Question

Remember in experiment 2 you used boiling chips; can the boiling sticks be replaced by boiling chips in this experiment? Explain your answer.

Experiment2:

Determination of Alcohol content of Wine by Fractional Distillation Introduction If a mixture of ethanol and water are warmed you might expect the more volatile (lower boiling) ethanol to boil first and then the water. This is not exactly true. As the mixture is warmed all the molecules within the flask will gain energy. In fact some water molecules will gain sufficient energy to boil at a lower temperature than normal. Pure ethanol boils at 78ºC. Pure water boils at 100 ºC. However, as a 50:50 mixture with ethanol, the water will boil at a much lower temperature, 87 ºC. This presents a problem; how can two liquids be easily separated? We will see in a later experiment that if the liquids form two layers (similar to oil and water in salad dressing), the layers can be separated by pouring one off and leaving the other behind. However, if the liquids are capable of dissolving in each other, as ethanol and water do, then a different technique will be required. Distillation is an ancient art used to purify liquids for medicinal properties. Distillation is part of the process by which gasoline is removed from a complex mixture of organic compounds known as crude oil. The apparatus has two main components; the fractionating column and the condenser. The condenser’s role is fairly apparent. The vapors that are escaping from the top of the fractionating column are cooled by the outer layer of the condenser and reform into a liquid dripping down the condenser to be collected and measured. The role of the fractionating column is a little more subtle and complex. First we need to visualize the vapors escaping from the surface of the liquid in the flask as a mixture of both ethanol and water. As the vapors reach the fractionating column the vapors start to cool. The water has a higher boiling point and so condenses first. The ethanol vapor continues up the column. Some water vapor is still able to climb up the column. However, as the surface becomes cooler and cooler the water is no longer able to stay in the vapor phase and all the remainder condenses to form liquid. The only remaining vapors are molecules of ethanol.

Objective The task for this lab is to deduce the alcohol content of table wine by performing fractional distillation of 50ml of wine. The temperature at the still-head will be monitored to track the temperature of the vapors exiting the fractionating column. A graph of the vapor temperature versus volume of distillate collected will be drawn. Experimental Procedure 1. Set up a fractional distillation apparatus as illustrated in Figure 1 at the end of this experiment. The apparatus must be set high enough that a sand bath heating mantel can be placed under the distillation flask. 2. Disconnect the fractionating column and pour 50ml wine into the round bottom flask to be heated. Measure the wine accurately using a measuring cylinder. Add 2 or 3 boiling chips to allow even boiling and prevent bumping. Empty any sand from the heating mantel and raise it to neatly fit around the round bottom flask. If the fit is not precise a little sand can be added to back fill the gaps. The flask should not be sitting on top of a pile of sand because this will slow the heating. Reattach the fractionating column. 3. Check that a slow trickle of water is flowing through your condenser and turn on the heat to your sand bath by turning the variac box to 4. 4. Control the heat to the sand bath with the variac box. A good distillation rate is about 1 drop per second. 5. Note the temperature at the still-head for every 1ml of liquid collected. Collect a total of 25ml. Results 1. Draw a graph of volume (x-axis) vs. temperature (y-axis). 2. From the graph predict the amount of ethanol collected and as a result the percentage (by volume) of the wine that was ethanol. 3. Compare your result to the label of the wine explain any difference. Waste Management 1. The distillate that was collected from the condenser is non-hazardous can be discarded down the sink. 2. The contents of the round bottom flask used for boiling is non-hazardous and can be discarded down the sink. 3. Wash the round bottom flask with soap and water to remove any remaining residue. Rinse the fractionating column with plenty of water to remove any residue. NOTE. 1. Plug the heating mantel into the variac box NOT directly into a wall outlet. 2. Make sure the thermometer is below the level of the condenser. 3. Ensure all the ground glass joints are clean and snug. Use a blue Keck clamp for any crucial joints. 15 4. Collect the distillate into a 10ml graduated cylinder to track the volume accurately. Empty it periodically.

Answer 1

Even though the purpose of boiling chips and boiling sticks is same i.e. to provide even boiling of the entire solution and to avoid bumping of solution while boiling, the only difference is their size. Boiling chips are small while the sticks are long.

Due to their small size, boiling chips can easily fit into the distillation flask which is further connected to the condensor. however, if we will use boiling sticks it will be very difficult to connect the flask and condensor. Thus, in this experiment boiling chips should be used and not boiling sticks.