Warm-up: Are cell phones and ipods allowed in the classroom? What will happen to them if the teacher sees or hears one (that includes headphones)?

Significant Figures - Measurements NO measurement is perfect. – All measurements have an uncertainty. – Human error IS NOT the cause of the uncertainly. Read and record a measurement to one decimal place beyond the smallest marking on that piece of equipment. With a digital device, record all digits.

What is the Length? We can see the markings between cm We can’t see the markings between the.6-.7 We must guess between.6 &.7 We record 1.67 cm as our measurement The last digit an 7 was our guess...stop there 3

0 1 2

0 1 2

0 1 2

Warm-up : Determine which of the following would give a more precise number if used. – OR 0 1

Where do we measure liquids A B C Always measure liquids at the bottom of the meniscus AND at eye level

2 1 0

1 0

Warm-up: Measure the following using proper measuring technique so the answer has the correct number of sig figs

Accuracy Agreement with accepted or true value. “Correctness”

Precision The degree to which a set of data agrees with each other. A smaller range, the more precise the data.

19. Which one is accurate but NOT precise A B D C

20. Which one is precise but NOT accurate A B D C

21. Which one is NOT accurate and NOT precise A B D C

22. Which one is accurate AND precise A B D C

Accuracy and Precision

Accuracy and Precision in Measurements Reading Thermometer 1 Thermometer 2 Thermometer 3 Thermometer °C97.5°C98.3°C97.5°C °C102.3°C98.5°C99.7°C °C99.7°C98.4°C96.2°C 499.9°C100.9°C98.7°C94.4°C Average99.98°C100.1°C98.5°C96.9°C Range0.2°C5.0°C0.4°C5.3°C Accurate Precise YES YES YES YES NO NO NO NO

To number or not to number, that is the question….. Observations or data that deals with numbers is called QUANTITATIVE. Observations or data that does NOT deal with numbers is called QUALITATIVE.

Qualitative or Quantitative? 1. There are 6 tables in the room – A) Qualitative – B) Quantitative 2. The room is hot – A) Qualitative – B) Quantitative 3. This powerpoint sucks – A) Qualitative – B) Quantitative 4. There are lot of people in this room – A) Qualitative – B) Quantitative

Types of Quantitative Information There are 2 types of quantitative data – Exact Anything that is counted – Ex. I have 10 fingers and 10 toes Exact relationships or predefined values – 12 inches = 1 foot – 1 dozen = 12 – Inexact (measured) Anything that you measure using a tool (ruler, scale, thermometer, etc) – The paper is 8.5 inches wide

Exact or Inexact #’s 5. 1 yard = 3 feet – A) Exact – B) Inexact (measured) 6. The diameter of a red blood cell is 6 x cm. – A) Exact – B) Inexact (measured) 7. There are 2 doors in this room. – A) Exact – B) Inexact (measured) 8. Gold melts at 1064°C – A) Exact – B) Inexact (measured)

Warm-up Come up with an example of the following: Exact number Inexact number Quantitative observation Qualitative observation

Significant Figures The significant figures (sig figs) of a number are those digits that carry meaning contributing to its precision. Exact numbers have an infinite number of sig figs Inexact numbers have a finite number based on rules of sig figs.

Significant Figures All non-zero numbers are always significant. Then use the following to determine if zeros are significant. – Determine if number has a decimal point. – If it does, look from left to right for the first non-zero digit. All digits after it are significant – If it does not, go from right to left looking for the first non-zero digit. All digits after it are significant.

Significant Figures – Zero Rules A zero in the number Decimal Count from Left No Decimal Count from Right

Counting Sig Figs No decimal 2543 SF 304,9004 SF

Counting Sig Figs with Decimal SF 7 SF 1,

Practice: How Many Sig Figs? g 1000 mL 3.14 m cm 3 SF 5 SF 1 SF 4 SF

Sig. Figs. in Calculations Addition and Subtraction By doing a math operation, you can not increase the number of significant figures! Addition and Subtraction – count DECIMAL PLACES – The number of decimal places in your answer should match the digit with the smallest number of decimal places.

Sig. Figs. in Calculations Multiplication and Division Multiplication and Division – Count SIGNIFICANT FIGURES. – The number of significant figures in your answer should match the digit with the smallest number of significant figures.

Adding & Subtracting Sig Figs cm cm = cm Estimated value

Practice g g = L L = 0.01 g g = 3000 N N = = 63.1 L = g g = 3144 N 1.12

Multiplying & Dividing Sig Figs 6.0 cm X 22.0 cm = 2 SF 3 SF 132 =130 cm 2 2 SF

Practice 56.3 g  33 mL = 4.0 m X 22.3 m = 0.21 cm X 1.11cm X 2.0 cm = 89.2 = 89 m = 1.7 g/mL cm 3