Notes on Density

```Science Study Notes
DENSITY
DENSITY – how heavy something is for its size
The amount of matter compared to the amount of space it occupies
The amount of atoms in a cubic centimeter
Low Density – the atoms are spread far apart from each other
High Density – the atoms are very close to one another
Note* Different materials have different densities as different kinds of atoms line up differently
In our experiment ( 4 metal bars) the different bars had different masses , even thought they had the
same volume (size)
We are able to deduct that density is the amount of matter (numbers of atoms) compared to the space it
occupies
We know that objects made of different materials may have different densities…BUT… how can we
measure density?
To measure density, we need to know 2 things: volume and mass
We use a formula to find density:
Density = mass
Volume
Also…think UNITS: example: One of our blocks had a mass of 27.3 g and a volume of 10cubic cm
The amount of matter
The space it occupies
Mass = 27.2g
Volume 10 cubic cm
Density = 2.72 g/cubic cm
Say a substance has a mass of 100 g and a volume of 10 cubic cm.
What is its Density?
The amount of matter
The space it occupies
Q.
Mass = 100g
Volume 10 cubic cm
(10 grams per cubic centimeter)
What happens to the density if we cut the substance in half?
The amount of matter
The space it occupies
Mass
= 50 g
Volume
5 cubic cm
(10 grams per cubic centimeter)
Answer: Nothing…the density remains the same regardless of the size of the substance
NOTE*** The density of a pure substance is always the same regardless of the size of the sample
Therefore… Density is a characteristic property
Characteristic Property = An identifying trait
i.e. you can identify an unknown material by finding its density - (need mass and volume)
A Characteristic Property doesn’t change regardless of the amount or size of the sample. Water
has a density of 1.0 whether you measure a drop, a capful or a swimming pool full.
Ultimate characteristic properties: your fingerprint, your DNA
 Every pure material has a specific density
 The density of a pure substance at room temperature is always the same
 Example Water has a density of about 1.0 g/mL whether it is a drop,
o
a cup, or a swimming pool full
Note* When you find density, you are actually finding the number of atoms in 1 cubic centimeter
See text – p 14 re: Layers and Density

Layers are formed according to the densities of the liquids. The heaviest will drop to the bottom of
the container, with the next heaviest layer forming on top of that, and the lightest layer forming at
the top
FORMULAS
Formula – used to show the relationship between variables
Ex.
D = M
V
shows the relationship between density, mass and volume (3 variables)
EX. A metal block has a mass of 100g and a volume of 10 cubic centimeters. What is its density?
D = M
V
100g + 10 grams/cubic centimeters
10 cc
Q. What happens if I cut the block in half? What will happen to the density?
M = 50g
V = 5 cc
A.
D= M
V
50g
5 cc
=
10 g/cc
Nothing changes – the density of a substance remains the same regardless of how much or how
little the sample is.
This is the formula for density, but from this formula we can find the formula for finding mass and volume
We must rearrange the formula to find mass or volume.
There are 4 ways to re-arrange a formula:
1. Algebra
2. Units
3. Triangle
4. Memorize the formula
(See notes on using the algebra, units and triangle methods)
OR….MEMORIZE!
D= M
V
M= D x V
V = M
D
NOTES ON SOLUBILITY
TERMS:



Solubility – how well one substance dissolves in another
Solute – the chemical which is being dissolved
Solvent – the chemical which dissolves the other chemical
Example:
Making hot tea – the tea leaves are the solvent and the hot water is the solute
Making chocolate milk - the chocolate syrup is the solvent and the mile is the solute
(If liquids are miscible (soluble) with each other, they simply dissolve and mix together
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