Analía Bellizzi – Chemistry Classes

Ronald Reagan High School

Matter Notes #3 Pure Substances and Mixtures

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

 mixture

or

pure 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