VKC ScienceChemistry for written exams Telegram

UPSC Combined Geo-Scientist

Chemist

  • 3 descriptive papers
  • 200 marks each
  • 3 h per paper

Mains Paper III covers analytical and organic chemistry.

UPSC Combined Geo-Scientist, Mains · 2022 · Mains Paper III

Q5(a). New method against a reference method: F-test and t-test

Question

The accuracy of a new spectrophotometric method for determining uranyl ions in aqueous medium is tested by comparing with a reference method. Results (ppm): new method 20.5, 21.3, 18.6, 19.5, 18.1, 20.9; reference method 20.2, 19.2, 21.4, 19.9, 20.8. Values of t for ν = 9: 1.833 (90 %), 2.262 (95 %), 3.250 (99 %), 3.690 (99.5 %). Values of F at the 95 % confidence level for ν₂ = 4: 6.39 (ν₁ = 4), 6.26 (ν₁ = 5), 6.16 (ν₁ = 6). Is there any statistical difference between the two methods at 95 % confidence level? Justify.

Answer in brief

No. F = 2.36 < 6.26, so the precisions agree; t = 0.715 < 2.262, so the means agree: at 95 % confidence the two methods give statistically the same result.

Part of VKC Basic

Read the key points and the full model answer with VKC Basic

VKC Basic (₹999 for 6 months) opens every solved answer, the notes, the handbook and the daily answer archive. Every Mains test series includes it.

See what is included Already a member? Sign in

The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

The handwritten model answer pages open with the VKC plan.
Read the whole 2022 solution2022 question paper

Topic notes: errors in chemical analysis, standard deviation, confidence limits and the Q-, t- and F-tests, with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversF-testt-testpooled standard deviationsignificance testmethod comparison

All parts of Question 5