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

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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

 

  1. 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)]

 

  1. 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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