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Unit 1: Chemistry – An Introduction

Unit 1: Chemistry – An Introduction. Chapter 1 Chemistry: An Introduction Chapter 2 Measurements and Calculations. Why is chemistry important?. used to produce NEW PRODUCTS develop ENERGY sources helps to fight and control DISEASES. Who needs to know chemistry?.

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Unit 1: Chemistry – An Introduction

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  1. Unit 1: Chemistry – An Introduction • Chapter 1 • Chemistry: An Introduction • Chapter 2 • Measurements and Calculations

  2. Why is chemistry important? • used to produce NEW PRODUCTS • develop ENERGYsources • helps to fight and control DISEASES

  3. Who needs to know chemistry? • Doctors and nurses • Environmentalists • Cosmetologists • Janitors

  4. Why is chemistry important to me? • helps you make informed decisions • you will become a better problem solver

  5. CHEMISTRY IS NOT EASY… • BUT IT’S NEVER IMPOSSIBLE!! • You will be successful if you… • ASK QUESTIONS & GET HELP • DON’T CHEAT • HAVE GOOD ATTENDANCE • BE ACTIVE IN YOUR EDUCATION

  6. Chemistry is… • What is the definition of chemistry? • The study of matter and all the changes it can go through • chemistry is the CENTRALscience!

  7. Steps of the Scientific Method 1. Make OBSERVATIONSabout the problem or situation you are studying. *can be QUANTITATIVE- measurement involving a number *can be QUALITATIVE- noting the quality of something

  8. Scientific Method continued… 2. Formulate a HYPOTHESISby proposing possible solutions or explanations for your observations.

  9. Scientific Method continued… 3. Test hypothesis with an EXPERIMENT. Variable: A FACTOR THAT CONTROLS THE OUTCOME OF THE EXPERIMENT Independent variable: FACTOR THAT YOU CONTROL **always graphed on the x-axis

  10. Scientific Method continued… Dependent variable: FACTOR THAT RESPONDS TO CHANGES IN THE INDEPENDENT VARIABLE **always graphed on the y-axis Controlled experiment: PROCEDURE THAT TESTS ONLY ONE FACTOR AT A TIME

  11. Scientific Method continued… 4. Assemble tested hypotheses into a THEORYor model. *gives overall explanation as to WHYnature behaves a certain way *can be proven FALSEif contradictory evidence becomes available

  12. Scientific Method continued… 5. Explanations for observed behaviors are known as LAWS. *tells you HOW nature will act *Law of gravity *Newton’s Laws of physics

  13. Chapter 2 Measurements and Calculations

  14. What are measurements? • QUANTITATIVE (numeric) observations and are very important to science

  15. Section 2.1 – Scientific Notation • scientific notation is used to make very BIGor very SMALLnumbers more compact and easier to write • PROPER scientific notation means… • # between 1 and 10 x 10A where A is the number of times the decimal point was moved **keep only one digit to the left of the decimal point

  16. Standard notation  scientific notation moving the decimal point LEFT = POSITIVE exponent 545,000 = ____________________ moving the decimal point RIGHT = NEGATIVE exponent 0.000167 = ____________________ remember LIP = left is positive!

  17. Standard notation  scientific notation moving the decimal point LEFT = POSITIVE exponent 545,000 = 5.45 x 105 moving the decimal point RIGHT = NEGATIVE exponent 0.000167 = 1.67 x 10-4 remember LIP = left is positive!

  18. Scientific notation  standard notation *POSITIVE EXPONENT = big number *NEGATIVE EXPONENT = small number 2.38 x 107 = ___________________ 4.3 x 10-2 = _______________

  19. Scientific notation  standard notation *POSITIVE EXPONENT = big number *NEGATIVE EXPONENT = small number 2.38 x 107 = 23800000 4.3 x 10-2 = 0.043

  20. Section 2.2 – Units • all measurement must have a UNIT • lets you know what SCALE is being used • English system • Metric system (used in science and most of the world)

  21. SI Units • based off the metric system and were decided as the fundamental units for certain quantities

  22. Metric Prefixes • SI units can be inconvenient in size, so we use METRIC prefixes to change the size of the unit.

  23. Section 2.3 – Measurements of Length, Volume and Mass • Length– SI unit meter • can use prefixes to make bigger or smaller (1 m = 39.37in.) or (1 in. = 2.54cm) *measured with a RULER or METER STICK

  24. Volume • Amount of 3-dimensional space take up by an object • SI Unit – cubic meter, m3 • called a DERIVED unit because it is a combination of units • not convenient to use the SI unit when measuring volume of liquids *measured with a RULERor a GRADUATED CYLINDER

  25. Volume • when measuring liquid volume, you must read the bottom of the curve of the liquid, called the MENISCUS • common units – liter or milliliter

  26. Mass • quantity of matter present in an object • SI unit kilogram • we will use grams, because the kilogram is too big • Measured with a BALANCE • MASS and WEIGHT are not the same! Weight is a FORCEproduced by the product of your mass and gravity. We use the term weight incorrectly!

