The Utilization of the Distillation Process to Purify Ethanol and Water Solutions

Introduction

The purpose of this experiment is to purify a solution of ethanol and water by distillation using different boiling points of ethanol and water.

Distillation is a commonly used method for purifying liquids and separating mixtures of liquids into their individual components. Distillation exploits the fact that different liquids have different boiling points. When a mixture of liquids is heated, the liquid with the lower(or lowest) boiling point vaporizes first. That vapor is routed through a condenser, which cools the vapor and causes it to condense as a liquid; the liquid is then collected in a receiving vessel. As the original liquid mixture continues being heated, eventually, some or all of the lower-boiling liquid is driven off, leaving only the higher-boiling liquid or liquids in the distillation vessel. However, distillation is an imperfect method for separating mixtures of liquids that form azeotropes-like an ethanol solution- called a constant boiling mixture, a mixture of two or more liquids at a specific ratio, whose composition cannot be altered by simple distillation. Therefore distillation is only effective if there is a significant difference between the boiling point of the two elements.

Fractional distillation is the more accurate way to separate or purify mixture of liquids. Mixtures of liquids whose boiling points are similar(separated by less than 70°C) cannot be separated by a single simple distillation. In simple distillation, the distillate would contain a majority of one liquid but would still contain a little of the other liquid. Fractional distillation essentially performs "re-distillations" automatically in a portion of the fractional distillation apparatus called the fractionating column. As the mixture boils, it turns to vapor and rises up the column. It reaches a certain point up the column and condenses. It then turns to vapor again and rises a little bit further up the column. This continues until the vapor rises all the way up the column and condenses in the condenser. At this point, the liquid has been completely purified.

The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of water is 100 ºC, and the boiling point of ethanol solution is 78 ºC to 79 ºC. In this experiment, ethanol solution is separated, or purified, from water by difference in boiling points.

My hypothesis in this experiment is that if we used a method of distillation using two different boiling points of ethanol and water, then we can separate pure ethanol from 30 % ethanol and water solution.

Materials

• 1 Ring Stand and 1 Stand
• 2 Clamps
• Iron Gauze
• Thermometer
• Rubber Stopper
• Bunsen Burner
• One-Armed Florence Flask
• Boiling Chips
• Condenser
• Grease
• 2 Rubber Hose(Tube)
• 7 Petri Dishes
• 30 % Ethanol Solution
• Graduated Cylinder
• Stemmed Funnel
• TI-Calculator
• Lighter

Table 1: Safety Information

Ethanol

• Hazardous when inhaled-may cause a burning sensation
• Irritant to eyes
• May cause dizziness, faintness, and vomiting

Experimental Procedure

1. Measure 80 mL of a 30 % ethanol in water solution.
2. Place the ethanol solution into distilling flask with boiling stones by using a long stemmed funnel.
3. Start heating the solution.
4. Read the temperature of the boiling solution as soon as the first drop of distillate is collected at 8 mL increments.
5. Switch receiving petri dish for every 8 mL increments. Follow this procedure until 7-8 samples are collected. Make sure to organize them in collected order.
6. Stop distillation. Turn the lights off to see fire clearly. Ignite the 7-8 samples of distillates

Results

Table 2 : Starting/Ending Temperature of Distilled Ethanol per Petri Dish

Dish 1 Dish 2 Dish 3 Dish 4 Dish 5 Dish 6 Dish 7

Starting 81.80 ºC 85.40ºC 86.40ºC 87.80ºC 89.20ºC 90.70ºC 92.40ºC

Ending 85.40ºC 86.40ºC 87.80ºC 89.20ºC 90.70ºC 92.40ºC 94.60ºC

Table 3 : Diagram of Water Left in Petri Dish after Burning Distilled Ethanol

Dish 1

Dish 4

Dish 7

Discussion

During this experiment, 30 % ethanol solution is purified by distillation. Purified samples of pure ethanol are burnt after distillation. The sample of first petri dish had a biggest fire, and in order, sizes of fire were decreased. However, the original 30 % ethanol solution did not burn because the original solution is more concentrated with water, so it is not supported for combustion. The samples of increments were burnt because they are pure ethanol that is distilled from the homogeneous mixture of ethanol and water solution.

The residue liquid after burning ethanol is found to be water, which is the only other liquid in the mixture. According to the diagram of petri dish with left water, the first dish had least amount of water left, and in order, the left amount of water increased, so the seventh dish had largest amount of water. This is because as the temperature increase closer to the boiling point of water, which is 100 ºC, more vapor of water was transferred together with pure ethanol. Therefore if we went over 100 ºC, then our increment would have more water in it.

As the temperature increases, the concentration of pure ethanol in collected samples decreases. We can see this from the sizes of fire when the samples were burnt, and the amount of residue, water, left in the petri dish after burning. The bigger size of fire means that pure ethanol was more concentrated than water therefore after all ethanol was burnt, there was smaller amount of residue.

The ranges of temperature are decreasing toward sample 7. This means that to gather same amount of sample, sample 1 needed more of higher temperature compared to sample 7. This result is because sample 1 had more of pure ethanol than that of other samples. Sample 7 had pure ethanol, but also more of water. Therefore the ranges of temperature at which the mixture first started to distill continually rise during the entire distillation process.

To get more pure ethanol, we can go through another distillation process with the samples we collected. Also, we can control the temperature so that it stays at the boiling point of ethanol which will allow us to have less residue of water in increments.

Conclusion

By the process of distillation, we could separate pure ethanol from 30 % ethanol solution.