Extracting Citric Acid From Lemons

Summary

This video demonstrates a DIY method to extract citric acid from lemons. The process involves juicing lemons, neutralizing with sodium hydroxide to form sodium citrate, then precipitating with calcium chloride to form calcium citrate. After vacuum filtration, sulfuric acid is used to revert it to citric acid and gypsum. The final step involves vacuum drying and recrystallization for pure citric acid crystals.

Takeaways

• 🍋 **Juice Extraction**: The process starts by juicing lemons to obtain citric acid.
• 🧪 **Neutralization**: Sodium hydroxide is added to neutralize the excess acid in the lemon juice.
• 💧 **Filtering**: The solution is filtered to remove any lemon debris.
• 🔴 **pH Adjustment**: The pH is raised to 9 to convert citric acid into sodium citrate, indicated by a color change.
• 🌟 **Precipitation**: Calcium chloride is added to convert soluble sodium citrate into insoluble calcium citrate.
• ⏱️ **Settling Time**: The solution is left to allow calcium citrate to settle.
• 💦 **Vacuum Filtration**: Vacuum filtration is used to isolate calcium citrate, noting the requirement for a vacuum.
• ❄️ **Cold Water Rinse**: It's suggested to rinse the filtered calcium citrate with cold water for cleaner results.
• 🚮 **Discard the Filtrate**: The filtrate is discarded as it is not needed for further steps.
• 🔄 **Reformation**: Sulfuric acid is used to convert calcium citrate back into citric acid and gypsum.
• 🧊 **Freezing**: The solution is frozen to form citric acid crystals.
• 🌬️ **Final Purification**: The citric acid crystals are purified by recrystallization and vacuum filtration with ice-cold water.

Q & A

What is the first step in extracting citric acid from lemons?

The first step is to slice up and juice a few lemons.

How much lemon juice is required to begin the process?

The process begins with the juice of an unspecified number of lemons, which is then poured into a 1000 milliliter beaker.

What is the purpose of adding a sodium hydroxide solution to the lemon juice?

A sodium hydroxide solution is added to neutralize the excess acid in the lemon juice.

What is the role of the coffee filter in the process?

The coffee filter is used to remove any lemon debris from the solution after the sodium hydroxide has been added.

Why is the pH of the solution adjusted to 9?

Adjusting the pH to 9 converts the citric acid from the lemons into sodium citrate, which is indicated by the solution's color shifting to a deep orange.

What is the function of adding calcium chloride solution to the mixture?

The calcium chloride solution converts the soluble sodium citrate into insoluble calcium citrate.

Why is vacuum filtration used to isolate calcium citrate?

Vacuum filtration is used to isolate calcium citrate because it allows for a more efficient separation of the solid from the solution.

What is the significance of rinsing the filtered calcium citrate with cold water?

Rinsing with cold water is important to remove any remaining impurities and to make future steps cleaner.

How does the addition of a dilute sulfuric acid solution affect the calcium citrate?

Adding a dilute sulfuric acid solution reacts with the calcium citrate to reform citric acid and precipitate white calcium sulfate, also known as gypsum.

Why is the filtered solution cooked down to 10 percent of its initial volume?

Cooking down the solution to 10 percent of its initial volume helps to concentrate the citric acid, making it easier to form crystals.

What is the purpose of placing the resulting solution in the freezer?

Placing the solution in the freezer allows the citric acid to crystallize, which can then be collected.

Why is recrystallization performed off-camera?

Recrystallization is performed off-camera to keep the video short, and it helps to form larger, purer crystals of citric acid.

What is the final step in obtaining pure citric acid crystals?

The final step is to dry the crystallized citric acid on a small filter, pulling a vacuum to rinse the crystals with ice-cold water.

What was the yield of citric acid from the process described in the script?

The final yield of citric acid was larger than what was shown in the video, as the process was done in batches.