Mixtures solutions and pure substances

MIXTURES, SOLUTIONS AND PURE SUBSTANCES

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.

Homogeneus Systems

Heterogeneus Systems

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).

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

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)

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

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

SolutionsThey are not always liquids

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)

Concentration of a solution:

– Expresses, in a numeric way, the quantity of soluto un a specific quantity of solution.

Solutions

concentration=amountofsolutoamountofsolution

There are many ways of express it, depending of the unit we use. We are going to study three of them.

Concentration: grams per liter of solution.

Solutions

concentration ( g /L )=massofsoluto (g )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

Concentration: percentage in mass

Solutions

concentration (mass )= massofsolutomassofsolution

·100

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

Concentration: percentage in volume

Solutions

concentration (volume )= volumeofsolutovolumeofsolution

·100

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

Solutions

How to separate its components:

– Evaporation and crystallization: a liquid evaporates at room temperature, but a solid doesn't.

Solutions How to separate its components:

– Distillation: this method is useful to separate:• Liquids whose boiling points are different

enough

• Liquids and solids

Pure SubstancesPure 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

CompoundCompound

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

CompoundCompound

¿Compound or Mixture?

ElementElement 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

Four kinds of matterFour kinds of matter

Four kinds of matterFour kinds of matter

Four kinds of matterFour kinds of matter