LAB 1

Question 1

What two quantities can we use t characterize the reliability of experimental measurements?

Answer 1

accuracy and precision

Question 2

what is accuracy

Answer 2

Accuracy measures the extent to which measurements agree with a known value.

HOW CLOSE IT IS TO THE VALUE

Question 3

what is precision

Answer 3

Precision measures the consistency of the measurements with each other, independent of their accuracy.

Question 4

Error can be grouped into two types:

Answer 4

random and systematic

Question 5

Random error (indeterminate) is observed when

Answer 5

repeated experiments give slightly different results. result of the limitations of instruments to produce the same result each time.

Question 6

Data that has a minimal amount of random error

Answer 6

is said to be precise.

Question 7

Systematic error

Answer 7

(determinate or bias) is observed when an experiment produces results that are consistently too high or too low.

• result of instruments not properly calibrated or an experimental design that is flawed

Question 8

Data that has minimal amount of systematic error

Answer 8

is said to be accurate.

Question 9

Precision is often expressed statistically by the

Answer 9

standard deviation (𝑠) of a series. A standard deviation close to zero indicates that the data points are very close to the mean.

KNOW FORMULA

Question 10

what does xi represent

Answer 10

individual measured values

Question 11

x̅ is

Answer 11

is the mean

Question 12

n is

Answer 12

number of measured values in the series.

Question 13

x̅±

Answer 13

Results are expressed as x̅ ± standard deviation

Question 14

If a ‘true’ or ‘accepted’ value is known

Answer 14

then accuracy can be expressed as the relative percent error:

Question 15

Volumetric glassware are used when

Answer 15

(glassware used to measure liquid volumes), such as volumetric flasks, pipets, and burets, are used when measurements are required to a high degree of accuracy and precision.

Question 16

For example, a typical 10-mL pipet used in the lab has a tolerance of

Answer 16

± 0.02 and the volume is recorded as 10.00 mL.

Question 17

When using graduated cylinders,

Answer 17

you need to determine the value of the smallest increment and then always estimate the measurement one decimal place beyond that value, even if the last estimated digit is a zero.

Question 18

Beakers and flasks are not usually used as

Answer 18

measuring devices and their markings are generally only accurate to within 5%.

Question 19

volume measured with

Answer 19

(using beakers, graduated cylinders, and pipets)

Question 20

mass measured using

Answer 20

scales

Question 21

relationship between volume and mass

Answer 21

. Density, d, is the amount of mass, m, per unit volume, v, of a substance.

Question 22

Density can be used to

Answer 22

• describe a pure substance (element/compound) or solution
• density measurements are affected by changes in temp and pressure
• for solution, density also changes with solution concentration

Question 23

calibration curve

Answer 23

how density changes as a function of concentration from which densities can be predicted at other concentrations, or vice versa.

Question 24

Figure 1

Answer 24

there is a linear relationship between density and concentration. for NaCl

Here the equation of the line is given by d = 0.0076c + 0.9988 (where d = density and c = %w/w concentration). Thus, if we have a salt solution which is 12.0% w/w then the calculated density is (0.0076 × 12.0) + 0.9988 = 1.09 gcm-3.

MADE UNDER 15.5 DEGREES, CONTROLLED ENVIRONMENT