1. Mixtures & Pure Substances

2. Pure Substance
Cannot be separated into simpler substances by physical methods
Can only be changed by chemical methods
Examples:
Elements
Compounds

3. Element Composed of identical atoms Ex: copper wire aluminum foil
periodic table elements
Courtesy Christy Johannesson

5. Compound Combination of 2 or more elements in a fixed ratio
Combined chemically
Can be separated into simpler substances only by chemical means.
Properties of compounds are different from those of individual elements
Examples:
Salt (NaCl)
Water (H2O)
Sucrose (C12H22O11)

6. Mixture Combination of 2 or more pure substances
Each pure substance retains its individual chemical properties
Combined physically
Examples:

7. https://www. google. com/search

8. How do we tell elements, compounds and mixtures apart
How do we tell elements, compounds and mixtures apart? We use our matter tree!

9. MATTER yes no MIXTURE PURE SUBSTANCE yes no Compound Element
Can it be physically separated?
MIXTURE
PURE SUBSTANCE
yes
Can it be chemically decomposed? no
Courtesy Christy Johannesson
Compound
Element

10. Element, Compound or Mixture?

11. Element, Compound or Mixture?
SiO2

12. Element, Compound or Mixture?
oxygen atoms
hydrogen
atoms
hydrogen
atoms
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 68
“Elements, Compounds, and Mixtures”
Description: This slide shows the molecular composition of an element, a compound, and two mixtures.
Basic Concepts
All samples of a substance have the same molecular composition and intensive properties and are homogeneous.
Elements and compounds are substances; mixtures are not.
The elements making up a compound combine in fixed ratios.
Mixtures can be separated by physical methods.
Mixtures that have a uniform composition throughout are homogeneous; those that have parts with different compositions are heterogeneous.
Teaching Suggestions
Use this transparency to help students visualize the molecular composition of elements, compounds, and mixtures and to review the definitions of these terms. Make sure students understand the difference between the terms matter and substance. Remind students that elements and compounds are always homogeneous, while mixtures can be either homogeneous or heterogeneous.
Questions:
Which of the bottles pictured above contain(s) matter? Which contain(s) a single substance? Explain your answers.
How many elements are present in each molecule of water shown in bottle (b)? What is the relative number of atoms of each element in a water molecule?
As you know, ice is frozen water. In other words, ice and water are the same substance, in different phases. What would you expect the ratio of hydrogen atoms to oxygen atoms to be in a molecule of ice? Explain your reasoning.
Bottle (c) and bottle (d) both contain mixtures. How are these mixtures similar? How are they different?
Suppose you find an unlabeled bottle containing a clear liquid. Can you tell by looking at it whether the material is a compound or a mixture? Explain your answer.
How can you prove that a sample of sea water is a mixture?
Classify the following items as elements, compounds or mixtures; rice pudding, copper, carbon dioxide, air, milk, magnesium chloride, granite, mercury, and maple syrup.
A chocolate-chip cookie with more chips in one part of the cookie than another can be used to demonstrate a heterogeneous mixture. Name two other materials that can be classified as heterogeneous mixtures. Explain your reasoning.
(a)
an element
(hydrogen)
(b)
a compound
(water)
(c)
a mixture
(hydrogen
and oxygen)
(d)
a mixture
(hydrogen
and oxygen)

13. Ways to Separate Mixtures
Magnetism
Force of attraction or repulsion between various substances is used to separate one from another

14. Distillation
Separates materials based upon different boiling points.

15. Filtration
A barrier is used to separate solid material from liquid material

16. Chromatography
Separates the components of a mixture by traveling across a surface at different rates

17. Crystallization produces pure solid particles from a dissolved solid

18. Practice
Identify the following as elements, compounds or mixtures

20. H2O

22. Sulfur

24. Li2SO4

25. Exercise 11, p. 41