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Chapter 1

Chapter 1. Chemistry: The Study of Change. Chemistry. How do we define Chemistry?. The study of how matter interacts with itself and other matter Matter is anything that has mass and volume (which is anything other than nothing). The Scientific Method.

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Chapter 1

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  1. Chapter 1 Chemistry: The Study of Change

  2. Chemistry • How do we define Chemistry? • The study of how matter interacts with itself and other matter • Matter is anything that has mass and volume (which is anything other than nothing)

  3. The Scientific Method • How is the scientific method organized? • Identify the problem • Do background research • Make a prediction (hypothesis) • Independent variable • Dependent variable • Test and record observations • Qualitative • Quantitative • Analyze the data

  4. The Scientific Method(Monty Python Style) • The following video is a scene from the 1975 cult film “Monty Python and the Holy Grail” where a woman is accused of being witch; a clever parody of the whole medieval approach to science. The middle ages was a time when… • 1 - matters of law were settled with jousts • 2 - witches and heretics were tested for truth by means of torture • 3 - alchemists spent their lives trying to turn lead into gold • 4 - explorers searched for the fountain of youth • 5 - people believed that dense items fell to earth faster than lighter items merely because Aristotle had said it a thousand years earlier.

  5. The Scientific Method(Monty Python Style) What is the primary fault in the procedure? What is the independent and dependent variable?

  6. The Method • Why is it important to limit the number of independent variables? • Why is it important to continue testing your hypothesis? • Impossible to tell which, if any, affected the result • Limit variables • Many controls • Multiple successful tests increases the validity of the results and decreases error

  7. Airplane Challenge • I challenge your team to build a paper airplane that will FLY the farthest distance. • Each team will build three planes. • 3 pieces of paper, 6 paper clips, scissors • Your team will test ONE variable to see which of your three prototypes will work the best.

  8. Airplane Challenge Before you fly! • What is your independent variable? • What is your dependent variable? • What is my first hypothesis? Explain. • What are 3 controls? After you fly! • What did I observe after the test flights? • Please answer these questions in your notebook.

  9. Classification • Please draw the graphic organizer below: • Mixtures • Elements • Pure Substances • Homogeneous • Matter • Heterogeneous • Compounds

  10. Classification

  11. Classification • What is the difference between pure substances and mixtures? • Pure substances - chemical combination (bonded) with constant composition • Mixtures - physical combination of two or more substances

  12. Classification • What is the difference between elements and compounds? • Elements - single atom or a chemical combination of the same element • Li or C60 • Compounds - chemical combination of two or more elements • H2O or CH4

  13. Classification • What is the difference between homo/heterogeneous? • Homogeneous - physical combination that is uniform (same throughout) • Salt water • Heterogeneous - physical combination that is not uniform (different throughout) • Sandy water

  14. Physical and Chemical Properties • What is the difference between a chemical and physical property? • Physical property can be measured/observed without changing the identity of the substance • Ex. Color, odor, phase, volume, mass... • Chemical property cannot be measured/observed without changing the substance

  15. Physical and Chemical Properties Physical properties can be divided into what two categories? • Extensive – depends on how much matter you have • Mass • Volume • Intensive – does not depend on how much matter you have • Density • Melting Point

  16. Physical and Chemical Properties Physical Property Chemical Property • Blue • Density greater than 1 • Solubility • Extremely sour • Melting point is 60°C • Hard • Slimy • Lustrous • Smells like feet • Flammability • Reacts with vinegar • Supports combustion • Reacts with water • Reacts with air • Does not react with ammonium hydroxide

  17. Physical and Chemical Properties

  18. Physical Change • What does it mean to undergo a physical change? • One or more physical properties change, we change the appearance • Color change • Mass change • Phase change • The composition does not change • Ex. Ice and water vapor are still H2O

  19. Chemical Change What does it mean to undergo a chemical change? • Two or more substances reacted and a new substance was made • Ex. Rust • Cannot get the substance back without using a chemical reaction • Indicators could be: • A gas is produced • Light is produced • A solid precipitate forms

  20. Physical and Chemical Changes Physical Change Chemical Change • Cutting your hair • Bending a piece of iron • Crushing Aspirin into a fine powder • Scratching glass with diamond • Crumpling a piece of paper • Water freezes to form ice • A candle melting • Chocolate syrup is dissolved in milk • Baking soda reacts with vinegar to create gas • Copper turns green when exposed to air • Two clear liquids are mixed and a yellow color forms • Burning wood to create ash • Food spoiling • A candle burning • Mixing two liquids creates light

  21. A Thought Experiment • A sealed flask of a clear, colorless liquid is left sitting on an interior sunny windowsill. After about an hour, there are droplets of a clear liquid on the glass above the solution, which has turned yellow. After two hours, the solution is dark brown with clear, colorless droplets of liquid on the glass. After sitting on the windowsill for a week, the walls of the flask have a silvery lining and both the solution and the droplets are colorless. • What are three physical properties of the initial substance? • Which of the following is not an indication that a chemical reaction has occurred?

