Unit 1. The Math of Chemistry

Transcription

1 Unit 1 The Math of Chemistry

2 Lab Safety

3 Lab Safety

4 Laboratory Equipment Graduated Cylinder Test Tube Beaker Funnel Test Tube Clamp Beaker Tongs Erlenmeyer Flask Clay Triangle

5 Laboratory Equipment Buret Scoopula Pipet Ring Stand Evaporating Dish Crucible w/cover Watch Glass Ring Stand

6 Laboratory Equipment Wire Gauze Bunsen Burner Rubber Stopper Crucible Tongs Hot Plate Stirring Rod Test Tube Rack Electronic Scale

7 How Many? Try to guess how many molecules of water are in the graduated cylinder. Actual number:

8 Scientific Notation Reflect Question: What is scientific notation and why do we use it?

9 Scientific Notation and % Error Scientific Notation: Consists of two numbers: 1 st is between 1 and 9 (the coefficient), the second is a power of 10 The exponent/power indicates how many places to move the decimal.

10 Scientific Notation 1.32 x 10-4 vs x 10 5

11 Scientific Notation and % Error Write the following in scientific notation: 1. 32, X ,024, X X X X X 10 4

12 Scientific Notation and % Error Write the following in standard notation: x x ,500, x x ,060, x x

13 Rules for fixing a number when it isn t in proper scientific notation: Example 1: Example 2: 19.6 x x 10-2 Rule: If you make one number bigger, make the other one smaller & vice versa.

14 Metric System

15 Metric System Reflect: In what way can we measure objects in science?

16 Measurement History Up until the time of Napoleon, every country had its own measuring system. This was based on the body part of the ruling monarch (thus the term ruler) length was based on the length of the king s foot (hence the measurement foot) Weight was in stones. # of = sized stones = mass of the king.

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18 Metric System

19 Metric System

20 Metric System When converting between units using the above Metric Line : -Mover you decimal in the same DIRECTION and # of SPACES you are moving on the Metric Line

21 Metric System Example 1: Convert 5 meters into millimeters 5000 mm Example 2: Convert μs into seconds 2.34 X 10^-7 Example 3: Convert 83.2 centimeters into meters

22 Metric System Example 4: Convert 1.2 kiloliters into liters. 1,200 L Example 5: Convert 5 x 10-6 μm to pm. 5 pm Example 6: Convert 186 m to nm X 10^11

23 World s Roundest Object The Metric System at work! Y

24 Precision in Measurement Reflect: When taking a measurement (volume, length, mass) does it matter if all of the instruments you will use are accurate to a different number of decimal places?

25 Precision in Measurement Reading & Taking Measurements in Science: When we read measuring devices, our measurement must take into account the capabilities of your instrument.

26 Precision in Measurement Question 1: Looking at the ruler below, to how many decimal places are you able to report your answer to? Question 2: Estimate the length of the object below.

27 Precision in Measurement Precision: Reproducibility/ repeatability Smaller variation = better precision Accuracy: How close your measured value is to actual/accepted value

28 Precision in Measurement Directions: Below are two rulers, each measuring the same length of a piece of wire. Below each ruler are measurements reported for the wire. Decide whether each listed measurement is a valid measurement or not based on the scale of the ruler. Write a V for VALID measurement or an I for an INVALED measurement next to each measurement taken.

29 Precision in Measurement V 2.9 cm: 3.0 cm: v 2.99 cm : i 3.01 cm : i 3 cm: i 2.98cm: i

30 Precision in Measurement V 3.00 cm: 3.0 cm: i 2.99 cm : V 3.01 cm : V 3 cm: i cm: i

31 Precision in Measurement Which ruler is a better choice for accurately measuring the length of the wire? Explain. The second ruler b/c it can be precise to a greater number of decimal places.

32 % Error Reflect: What is percent error?

33 % Error Your Value (measured) is greater than the accepted value Your Value (measured) is smaller than the accepted value

34 Practice

35 Significant Digits Reflect: When reporting a measurement or calculation, how many decimal places should your answer have? How do you figure it out?

