Unit 4: Acid Value and Ascorbic Acid - Practice Quiz

1 What does the acid value of a fat measure?

2 The acid value is expressed as the milligrams of which substance required to neutralize free fatty acids in 1 g of fat?

3 Which type of titration is commonly used to determine the acid value of a fat?

4 Which reagent is commonly used as the titrant in acid value determination?

5 Which indicator is commonly used in the titration of free fatty acids in fat?

6 What is the usual endpoint color when phenolphthalein is used in acid value determination?

7 A high acid value in a fat generally indicates:

8 Which process commonly causes an increase in the acid value of stored fat?

9 Why is a fat sample often dissolved in an alcohol-containing solvent before titration?

10 In the acid value equation, the sample mass is usually expressed in:

11 Ascorbic acid is commonly known as:

12 Which property of ascorbic acid is used in its titrimetric determination?

13 Which reagent is commonly used to estimate ascorbic acid in fruit juice?

14 What happens to DCPIP when it reacts with ascorbic acid?

15 What is the usual endpoint in the DCPIP titration of ascorbic acid?

16 Why is fruit juice usually filtered before determining its ascorbic acid content?

17 Ascorbic acid is easily destroyed by exposure to:

18 Why should a fruit juice sample be analyzed soon after preparation?

19 What is usually prepared before analyzing an unknown fruit juice sample?

20 The ascorbic acid content of fruit juice is commonly reported as:

21 A 2.50 g fat sample requires 1.80 mL of 0.100 M KOH for neutralization. If the blank requires 0.20 mL, what is the acid value of the fat?

22 Why is a blank titration performed during acid value determination?

23 A fat sample is titrated with 0.050 M KOH. The sample mass is 4.00 g, and the blank-corrected titre is 3.00 mL. What is the acid value?

24 An increased acid value in an oil sample most directly indicates:

25 If the fat sample mass is doubled while the amount of free fatty acid remains proportional to the sample mass, what happens to the acid value?

26 Which endpoint observation is generally used when phenolphthalein is the indicator in acid value determination?

27 A 5.00 g fat sample gives a titre of 4.50 mL with 0.100 N KOH. The blank titre is 0.50 mL. What is the acid value?

28 Why is the fat commonly dissolved in a neutralized alcohol-containing solvent before titration?

29 A technician uses 0.200 N KOH instead of 0.100 N KOH in the calculation without changing the recorded titre. What is the effect on the calculated acid value?

30 Which procedural mistake would most likely produce an acid value that is too high?

31 In the DCPIP method, ascorbic acid is quantified because it:

32 A standard solution contains 1.00 mg of ascorbic acid and requires 2.00 mL of DCPIP. A 10.0 mL juice aliquot requires 1.50 mL of DCPIP. How much ascorbic acid is present in the aliquot?

33 A 10.0 mL juice aliquot contains 0.75 mg of ascorbic acid. What is the concentration of ascorbic acid in the juice?

34 Why should a fruit juice sample be analyzed promptly or protected from air and light?

35 A 25.0 mL juice sample is diluted to 100.0 mL. A 10.0 mL portion of the diluted sample contains 2.00 mg of ascorbic acid. What is the ascorbic acid content of the original juice?

36 A 25.0 mL juice sample is diluted to 100.0 mL. A 10.0 mL portion of the diluted sample contains 2.00 mg of ascorbic acid. What is the ascorbic acid content of the original juice?

37 What indicates the endpoint in a DCPIP titration of ascorbic acid?

38 If a juice aliquot is diluted twofold before titration and the dilution is not included in the calculation, the reported ascorbic acid concentration will be:

39 A standardization shows that 1.00 mL DCPIP is equivalent to 0.400 mg ascorbic acid. If 15.0 mL of juice requires 2.50 mL DCPIP, what is the concentration in the juice?

40 A standardization shows that 1.00 mL DCPIP is equivalent to 0.400 mg ascorbic acid. If 15.0 mL of juice requires 2.50 mL DCPIP, what is the concentration in the juice?

41 A fat sample requires of alcoholic KOH, while the reagent blank requires . What is the acid value of the fat?

42 A fat sample is titrated using alcoholic KOH that was standardized with potassium hydrogen phthalate (molar mass ). The KHP requires of the KOH solution. What is the actual normality of the KOH?

43 A fat sample requires of KOH, and the blank requires . Which result is closest to the acid value?

44 If the endpoint is exceeded by during titration of a sample with KOH, what is the resulting error in the reported acid value?

45 A fat has an acid value of . Assuming its free fatty acids are entirely oleic acid, what is the approximate percentage of free oleic acid by mass? Use molar mass of oleic acid .

46 Two samples are titrated with KOH. Sample A weighs and consumes after a blank correction. Sample B weighs and consumes after the same correction. Which interpretation is correct?

47 Why is a reagent blank essential in acid-value determination even when the fat itself is the only intended acid source?

48 A poorly dried fat sample contains water by mass. If the measured acid value is calculated using the wet sample mass, how will the result compare with the acid value calculated on a dry-mass basis, assuming water consumes no KOH?

49 Which observation most strongly indicates that an acid-value titration result may be falsely high because of incomplete sample dissolution?

50 Which statement best distinguishes acid value from saponification value?

51 A fruit juice sample is diluted to . A aliquot requires of DCPIP, and DCPIP is equivalent to ascorbic acid. What is the ascorbic acid concentration in the original juice?

52 A DCPIP solution is standardized using pure ascorbic acid, requiring DCPIP. A juice sample then requires . What mass of ascorbic acid is present per juice?

53 A juice sample is diluted to . A aliquot requires DCPIP, standardized as ascorbic acid. What is the concentration in the original juice?

54 In an ascorbic acid titration with DCPIP, the endpoint is identified by a faint pink color that persists briefly. The persistence occurs because:

55 Why is metaphosphoric acid or another suitable stabilizing acid commonly used during preparation of fruit-juice samples for ascorbic acid analysis?

56 A juice contains a strongly colored pigment that masks the DCPIP endpoint. Which modification most directly improves the analytical result without changing the redox chemistry?

57 A juice sample gives titration volumes of , , and DCPIP. What is the most appropriate treatment before calculating the ascorbic acid content?

58 If a juice sample is left exposed to air and light for several hours before DCPIP titration, the measured ascorbic acid content will most likely be:

59 A juice aliquot requires DCPIP. A matrix blank requires , and the standardized factor is ascorbic acid per milliliter of DCPIP. What mass of ascorbic acid is in the aliquot?

60 A method reports ascorbic acid in a juice, but the juice was first diluted and the analyst forgot to apply the dilution factor. What should the corrected concentration be?