Unit 6: Nutrient Analysis in Fertilizers - Practice Quiz

1 Which method is commonly used to determine total nitrogen in fertilizers?

2 What is the main purpose of digestion in the Kjeldahl method?

3 Which acid is commonly used for digestion in the Kjeldahl method?

4 Which gas is released when the Kjeldahl digest is made alkaline?

5 Which solution is commonly added to make a Kjeldahl digest alkaline before distillation?

6 In a common Kjeldahl procedure, the distilled ammonia is collected in which solution?

7 What measurement is used to calculate nitrogen after ammonia has been collected in the Kjeldahl method?

8 Phosphate content in fertilizers is commonly expressed as the percentage of which compound?

9 Which ion is measured during the analysis of phosphatic fertilizers?

10 Which reagent is commonly used to form a yellow precipitate with phosphate?

11 What is the characteristic color of ammonium phosphomolybdate precipitate?

12 Which instrument measures color intensity in a colorimetric phosphate determination?

13 In the molybdenum blue method, the intensity of the blue color generally increases with what?

14 What should be done to a precipitate before it is weighed in a gravimetric phosphate analysis?

15 Potassium content in fertilizers is commonly reported as the percentage of which compound?

16 Which instrument is commonly used for the rapid determination of potassium in fertilizer solutions?

17 What happens to potassium atoms in the flame of a flame photometer?

18 Which wavelength is commonly associated with potassium emission in flame photometry?

19 Why is a potassium calibration curve prepared in flame photometry?

20 Which reagent can precipitate potassium in a gravimetric determination?

21 In a Kjeldahl analysis, a fertilizer sample requires of acid after blank correction. What is the percentage of nitrogen in the sample? Use as the atomic mass of nitrogen.

22 Why is concentrated sulfuric acid used during Kjeldahl digestion of a nitrogenous fertilizer?

23 A fertilizer contains nitrate nitrogen in addition to ammoniacal nitrogen. What must be done before applying the conventional Kjeldahl determination for total nitrogen?

24 During Kjeldahl distillation, insufficient sodium hydroxide is added to the digest. What is the most likely effect on the reported nitrogen content?

25 A Kjeldahl distillate consumes of acid, while the reagent blank consumes . Which volume should be used to calculate nitrogen?

26 A mixed fertilizer gives nitrogen by a method measuring both nitrate and ammoniacal nitrogen, but only by conventional Kjeldahl analysis. What best explains the difference?

27 Which observation most strongly indicates that Kjeldahl digestion of a fertilizer sample is complete?

28 A fertilizer contains elemental phosphorus. Approximately what is its phosphorus content expressed as ? Use the conversion factor .

29 In the ammonium phosphomolybdate method, why must precipitation conditions such as acidity and temperature be carefully controlled?

30 A fertilizer sample produces of . If the gravimetric factor from to is , what is the percentage of ?

31 In a colorimetric phosphate determination, the absorbance of the sample solution exceeds the highest calibration standard. What is the most appropriate action?

32 Why is a reagent blank used in the spectrophotometric determination of phosphate in fertilizers?

33 A phosphate precipitate is washed with an unsuitable solution that dissolves a small amount of it. How will this affect a gravimetric phosphate result?

34 Two laboratories report the same fertilizer as P and , respectively. Using , how should the results be interpreted?

35 A fertilizer contains elemental potassium. What is its potassium content expressed as using the factor ?

36 In flame photometric potassium analysis, why should standards and fertilizer samples have similar acid and salt concentrations?

37 A flame photometer gives readings of and units for potassium standards of and , respectively. Assuming linear response, what concentration corresponds to a sample reading of units?

38 A diluted fertilizer solution contains potassium. It was prepared by diluting of the original extract to . What was the potassium concentration in the original extract?

39 During gravimetric determination of potassium as potassium tetraphenylborate, the precipitate is filtered before precipitation is complete. What is the expected effect?

40 Successive flame photometer readings for the same potassium solution steadily increase. Which action should be taken first?

41 A fertilizer sample is digested by the Kjeldahl method. The liberated ammonia is collected in of sulfuric acid, and the excess acid requires of sodium hydroxide. A blank correction is negligible. What is the total nitrogen content?

42 In a Kjeldahl determination, ammonia from a sample is absorbed in boric acid and titrated with hydrochloric acid. The sample and blank consume and , respectively. What percentage of nitrogen is present?

43 A fertilizer contains ammonium sulfate and potassium nitrate. Conventional Kjeldahl digestion without a nitrate modification gives a reproducible result that is lower than the certified total nitrogen. What is the most likely cause?

44 Which sequence is most appropriate for determining total nitrogen in a fertilizer containing substantial nitrate by a salicylic acid modification of the Kjeldahl method?

45 During Kjeldahl distillation, concentrated sodium hydroxide is added, but the digest remains locally acidic because the solutions are not mixed. What analytical effect is most probable?

46 A nitrogen fertilizer is reported as N on an as-received basis and contains moisture. What is its nitrogen content on a dry basis?

47 A Kjeldahl catalyst tablet is accidentally included in the sample determination but omitted from the reagent blank. The tablet contains a small amount of ammonium contamination. How will blank-corrected nitrogen most likely be affected?

48 A fertilizer sample yields of quinolinium phosphomolybdate precipitate. If the gravimetric factor from precipitate to is , what is the phosphate content expressed as ?

49 A sample is diluted to . A aliquot is diluted to and found to contain of elemental phosphorus. Using , what is the fertilizer grade as ?

50 In a molybdenum-blue spectrophotometric determination, sample absorbance lies above the highest calibration standard. Which action best preserves analytical validity?

51 A phosphatic fertilizer contains condensed phosphates that are not fully hydrolyzed during sample preparation. An orthophosphate-specific colorimetric method is then applied. What result is expected?

52 A laboratory obtains elemental phosphorus but reports the same numerical value as . What should the correctly converted result be?

53 During gravimetric phosphate determination, the phosphomolybdate precipitate is washed with excessive pure water instead of the prescribed wash solution. The precipitate has slight solubility in pure water. What is the likely consequence?

54 Two methods are applied to the same fertilizer: total digestion gives , while neutral ammonium citrate extraction gives . Which interpretation is analytically justified?

55 A sample is diluted to . A aliquot is diluted to and gives K by flame photometry. Using , what is the potassium content as ?

56 In flame-emission analysis of a high-potassium fertilizer, calibration standards are prepared in dilute acid, while the sample solutions contain high concentrations of sodium and dissolved salts. The sample signal is suppressed. Which correction is most appropriate?

57 A fertilizer contains elemental potassium. What grade should be reported as potassium oxide equivalent, using ?

58 In a gravimetric tetraphenylborate determination of potassium, the precipitate is weighed before it reaches constant mass and still retains wash liquid. What bias will this introduce?

59 A flame photometer is calibrated at , , , and K. A diluted fertilizer solution reads . After a further twofold dilution, it reads . Which value should be used for the concentration before the additional dilution?

60 A fertilizer sample is reported as on the as-received basis. Moisture analysis shows water. What is the content on a dry basis?