Chapter 1: Introduction

1. Chapter 1: Introduction Chemistry 1020: Interpretive chemistry Andy Aspaas, Instructor

2. What is chemistry? • “The science that deals with the materials of the universe and the changes that these materials undergo.” • Chemistry in relation to other sciences

3. Chemistry around us • Advances from chemistry • Medicine • Agriculture • Energy • Plastics • Problems from chemistry?

4. Scientific problem solving • The scientific method: process behind all scientific inquiry • Flexible, changes when new information is learned • Start with a question, problem or observation • Hypothesis: possible explanation • Experimentation: controlled process of gathering new information • Observations, do they support the hypothesis? • Theory: a tested hypothesis, can still be revised

5. Law vs. theory • Natural law: generally observed behavior, result of measurements • Theory: our attempt to explain why certain behaviors happen • Scientific method is still limited by human imperfection

6. How to learn chemistry • Reading, vocabulary, memorization are only a start • Should be considered a minor part of your learning process in chemistry • Problem solving skills are even more important! • Why practice homework problems are assigned • Struggle with them, use answers carefully • Mistakes can be valuable

7. Chapter 2: Scientific Notation Chemistry 1020: Interpretive chemistry Andy Aspaas, Instructor

8. Types of observations • Observations are a key part of any type of scientific research • Qualitative: a description (a white solid was formed) • Quantitative: a specific measurement (the product weighs 1.43 grams)

9. Measurements and numbers • Measurements must contain both a number and a unit - without both, the measurement is meaningless • Many numbers in measurements are very large or very small • Distance from earth to sun: 93,000,000 miles • Width of an oxygen atom: 0.00000000013 meters • Is there an easier way to deal with such ungainly numbers?

10. Scientific notation • Used to make very large or very small numbers more manageable • Multiply a number between 1 and 10 by any power of 10 • 200 in scientific notation? • For even larger numbers, count the number of places the decimal point must move, and make that the power of 10 • 230,000,000,000 in scientific notation?

11. Scientific notation • Works with small numbers too • For small numbers, move the decimal point to the right, and use that as the negative power of 10 • Left is positive, “LIP” • Using a calculator • The E or EE button on your scientific calculator

12. Units of measurement • Unit: which scale or standard is used for a particular measurement • English system: US residents are most familiar with • Metric system: used in most of the rest of the world • SI, or International System, used in scientific work • Based on metric system • Agreed upon by scientists worldwide

13. Some fundamental SI units Quantity Name of unit Abbreviation mass kilogram kg length meter m time second s temperature kelvin K • Most other SI units can be derived from these

14. Prefixes to SI units Prefix Symbol Meaning Power of 10 mega M 1,000,000 106 kilo k 1000 103 deci d 0.1 10-1 milli m 0.001 10-3 micro µ 0.000001 10-6 nano n 0.000000001 10-9

15. Length • Fundamental SI unit for length: meter • A little longer than a yard • Using prefixes as the power of 10 • 1 mm = 10-3 m = 0.001 m • 1 inch = 2.54 cm • Measured with a ruler or caliper

16. Volume • Amount of 3-dimensional space occupied by an object • Unit: liter (L) • 1 L = 1 dm3 (cubic decimeter) • 1 millileter (mL) = 1 cm3 • Commonly used volume unit in chemistry • Volume measurements: • Graduated cylinder • Syringe • Buret

17. Mass • The specific amount of matter present in an object • Measured on a balance • Not to be confused with weight • (Force of gravity acting on the mass of an object) • Dependent on the strength of gravity • Earth vs. moon? • Measured on a scale • Mass used much more commonly in chemistry • SI fundamental unit: kilogram

18. Uncertainty in measurement • Analog measurements - measured mechanically against some type of physical scale • Estimate required for last digit of measurement • Last digit = the uncertain digit • Can be expressed as ± amount of the uncertain digit (4.542 ± 0.001) • Digital measurements - read from a display • Last digit still uncertain even though you don’t do an estimation

19. Accuracy vs. Precision • Accuracy: how close a single measurement or set of measurements are to their true value • Precision: how similar a number of measurements are • Dartboard example • Beaker of water example

20. Significant figures • Sum of all certain numbers in a measurement plus the first uncertain number • Indicates the amount of precision with which a measurement can be made • Since each measurement contains uncertainty, that uncertainty must be tracked when manipulating the measurements

21. How many sig figs does a measurement have? • Nonzero integers are always significant (1 thru 9) • Leading zeroes (on the left) are never significant • Captive zeroes are always significant • Trailing zeroes (at the end) are only significant if there’s a decimal point • Exact numbers (obtained by counting) have an infinite number of sig figs

22. Rounding off • Calculators don’t understand sig figs • Will return as many digits to you as possible • You must round the answer to the correct number of sig figs • Look at the digit to the right of the last sig fig • 0-4, just drop it and everything to the right • 5-9, increase last sig fig by one, drop rest • Look only at the one digit to the right of the last sig fig, ignore all others!

23. Determining sig figs in calculations • When multiplying or dividing, find the measurement with the smallest number of sig figs • Answer must be rounded to that many sig figs • When adding or subtracting, find the measurement with the smallest number of decimal places • Answer must be rounded to that many decimal places • Practice!

24. Dimensional analysis introduction • We do this all the time without even thinking about it • Example: planning a party • 15 guests • 3 drinks per guest • How many drinks should you buy? • Conversion factor: a ratio of two measurements with different units that are equal to each other • Expressed as a fraction, two possible orders!

25. Dimensional analysis calculations • Set up an equation like this Known quantity x conversion factor =unknown quantity • Orient conversion factor so units of known quantity are cancelled • Multiply the known by the conversion factor • The only remaining unit should be the one you’re solving for • Correct for sig figs • Does the answer make sense? • Practice, practice, practice, practice, practice!

26. Temperature scales • Fahrenheit scale: used in the US • Celsius scale: used in most rest of world, and by most scientists • Kelvin scale: SI base unit of temperature • 0 K is lowest possible theoretical temperature

27. Temperature scales

28. Temperature conversions • Celsius to Kelvin • Temperature units are the same size • Zero points are different TK= T°C + 273 • Kelvin to Celsius • Solve above for T°C T°C = TK - 273

29. Fahrenheit and Celsius • Different degree units and zero points T°F = 1.80(T°C) + 32 T°C = (T°F - 32) / 1.80

30. Density • Density: amount of matter present in a given volume of substance Density = mass / volume • Units could be kg/L, g/cm3, g/mL, etc.