Is there a correlation between the values of the distribution coefficients and the polarities of the three compounds? Explain.
Place 0.050 g of one of the solids (benzoic acid, succinic acid, or sodium benzoate) in a vial and add 2 mL of methylene chloride and 2 mL of water. Calculate the distribution coefficient for the solid between methylene chloride and water. Because the volume of methylene chloride and water was the same, the distribution coefficient can be calculated by dividing the weight of solute in methylene chloride by the weight of solute in water. I'm confused by what they mean and the correlation between polarities?
Kd is the distribution coefficient.
I assume you have done an experiment in which you weighed 0.050 g benzoic acid, for example, then determined how much was in the water and how much was in the methylene chloride. As the problem states, divide the mass of one by the mass of the other and determine Kd. Then do the same thing for succinic acid and sodium benzoate. When you have the Kd for each of them, them make a correlation, if there is one, between the Kd you found and the polarity of the three compounds. Sodium benzoate should be the most polar and I think (but you had better check me out on this) succinic acid should be next with benzoic acid (although polar) bringing up the rear. The most polar should be most soluble in water and the least polar should be the most soluble in methylene chloride. Since
Kd = mass in organic layer/mass in water layer,
the most polar should have the least Kd and the least polar should have the highest Kd.
this is a problem from an experiment we did not perform, but have to answer... that is why
I do not know what values to use for the division?
Here is what a worksheet says.
Assume 50 mg of a compound was extracted between equal volumes (2 ml) of water and methylene chloride. Calculate the distribution coefficients for each compound, given the following results:
a. 1 mg of sodium benzoate was recovered from the methylene chloride layer
b. 40 mg of benzoic acid were isolated from the methylene chloride layer
c. 6 mg of succinic acid were isolated from the methylene chloride layer
You have it made, then.
a. 1 mg of sodium benzoate was recovered from the methylene chloride layer
So Kd = 1/49
b. 40 mg of benzoic acid were isolated from the methylene chloride layer
So Kd = 40/10
c. 6 mg of succinic acid were isolated from the methylene chloride layer
So Kd = 6/44
Note that 44+6, 1+49, and 40+10 all equal 50 which is what you started with.
1/49 will be the smallest number which means the sodium benzoate is the most polar and the least soluble in organic layer (what we thought), 40/10 is the largest number and the most soluble in the organic layer (what we thought for benzoic acid), and succinic acid is the middle one (with a value in the middle). Check my thinking.
It seems logical to me. One last question: What does a distribution coefficient of one (K=1) indicate about a compound's solubility between organic and aqueous phases?
I think I remember my teacher saying that it is impossible to have a K=1?
Kd=1.
Like one of your examples it would mean 25 mg on the aqueous phase and 25 mg in the organic phase. Thus it is equally soluble in the two phases. Not impossible, but perhaps unlikely.
how do know witch layer is water and methylene chloride?
density...
the methylene chloride is the one down...
The distribution coefficient (Kd) is a measure of how a solute distributes itself between two immiscible solvents, in this case, methylene chloride (CH2Cl2) and water. It can be calculated by dividing the weight of the solute present in the methylene chloride phase by the weight of the solute present in the water phase.
To understand the correlation between the values of the distribution coefficients and the polarities of the three compounds (benzoic acid, succinic acid, and sodium benzoate), we need to consider the solubility of these compounds in the two solvents.
Methylene chloride is a non-polar solvent, while water is a polar solvent. Polar solvents are better at dissolving polar compounds, while non-polar solvents are better at dissolving non-polar compounds. This is due to the principle of "like dissolves like."
Benzoic acid is a polar compound due to the presence of the carboxylic acid group. Succinic acid is also a polar compound because it contains two carboxylic acid groups. Sodium benzoate, on the other hand, is a salt and is ionic in nature.
Based on the principles of solubility and polarity, we can predict the behavior of each compound when placed in a mixture of methylene chloride and water:
1. Benzoic acid: Being polar, it is likely to have a higher solubility in water compared to methylene chloride. Therefore, a larger proportion of benzoic acid will be present in the water phase relative to methylene chloride. As a result, the Kd value for benzoic acid will be less than 1.
2. Succinic acid: Similar to benzoic acid, succinic acid is polar and should have a higher solubility in water. Therefore, it will also have a Kd value less than 1.
3. Sodium benzoate: Being ionic, sodium benzoate is more likely to dissolve in the polar solvent (water) rather than the non-polar solvent (methylene chloride). This means that sodium benzoate will have a higher proportion in the water phase compared to the methylene chloride phase. As a result, the Kd value for sodium benzoate will be greater than 1.
In summary, compounds with higher polarities (benzoic acid, succinic acid) are expected to have smaller Kd values (< 1) as they preferentially dissolve in the polar solvent (water). In contrast, the less polar and ionic compound (sodium benzoate) is expected to have a larger Kd value (> 1) as it preferentially dissolves in the non-polar solvent (methylene chloride).