Week 1 -2 CHEMISTRY and MEASUREMENTS Here GENERAL is where your CHEMISTRY presentation begins Origin of Chemistry Alchemy Earthen Metals The Art Chemistry chemeia ( greek word) Definition a science that deals with the composition, structure, and properties of substances and with the transformations that they undergo Properties of Substances Physical • Form of appearance or substance. • Fundamental nature stays the same. Chemical • • Combines or is converted to another substance. Cannot be reverted to original state. Physical Changes Cutting, bending, dissolving, freezing, boiling, and melting are some examples of physical changes. Chemical Changes Combustion, rotting, rusting, digestion, and cooking are some examples of chemical changes. Types of Substances Pure • Cannot be separated into other kinds of matter by any physical means Mixtures • Combination of pure substances but not chemically combined. Pure Substances H H H O Elements O Compounds Mixtures Homogeneous Heterogeneous What is the relationship between Chemistry and Measurements? Macroscopic Microscopic Measurement • • Provide the macroscopic information that is the basis of most of the hypotheses, theories, and laws that describe the behavior of matter. Provides two kinds of information: the size or magnitude of the measurement (a number or quantity); and a standard of comparison for the measurement (a unit). Which is correct? International System of Units • • • From the French, Le Système International d’Unités. The standards for these units are fixed by international agreement. Have been used by the United States National Institute of Standards and Technology (NIST) since 1964. SI Units m kg s Length Mass Time meter kilogram second K A mol Temperature Electric Current kelvin ampere Amount of Substance mole Significant Figures Non-zero digits 3,459 = Four SF Any zeros between two significant digits 3008 = Fours SF A final zero or trailing zeros in the decimal portion ONLY 5. 6890 = 5 SF; 0.00088= 2 SF How many SF are there in each given? 4.5687 5 sf 300,008.005 7 or 9 sf 20350.00 5 sf Scientific Notation Use to denote numbers that are too big or small. Move the decimal point to the left 6400 -> 6.4 x 10 Positive Integer 3 Move the decimal point to the right 0.0064 -> 6.6 x 10 Negative Integer -3 Convert the following into scientific notation. 0.000045637 4.56 x 10^ -5 13452.89000 1.35 x 10 ^4 456,908 4.57 x 10 ^5 Unit Prefixes PREFIX femto SYMBOL f FACTOR 10−15 pico p 10−12 nano micro milli centi deci kilo mega giga tera n µ m c d k M G T 10−9 10−6 10−3 10−2 10−1 103 106 109 1012 Unit Conversion 6 kgs 7 lbs 01 Mass 1kg = 1, 000,000 mg = 100,000 centigrams = 10,000 decigrams = 1000 grams = 100 decagrams = 10 hectograms Factor Label Method Example: Convert 500 grams to kilograms Example 1: Convert 500 grams to kilograms Step 1: Identify what is needed to be converted 500 grams -> kilograms Example 1: Convert 500 grams to kilograms Step 2: Identify the conversion factor needed to be used. 1 kilogram-> 1000 grams Note: For larger numbers, you can use the scientific exponent form. Example 1: Convert 500 grams to kilograms Step 3: Use the factor label method to convert the given. (Conversion factor) 500 g x Unit to be converted Unit to be removed (same unit as the given) 500 g x 1kilograms = 0.5 kilograms 1 gram / / Note: For larger numbers, you can use the scientific exponent form. Factor Label Method (Multiple Conversions) Example: Convert 246 inches to feet and cm Example: Convert 246 inches to feet and meter. Step 1: Identify what is needed to be converted 246 inches -> feet -> meter Example: Convert 246 inches to feet and meter. Step 2: Identify the conversion factor needed to be used. 1 inch= 2.54 centimeters 1 foot= 12 inches 1 meter= 100 cm Note: For larger numbers, you can use the scientific exponent form. Example: Convert 246 inches to feet and meter. Step 3: Use the factor label method to convert the given. (Conversion factor) 246 in x Unit to be converted Unit to be removed (same unit as the given) / 246 inches 1 foot = 20.5 ft 12 inches / Note: For larger numbers, you can use the scientific exponent form. Example: Convert 246 inches to feet and meter. Step 3: Use the factor label method to convert the given. 1 meter 2.54 cm x = 6.25 meter 246 inches x 100 cm 1 inch / / Note: For larger numbers, you can use the scientific exponent form. Common Conversion Factors Length Mass/ Volume 1 inch (in.) = 2.54 cm 1 liter (l) = 1000cm3 = 1.057 quart (qt) = 61.02 in3 = 0.03532 ft3 1 foot (ft.) = 12 inches 1 cubic meter (m3) = 1000 L = 35.32 ft3 1 mile = 1.609 km 1 kilogram (kg) = 2.2046 pounds (lb) 1 meter= 39.37 inches Errors in measurement Indeterminate error Relative Error • • • • Caused by uncontrollable variables, which can not be defined/eliminated. Rounding off, estimations, The ratio of the absolute error of the measurement to the actual measurement. Determines the magnitude of the absolute error in terms of the actual size of the measurement. Sample Problems Sample Problem 1: Classify the following changes as physical and chemical changes a. Melting of water b. Rusting of iron c. Boiling of sugar to make syrup d. Paper burning e. Magnesium dissolved in acid Sample Problem 2: How many a.kilometers, b. meters, c. centimeters, d. milliliters are there in 0.800 miles. Show in 3 significant digits.