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Experiment 2
Experiments 2
| Question | Answer |
|---|---|
| Liquid-liquid extraction | is a separation method based upon differential solubility of components in a mixture between two immiscible1 solvents. |
| The distribution of a compound between two immiscible solvents is expressed as a | "distribution" or "partition" coefficient (K). |
| The partition coefficient, K... | the ratio of the solubility of the compound in the two solvents; typically, grams/mL in the organic solvent divided by the g/mL in water |
| washing is... | water soluble (i.e. not organic) compounds are not desired and the aqueous layer is thrown away. |
| First, dissolve the mixture in a suitable solvent (usually organic), then... | add the immiscible solvent (usually water) |
| organic solvents that are miscible with water (i.e. alcohols) | are not suitable for use with this method. |
| If the two solvents are immiscible | they will form two layers with the denser (heavier) layer on the bottom. |
| The components of the mixture will partition between | the layers based upon the ratio of their solubilities in each solvent (i.e. K, the distribution coefficient) |
| After thorough mixing, the two layers are separated using | an angled separatory funnel or a centrifuge tube with a pipette (microscale). |
| Although water and organic solvents are "immiscible", | they are still partially soluble (miscible). |
| What is the primary data for experiment 2 | Sublimation directly supports claim of isolation and purification of caffeine |
| what is the scientific claim for experiment 2 | Caffeine was purified) |
| The two layers must be thoroughly mixed to enable | the compounds to rapidly partition between the two solvents. |
| Check the solvent density to determine | the identity of the top and bottom layers |
| Overly vigorous shaking can lead to | emulsions which appears as bubbles between layers. |
| Brine (salt water) is often used instead of plain water to help | reduce emulsions |
| the organic solvent will always contain... | small amounts of water. |
| The water needs to be completely removed in order to | obtain an accurate mass at the end. |
| First, the organic layer is "washed" with brine | This helps remove any remaining water-soluble impurities - including much of the dissolved water. |
| The desired compound is isolated by first filtering the solution to remove drying agents | then removing the solvent via evaporation. |
| The obtained compound might still not be pure | most organic compounds are quite soluble in organic solutions. Extraction is a separation technique not a purification technique. Purification can be accomplished through recrystallization or distillation. |
| Determination of Partition Coefficients You will use liquid-liquid extraction to determine the partition coefficient of | benzoic acid between methyl t-butyl ether (MTBE) and water |
| Extraction Summary 1. Solid-liquid Extraction | Add the tea bag to hot water that also contains sodium carbonate to hydrolyze the tannins and deprotonate any caffeine salts. There will be solids floating in the tea. Centrifuge the solution before filtering to help the filtration. |
| Extraction Summary 2. Liquid-liquid Extraction | Extract caffeine from the basic tea solution with methylene chloride (as in experiment 2). Tea saponins will cause emulsions to form. You will use the centrifuge to help separate the layers. |
| Water goes from ice to vapor (called freeze drying) | but only at low pressures. |
| Chemists use sublimation to purify compounds with | substantial vapor pressures. |
| what is the objective of experiment 2 | Use solubility differences between two solvents to determine the partition coefficient of a benzoic acid. Remember that partition coefficient is specific to both solvents, the organic solvent especially. Complete answer includes MTBE and water. |
| what is the scientific claim of experiment 2 | Results clearly state partition coefficient was determined (or not) and provides Kd value |
| Explain why the maximum amount of recovered caffeine is or is not different | The different partition coefficient means that caffeine was less soluble in ethyl acetate than methylene chloride, and so the resulting recovered caffeine is less. |
| what is the secondary data of experiment 2 | Crude mass indirectly supports the isolation claim (does not confirm identity). Optional: purified mass or physical description (white color) indirectly supports purification. |
| SAFETY: What is the purpose of venting the separatory funnel? | The pressure can build due to the volatility of the organic solvent, or if a reaction occurs between a product and another component of the mixture that releases a gas, such as carbon dioxide |
| When adding drying agent, how do you know when you have added enough? | When the solvent is wet and drying agent is added, it forms clumps as it starts to absorb the water. When clumps no longer form, the water has all been absorbed. |
| SAFETY: Which of the following are advantages of performing experiments at microscale level? | Microscale experiments use small quantities of chemicals. This reduces the risks involved in handling and heating chemicals; however, strict safety procedures should always be followed, even when using small amounts of chemicals in the laboratory. |
| why is it important that the aq.solvent is cooler than the organic solvent | if too warm it can start to boil off |
| why use magnesium sulfate over sodium sulfate to dry the organic solution | it works quicker |
| why would someone opt for sodium sulfate | has more of an effect when removing water |
| when should sublimation be used | if a compound can vaporize without melting first/ has extremely high mp and vp |
Created by:
lyndsayy