Chemical Foundations Chapter 1

The Scientific Method Summary of observed (measurable) behavior Ex: law of conservation of mass Observation Hypothesis Experiment Theory (model) Law Theory Modified As needed Prediction A Theory (model) attempts to explain why it happens Experiment

The Scientific Method Qualitative Quantitative Overview: Deals with descriptions Data can be observed but not measured Colors, textures, smells etc. Qualitative -----Quality Deals with numbers Data which can be measured Length, Height, volume, weight, speed, time, temp Quantitative-----Quantity Example: Oil Painting Blue & green paint Gold frame Masterful brush strokes 10” x 14” surface area 140 in2 Weight: 8.5 pounds

Units of Measurement (1.3) SI System: based on the metric system and units derived from the metric system. Physical Quantity Name of Unit Abbreviation Mass Kilogram kg Length Meter m Time Second s Temperature Kelvin k Electric Current Ampere A Amount of substance Mole mol Luminous intensity Candela cd

Units of Measurement (1.3) Symbol Prefix Factor G giga 109 M mega 106 k kilo 103 h hecto 102 da deka 101 BASE d deci 10-1 c centi 10-2 m milli 10-3 μ micro 10-6 n nano 10-9

Units of Measurement (1.3) Volume: is not a fundamental SI unit but is extremely important in chemistry. Volume can be derived from length.

Units of Measurement (1.3) Mass vs. Weight Remember MASS IS NOT THE SAME AS WEIGHT! Mass is a measure of the resistance of an object to a change in its motion. Weight is the response of mass to the force of gravity.

Uncertainty in Measurement (1.4) Uncertainty: the uncertainty of measurement depends on the precision of the measuring device. Report any observed measurements by recording all the certain digits plus the first uncertain digit. 20.15 ml 20.1 is certain 0.05 is uncertain

Precision and Accuracy (1.4) Accuracy: agreement of a particular value with the accepted value. Precision: agreement among several measurements of the same quantity (reproducibility).

Precision and Accuracy (1.4) Random Error: equal probability of being high or low. Systematic Error: error that occurs in the same direction each time.

Significant Figures & Calculations (1.5) Scientific Notation 98,500,000 = ? 9.85 x 107 64,100,000,000 = ? 6.41 x 1010 0.0000000279 = ? 2.79 x 10-8 4,200,000 = ? 4.2 x 106

Significant Figures & Calculations (1.5) Rules for counting Significant Figures: 1. Nonzero integers always count! 2. Zeroes (3 classes): a. Leading zeroes do not count (place holders) b. Captive zeroes do count c. Trailing zeroes are if there is a decimal point 3. Exact numbers (counting or from definitions)

Significant Figures & Calculations (1.5) Rules for Significant Figures in calculations: 1. For multiplication or division: the resultant is the same as the LEAST precise number in the calculation. 2. For addition or subtraction: the resultant is the same number of decimal places as the least precise measurement in the calculation. 3. Rounding: DO NOT round until all calculations are completed. Use only the first number to the right of the last significant figure.

Significant Figures & Calculations (1.5) Example: 12.11 18.0 + 1.013 31.123 31.1

Dimensional Analysis (1.6) Unit Factor Method/Dimensional Analysis: converting a given result from one system of units to another. Rules for Dimensional Analysis: Start with what value is known, proceed to the unknown. Draw the dimensional lines. Insert the unit relationships. Cancel the units. Do the math, include units in answer.

Temperature (1.7) Fahrenheit Celsius Kelvin 32 ˚F 212 ˚F 180˚F 100 ˚C Boiling point of water 32 ˚F 212 ˚F 180˚F 100 ˚C 0 ˚C 100˚C 373 K 273 K 100 K Freezing point of water Notice that 1 kelvin = 1 degree Celsius

Temperature (1.7) Tf = Tc x 9oF/5oC + 32o F Tc = 5oC/9oF(Tf – 32o F) Tk = Tc + 273.15

Density (1.7) Recall that you can measure either the volume or the mass of an object. Density is a property that describes the relationship between these two measurements.

Density (1.7) Compound Density in g/cm3 at 20o C Chloroform 1.492 Diethyl ether 0.714 Ethanol 0.789 Isopropyl alcohol 0.785 Toluene 0.867 A chemist has an unknown solution that he wants to identify. He measured out exactly 25.00 ml (cm3) of the substance and found that it has a mass of 19.735 g at 20 C. Density = 19.735 g/25.00 cm3 = 0.7894 g/cm3

Classifying Matter Mixtures (a variable composition) A homogeneous mixture is the same throughout with visibly indistinguishable parts. (Solutions) A heterogeneous mixture is one that has visibly distinguishable parts.

Classifying Matter Substances, on the other hand, cannot be separated into different kinds of matter by physical means such as sorting, filtering, heating, or cooling. (ex: Table salt) Some substances, like silver, contain only one kind of matter. These substances are called elements.

Classifying Matter Matter Homogenous Heterogeneous Physical Means Pure Substances Compounds Elements Chemical Means