Limit tests

Which of the following explains the blue color observed when potassium iodide is exposed to peroxides or other oxidizing substances in an acid medium?

• Peroxides reduce potassium iodide to iodine, which reacts with starch.

• peroxides oxidize potassium iodide to iodine, which turns starch solution blue.

• Potassium iodide reacts directly with starch, producing a blue complex.

• Acid medium neutralizes potassium iodide, forming a blue-colored solution.

Which of the following is true regarding the use of KMnO4 in testing for oxidizable substances?

• KMnO4 reduces oxidizable substances, changing its color to blue.

• The test is positive when KMnO4 remains colorless after the reaction.

• The amount of KMnO4 used determines the limit for oxidizable substances.

• KMnO4 reacts with starch to produce a blue color.

In the test for chlorine impurity, what determines the limit of chlorine?

• The volume of KMnO4 used in the reaction

• The color change of starch solution

• The volume of Na2S2O3 (sodium thiosulfate) used in the titration

• The formation of a blue complex with iodine

Which of the following are the main reagents used in the semi-micro determination of water by Karl Fischer titration in pharmaceutical analysis?

• Iodine, sulfuric acid, and ethanol

• Sodium thiosulfate, iodine, and starch solution

• Potassium iodide, hydrochloric acid, and acetone

• Iodine, sulfur dioxide, a base (like pyridine or imidazole), and methanol

Which of the following is NOT a type of gravimetric test in pharmaceutical analysis?

• Determination of volatile impurities by titration

• Loss on drying

• Sulfated ash

• Total ash