Chapter 1 Introduction: Matter and Measurement Adapted from: Chemistry, The Central Science, 11th edition. Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Chemistry In this science we study matter and the changes it undergoes. Chemistry is the study of the properties and behavior of matter. The Study of Chemistry • The science that deals with the materials of the universe and the changes these materials undergo • The Central Science • Understanding most other fields of science requires an understanding of Chemistry • Chemistry is central to a fundamental understanding of governing principles in many science-related fields. The Central Science The Scientific Method The scientific method is simply a systematic approach to solving problems. The Scientific Method • Make Observations • Qualitative – Descriptions • Quantitative – Measurements • Formulate Hypotheses • Possible (tentative) explanations for observed characteristics or behaviors • Perform Experiments • Test Hypothesis • Repeat the process until we get a well-tested explanation The Scientific Method • Theory – an explanation of the general causes of certain phenomena, with considerable evidence or facts to support it. • May need to be modified or discarded as new information (observations) becomes known. • Law – a generally observed behavior • While experimenting we may observe the same behavior all the time, and therefore be able to predict this behavior will always occur in the future Matter We define matter as anything that has mass and takes up space. Matter can be solid, liquid, or gas. States of Matter Pure Substances and Mixtures • Atoms are the building blocks of matter. • Each element is made of the same kind of atom. • A compound is made of two or more different kinds of elements. Compounds and Composition • Compounds have a definite composition. That means that the relative number of atoms of each element that makes up the compound is the same in any sample. • This is The Law of Constant Composition (or The Law of Definite Proportions) Mixtures • Heterogeneous mixtures do not have the same composition, properties, and appearance throughout. • A homogenous mixture is uniform throughout and have no visible boundaries. Pure Substances and Mixtures Classification of Matter Exercise: Classification of Matter 1. “White gold” contains gold and a “white” metal, such as palladium. Two samples of white gold differ in the relative amounts of gold and palladium they contain. Both samples are uniform in composition throughout. Use the figure to classify white gold. Solution: Because the material is uniform throughout, it is homogeneous. Because its composition differs for the two samples, it cannot be a compound. Instead, it must be a homogeneous mixture. Exercise: Classification of Matter 2. When oil and water are combined, they do not mix evenly, but instead form two separate layers. Use the figure to classify a combination of oil and water. Solution: It is a heterogeneous mixture because it is not uniform throughout. Exercise: Classification of Matter 3. Aspirin is composed of 60.0% carbon, 4.5% hydrogen, and 35.5% oxygen by mass, regardless of its source. Use the figure to classify aspirin. Solution: It is a compound because it has constant composition and can be separated into several elements. Properties and Changes of Matter Types of Properties • Physical Properties… • Can be observed without changing a substance into another substance. • Boiling point, density, mass, volume, etc. • Chemical Properties… • Can only be observed when a substance is changed into another substance. • Flammability, corrosiveness, reactivity with acid, etc. Types of Properties • Intensive Properties… • Are independent of the amount of the substance that is present. • Density, boiling point, color, etc. • Extensive Properties… • Depend upon the amount of the substance present. • Mass, volume, energy, etc. Types of Changes • Physical Changes • These are changes in matter that do not change the composition of a substance. • Changes of state, temperature, volume, etc. • Chemical Changes • Chemical changes result in new substances. • Combustion, oxidation, decomposition, etc. Chemical Reactions Chemical Reactions Compounds Compounds can be broken down into more elemental particles. Separation of Mixtures Separating Mixtures • Mixtures can be separated based on physical properties of the components of the mixture. Some methods used are: • Filtration • Distillation • Chromatography Distillation Distillation uses differences in the boiling points of substances to separate a homogeneous mixture into its components. Filtration In filtration solid substances are separated from liquids and solutions. Chromatography This technique separates substances on the basis of differences in solubility in a solvent.