Organic Lab Final Part 5

Question 1

Discuss impact on results for high or low caffeine mass percentages if we used water to extract tea bags but not tea powder.

Answer 1

We would get a mixture of caffeine and other water-soluble compounds, resulting in low caffeine mass percentages. Because, to isolate caffeine, we need to add a base like sodium carbonate to prevent it from reacting with acids and then use an organic solvent to only dissolve the caffeine.

Question 2

Discuss impact on results for high or low caffeine mass percentages if we didn’t shake well during solvent fractionation.

Answer 2

Most of the caffeine molecules won’t stay at the bottom layer with DCM, so the organic layer can’t be released or collected properly. There will be less crude extract obtained and the caffeine mass percentage will be low.

Question 3

Discuss impact on results for high or low caffeine mass percentages if we used tab water instead of ice water in the 250-mL beaker or a 250-mL Erlenmeyer flask for sublimation.

Answer 3

Likely result in an increase in the caffeine mass percentages. Sublimation relies on the difference in vapor pressure at different temperatures, and using ice water would decrease the temperature, causing caffeine to sublime at a lower rate.

Question 4

The crude caffeine isolated from tea often has a green tinge. Why?

Answer 4

It often has a green tinge because of the chlorophyll that is naturally found in the leaves of tea.

Question 5

Why is it necessary to remove the stopper from a separatory funnel when liquid is being drained from it through the stopcock?

Answer 5

The vapor pressure can accumulate inside the separatory funnel during draining, which can lead to an explosion. It could also slow down the rate of draining from the vacuum build up above the liquid.

Question 6

How does calcium chloride break emulsions?

Answer 6

As a drying agent, it destabilizes the emulsion layers by absorbing the water in the solution and decreases the water activity within the emulsion.

Question 7

Why is a sealed tube used for the measurement of caffeine melting point?

Answer 7

Because it prevents the decomposition of caffeine, minimizes contamination, protects against the loss of material, and can ensure that the measurement is as accurate as possible.

Question 8

Write a balanced equation for the conversion of sucrose to ethanol.

Answer 8

C12H22O11 + H2O –> 2CO2 + 2C2H5OH

Question 9

Why is the air trap necessary in the fermentation?

Answer 9

Prevent contamination. The contaminants can ruin the process of fermentation and the final product.

Question 10

Comparing the results from fractional and simple distillation. Which method was better for the distillation of ethanol? Why?

Answer 10

Fractional distillation was better in results because F1 had the lowest density, which means the percentage of ethanol by weight is higher compared to the other obtained densities.

Question 11

Define the term boiling point.

Answer 11

Boiling point is the point at which a compound in its liquid state boils and turns to vapor.

Question 12

What effect would a reduction in the atmospheric pressure have on the boiling point of a liquid?

Answer 12

Lowers the boiling point of a liquid because when the boiling point is reached, its vapor pressure of the liquid matches the atmospheric pressure. So, lowering the atmospheric pressure decreases the force pushing the liquid particles to stay in a container, thus making the change in phase to be easier.

Question 13

What error is introduced into the determination of a Rf value if the top is left open in the developing chamber.

Answer 13

If the top is left open, the mixture in the developing chamber would evaporate a lot faster. So, less of the mixture won’t be absorbed by the TLC plate, then decreasing the “a” and “b” values which are used to calculate the Rf value.

Question 14

What will be the result of applying too much compound to a TLC plate?

Answer 14

The compounds will show trailing, streaked and run together.

Question 15

What will be the appearance of a TLC plate if a solvent of too low polarity is used for development? And too high polarity?

Answer 15

If a solvent of too high a polarity is used, all components in the mixture will move along with the solvent and no separation will be observed (Rf value will be too large). If the solvent is of too low a polarity the components will not move enough, and again separation will not occur (Rf value will be too small).

Question 16

In the tests with sodium iodide in acetone and silver nitrate in ethanol, which reacted faster,
2-bromobutane or 2-chlorobutane? Why?

Answer 16

2-bromobutane reacted faster than 2-chlorobutane because between the two leaving groups (Br- and Cl-), Br is larger and thus more stable.

Question 17

When the substrate is treated with sodium iodide in acetone, which reacts much faster?
Benzyl chloride or 1-chlorobutane? Why?

Answer 17

Benzyl chloride is expected to react much faster than 1-chlorobutane. Benzyl chloride is a primary alkyl halide with a benzene ring attached, and it tends to undergo an SN2 reaction more readily. 1-Chlorobutane, on the other hand, is a secondary alkyl halide, and it is more prone to undergo SN1 reactions.

Question 18

Describe the Williamson ether synthesis.

Answer 18

The Williamson ether synthesis involves the conversion of an alcohol into an ether using a primary alkyl halide with a good leaving group.

Question 19

Describe the impact on recrystallization if too much volume of methanol is added.

Answer 19

It can lead to reduced effectiveness and lower yields. Recrystallization relies on the controlled solubility of the compound of interest in the solvent, adding too much methanol can oversaturate the solution.

Question 20

Describe the impact on recrystallization if too much water is added and the solution is clouded all the time.

Answer 20

It can hinder the purification process. The cloudiness suggests that the solvent system is not suitable for dissolving the compound at the prevailing temperature.

Question 21

Describe the impact on recrystallization if after water is added into the warm methanol, the solution becomes cloudy and clear again right away, and then no more water is added into the solution.

Answer 21

The system has reached equilibrium when solution becomes clear. This process can assist in concentrating the compound in solution and enhance recrystallization efficiency.