Chemical Foundations Chapter 1

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

The Scientific Method QualitativeQuantitative Overview: Deals with descriptions Data can be observed but not measured Colors, textures, smells etc. Qualitative -----Quality Overview: 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 Example: Oil Painting 10” x 14” surface area 140 in 2 Weight: 8.5 pounds

Units of Measurement (1.3) SI System: based on the metric system and units derived from the metric system.

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 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 ,100,000,000 = ? 6.41 x = ? 2.79 x ,200,000 = ? 4.2 x 10 6

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 :

Dimensional Analysis (1.6) Unit Factor Method/Dimensional Analysis: converting a given result from one system of units to another. 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. Rules for Dimensional Analysis:

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

T f = T c x 9 o F/5 o C + 32 o F T c = 5 o C/9 o F(T f – 32 o F) T k = T c

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) A chemist has an unknown solution that he wants to identify. He measured out exactly ml (cm 3 ) of the substance and found that it has a mass of g at 20 C. Density = g/25.00 cm 3 = g/cm 3

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

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) Classifying Matter Some substances, like silver, contain only one kind of matter. These substances are called elements.

Classifying Matter Matter Heterogeneous Homogenous Physical Means Pure Substances CompoundsElements Chemical Means