Chapter 1:Unit 5. Pure Substances and Mixtures
Pure Substances and Mixtures
A pure substance is composed of a single component and has a constant composition, regardless of the sample size and the origin of the sample. Pure substance can be either an element composed of only one identical type of substances or a compound when two or more different elements chemically combined to produce a new substance with own properties and reactions. In both cases they have only one type of particles.
A mixture is composed of more than one substance physically combined. The composition of a mixture can vary depending on the sample. Components of the mixture can be separated by any physical process. Mixture can be classified in two categories: homogeneous (single phase) and heterogeneous ( two difference phases).
Some examples of pure substances: water, aluminum wire, rust etc.
Some examples of mixtures: metal alloy, air, saline solution, smoothie etc.
Mix of oil and water ( heterogeneous) Copper wire (element)
Pure water -compound
Vanilla Ice creme homogeneous mixture
Classification of matter is very important because it gives idea how to handle the substance. When we have a matter, first we ask the question whether it has a constant composition and properties. Uniform composition and properties of a matter indicate pure substance whereas mixtures contain variable composition and different properties.
If it is pure, then the next question is if the substance can be broken down into any other substance by a chemical method. if the answer is yes, then it is a compound, it not then te substance is element. A compound is chemically combined two or more elements, for example water contains hydrogen and oxygen as two constituent elements.
If the substance is mixture, then we ask whether it has uniform composition or not. If it has uniform composition, then the substance is a homogeneous mixture, for example Vanilla ice creme.
if not, then heterogeneous mixture, oil and water.
Questions:
- Identify each of the following as an element, a compound or a mixture? Coke, mud, Ozone gas, table sugar, baking soda, copper wire
a) compound: two or more substances chemically combined
b) element: same type of substances either one or two
c) mixture
- What is the basic difference between elements and compounds?
- What is the similarity between elements and compounds?
Ans: 1. Coke: mixture, Mud: mixture, Ozone gas: element, Table sugar: compound, Baking Soda: compound, copper wire: element
2. Elements are composed of only one type of pure substances. Whereas, compounds are pure substances but they are made of two or more different types of pure substances combined together to produce a new substance with unique properties and characteristics.
3. Both elements and compounds are pure substances and their composition is uniform and they have their own characteristics and properties.