36 Significant Digits in Measurement Significant Digits (or Significant Figures): The significant figures of a number are those digits that carry meaning contributing to its precision.

37 Significant Digits in Measurement

38 Significant Digits in Measurement 5 Rules for Significant Digits 1. All non-zero numbers are significant 2. Sandwiched zeros (those that occur between two significant digits) are significant. 3. Zeros that are only placeholders for a decimal are not significant. 4. Zeros at the end of a number that also contains a decimal are significant. 5. Exact numbers (no doubt or uncertainty in the value) may be thought of as having an infinite number of significant digits. These include numbers that were counted or are defined values (i.e. conversion factors).

39 Significant Digits in Measurement 5 Rules for Significant Digits 1. All non-zero numbers are significant 2. Sandwiched zeros (those that occur between two significant digits) are significant. 3. Zeros that are only placeholders for a decimal are not significant. 4. Zeros at the end of a number that also contains a decimal are significant. 5. Exact numbers (no doubt or uncertainty in the value) may be thought of as having an infinite number of significant digits. These include numbers that were counted or are defined values (i.e. conversion factors).

40 Significant Digits in Measurement 5 Rules for Significant Digits 1. All non-zero numbers are significant 2. Sandwiched zeros (those that occur between two significant digits) are significant. 3. Zeros that are only placeholders for a decimal are not significant. 4. Zeros at the end of a number that also contains a decimal are significant. 5. Exact numbers (no doubt or uncertainty in the value) may be thought of as having an infinite number of significant digits. These include numbers that were counted or are defined values (i.e. conversion factors).

41 Significant Digits in Measurement Just because we changed units, our measurement did not get more/less precise. The zeros we added are simply holding a place, they are not significant.

42 Significant Digits in Measurement 5 Rules for Significant Digits 1. All non-zero numbers are significant 2. Sandwiched zeros (those that occur between two significant digits) are significant. 3. Zeros that are only placeholders for a decimal are not significant. 4. Zeros at the end of a number that also contains a decimal are significant. 5. Exact numbers (no doubt or uncertainty in the value) may be thought of as having an infinite number of significant digits. These include numbers that were counted or are defined values (i.e. conversion factors).

43 Significant Digits in Measurement 5 Rules for Significant Digits 5. Exact numbers (no doubt or uncertainty in the value) may be thought of as having an infinite number of significant digits. These include numbers that were counted or are defined values (i.e. conversion factors).

44 Significant Digits in Measurement

45 Significant Digits in Measurement

46 Significant Digits in Measurement When multiplying or dividing, limit your answer to the same number of significant digits as the digit with the least number of significant digits. V = l x w x h V = (3.052 m)(2.10 m)(0.75 m) V = (4 sig figs)(3 sig figs)(2 sig figs) V = m 3 V = 4.8 m 3

47 Significant Digits in Measurement When adding or subtracting, limit your answer to the same decimal places as the factor with the least number of decimal places

48 Practice

49 Density Reflect: What is density? Write down any words, formulas, concepts, pictures, phrases, comparisons or numbers that will help you answer this question.

50 Defining Density: Words Density Pictures Mathematical Formula

51 Ways to Calculate the Density of an Object Aluminum Bar Rubber Stopper A Liquid

52 Ways to Calculate the Density of an Object Aluminum Bar Rubber Stopper A Liquid 1. Mass the Bar 2. Measure L, W, H 3. Calculate Volume 4. Solve For density 1. Mass stopper 2. Volume by displacement 3. Solve for density 1. Mass by difference 2. Measure volume in Graduated Cylinder

53 Calculated Density for Each Object Aluminum Bar Rubber Stopper A Liquid

54 Comparing Densities Compare the MOST dense with the LEAST dense object, in terms of particle arrangement, citing evidence from your calculations.

55 Comparing Densities The density of mineral oil is 0.8 g/ml, if all three substances were placed in the mineral oil would they sink or float? Explain.

56 Practice Problems g/cm^3

57 Practice Problems