Exam 1

Question 1

What’s the difference between implicit and explicit uncertainty?

Answer 1

Explicit uncertainty is explicitly stated

ex) 0.03+/- implies an uncertainty of 0.03

implicit uncertainty is implied by the number of significant figures reported

ex) 399.32 implies an uncertainty of 0.01

Question 2

what is absolute uncertainty

Answer 2

it expresses the margin of uncertainty associated with a specific measurement

Question 3

what is relative uncertainty

Answer 3

it compares the absolute uncertainty with the measurement itself.

This allows us to have a perspective on how much the uncertainty might have on a sample

usually smaller samples are impacted more by uncertainties than larger samples

Question 4

what is determinate error

Answer 4

it is caused by the way you make a measurement, it always occurs in one direction and is constant

Question 5

what is an indeterminate error

Answer 5

it is harder to detect but it can occur in either direction. It is not constant and is always present + random

Question 6

What type of error is a precision error

Answer 6

indeterminate

Question 7

what are the errors that affect precision

Answer 7

repeatability and reproducibility

Question 8

what is repeatability

Answer 8

the precision accomplished in one session (weighing something over and over)

Question 9

what is reproducibility

Answer 9

day-to-day laboratory precision, the precision of another person or under a different set of conditions

Question 10

Can reproducibility be less than repeatability?

Answer 10

No, reproducibility includes repeatability

Question 11

what is error

Answer 11

error is the difference between a single measurement and its expected value

Question 12

what is uncertainty

Answer 12

it expresses the range of possible values for a measurement or result, it includes determinate and indeterminate errors

Question 13

what is absolute error

Answer 13

experimental-actual value

Question 14

what is the relative error

Answer 14

absolute error divided by the actual

Question 15

Q
what is the uncertainty in this? 10.00 ± 0.02

Answer 15

0.02

Question 16

Q
A 25 mL pipette consistently delivers 25.031 ± 0.009 mL. Is the error determinate, indeterminate or both?

Answer 16

Determinate: 0.031

indeterminate ± 0.009mL

Question 17

what does the uncertainty express

Answer 17

it accompasses a range of what the values could be

Question 18

Q
In a normal distrubution graph, what does the area under the curve tell us?

Answer 18

the probability of finding a member of a population in a range of values

Question 19

what is z

Answer 19

it is a standard score that tells us how many standard deviations we are away from the mean

Question 20

when do we use normal distribution curves?

Answer 20

When we think our sample set is normal and we want to see the probability of a certain event occuring/not occurring

Question 21

The formula weight of CaCO3 is 100.087 +/- 0.004 g/mol,

what is the the +/- 0.004 g/mol representative of?

Answer 21

explicit uncertainty

Question 22

Precision and Accuracy can both be measured in the laboratory, however, precision is almost always easier to measure why?

Answer 22

One can almost always make repreated measurements but sometimes we can’t evaluate the accuracy of something due to the lack of knowledge of the true value

Question 23

A student is measuring 500.00 mL using a volumetric flask with a specified tolerance of 0.08 mL. The studuent fills the flask below the line. What type of error is this

Answer 23

the student ALWAYS fails to fill up the flask, it is always a constant underestimation so it is a determinate (systematic error)

Question 24

When do we use a paired t-test?

Answer 24

When we have pairs of data and want to see the change in variances. We do not want to analyze the means. We assume that the variance is not equal

Question 25

when do we use an unpaired t-test

Answer 25

when we want to know if the means are statistically different and we assume that the standard deviations are equal.

Question 26

what is a false positive

Answer 26

it is when the null hypothesis is true but we say that it is false

Question 27

what is a false negative

Answer 27

it is when the null hypothesis is not true but we say that it is

Question 28

when do we use a comparing x to u test

Answer 28

if you have a mean value and are trying to determine if it is different from a known value (also called the reference value)

you are comparing the mean of your sample set to a known value (u)

Question 29

When do we use an F test

Answer 29

to check if the standard deviations from sample set one and sample set two are different

always arrange s1 and s2 so that F>1

if F calculated > F table, then the difference in the standard deviations is signifiant

Question 30

when do we use a grubbs test

Answer 30

when we want to know if we have an outlier

you can calculate it with with |(questionable value - mean)/standard deviation|

if Gcalculated is > Gtable, then we have an outlier

Question 31

Errors that affect accuracy are

Answer 31

determinate

Question 32

errors that affect precision are

Answer 32

indeteminate

Question 33

what is ppm equivalent to

Answer 33

ug/g, mg/L, ug/mL

Question 34

what is ppb equivalent to

Answer 34

ng/g,ug/L,ng/mL