EDUCATIONAL CHALLENGES
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DENSITY OF A LIQUID
Problem: You are given two unknown liquids. Find the density of each.

Materials: 100ml graduated cylinder, triple beam balance, calculator, 2 unknown liquids.

Procedure:

1) Find the mass of the empty graduated cylinder.

2) Pour unknown liquid #1 into the graduated cylinder to the 50 ml. level.

3) Find the mass of the graduated cylinder with 50ml of unknown liquid #1.

4) Repeat steps 1-3 for unknown liquid #2.

We can calculate density of a liquid using the formula:

Density= Mass/Volume

where mass is that for just the liquid (you must subtract out the mass of the graduated cylinder).

Now let's calculate the densities of the two liquids using the following given data.

Liquid #1:

Given: Mass of empty graduated cylinder = 78 grams

Mass of graduated cylinder with unknown liquid #1= 128 grams.

Find:

a) Mass of just the liquid = ____
b) Volume of liquid=_____
c) Density of liquid #1 =____

Liquid #2:

Given: Mass of empty graduated cylinder = 78 grams

Mass of graduated cylinder with unknown liquid #2= 117.5 grams.

Find:

a) Mass of just the liquid = ____
b) Volume of liquid =_____
c) Density of liquid #2=____

Density of Liquid 1:

grams/cubic cm.
If you need a calculator one is available. Click on calculator in right frame.

Density of Liquid 2:

grams/cubic cm.
If you need a calculator one is available. Click on calculator in right frame.

What is each liquid?

Using the table below it is now possible for you to determine what each liquid is.

### Densities for some common liquids are:

 Substance Density (gm/cu.cm) Water 1.00 Cooking oil 0.92 Sea Water 1.025 Carbon tetrachloride 1.58 Benzene 0.87 Glycerin 1.26 Methanol 0.79

Unknown liquid #1 is:

Unknown liquid #2 is:

FINDING THE DENSITY OF A LIQUID USING A HYDROMETER

The density of a liquid can also be measured using a simple device known as a hydrometer.

Literally meaning "water measurer," a hydrometer is an instrument comprised of a vertical scale inside a sealed glass tube weighted at one end. It's used to measure the ratio (called specific gravity) of the density of a liquid grape to that of pure water.

A hydrometer is basically a sealed tube which is narrow at the top and is weighted with a dense material such as lead at the bottom. You may have seen one in a salt-water fish aquarium. The hydrometer is often considered the most valuable tool in wine making.

When a hydrometer is inserted into a liquid, the tube floats vertically so that the narrow part sticks out of the liquid while the heavy end sinks. The narrow part is calibrated for the density. The hydrometer floats higher in liquids of higher density and lower in liquids of lower density.

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