Chemical Foundations

Why is Chemistry Important? New materials New pharmaceuticals New energy sources Food supplies Help the environment Can you think of others?

What is Chemistry? Biology Physics Chemistry Earth Sciences Chemistry is a central science that deals with the materials of the universe and the changes they undergo. Physics Chemistry Biology Earth Sciences

The Scientific Method Observation Summary of What Happens Hypothesis (measurable) Ex: law of conservation of mass Observation Hypothesis Experiment Theory (model) Law Theory Modified as needed Prediction Model which attempts to explain why it happens Atomic Theory Experiment

NGSS: A modified way of thinking for scientists Asking questions (for science) and defining problems (for engineering) Developing useful models Planning and carrying out investigations Analyzing and interpreting data Using mathematics and computations thinking Constructing explanations (for science) and designing solutions (engineering) Engaging in argument from evidence Obtaining, evaluating, and communicating information Focus on application and practice

Types of observations 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

Qualitative observations

Measurements in chemistry Quantitative observation. Has 2 parts – number and unit. Number tells comparison. Unit tells scale.

Measurements in chemistry (con’t) Scientific Notation Technique used to express very large or very small numbers. Move the decimal so that one non zero integer is to left If you moved to the left then the exponent is positive (number is big) If you moved to the right then the exponent is negative (number is small)

Units of Measurement SI System (Système International d'Unités) 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 Prefixes are used to change the size of the unit.

Volume Measure of the amount of 3-D space occupied by a substance. SI unit = cubic meter (m3) Commonly measure solid volume in cm3. 1 mL = 1 cm3 1 L = 1 dm3

Precision and Accuracy Accuracy: agreement of a particular value with the accepted value. Precision: agreement among several measurements of the same quantity (reproducibility). Using an instrument to measure an object Pipette analogy – you have to calibrate the instrument. Accuracy is the ACTUAL number you want Precision is reproducible.

Uncertainty in Measurement (2.4) The length of the pin occurs at about 2.85 cm. Certain digits: 2.8 5 Uncertain digit: 2.8 5

Uncertainty in Measurement (2.4) Volume of a container Certain digits: 21.1 5 ml Uncertain digits: 21.1 5 ml

Significant Figures & Calculations (2.5) Rules for counting Significant Figures: 1. Nonzero integers always count! 2. Zeroes (3 classes): 0.0065 Leading! a. Leading zeroes do not count (place holders) b. Captive zeroes do count 4005 Captive! c. Trailing zeroes are if there is a decimal point 65.00 Trailing! 3. Exact numbers (counting or from definitions) 9 pencils, 24 students etc.

Significant Figures & Calculations (2.5) Rules for Significant Figures in calculations: 1. For multiplication or division: the answer is the same as the LEAST precise number in the calculation. 67.64 grams x 43 grams = 2908.52 grams2 4 Sig Figs 2 Sig Figs Answer must have 2 Sig Figs Count from the left starting with the first Integer 2908.52 grams2 Use the first number past to round (up if 5 or more) Answer = 2900 grams2

Significant Figures & Calculations (2.5) Rules for Significant Figures in calculations: 2. For addition or subtraction: the answer has the same number of decimal places as the least precise measurement in the calculation. 3 decimals The answer MUST have only 2 decimal places! 37.113 grams 115.02 grams 6.175 grams Count the two then use the one right after to round. (up if 5 or more) 2 decimals 158.308 grams 3 decimals 158.308 grams Answer = 158.31 grams

Significant Figures & Calculations (2.5) Rules for Significant Figures in calculations: 3. Rounding: DO NOT round until all calculations are completed. Use only the first number to the right of the last significant figure.

Atlantic/ Pacific Rule