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AHS Chemistry

AHS Chemistry. Accuracy and Precision. Accuracy: The degree of conformity with a standard (often called true, accepted or theoretical) value. There are times when a calculated value will be used as the standard . Precision

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AHS Chemistry

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  1. AHS Chemistry Accuracy and Precision

  2. Accuracy: • The degree of conformity with a standard (often called true, accepted or theoretical) value. There are times when a calculated value will be used as the standard. • Precision • How close measurements are to one another. Repeated measurements determine reproducibility or precision. Precision tells you how to report results.

  3. **Four lab groups performed the same experiment four times to determine the melting point of naphthalene (moth balls). The accepted melting point is 79.0°C. Indicate whether the following sets of data are precise, accurate, both or neither.

  4. AHS Chemistry Measurement and data review

  5. What is a qualitative measurement? • Non-numerical or descriptive data (color, texture, etc.) • What is a quantitative measurement? • Numerical information (anything that contains numbers)

  6. Explain the process of making a detailed measurement. • Every time you take a measurement you should estimate between the lines. If the measurement is on a line, add a zero to show that you are estimating to be exactly on the line. Always include one estimated digit. • How do you take measurements when a meniscus is present? • From the bottom of the meniscus

  7. What is the difference between a burette and a graduated cylinder? How can you tell which one you are working with? Burettes measure the amount of liquid that is released through a stopcock. A graduated cylinder measures how much liquid it is holding: You can tell the difference because a burette will be marked “upside down” compared to a graduated cylinder. (The numbers increase going down on a burette).

  8. A B C D E F A A. B. C. D. E. F

  9. 10 mL 20 mL A A B

  10. AHS Chemistry Significant Figures

  11. Significant figures indicate how much ___________ or estimation of a measurement is known: Write the four rules for using sig figs below: • 1) Non-zero digits are always significant • (24 has two sig figs) • 2)Leading zeros are never significant • (0.0024 has two sig figs) • 3) Middle or “trapped” zeros are always significant • (204 has three sig figs) • 4) Tail zeros are significant if there is a decimal point in the number • (24.0 has three sig figs, 240 has two sig figs.)

  12. Count an underline the significant figures in each of the following numbers. 1) 4,000 2) 0.0045 3) 0.00909 4) 2.050x1024 5) 3.990 6) 100.0 7) 1010 8)100.

  13. Round to three significant figures 1) 123,499 2) -234,999 3) 0.231451 4)18.99

  14. Multiplication and Division: In multiplication and division, the answer can have no more sig figs than are in the measurement with the _____________ number of sig figs. ____________ numbers such as ___________ numbers and _______________________ are not included when counting sig figs.

  15. Indicate how many sig figs would be in your answer for the following equations, and then answer each question. 1) 0.006760 / 32 2) 1,234,000 / 0.0000345 3) 278.4 x 25.2 4) 89.554 x 43.1

  16. AHS Chemistry Scientific notation

  17. Scientific Notation Scientific notation is used to represent numbers that are very large or very small. It looks like this on paper: 5.25x1060 In your calculator you will never type in the x10 ect…you will use EE on your calculator. You calculator would read 5.25E60

  18. To convert from decimal form to scientific notation: • Move the decimal point to the left or the right so that only one nonzero digit remains to the left of the decimal point. The exponent is the number of places that you moved the decimal point. If you moved the decimal to the left, the exponent is positive. If you moved it to the right, the exponent is negative.

  19. To convert from Scientific notation to decimal form: • Move the decimal point to the right if the exponent is positive (add zeroes if needed). Move the decimal to the left if the exponent is negative (add zeroes if needed).

  20. To Correct scientific notation: • 1) Move the decimal so that only one _______________ digit remains to the left of the decimal. • 2) Increase the exponent if: • You moved the decimal to the left • 3) Decrease the exponent if: • You moved the decimal to the left

  21. Convert to decimal form 1) 1.1x103 2) -2.35x105 3) 1.12x10-3 4) -2.35x10-5

  22. Convert to Scientific Notation 1) 75,100,000 2)-234,900 3)0.00000231 4)-0.00003549

  23. AHS Chemistry Algebra and density

  24. Algebraic Manipulation: 1) 2)

  25. Density • Define density: • The mass of a substance per unit volume or how much it weighs per given volume. (it is an intensive physical property. • What are the Units? • Grams/milliliter (g/mL) or • Grams/cubic centimeter (g/cm3) • Write the equation for density: • Density = mass / volume D=m/V • What is the density of water: • 1.0 g/mL or 1.0 g/cm3

  26. Density • Under what circumstances will something float on water? • If the density of a substance is less than the density of water • Using what you have learned so far, what is more dense, ice or liquid water? • Ice floats on water, so it is less dense

  27. Density A certain solid has a volume of 35.7 cm3 and a mass of 85 g. What is its density? The density of gold is 19.3 g/mL. What is the volume of 200 g of gold?

  28. AHS Chemistry Units of Measurement

  29. Units of measurement 1) Mass (m): kilograms (kg) or grams (g) 2) Temperature (T): Kelvin (K) or Celcius (C) 3) Volume (V): Liter (L) or milliliter (mL) 4) Amount (mol): mole (mol) 5) Wavelength(λ):meter(m) or nanometer (nm) 6) Frequency (f): Hertz (Hz) inverse seconds (sec-1) 7) Energy (E): Joules (J)

  30. AHS Chemistry Dimensional analysis

  31. Dimensional Analysis Way of converting from one unit to another 1) Draw the dimensional analysis grid 2) Write the given number and unit in the upper left corner 3) Copy the unit from the upper left to the lower right corner 4) Write the desired unit in the upper right corner 5)Fill in the correct numerical relationship which exists between the two units

  32. Dimensional Analysis continued 6) Cancel any units which appear in both the numerator and the denominator grid 7) Multiply everything together that is above the grid line. Divide by everything that is below 8) Express your answer in the same number of sig figs as were given in the original problem 9) The units which did not cancel are the units for your answer

  33. Dimensional Analysis How many hours are there in 190.7 minutes Convert 378.4 cm to meters Convert 4.32x10-4 to mg

  34. 2-step D.A. To go from one side of the base unit to the other side of the base unit, you must do a two step grid. First convert to the base unit, then convert from the base unit Ex: Convert 231 mm to km

  35. 2-step D.A. Convert 5.43 KL to dl Convert 6.99x108 kg to cg

  36. Questions! Write down three questions and give them to your teacher tomorrow.

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