A sample of benzoic acid contaminated with NaCl and sand is to be recrystallized:

Benzoid Acid: Solubility in water at 100 degrees Celsius in g/100 mL = 6.8, at 0 degrees Celsius in g/100 mL = 0.2. NaCl: Solubility in water at 100 degrees Celsius in g/100 mL = 39.1, at 0 degrees Celsius in g/100 mL = 35.7.
Sand:Solubility in water at 100 degrees Celsius in g/100 mL = Insoluble, at 0 degrees Celsius in g/100 mL = insoluble

The sample initially contained 4.0 g of benzoic acid, 2.0 g of NaCl and 1.0 g of sand and was treated with 50 mL of boiling water, filtered by gravity and then cooled in ice to obtain a precipitate which was isolated by suction filtration. How much benzoic acid should be formed?

At 100 C what dissolves?

6.8 x (50 mL/100 mL) = 3.4 g goes into solution for benzoic acid.

NaCl is
39.1 x (50 mL/100 mL) = 19.5 g so the entire 2 g NaCl goes into solution.

Sand of course stays out.

Filtered. You now have 3.4 g benzoic acid and 2.0 g NaCl in the filtrate.

What comes out at 0C?
0.2g benzoic acid x (50/100) = 0.1 g is in solution. The remainder ppts which is 3.4g - 0.1 g = ?

NaCl?
That's 35.7g x (50/100) = about 18 g in soln so no NaCl ppts.

To determine the amount of benzoic acid that should be formed, we need to consider its solubility and the purification process involved.

First, let's examine the solubilities of the substances in water at the given temperatures:

- Benzoic Acid: Solubility at 100°C = 6.8 g/100 mL, Solubility at 0°C = 0.2 g/100 mL
- NaCl: Solubility at 100°C = 39.1 g/100 mL, Solubility at 0°C = 35.7 g/100 mL
- Sand: Insoluble in water at both 100°C and 0°C

The purification process involves recrystallization, which takes advantage of the different solubilities of the substances. Here's how to proceed:

1. Start with the sample mixture containing 4.0 g of benzoic acid, 2.0 g of NaCl, and 1.0 g of sand.
2. Add 50 mL of boiling water to the mixture and stir until all the compounds are dissolved. Heat aids dissolution.
3. Filter the hot solution using gravity filtration to separate the insoluble sand particles.
4. Collect the filtrate, which should contain dissolved benzoic acid and NaCl.
5. Place the filtrate in an ice bath to cool it rapidly. Cooling promotes crystallization.
6. As the solution cools, the solubility of benzoic acid decreases, leading to the formation of benzoic acid crystals.
7. Isolate the benzoic acid crystals by performing suction filtration, where the crystals are collected on the filter paper and the liquid passes through the filter.
8. Wash the crystals with a small amount of cold water to remove any impurities.
9. Dry the benzoic acid crystals to remove any remaining water.

Now, let's calculate the amount of benzoic acid that should be formed:

Since we started with 4.0 g of benzoic acid and it has a solubility of 6.8 g/100 mL at 100°C, we can assume that all the benzoic acid dissolved initially.

Next, we need to determine the final solubility of benzoic acid at 0°C. This is given as 0.2 g/100 mL.

Since we used 50 mL of water for the recrystallization process, we'll consider the solubility at 0°C for that volume.
So, at 0°C and with a solubility of 0.2 g/100 mL, the maximum amount of benzoic acid that can remain in solution is:
(0.2 g/100 mL) x 50 mL = 0.1 g

Therefore, the amount of benzoic acid that should be formed through recrystallization is:
Initial amount - Remaining amount = 4.0 g - 0.1 g = 3.9 g

Hence, approximately 3.9 grams of benzoic acid should be formed after the purification process.

To determine the amount of benzoic acid that should be formed, we need to consider the solubilities of the substances involved.

1. Benzoic acid has a solubility of 6.8 g/100 mL at 100 degrees Celsius and 0.2 g/100 mL at 0 degrees Celsius.
2. NaCl has a solubility of 39.1 g/100 mL at 100 degrees Celsius and 35.7 g/100 mL at 0 degrees Celsius.
3. Sand is insoluble in water at both temperatures.

Based on the given information, we can proceed with the following steps:

1. Calculate the volume of water needed to dissolve 4.0 g of benzoic acid at 100 degrees Celsius.
- Using the formula: x = (mass of solute / solubility of solute in water) * 100
- x = (4.0 g / 6.8 g/100 mL) * 100 = 58.82 mL

2. Calculate the volume of water needed to dissolve 2.0 g of NaCl at 100 degrees Celsius.
- Using the formula: x = (mass of solute / solubility of solute in water) * 100
- x = (2.0 g / 39.1 g/100 mL) * 100 = 5.12 mL

3. Calculate the total volume of water required by adding the volumes calculated in steps 1 and 2.
- Total volume = 58.82 mL + 5.12 mL = 63.94 mL

4. Since there is a limited amount of water (50 mL) available, only the benzoic acid will dissolve completely, while the NaCl and sand will remain insoluble.

5. Filter the mixture by gravity to separate the insoluble NaCl and sand from the solution.

6. Cool the solution to 0 degrees Celsius, either by placing it in an ice bath or refrigerator.

7. As the solution cools, the benzoic acid will start to crystallize out of the solution. This forms a precipitate.

8. Perform suction filtration to isolate the precipitate (benzoic acid crystals). Measure and record the weight of the obtained crystals.

9. The weight of the isolated benzoic acid crystals should correspond to the amount of benzoic acid formed.

By following these steps, you will be able to determine the amount of benzoic acid that should be formed from the given sample.