1. What is the minimum volume of hot water needed to dissolve 0.200g phenacetin? How much phenacetin will remain in that volume of water once it cools?
2. Why is it important that all the solid dissolves in the hot solvent, before the solution is cooled?
3. How would you develop a simple, small scale test to determine a good recrystallization solvent if one is not listed in the procedure?
You need ro know the solubility of phenacetin in water (what temperature is hot?) as well as the solubility in cool (what is the temperature of cool?) water.
1. To determine the minimum volume of hot water needed to dissolve 0.200g phenacetin, we need to know its solubility in water at a specific temperature. Solubility is usually listed in terms of grams of solute per 100 mL of water (g/100 mL).
To find the minimum volume, you should consult a solubility chart or a reliable database to determine the solubility of phenacetin at the required temperature. Let's assume, for example, that the solubility of phenacetin at the given temperature is 1.0g/100 mL.
To calculate the minimum volume of hot water, you can use the formula:
Minimum volume (mL) = (mass of phenacetin / solubility in g/100 mL)
Substituting the values, we get:
Minimum volume (mL) = (0.200g / 1.0g/100 mL) = 20 mL
So, the minimum volume of hot water needed to dissolve 0.200g phenacetin would be 20 mL.
Regarding the amount of phenacetin that will remain in that volume of water once it cools, it depends on the solubility of phenacetin at the lower temperature. If phenacetin is less soluble at lower temperatures, some of it will precipitate out of the solution as it cools. If phenacetin is still at or above its solubility limit at the lower temperature, then no solid will remain in the cooled solution. You would need to consult a solubility chart or perform experimental data to determine the actual amount of phenacetin that will remain in the cooled solution.
2. It is important that all the solid dissolves in the hot solvent before the solution is cooled for several reasons:
a. Complete dissolution ensures that the maximum amount of solute (solid) is incorporated into the solvent solution. This allows for the best efficiency in the subsequent steps of the process.
b. If some solid remains undissolved, it may lead to the formation of impurities or by-products that can affect the purity of the final product.
c. Cooling the solution after complete dissolution encourages the solute to re-crystallize in a controlled manner, as the solubility of most compounds decreases as temperature decreases. This allows for the selective purification of the solute by filtering out impurities.
In summary, ensuring complete dissolution in the hot solvent before cooling is crucial to maximize purity and achieve an effective recrystallization process.
3. To develop a simple, small-scale test to determine a good recrystallization solvent, follow the steps below:
a. Collect a small sample of the compound you want to recrystallize (generally less than 1 gram).
b. Choose a few potential solvents that are known to dissolve your compound to some extent. Select solvents that are non-reactive and have different properties (polarity, boiling points, etc.). Common solvents used for recrystallization include water, ethanol, methanol, and acetone.
c. Take several clean test tubes and add a small amount of the compound to each tube.
d. Add a different solvent to each test tube, ensuring that the solvent covers the solid compound in each tube.
e. Gently swirl or stir each test tube to aid dissolution of the compound in the solvent.
f. Observe the behavior of the compound in each solvent. Look for signs of dissolution, such as the formation of a clear solution or the disappearance of solid particles.
g. If the compound dissolves completely or to a large extent in a particular solvent, it indicates that the solvent is a good candidate for recrystallization. If the compound remains mostly solid in a solvent or forms a suspension, it suggests that the solvent is not suitable for recrystallization.
h. Based on the results, choose the solvent that showed the best dissolution as the potential recrystallization solvent for your compound.
Note that this is a preliminary test, and further optimization and evaluation may be required to find the most appropriate solvent for recrystallization.