Question

Describe the differences between
i. a gross sample and a laboratory sample (2)
ii. blank and reagent blank (2)
iii. mean and median (2)
iv. endpoint and equivalence point (2)
v. paired test and F-test

Answer 1

i) 1. Gross sample- The collection of sampling units or increments is called the gross sample. Laboratory sample- for laboratory analysis, the gross sample is usually reduced in size and homogenized to create the laboratory sample. 2. The laboratory sample consists of a few grams to at most a few hundred grams. It may constitute as little as 1 part in 107-108 of the bulk material. Gross sample (Analytical chemistry) One or more increments taken from a larger quantity of a material. ii) 1. A sample blank refers to using the sample for zeroing an instrument during a test procedure. A reagent blank refers to a small positive error in test results that comes from the reagents themselves. 2. A sample blank can correct for potential error from existing colour or turbidity in the sample before reagents are added. A reagent blank is a test sample that has undergone all the same treatment as your challenge sample but without the addition of a test sample.

iii) 1. The "mean" is the "average" you're used to, where you add up all the numbers and then divide by the number of numbers. The "median" is the "middle" value in the list of numbers. 2. The mean is used for normal distributions The median is generally used for skewed distributions. iv) 1. The equivalence point is the exact point in a titration when moles of one titrant equal the moles of the substance being titrated. The endpoint is the point where the system changes when the moles of the reacting titrant exceed the moles of the substance being titrated. 2. Equivalence point, on the other hand, is the stage just before the endpoint that signals the stoichiometric point with equal number of moles between the analyte and the titrant in line with the chemical equation. Endpoint is the stage in titration that is indicated by a color change as a sign that titration is complete and the equivalence point has been achieved.

1. Paired test is a univariate hypothesis test, that is applied when standard deviation is not known and the sample size is small. F-test is statistical test that determines the equality of the variances of the two normal populations. Paired test follows Student t-distribution, under null hypothesis. F-statistic follows Snedecor f-distribution, under null hypothesis.