How to find the volume of hot water required to dissolve the mass of acid, if we have 20g of benzoic acid contaminated with 0.4g of salicylic acid?
What is the mass of benzoic acid which participates when the solution is cooled to 20°C? Deduce.
What is the mass of salicylic acid which co-precipitated with the mass of benzoic acid?
What is the percentage of benzoic acid obtained after the recrystallisation?
Solubility (g/100ml) of BA at 20°C :0.29 and at 100°C:6.8
Solubility (g/100ml) of SA at 20°C:0.22 and at 100°C:6.67
When do these I ignore the water necessary to dissolve the impurity; often the minimum amount of H2O needed is just the amount to dissolve the major element and the impurity is dissolved in that same amount of water.
100 mL x (20g/6.67) = about 300 mL a 100 C.
How much will ppt at 20 C?
BA = 0.29 x (300/100) = about 0.9 lost.
SA = 0.22 x (300/100) = about 0.7 lost.
amount BA pptd 20-0.9 = ?
amount SA pptd 0.4-0.7 = 0
etc.
To find the volume of hot water required to dissolve the mass of acid, you would need to know the solubility of the acid in water at the desired temperature. You mentioned that the solubility of benzoic acid (BA) at 20°C is 0.29 g/100 ml.
Step 1: Calculate the amount of water needed to dissolve 20g of benzoic acid.
- Since the solubility is given in g/100 ml, we can set up a proportion:
(20 g BA) / (0.29 g/100 ml) = (x ml water) / 100 ml
- Cross-multiply and solve for x:
x ml water = (20 g BA) * (100 ml) / (0.29 g)
x ml water = 6897 ml (rounded to the nearest whole number)
Therefore, approximately 6897 ml of hot water is required to dissolve the 20g of benzoic acid.
Next, let's move on to the next part of the question.
To deduce the mass of benzoic acid that participates when the solution is cooled to 20°C, we need to consider the solubility of the acid at different temperatures and the fact that benzoic acid is less soluble at lower temperatures.
Step 2: Determine the solubility of benzoic acid at 20°C.
- The solubility of benzoic acid at 20°C is given in the question as 0.29 g/100 ml.
Step 3: Calculate the maximum amount of benzoic acid that can remain dissolved in 100 ml of water at 20°C.
- This can be found by multiplying the solubility by the volume of water used (6897 ml / 100 = 68.97, rounded to 69):
Mass of benzoic acid remaining dissolved = 0.29 g/100 ml * 69 ml = 20.01 g
Therefore, the mass of benzoic acid that participates when the solution is cooled to 20°C is approximately 20.01 g.
Moving on to the next part of the question.
To find the mass of salicylic acid that co-precipitated with the mass of benzoic acid, you need to consider the difference in solubilities between the two acids.
Step 4: Calculate the amount of salicylic acid that could also be dissolved in the same volume of water at 20°C.
- The solubility of salicylic acid (SA) at 20°C is given as 0.22 g/100 ml.
- Using the same volume of water (6897 ml / 100 = 68.97, rounded to 69):
Mass of salicylic acid dissolved = 0.22 g/100 ml * 69 ml = 0.152 g
Therefore, approximately 0.152 g of salicylic acid co-precipitated with the mass of benzoic acid.
Lastly, we can determine the percentage of benzoic acid obtained after recrystallization.
Step 5: Calculate the percentage of benzoic acid obtained after recrystallization.
- We know that the initial mass of benzoic acid was 20g, and we found that approximately 20.01 g of benzoic acid participates when cooled to 20°C.
- Calculate the percentage using the formula:
Percentage of benzoic acid = (mass of benzoic acid obtained / initial mass of benzoic acid) * 100
Percentage of benzoic acid = (20.01 g / 20 g) * 100
Percentage of benzoic acid = 100.05%
Therefore, the percentage of benzoic acid obtained after recrystallization is approximately 100.05%.
To find the volume of hot water required to dissolve the mass of acid, you will need to consider the solubility of benzoic acid (BA) and salicylic acid (SA) at different temperatures.
1. Calculate the mass of benzoic acid that needs to be dissolved:
- Given: 20g benzoic acid + 0.4g salicylic acid
- Mass of benzoic acid = 20g - 0.4g = 19.6g
2. Determine the solubility of benzoic acid at 20°C and 100°C:
- Solubility of BA at 20°C: 0.29g/100ml
- Solubility of BA at 100°C: 6.8g/100ml
3. Calculate the volume of water needed to dissolve the mass of benzoic acid at each temperature:
- Volume at 20°C = (Mass of benzoic acid / Solubility at 20°C) * 100
- Volume at 100°C = (Mass of benzoic acid / Solubility at 100°C) * 100
4. Deduce the mass of benzoic acid that participates when the solution is cooled to 20°C:
- Since the solution is cooled, some benzoic acid may precipitate out depending on its solubility at the lower temperature. You can calculate this by multiplying the volume at 20°C by the solubility at 20°C:
- Mass of benzoic acid after cooling to 20°C = (Volume at 20°C / 100) * Solubility at 20°C
5. Calculate the mass of salicylic acid that co-precipitated with the mass of benzoic acid:
- Mass of salicylic acid co-precipitated = Mass of salicylic acid initially - Mass of salicylic acid remaining in solution after cooling
6. Calculate the percentage of benzoic acid obtained after recrystallization:
- Percentage of benzoic acid obtained = (Mass of benzoic acid after cooling to 20°C / Mass of benzoic acid) * 100