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Math Review

Math Review. Reviewing Fractions. The Rule: The denominator(s) must be the same Ex: 3 + 5 - 1 = ? 4 8 3 Common denominator is….. …..24 …. (8x3 & 6x4). Multiply each fraction to give you 24 on the bottom.

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Math Review

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  1. Math Review

  2. Reviewing Fractions

  3. The Rule: The denominator(s) must be the same Ex: 3 + 5 - 1 = ? 4 8 3 Common denominator is….. …..24 …. (8x3 & 6x4). Multiply each fraction to give you 24 on the bottom. Then you can add/subtract as needed. Adding & Subtracting

  4. 18 + 15 - 8 = 25 24 24 24 24 • Don’t forget to reduce!!! Adding & Subtracting

  5. DO NOT CROSS MULTIPLY!!!! Just multiply/divide across both the top and bottom. Then reduce as needed Ex: 1 x 3 x 5 x 7 = 105 or 1 x 3 x 5 x 7= 35 2 4 6 8 384 2 4 6(2) 8 128 105 & 324 are both divisible by 3 Multiplying & Dividing

  6. We don’t usually use just fractions in chemistry. • However, when we solve “OUR” problems they will be set up just like multiplying fractions. Fractions Continued

  7. EX. How many feet are in 8.7 km? (1 in = 2.54 cm) 8.7km x 1000m x 100 cm x 1in x 1 ft= 87000= 3854.33 ft 1km 1m 2.54cm 12in 30.48 To solve you multiple across the top and the bottom separately and then divide. We won’t be using x for multiplying, we use a grid. Fractions Continued

  8. Problem Solving Worksheet 5

  9. There are A LOT of formulas in Chemistry. • You must be able to rearrange those formula’s to solve for the variable you need. Solving for variables

  10. There are 2 basic rules that you must follow: 1. Whatever is done to one side MUST be done to the other 2. You CAN NOT solve for a variable in the denominator!! • It must first be moved to the numerator (by multiplying) Solving for variables

  11. For example: Solve for peace? Solving for variables

  12. 1st Multiply both sides by the sun Now, move the flower

  13. Then divide both sides by the flower Finally symbols or letters are not as important as knowing how to rearrange the formula

  14. Now try it on these “real” chemistry formulas. • Solve for volume D = m/v (Density) • Solve for T PV=nRT (Ideal Gas Law) • Solve for M2 M1V1 = M2V2 (Dilution Formula) Variable’s Cont.

  15. V = m D • T = PV nR • M2 =M1V1 V2 Answers

  16. Problem Solving Worksheet 10

  17. Percents

  18. Percent Error • Percent Yield • Percent Composition 3 Types

  19. Percent Error tells you how accurate your results are. Percent Error

  20. Percent Error = (Measured Value - Accepted Value) x 100 Accepted Value Percent Error

  21. A student calculates the density of iron as 6.80 g/cm3 by using lab data for mass and volume. A handbook reveals that the correct value is 7.86 g/cm3. What is the percent error? Example

  22. Precision versus Accuracy

  23. Precision- getting the same results again & again (reproducible) Accuracy- getting results close to the accepted or standard value Precision vs. Accuracy

  24. If the is the target or bulls-eye Which does this represent? Precision vs Accuracy

  25. And this one? Precision vs Accuracy

  26. You draw Accurate but not precise Precision vs Accuracy

  27. The accepted value is 29.35. Describe the data below in terms of accuracy and precision Example

  28. Density Mass: put matter on balance Volume: - graduated cylinder - geometry volume formulas - displacement D= Mass_ Volume

  29. Volume by Displacement

  30. An unknown mineral has a mass of 16 grams. A graduated cylinder is filled with 10. mL of water. The mineral is dropped into the cylinder and the water level rises to 18 mL. What is the density of the mineral? Example

  31. MUST SHOW YOUR WORK!!!! Solve for T2P1V1 = P2V2 (Combined Gas Law) T1T2 Exit Ticket #1

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