2. Matter and its appearance
According to its appearance, there are two
kinds of material systems:
Homogeneus systems: they have the
same properties and compositions in all
different parts of them.
Heterogeneus systems: different parts
with different properties can be found in
them.
5. Heterogeneus Mixtures
Systems with several different
substances that can be
distinguished:
Oil and water.
Granite is a rock that has three
different substances: quartz, mica and
felspar.
Blood: using a microscope we can see
a liquid (plasma) and different kinds of
cells.
Smoke: has solid particles in a gas
(air).
6. Heterogeneous Mixtures
How to separe their
components:
– If the components
are a solid and a
liquid, we can separe
them by filtering.
• E. g.: water and
sand
7. Heterogeneous Mixtures
How to separe their components:
– Decantation: This method uses the
different densities of the components to
separe them:
• (E.g.: oil and water)
8. Homogeneous Systems
There are two kinds of homogeneous
systems:
Pure substances:
• They have an only component
• They have constant
composition and properties.
Solutions:
• They have several components.
• Their composition can be
changed
9. Solutions
A solution has, at least, two components:
Solute:
It is the component that is present in a lower
quantity in the solution.
Solvent:
It is the component that is present in excess.
Its state never changes when the solution is being
formed
A simple sample: salty water:
There is much more water than salt
Water is a liquid and the solution too.
SOLUTE = SALT and SOLVENT = WATER
11. Solutions
There three kinds of solutions:
Solvent + a small amount of solute =
diluid solution.
Solvent + a large amount of solute =
concentrate solution.
The quantity of solute that can be
dissolved has a limit (solubility). In this
case we have a satured solution.
If we try to dissolve more solute in a satured
solution, the extra quantity of solute will fall
onto the botton of the container.
(precipitation)
12. Solutions
Concentration of a solution:
– Expresses, in a numeric way, the quantity
of soluto un a specific quantity of
solution.
amountofsoluto
concentration=
amountofsolution
There are many ways of express it, depending of the
unit we use. We are going to study three of them.
13. Solutions
Concentration: grams per liter of solution.
massofsoluto ( g )
concentration ( g / L )=
Volumenofsolution
Sample: we put 20 grams of sugar in a 500-mililiters flask
and fill it in with water.
In the flask, there are:
20 g of soluto (sugar)
Soluto and solvent with a total volume of 500 mL = 0,5 L
concentration (g/L) = 20 g / 0,5 L = 40 g/L
14. Solutions
Concentration: percentage in mass
massofsoluto
concentration ( mass )= · 100
massofsolution
Sample: we add 25 grams of salt into a flask that contains
100 grams of water.
In the flask, there are:
25 g of soluto (salt)
100 g + 25 g = 125 g of solution (salt + water)
% mass = (25 g / 125 g) · 100 = 20 % in mass
15. Solutions
Concentration: percentage in volume
volumeofsoluto
concentration ( volume )= · 100
volumeofsolution
Sample: we mixure 20 mililiters of alcohol and 130 mililiters
of water:
We have:
20 mL of alcohol (alcohol)
130 mL + 20 mL = 150 mL of solution (alcohol + water)
% mass = (20 mL / 150 mL) · 100 = 13.3 % in volume
16. Solutions
How to separate its components:
– Evaporation and crystallization: a liquid
evaporates at room temperature, but a
solid doesn't.
17. Solutions
How to separate its components:
– Distillation: this method is useful to separate:
• Liquids whose boiling points are different
enough
• Liquids and solids
18. Pure Substances
Pure substances:
They have a constant composition.
They can't be separated in simpler
substances using physical methods.
There are two different kinds of pure
substances:
Chemical compounds: pure substances
that can be separated in others using
chemical methods.
Elements: pure substances that can't be
separated in others
19. Compound
Pure substance composed of two or more different elements
joined by chemical bonds.
Made of elements in a specific ratio that is always
the same
Has a chemical formula
Can only be separated by chemical means, not
physically
There are millions of different compounds in nature
21. Element
It is the simplest kind of matter.
Has a chemical symbol.
Can't be separated in
others substances
There are only about one hundred
elements in natures. All of them are
in the Periodic Table