  27. Section 2.4 – Uncertainty in Measurement • a measurement requires ESTIMATION • everyone estimates differently, which leads to UNCERTAINTY

  28. Section 2.4 – Uncertainty in Measurement • what would you say is the length of this cube? • we know it is definitely between the 3.1 cm and 3.2 cm, but the number in the hundredths place is estimated – called an UNCERTAIN number.

  29. Significant Figures (sig figs): • In a measurement, all the known digits plus one estimated digit • good measurements need to be ACCURATEand PRECISE

  30. Accuracy and Precision • ACCURACY: closeness of a measurement to its true value *can be evaluated using percent error

  31. Accuracy and Precision • PRECISION: the exactness of a measurement • determined by the # of decimal places and repeatability of the measurement

  32. Section 2.5 – Significant Figures • chemistry requires calculations of different measurements • important to know the degree of uncertainty of your final result • Rules determine how many digits we have in our answers

  33. Counting Sig Figs – The Rules 1. All nonzero numbers are significant. 5742 cm has ______ sig figs

  34. Counting Sig Figs – The Rules 2. Leading zeros preceding all nonzero numbers are NOT significant. 0.005742 kg has ______ sig figs

  35. Counting Sig Figs – The Rules 3. Captive zeros are found between nonzero numbers and are significant. 0.00570042 mi has ________ sig figs

  36. Counting Sig Figs – The Rules 4. Trailing zeros are found at the right end of the nonzero digits and are only significant if the number is written with a decimal point. 1200 cm has _____ sig figs 1200. cm has ______ sig figs

  37. Counting Sig Figs – The Rules 5. Exact numbers are determined by counting or are a part of a definition and have an unlimited number of sig figs. 1 mi = 5280 feet 25 students *these kinds of numbers are not used to determine how many sig figs are in your final answer

  38. Counting Sig Figs – The Rules 6. These rules also count for number written in scientific notation. 6.0 x 10-5 km has _______ sig figs

  39. Rounding Numbers 1. If the digit to be removed is a. < 5, the preceding digit REMAINS THE SAME 1.33 rounded to 2 sig figs is _________ b. ≥ 5, the preceding digit is ROUNDED UP 1.36 rounded to 2 sig figs is _________

  40. Rounding Numbers 2. When doing several calculations, carry the extra digits through all of the calculations then round the FINAL ANSWER. *when rounding, only look to the first number to right of the digit to be rounded 4.348 rounded to 2 sig figs is 4.3, NOT 4.4!

  41. Determining Sig Figs in Calculations 1. Multiplication and Division – the number of sig figs in the final answer is the same as the measurement with the LEASTnumber of sig figs. You have to count the sig figs is the measurement(s). 4.56 x 1.4 = 6.384  6.4 (3 sig figs) (2 sig figs) (2 sig figs in answer) 5.18 X 0.0208 = __________________

  42. Determining Sig Figs in Calculations 2. Addition and Subtraction – the answer is limited by the measurement with the LEASTnumber of decimal places. 12.11 18.0 + 1.013 31.123  31.1

  43. Determining Sig Figs in Calculations 3. For combined operations, round in between operations so that you can keep track of the correct number of sig figs.

  44. Section 2.6 – Problem Solving and Dimensional Analysis • Dimensional analysis – method of CONVERTING UNITS • Equivalence statement – relationship between two different UNITSthat equal the same quantity • Conversion factor – a ratio of the two parts of the EQUIVALENCEstatement that relates the two units

  45.  Dimensional Analysis • every equivalency gives 2 conversion factors • choose the factor that has the WANTED unit on top of the GIVEN unit you are trying to cancel out

  46. Dimensional Analysis PROBLEM: Convert 2.85 cm to inches Step 1. Choose the equivalence statement that relates the two units. Step 2. Choose the appropriate conversion factor (wanted units over given).

  47. Dimensional Analysis Step 3. Multiply the given quantity by the conversion factor. Step 4. Check that you have the correct number of sig figs in your answer. Step 5. Does your answer make sense?

  48. Dimensional Analysis • You will have to do multi-step conversions. These will require more than one conversion factor. • Do all of the math at one time and round the final answer!

  49. Dimensional Analysis • PROBLEM: Racing cars at the Indianapolis Motor Speedway now routinely travel around the track at an average speed of 225 mi/h. What is this speed in kilometers per minute?

  50. Section 2.7 – Temperature Conversions Three different temperature scales: 1. Fahrenheit- scale mostly used in the US and Great Britain (unit °F) 2. Celsius- used in most other countries, based off the freezing point and boiling point of water (units °C) 3. Kelvin- used in the sciences, absolute scale, NEVER A NEGATIVE VALUE (unit K, not degrees!)

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