1. Measurements in Science
Accuracy and Precision
EQ:How do you determine the accuracy and precision of your measurements?
Chemistry
Jacqueline P. Hancock, B.S., M.Ed

2. Quantity with both a number and unit
1.1
Measurements
Quantity with both a number and unit
Fundamental to experimentation

3. Scientific Notation Standard Notation Exponential Notation Coefficient
Power of 10
Positive exponent > 1
Negative exponent < 1
Example x1023
Standard Notation
602,000,000,000,000,000,000,000

4. Accuracy vs. Precision
Accuracy-how close a measurement comes to the actual value
Precision-how close a series of measurements are to each other
______________________________
How do accuracy and precision differ?
How do you determine accuracy and precision of your measurements?

5. ACCURACY & PRECISION

6. Accurate vs. Inaccurate
Error
The difference between the accepted value and the experimental value
Error= (experimental value - accepted value)
Percent Error
The absolute value of the error divided by the accepted value, multiplied by 100%
Percent Error = ____|error|_ x 100%
accepted value

7. Accepted/Actual Values
Homework: Calculate Error & Percent Error
Sheet of Paper
Length cm
Width cm
Index Card
Length cm
Width cm

8. Significant Figures
All figures that are known plus a last estimated digit.
Applies only to measured quantities
Necessary for precision

9. Are Significant Figures Important?
A Fable A student once needed a cube of metal that had to have a mass of 83 grams. He knew the density of this metal was 8.67 g/mL, which told him the cube's volume.
Believing significant figures were invented just to make life difficult for chemistry students and had no practical use in the real world, he calculated the volume of the cube as mL.

10. He thus determined that the edge of the cube had to be 2.097 cm.
He took his plans to the machine shop where his friend had the same type of work done the previous year.
The shop foreman said, "Yes, we can make this according to your specifications - but it will be expensive." "That's OK," replied the student. "It's important." He knew his friend has paid $35, and he had been given $50 out of the school's research budget to get the job done.

11. He returned the next day, expecting the job to be done
He returned the next day, expecting the job to be done. "Sorry," said the foreman. "We're still working on it. Try next week." Finally the day came, and our friend got his cube. It looked very, very smooth and shiny and beautiful in its velvet case. Seeing it, our hero had a premonition of disaster and became a bit nervous.
But he summoned up enough courage to ask for the bill. "$500, and cheap at the price. We had a terrific job getting it right -- had to make three before we got one right.“

12. "But--but--my friend paid only $35 for the same thing!"
"No. He wanted a cube 2.1 cm on an edge, and your specifications called for We had yours roughed out to 2.1 that very afternoon, but it was the precision grinding and lapping to get it down to which took so long and cost the big money. The first one we made was on one edge when we got finished, so we had to scrap it. The second was closer, but still not what you specified. That's why the three tries."

13. Is the digit significant?
Every nonzero digit is assumed
Zeros between nonzero digits
Left most zeros in front of nonzero are placeholders
Zeros at end of number and to right of decimal point are always significant
Zeros at rightmost end to left of decimal are not if they are placeholders unless they are measured values

14. Questions & Discussion

15. MEASUREMENTS IN SCIENCE
SI System:
Why does the scientific community use the SI system? ~To communicate
SI system is based on 10

19. Metric Drawing Assignment

20. `
K H D (base)

21. Complete the Chart SYMBOL PREFIX MEGA KILO HECTO DEKA B DECI CENTI
MILLI
MICRO
NANO
PICO
EXPANDED FORM
EXPONENTIAL FORM

22. UNIT CONVERSIONS TO CONVERT TO A LARGER NUMBER
MOVE THE DECIMAL POINT TO THE LEFT AND STOP IN FRONT OF THE DESIRED PREFIX
TO CONVERT TO A SMALLER NUMBER
MOVE THE DECIMAL POINT TO THE RIGHT AND STOP BEHIND THE DESIRED PREFIX