Quiz of the Day – No notes
Please take out a separate sheet of paper. Put name
in upper right corner:
Which salt makes up the largest percentage of salt dissolved in
seawater
1)
a.
b.
c.
d.
2)
3)
4)
Sodium chloride (NaCl)
Magnesium chloride (MgCl2)
Calcium carbonate (CaCO3)
None of the above
Define salinity
Why is the ocean salty? Why are lakes and rivers not salty?
What is the average salinity of the oceans?
a. 15 ppt (1.5%)
b. 35 ppt (3.5%)
C. 350 ppt (35%)
d. 2.72 ppt (0.272%)
Hydrometer
Hydrometer: An instrument used to measure the
“relative density” of liquids.
“Relative density”: The ratio of the density of a
substance to the density of pure water. Pure
water is assigned a density of 1.
Examples:
Wood <1
Metal >1
Make a better Hydrometer
On the front table is a variety of
supplies to make a better hydrometer.
Your mission will be to create a better
hydrometer to compare the density of
water with varying amounts of salt
Making the hydrometer-materials
You will need a piece of graph paper to record
your lab design and to record and graph your
data for the comparison of density and salinity
lab.
The following may be used to design your
hydrometer:
Straws, coffee stirrer, clay (there are different
types) tape (to create measurements), ball
bearings/bb’s, rubber stoppers
Making the hydrometer
Look at the designs of the example hydrometers, think
about what might help them work well and what flaws
they may have. Make sure that your design includes
the following:
1.
You must have a measuring scale on your hydrometer
in mm. Use the tape and mark off each mm. Make
your 5mm marks longer (so 5mm, 10, 15, 20, etc will
be more visible)
2.
The 0 mm. will be at the top of your hydrometer
(opposite end of the “bulb”)
3.
Make sure your hydrometer floats upright. The higher
your hydrometer floats the greater the density of the
liquid in which the hydrometer is floating
Making the hydrometer

Testing your hydrometer

Use 90 ml of water. Place your hydrometer in
the water and make sure it floats but that it is
low in your water. Add weight if necessary.
Make sure the hydrometer remains upright, so
that you can easily measure. Make sure you
have done the marks in waterproof ink.
Using your hydrometer:
Comparing density and Salinity
1.
2.
Fill a 100ml Graduated cylinder with 90
ml of water. Place your hydrometer in
the water.
Create a data table. In your data table,
record what the water comes to on your
mm scale (measure from top down)
Using your hydrometer:
Comparing density and Salinity
Data Table
Total
Salt
(grams)
0
1
3.5
12
45
Example
Fresh
water
Brackish
Water
Salt
water
Great
Salt
Lake
Dead
Sea
Hydro
meter
Reading(
mm)
Sample
A
Sample
B
Using your hydrometer:
Comparing density and Salinity
3.
4.
5.
Remove the hydrometer and mix in 1 g
of salt. Replace the hydrometer and
record the water level
Repeat step 3 four more times, each
time increasing the TOTAL amount of
salt to the water. Record the water level
each time in the data table
Plot your data on a graph, making sure
to label your x and y axis.
Using your hydrometer:
Comparing density and Salinity
Conclusion:
Make sure to include the following in your
conclusion:

Why did you design the hydrometer the way
you did? Did it float? Were you able to use it
to measure density?

What did your data show you about salinity
and density?

What general conclusion can you make about
increasing salinity in water?
Clean Up
1.
2.
3.
Make sure to rinse your graduated
Cylinder and return it to the prep table.
Clean up any spilled salt and wipe down
lab space.
Turn in lab papers to Period 4 slot
To be turned in at 9:45am
Lab write up with:
Two names
Sketch of hydrometer
Table and Graph
Conclusions:

Why did you design the hydrometer the way you
did? Did it float? Were you able to use it to
measure density?

What did your data show you about salinity and
density?

What general conclusion can you make about
increasing salinity in water?