Honors Chemistry – Mini-Lab #2
Density
Purpose: To experimentally calculate the density of three liquids.
Materials: (All materials will be found on the lab cart and will be returned clean and dry at the end of lab. All liquids may be disposed of down the sink with copious
amounts of water)
10 mL graduated cylinder
Electronic Balance
Pipets
Distilled Water
Rubbing Alcohol (propan-2-ol)
Vinegar (ethanoic acid)
Procedure:
1. Fill a pipet with water, dry the outside of the pipet and record the mass of the entire unit. WATCH YOUR SIG
FIGS!!!
2. Empty the water into the graduated cylinder and record the volume. WATCH YOUR SIG FIGS!!!
3. Record the mass of the empty pipet. WATCH YOUR SIG FIGS!!!
4. Calculate the density (in g/mL) of water, observing the rules for significant figures. (Record all 4 steps of
each calculation)
5. Repeat steps #1 through #4 twice. Then determine the average density of water, again observing the rules
for significant figures.
6. Repeat steps #1 through #5 using rubbing alcohol instead of water.
7. Clean-up.
Data:
Density of Water
1st trial
2nd trial
3rd trial
Mass of full pipet (g)
Mass of empty pipet (g)
Showing Calculations: ALL calculations must be
shown in your lab notebook during the
semester. To receive full credit for your
calculations, the following format of 1, 2, 3, 4
should always be followed.
-Write down any formulas that you use in your
calculations.
-Each step in the calculation should be shown
clearly.
-Report the result of the calculation with units
(unrounded)
-Report the final answer, with units, to the correct
number of significant figures.
Example: A = l x w
A = 2.34 cm x 1.2 cm
A = 2.808 cm2
A = 2.8 cm2
Mass of water (g)
Volume of water (ml)
Density of water (g/ml)
Density of Rubbing Alcohol
1st trial
2nd trial
3rd trial
Mass of full pipet (g)
Mass of empty pipet (g)
Volume of Rubbing Alcohol (ml)
Percent Error – How To
Step 1: Calculate the error (subtract one value form
the other) ignore any minus sign.
Density of Rubbing Alcohol (g/ml)
Step 2: Divide the error by the exact value (you will
get a decimal number)
Mass of Rubbing Alcohol (g)
Step 3: Convert that to a percentage (by multiplying
by 100 and adding a "%" sign)
Calculations:
-Example density calculation.
-Example average density calculation.
-Example percent error calculation.
Data Analysis: (You do not need to rewrite the questions, simply number the responses)
1. What is the purpose of repeating each experiment three times?
Percent Error – As A Formula
This is the formula for "Percentage Error":
|Approximate Value − Exact Value|
× 100%
|Exact Value|
(The "|" symbols mean absolute value, so negatives
become positive)
2. Why is it important to dry the outside of the pipet each time before massing it?
3. What was your percent error in each experiment (meaning compare to the average) by using a reliable reference source for the actual value of the density of liquids used?
Reminders:
-DO NOT forget your header on every page.
-NO LATE WORK will be accepted for credit.