaker plans to use only the data from the second, more accurate titration in the final calculation, as the trial data showed an overshoot, making it less reliable.