### Processing Lab Data

```Processing Lab Data
MRS. PAGE
2014-2015
After Collecting Data = Process Data


Raw Data: the data you collect during lab without any calculations

Qualitative Data: Descriptive data – observed with senses, (i.e. what does it look
like, sound like, feel like)

Quantitative Data: Measured data using tools. Will be number values.
Processed Data: data as a result of performing calculations AFTER all
data has been collected
 Raw
Data & Processed Data are kept on SEPARATE
DATA TABLES!!!
DENSITY

Density is a physical property of matter

Density refers to how tightly packed the particles are in an
object
 Tightly
packed = more dense
 Loosely


=
packed = less dense

or  =
Units for density are

or

3
(note: 1 = 13 )
Practice Calculating Density

If you measure an object that has a mass of 8.47 g and a volume of 3.1
cm3. Calculate the density of the object.
=

=
8.47
3.13
=
8.4
3.13
= 2.7

3
Remember Sig. Fig. Rules
YOU TRY
 What
is the density of an 84.70 g sample of an
unknown substance if the sample occupies 49.6 mL?
.

 What
volume would be occupied by 7.75 g of the
same substance? (Use the density from the first
problem)
.
Accuracy vs. Precision

Accuracy: how close a
measurement is to an
accepted value (literature
value)

Precision: how close the
measurements are to each
other
Percentage Error

You can determine how accurate your data is by calculating the
percentage error

=

The larger the percentage error, the more inaccurate your data is

The smaller the percentage error, the more accurate and reliable your
results are.

Note: error can be positive or negative, this just means your values are
higher or lower than the accepted value
−

× 100
Practice Calculating Percentage Error

What is the percentage error for a mass measurement of
17.8 g, given that the correct value is 21.2 g?
−
%  =
× 100

17.8 − 21.2
%  =
× 100
21.2
−3.4
=
× 100
21.2
= −16.0%
Remember Sig. Fig. Rules
YOU TRY…

A volume is measured experimentally as 4.26 mL. What is the
percentage error, given that the correct value is 4.15 mL?
. %

A student measures the mass and volume of a substance and
calculates its density as 1.40 g/mL. The correct, accepted, value
of the density is 1.30 g/mL. What is the percentage error of the
student’s measurement?
. %
Experimental Errors

2 Types: Random & Systematic

Random Errors: unpredictable, chance variations that experimenter has
little control over– using many trials and averaging results helps alleviate
this type of error. (ex: parallax error)

Systematic Errors: caused by the way in which the experiment was
conducted (design). Systematic errors can not be eliminated by
averaging. Must change how experiment is conducted. (ex: not
calibrating instruments)

Human Error: should not occur if you are focused and careful
HOMEWORK