Unit 2: Qualitative Tests - Practice Quiz

1 Which reagent is commonly used in Molisch's test for carbohydrates?

2 What color ring indicates a positive Molisch's test?

3 Which test is commonly used to identify reducing sugars?

4 What color precipitate may form in a positive Benedict's test?

5 Which reagent is used in the iodine test for starch?

6 What color does starch produce with iodine solution?

7 Seliwanoff's test is mainly used to distinguish between which types of sugars?

8 Which sugar gives a rapid cherry-red color in Seliwanoff's test?

9 Which reagent is commonly used to test for amino acids?

10 What color is commonly produced by most amino acids in the ninhydrin test?

11 Which amino acid commonly gives a yellow color with ninhydrin?

12 Which test is used to detect peptide bonds in proteins?

13 What color indicates a positive Biuret test?

14 Which element is detected by the sulfur test for proteins?

15 The xanthoproteic test is mainly used to detect which type of amino acid residue?

16 What color is associated with a positive xanthoproteic test?

17 Millon's test is mainly used to detect which amino acid in proteins?

18 Which test can be used to detect tryptophan in a protein sample?

19 A positive Hopkins-Cole test usually produces which color ring?

20 Proteins are made up of chains of which basic units?

21 A sample gives a brick-red precipitate with Benedict's reagent after heating. Which conclusion is best supported?

22 Why is concentrated sulfuric acid added carefully along the side of the tube in Molisch's test?

23 A carbohydrate produces a red precipitate with Benedict's reagent but gives a negative iodine test. Which substance is most consistent with these results?

24 A sample gives a blue-black color with iodine solution. What structural feature most likely accounts for this observation?

25 A sample is negative in Benedict's test but positive in Molisch's test. Which interpretation is most appropriate?

26 Which result would most strongly indicate the presence of a pentose rather than a hexose?

27 A student performs Seliwanoff's test and observes a rapid cherry-red color. Which class of carbohydrate is most likely present?

28 A protein solution gives a violet color after treatment with alkaline copper sulfate. Which structural feature is being detected?

29 A sample gives a positive ninhydrin test but a negative biuret test. Which conclusion is most likely?

30 Which amino acid would be expected to give a positive xanthoproteic test because of its aromatic side chain?

31 A protein gives a positive Millon's test. Which amino acid residue most likely accounts for the result?

32 A protein sample produces a black precipitate after treatment with lead acetate in an alkaline medium. What does this indicate?

33 Why may a protein containing tryptophan give a positive Hopkins-Cole test?

34 A gelatin sample gives a weak or negative xanthoproteic test but a positive biuret test. Which explanation is most appropriate?

35 Which observation best distinguishes a protein from a mixture containing only free amino acids?

36 A sample gives a purple ninhydrin color, but the color is weaker than expected. Which factor could explain this result?

37 A protein solution is heated and becomes cloudy, but the precipitate dissolves after adding a strong acid. This observation most likely represents:

38 A student obtains a negative biuret test with a very dilute protein sample. Which is the best interpretation?

39 Which combination of results most strongly supports the presence of a sulfur-containing protein?

40 A solution gives a positive ninhydrin test and a positive xanthoproteic test. Which compound could produce both results?

41 A sample gives a positive Molisch test, remains negative in Benedict's test before hydrolysis, and becomes strongly positive after acid hydrolysis followed by neutralization. Which composition best explains the result?

42 In the Barfoed test, a carbohydrate produces red cuprous oxide only after prolonged heating. Which interpretation is most appropriate?

43 A sample gives a rapid positive Seliwanoff test but also reacts positively with Benedict's reagent. Which conclusion is most defensible?

44 A carbohydrate gives a positive iodine test at room temperature, but the color disappears on heating and returns after cooling. Which structural feature best accounts for this behavior?

45 Two carbohydrates both produce osazone crystals with phenylhydrazine. Why can osazone formation fail to distinguish certain sugars?

46 A sample is positive in Molisch's test and Bial's test but negative in Seliwanoff's test. Which inference is most consistent with these results?

47 A galactose-containing sample is hydrolyzed, oxidized with nitric acid, and yields an insoluble crystalline product. Which product is expected?

48 A reducing sugar gives a weak Benedict's reaction despite being present at substantial concentration. Which factor could most directly suppress the observed color change?

49 An unknown amino acid produces a yellow ninhydrin color rather than the usual blue-violet color. Which structural explanation is most likely?

50 A protein hydrolysate gives a positive ninhydrin test but a negative biuret test. Which explanation best fits the result?

51 A protein gives a positive xanthoproteic test but a negative Millon's test. Which conclusion is most reasonable?

52 A protein gives a negative Hopkins-Cole test but a positive xanthoproteic test. Which amino acid profile best explains the observations?

53 A protein sample gives a positive Sakaguchi test even after denaturation by heat. What does this result specifically indicate?

54 A protein gives a black precipitate with lead acetate after alkaline treatment. Which residue is most directly implicated?

55 A protein solution is negative in the biuret test immediately after extensive acid hydrolysis. Which reason is most likely?

56 A protein initially gives a positive biuret test, but the result becomes negative after complete enzymatic digestion. Which interpretation is correct?

57 A protein precipitates at one pH but redissolves when the pH is made either more acidic or more basic. Which property explains this behavior?

58 A heat-coagulation test is negative for a protein solution even though the biuret test is positive. Which explanation is most plausible?

59 A sample gives a positive Molisch test and a positive biuret test. Which conclusion is safest without additional tests?

60 A carbohydrate sample produces a red color in Seliwanoff's test only after extended heating. Why should this result be interpreted cautiously?