  22. Physical and Chemical Properties

  23. Factor-Label Method (Dimensional Analysis) Why is the factor-label method very important in chemistry? It allows us to easily convert between units using a series of fractions based on equivalencies

  24. Factor-Label Method (Dimensional Analysis) How many different types are there? • Three types: • Two step - converting to or from a base unit • Multiple step - converting from a non-base unit to a non-base unit • Formula conversion – converting between two different measuring systems • Ex. Celsius to Fahrenheit

  25. Factor-Label Method (Dimensional Analysis) • Two-Step • Convert: • 2.5 cm to m • 5.08 g to kg • 3.21 L to ML • 0.19 mol to mmol • 6.7 µm to m

  26. Factor-Label Method (Dimensional Analysis) • Multi-Step • Convert: • 0.04 mJ to kJ • 36.0 μL to pL • 5 mmol to Mmol • 37 hours to seconds • 8 ounces to kilograms

  27. Factor-Label Method (Dimensional Analysis) Challenge #1 • Given the following conversion factors convert 1 fizzle to frizzles • 3 swizzles = 7 twizzles • 1 fizzle = 2 drizzles • 3 twizzles = 14 sizzles • 1 swizzles = 22 frizzles • 8 drizzles = 5 sizzles

  28. Factor-Label Method (Dimensional Analysis) Challenge #2 • Jules Vern wrote a book called Twenty Thousand Leagues Under the Sea. Using the conversion factors below, convert 20,000 leagues to inches. • 12 in = 1 ft • 3 ft = 1 yd • 1 fathom = 2 yds • 1 mile = 5280 ft • 1 nautical mile = 6080 ft • 1 league = 3 nautical miles

  29. Factor-Label Method (Dimensional Analysis) Challenge #3 • A car’s engine is rated at 3.60 L (volume in the cylinders). How many cubic inches is this? • 1 L is a cube that is 10 cm on a side • 1 inch = 2.54 cm

  30. Significant Figures (Sig figs) • Why are significant figures important? • Indicates how precise the measurement is • You are only as precise as your least precise measurement!

  31. Significant Figures (Sig figs) • How do you determine what figures are significant? • Always significant: • Any non-zero number • 2132has four sig figs • Any zero between two non-zero numbers • 2002 has four sig figs – two 0’s and two 2’s

  32. Significant Figures (Sig figs) • How do you determine what figures are significant? • Never significant: • All zeros in front of the first non-zero number • 0.0012 has two sig figs –1 and 2

  33. Significant Figures (Sig figs) • How do you determine what figures are significant? • Sometimes significant: • Zeros at the end of a number are significantwhenever there is a decimal present • 0.075900 has 5 sig figs; the first two zeros do not count • 14000.has 5 sig figs • 14000.0has 6 sig figs

  34. Significant Figures (Sig figs) • How do you determine what figures are significant? • Sometimes significant: • Zeros at the end of a number are not usuallysignificant when there is not a decimal point • 14,000 has only 2 sig figs

  35. Significant Figures (Sig figs) • How many sig figs do the following numbers have? • 0.0013 • 1.20 • 0.0101010 • 450 • 350.0 • 2 sig figs • 3 sig figs • 6 sig figs • 2 sig figs • 4 sig figs

  36. Significant Figures (Sig figs) • Leading zeroes don't count, middle zeros do count, ending zeros only count if a decimal's in the amount!

  37. Significant Figures (Sig figs) • How do you add/subtract with sig figs? • Look at decimal places. Your answer should end in the same decimal place as your least precise measurement • 200.27 + 45.8 + 31.456 = • 277.5

  38. Significant Figures (Sig figs) • How do you multiply/divide with sig figs? • What about mixed operations? • Your answer should have the same number of significant figures as the measurement with the fewest significant figures • 25.03 x 0.02 = • 0.5 • Follow sig fig rules for each step of the calculation

  39. Significant Figures (Sig figs) • 100.1 + 34 = • 7.892 – 2.9 • 3.44 – 11 + 0.009 = • 1.23 x 4.0 = • (100.1)(10.00) / 0.01000 = • (100.0 + 23 + 99.99) / 89.99 = • 134 • 5.0 • -8 • 4.9 • 100100 • 2.48

  40. Uncertainties • What is an uncertainty? • A measured value that cannot be determined exactly • Actual number could be above or below the measured reading • Error in precision

  41. Uncertainties • How do we represent uncertainties? • Need a range • Use +/- • Make it reasonable! • Examples • 25.2 +/- 0.1 mL • 23.0 +/- 0.5 °C • Depends on how precise your measuring device is

  42. Precision vs. Accuracy • What is the difference between precision and accuracy? • Accuracy refers to how close a measurement (average) is to the true or accepted value • Precision indicates how close together a group of measurements are to each other

  43. Precision vs. Accuracy

  44. Precision vs. Accuracy • Assuming the center bull's-eye is our accepted value: • Who is the most accurate at throwing darts? • Who is the least precise? Matt John Dan Pete

  45. Practice Problem • Below is a data table produced by four groups of students who were measuring the mass of a paper clip which had a known mass of 1.0003 g. • NOTE: The last row is the average of their measurements. • Which group(s) are the most accurate? • Which group(s) are the most precise? • Which group is the most accurate and precise?

  46. Practice Problem • Suppose a GPS (Global Positioning System) which measures your position on earth, is not calibrated correctly. You take 3 readings at the same place and they are all close together but 14 miles from your actual position. • Explain your results in terms of precision and accuracy.

  47. Practice Problem • What is the difference in the measurements 4 vs 4.00 vs 4.00000? In terms of taking measurements, explain why we use significant figures.

  48. Percent Error • What is percent error? • Used to determine how accurate your final results are What you should have got! What you actually got!

  49. Types of Errors • What are the three types of errors? • 1 – Blunder • Errors made by mistakes in your lab techniques • Spillage, misreading instruments, writing measurements down wrong, etc. • Do not count these! REDO them!

  50. Types of Errors • What are the three types of errors? • 2 – Systematic • Error in accuracy • An error that is consistently repeated • Human error/ignorance • Inaccurate/limiting equipment • Cannot be reduced by repeatability

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