MATTER - PURE SUBSTANCES AND MIXTURES.
Matter exist in nature as pure substances and mixtures. Pure substances are not very common. The vast majority of substances are mixtures.
Analyze the following classification to understand better the classification
Pure substances and Mixtures
Substances can be pure or impure.
Pure substances
Pure substances are the ones that have a definite composition, this means that if we take a sample from different zones in the substance, the properties will be the same.
They can be identified by their intensive properties. Example: Boiling and Melting point, density, etc.
Elements are pure substances:
Elements cannot be broken into simpler substances because they contain only one kind of atoms. Examples: H2, O2, Cl2, Na, Ne, Ar, etc.
These elements can be found in the periodic table.
Compounds are pure substances:
Compounds that can be broken in simpler substances because they are formed by 2 or more atoms combined together. Examples: water, sulfuric acid, sodium chloride, ethanol, etc
Heterogeneous Mixtures
Their properties very throughout the substance
Homogeneous Mixtures – Solutions
Their properties are the same in any point of the substance. Homogeneous mixtures are also called solutions. Example: Sea water, brass, bronze, etc. These mixtures can be solid, liquid or gases
Solutions
SOLUTIONS: Are homogeneous mixtures.
SOLVENT: The chemical in bigger proportion.
SOLUTE: The chemical in lower proportion.
We will concentrate our attention in the AQUEOUS solutions since these are the ones that we use in the chemistry lab most of the time. Aqueous solutions are the ones in which the solvent is water. We can also find ALCOHOLIC SOLUTIONS, where the solvent is alcohol.
ELECTROLYTES: If the solute liberates ions in solution, (Ionic compounds that separate in their ions or acids that release hydrogen ions in solution) those ions will allow the solution to conduct electricity. These substances are called electrolytes.
Why are solutions so important?
The chemicals contained in solutions will collide faster and better so the chances for the reaction to occur are bigger. That’s why we use solutions in chemistry.
Concentration of a solution:
Concentration: is a measurement of how much solute is present in the solution.
- The more solute a solution has per unit of volume, the more CONCENTRATED it is.
- The less solute it has per unit of volume, the more DILUTED it is.
A microscopic view:
When the solute dissolves, the particles will locate in between the solvent molecules (see graph below).
Solvent molecules move all the time, but the amount of free spaces determine how much solute will be able to dissolve in the liquid.
Based on the amount of solute and solvent a solution can be:
- UNSATURATED SOLUTION: There are free spaces available to receive more solute.
- SATURATED SOLUTION: This kind of solution will be formed when the solute occupies all free spaces in between the solvent molecules.
- SUPER SATURATED SOLUTION: If we heat up the liquid or we give them energy by swirling or shaking, it will create a temporary state with extra spaces. as soon as the energy get back to normal, those extra spaces will disappear and we will be able to see some solute at the bottom of the container.
Exercises
Classify the following substances in pure substances (elements or compounds) and mixtures (homogeneous or heterogeneous).
substance | mixtureorpure substance | elementorcompound | homogeneousorheterogeneous |
sodium | |||
iron | |||
water | |||
salt water | |||
soil | |||
acetone | |||
coffee | |||
nitrogen | |||
oxygen | |||
Eggs | |||
isopropyl alcohol | |||
Blood | |||
carbon dioxide | |||
table salt | |||
carbon dioxide | |||
gasoline | |||
air | |||
milk | |||
sulfuric acid | |||
silver nitrate |