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Chemistry is a “science”

Chemistry is a “science”. A science is a body of organized knowledge that is continuously updated through inquiry – includes testable explanations and predictions. Chapters 1 & 2 Matter and Change. 1.1 Chemistry. The study of the composition of matter and the changes that matter undergoes.

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Chemistry is a “science”

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  1. Chemistry is a “science” • A science is a body of organized knowledge that is continuously updated through inquiry – includes testable explanations and predictions

  2. Chapters 1 & 2Matter and Change

  3. 1.1 Chemistry The study of the composition of matter and the changes that matter undergoes. There are five branches: Organic, inorganic, analytical, physical, and biochemistry

  4. Pure vs Applied Chemistry • Pure chemistry- • What does a chemist do? • making nylon • Applied chemistry-

  5. Why Chemistry? • Understanding natural world • Preparing for a career • Being an informed citizen

  6. 1.3 The Scientific Method An approach to problem-solving Observation of a problem Hypothesis: educated guess, possible solution Experiment: collecting data, testing variables Theory: well-tested explanation, conclusion Scientific Method Law- a statement of fact regarding natural phenomenon, does not explain why.

  7. 2.1 Properties of Matter • Physical Properties help identify a substance. They can be observed or measured without changing the substance’s composition. • Ex. Color, texture, hardness, density, melting point, boiling point, solubility (See examples on p R47- 49)

  8. Chemical properties are described as the ability of a substance to change in composition. They are observed when a substance undergoes a chemical change. • Ex. Flammability, Corrosiveness, reacts with ….

  9. Properties of Potassium • Potassium is a metal and is the seventh most abundant and makes up about 1.5 % by weight of the earth's crust. Potassium is an essential constituent for plant growth and it is found in most soils. It is also a vital element in the human diet. • Potassium is never found free in nature, but is obtained by electrolysis of the chloride or hydroxide, much in the same manner as prepared by Davy. It is one of the most reactive and electropositive of metals and, apart from lithium, it is the least dense known metal. It is soft and easily cut with a knife. It is silvery in appearance immediately after a fresh surface is exposed. • It oxidizes very rapidly in air and must be stored under argon or under a suitable mineral oil. As do all the other metals of the alkali group, it decomposes in water with the evolution of hydrogen. It usually catches fire during the reaction with water. Potassium and its salts impart a lilac color to flames.

  10. 2.1 States of Matter • Solids– rigid, not compressible, molecules tightly packed. • Liquids – definite volume, but not shape, molecules close, but able to move • Gases - are compressible, take the shape and volume of the container. Molecules are spaced farther apart. • Plasmas – occur at very high temperatures and energies. Electrons leave the nucleus.

  11. 2.1, 2.4 Changes • Physical changes do not change the composition of the substance. Ex. Grinding, melting, boiling • Chemical changes result in the formation of a new substance(s). Ex. Burning, corroding, gas formation, precipitates forming

  12. 2.2 Mixtures • A physical blend of two or more substances. They can be separated by simple means using the differences in their physical properties. Ex. Filtering, sifting, distilling, using a magnet • Two types of mixtures: Heterogeneous – more than one phase can be observed. They are not uniform throughout. Homogenous- appears uniform throughout Sometimes called solutions

  13. 2.3 Pure Substances Pure substances are classified as either an element or a compound. • Elements are the simplest types of matter. They are the building blocks for all substances. Presently there are118 known elements. • Each element is represented by a chemical symbol and found on a periodic table.

  14. Compounds are two or more elements that are combined chemically. These can be broken down only by a chemical reaction. • Compounds are represented by chemical formulas, which show the type of atoms, and the proportions which they are combined. Ex. AgNO3 Shows 1 atom of silver, 1 atom of nitrogen and 3 atoms of oxygen combine to form silver nitrate.

  15. 2.4 Chemical Reactions • During chemical reactions, a chemical change takes place and a new substance forms. • The starting substances are called “reactants” and the new substances are called “products” • We can represent a chemical reaction by writing a chemical equation. Ex. Iron + Sulfur -- Iron Sulfide (reactants) (product)

  16. 2.4 Law of Conservation of Mass • In any physical or chemical change, mass is neither destroyed nor created. The total mass will remain the same.

  17. 2.3 grams of zinc react with 5.8 grams of hydrogen chloride to produce zinc chloride and hydrogen gas. Identify the reactants. Identify the products. What is the total mass of the products formed?

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