Chapters 1 & 3 Chemistry- A Study of the Properties and Changes of Matter

Science vs. Chemistry Science- "knowledge attained through study or practice“ (Webster’s) Translation: Systematic approach to determine the nature of the universe Chemistry- “the study of the composition and changes undergone by materials” Translation: Using the scientific method to figure out what stuff is and what it can do

Chemistry Can Be… Pure For the advancement of knowledge about our world Applied For a specific issue that faces society Pharmaceuticals, etc.

Scientific Method Question Hypothesis Experiment Results Conclusion Peer review Maybe, much, much later… Theory

Question After making observations of a phenomenon Generate a SPECIFIC question to investigate EX: Why do apples turn brown if left out?

Hypothesis After RESEARCH ….is an EXPLANATION of the observations Followed by a specific prediction based on past experimental results or research Usually in the IF…, THEN… format EX: Browning of apples is caused by heat Prediction: If apples are allowed to reach a temperature of 20 degrees Celsius, then browning will occur

Variables Independent variable: controlled by experimenter If results are graphed, independent variable goes on the x axis (time is usually independent) Dependent variable: depends on independent variable If graphed, results go on y axis

Experiment Designed to INVESTIGATE THE HYPOTHESIS EX: 10 apples are kept below 20 C 10 apples at 20 C 10 apples above 20 C

Results/Data Analysis Compile and LOOK FOR PATTERNS in experimental results Experimental results confirm or contradict predictions made on the basis of a hypothetical explanation EX: 0 apples browned below 20 C, but 50% of apples above 20 C started browning within 24 hours

Conclusion Addresses whether or not the results SUPPORT or REFUTE the HYPOTHESIS Errors and future research are offered here EX: The results show some support for the hypothesis in that half of the apples kept above 20 C did brown. However, …

Peer Review After SEVERAL TRIALS and repeatable results Publish experiment in a scientific journal after peer review

Theory A theory is a well-supported hypothesis Formulated after EXTENSIVE, DIVERSE, AND RELIABLE data exists to support an explanation of a phenomenon Requires many years of research and support from many fields

Important Distinctions Qualitative- sensory observations (EX: brown) Quantitative- numerical measurements (EX: 5 lbs) Theory- Explains why for a given phenomenon Law- Describes a given phenomenon The Law of Gravity is that what goes up must come down. A Theory of Gravity would explain why this happens Observation- objective description of phenomena Inference- subjective explanation of phenomena

Matter Classification  Matter Flowchart  Pure Substances  Mixtures

A. Matter Flowchart MATTER Can it be physically separated? Homogeneous Mixture (solution) Heterogeneous MixtureCompoundElement MIXTUREPURE SUBSTANCE yesno Can it be chemically decomposed? noyes Is the composition uniform? noyes ColloidsSuspensions

A. Matter Flowchart  Examples:  graphite  pepper  sugar (sucrose)  paint  soda element hetero. mixture compound hetero. mixture solution

B. Pure Substances  Element  composed of identical atoms  EX: copper wire, aluminum foil

B. Pure Substances  Compound  composed of 2 or more elements in a fixed ratio  properties differ from those of individual elements  EX: table salt (NaCl)

B. Pure Substances  For example… Two different compounds, each has a definite composition.

C. Mixtures  Variable combination of 2 or more pure substances. HeterogeneousHomogeneous

Tyndall Effect Disperses Light

C. Mixtures  Solution  homogeneous  very small particles  no Tyndall effect Tyndall Effect  particles don’t settle  EX: rubbing alcohol

C. Mixtures  Colloid  heterogeneous  medium-sized particles  Tyndall effect  particles don’t settle  EX: milk

C. Mixtures SSuspension hheterogeneous llarge particles TTyndall effect pparticles settle EEX:fresh-squeezed lemonade

 Examples:  mayonnaise  muddy water  fog  saltwater  Italian salad dressing colloid suspension colloid solution suspension

More Important Distinctions Intensive/extensive Material- specific type of matter Matter- has mass and takes up space (has property of inertia)  Mass- amount of stuff in an object  Weight- force of gravity of mass Mixture- composed of 2 or more substances physically combined  Physical change- occurs without altering makeup  Chemical change- occurs through alteration of substance Substance- purely 1 type of matter

Separating Mixtures ALL MIXTURES CAN BE SEPARATED PHYSICALLY Filtration- used to separate a mixture with widely varying particle size EX: rocks and water Distillation- used to separate a liquid mixture EX: alcohol and water Crystallization- used to purify a solid EX: impure aspirin can be dissolved and recrystallized from an alcohol/water solution Chromatography- separates a mixture based on polarity (affinity for stationary/mobile phase)

Substances Compounds can only be formed or broken down by chemical reactions Law of Conservation of Mass- mass can be neither be created nor destroyed in a chemical reaction Matter CAN change state SOLIDLIQUIDGAS Definite Shape YESNO Definite Volume YES NO Particle Spacing CLOSE WIDE

Laws of Compounds Law of Definite Proportions Ratio of elements in a compound is constant EX: H 2 O is always 16g of O for every 2g of H Percent by Mass % mass = (mass element/mass compound) *100 %O in H 2 O = (16g/18g)* 100 = 88.9% Law of Multiple Proportions If two compounds can result from the same element, the ratio will be in small whole numbers EX: H 2 O vs H 2 O 2

Chemical and Physical changes A chemical change results in the formation of new stuff. Burning Rusting/Corrosion Decomposition A physical change does not make new stuff. Melting/freezing/boiling Crushing Dissolving

The Periodic Table of Elements Elements are arranged by increasing atomic number Groups- vertical columns in the table that share chemical properties Periods- horizontal rows in the table that share the same principal energy level