Read the Limit Test for salicylic acid in aspirin below then answer the question below. Remember: Aspirin = acetyl salicylic acid (ASA), and salicylic acid = SA
Read the Limit Test for salicylic acid in aspirin below then answer the question below.
Remember: Aspirin = acetyl salicylic acid (ASA), and salicylic acid = SA
Limit Test for salicylic acid:
Extract powdered Aspirin tablets (i.e., active + excipient) containing 0.4g acetylsalicylic acid (i.e., active) with 4 mL of 95% ethanol. Add water to give a final volume of 100.0 mL and mix.
Transfer 50.0 mL of the filtrate to a Nessler Cylinder and add 1.0 mL of acidified ferric ammonium sulfate solution. Mix and allow to stand.
Prepare the standard solution used for comparison as follows: To another Nessler Cylinder add 3.0 mL of freshly prepared 0.01% (wt/vol) salicylic acid, 2.0 mL of ethanol, 1.0 mL of acidified ferric ammonium sulfate solution and sufficient water to give a total volume of 51.0 mL. Mix.
A violet colour produced by the sample should not be more intense than that of the standard, used for comparison.
Example of "Limit" calculations:
Based on the above limit test, the Limit of Salicylic Acid in Aspirin =
Amount of Standard (i.e., salicylic acid) in the colour comparison tube *100
Amount of Sample (i.e., Aspirin) in the colour comparison tube
- Amount of salicylic acid standard in the Nessler Cylinder = 3 mL of 0.01% (wt/ vol) salicylic acid = 0.3mg salicylic acid
[How was 0.3 mg obtained?
0.01% SA solution has 0.01g SA in 100 mL volume,
which gives 0.01g/100 mL = 0.0001g per mL or 0.0003g per 3 mL or
(0.0003g ´ 1000mg/g) per 3 mL = 0.3mg SA per 3 mL
Amount of Aspirin = 0.2g = 200mg (i.e., half of a 0.4g in 100 mL solution)]
- Amount of aspirin sample in the Nessler Cylinder = 200mg
[How was 200 mg obtained?
0.4g aspirin ds (ASA) was dissolved in 100 mL water/ethanol
Since only 50 mL was transferred into the Nessler Cylinder, then the sample cylinder contains 0.2g ASA or 200 mg aspirin.]
Therefore, the Limit of Salicylic Acid in Aspirin = 0.3mg SA * 100 = 0.15% (wt/wt)
200mg ASA
Question: If the limit of free salicylic acid is set at not more than (NMT) 0.5%,
how many mLs of a 0.01% (wt/vol) standard solution of salicylic acid must be used in the above method.
Do not include units (mL) with your numeric answer!
| a. |
10 |
|
| b. |
1 |
|
| c. |
None of the other answers |
|
| d. |
20 |
|
| e. |
0.1 |
|
| f. |
2 |
|
| g. |
100 |
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