- Systematic (determinate) error – error that can be discovered and correct
ex: pH buffer
is labeled 7.00 pH when in actuality it is 7.08 pH.
- Random (indeterminate) error – arises from limitations in ability to make physical
measurements
ex: you are reading a scale and the mass is between 1.4-g and 1.5-g and u
have to estimate the last significant figure
- Significant figures – refers to the digits known with certainty plus the first estimated
digit
- Precision – the repetition of a measurement several times or the reproducibility of a
measurement
- Accuracy – nearness to the true measurement
- Normal (Gaussian) distribution – characterized with the most probable answer in the
center and the probability of other answers decreases and the distance from the center
increases. This type of distribution when concerning a lot of different values is often
plotted on a bell-shaped curve.
- Mean (x-bar, average) – the sum of the measured values divided by the number of
measurements.
- Standard deviation – a measure of the width of the distribution. The scatter of measured
values about a mean (or deviations from the mean) is a measure of precision. The smaller
the standard deviation the more precise the measurement.
(
29
1
2
-
-
=
∑
n
x
x
s
i
i
- Degrees of freedom – (n – 1) in the standard deviation equation. After computing the
mean there are only (n – 1) independent pieces o information left.
- In a normal distribution mean ± 1s 68.3% of observations; mean ± 2s 95.5%
observations; mean ± 3s 99.7% observations
- A result more than ± 2s from the mean should be discarded.
- Q test – a statistical method used to test if a point should be rejected. To apply method
arrange data in increasing order and use this formula
range
gap
Q
=
- The gap is the distance from the questionable point and the nearest value and the range
is the range of all the values. Q is then compared to a chart which based on the number of
observations tells you if Q should or should not be discarded.
- Tare – the weight of a container deducted from the total weight of the container and its
contents.
- Mass by difference – this method determines the weight of a sample by subtracting the
amount of sample removed from the weighing container rather than adding it.
- Analytical balances is sensitive within ± 0.003-g
- Water has surface tension which means that water molecules have a greater attraction to
the molecules in the glass than to other water molecules.
- Meniscus – the curved surface of water in glassware caused by the wetting of the glass
walls by the solution. Water volumes are to be read at the bottom of the meniscus.
This
preview
has intentionally blurred sections.
Sign up to view the full version.
- Because of the surface tension of water some glassware is calibrated to contacting (TC)
and other glassware is calibrated to deliver (TD) a certain volume of water. This is turn is
also calibrated for a certain temperature because the density of water changes as
temperature changes.

This is the end of the preview.
Sign up
to
access the rest of the document.