1. Measurements and Mathematics in Chemistry

2. Precision
refers to the degree of reproducibility of a measured quantity, that is, the closeness of agreement when the same quantity in measured several times

3. Accuracy
Refers to how close a measured value is to the accepted or “real” value. High precision numbers are not always accurate. But it is more likely that measurements of high precision are more accurate.

4. Metric Units Basic units
The basic metric unit for the measurement of length is known as the ______________.
The basic metric unit of volume is the _____________.
Volume can also be measured using cm.
1 cm3 = _____ mL
Tool used to measure volume is the ________________________________________
Smallest increment marked: __________________________________
Measurements should be read to the nearest: _______________________

5. The basic metric unit of mass is the _____________.
Tool used to measure mass is the _________________________________
Smallest increment marked: __________________________________
Measurements should be read to the nearest: _______________________

6. The basic metric unit for temperature is ________________________.
Tool used to measure temperature is the ______________________________
Smallest increment marked: __________________________________
Measurements should be read to the nearest: _______________________-
The temperatures in this scale can easily be converted to the Kelvin scale, or the absolute scale, by the following formula:
****K =

7. Prefixes
Prefix symbol numerical value 10x (times greater than base) ____________ _______ 1,000,000 _______ ____________ _______ 1,000 _______ ____________ _______ 100 _______ ____________ _______ 10 _______ Basic unit (_____,_____,_____) 1

8. Prefixes Prefix symbol numerical value 10x (times greater than base)
____________ _______ 0.1 _______
____________ _______ _______
____________ _______ _______

9. Practice
.0063 m = ____________ mm 390,000 g = ____________ kg kL = ____________ L 22.4 mL = ____________ cm3 25 °C = ____________ K
377 mm = ____________ cm 275 K = ____________ °C 42,000 cm = ____________ km 250cm = ____________ m 432 cm3 = ____________ L

10. Percent Error
For example, if you measure the mass of oxygen in a sample to be 25.0 grams and the theoretical value is 30.0 grams, the percent error would be:

11. What is the length of the following?

12. Significant Figures
Definition: all the known values from a measurement including a last estimated digit

13. Determining the # of Sig Figs in a measurement
Is the decimal present or absent?
Begin at the appropriate ocean side of the measurement
Move to the first non-zero digit
Count all digits moving across

14. Recall the measured value from earlier:
How many significant digits are there in our measured value?

15. Practice
Indicate the number of significant figures in the following measurements: cm3 _____ 510 mL _____ 510. mL _____

16. Do Now:
Indicate the number of significant figures in the following measurements and identify the estimated digit: g _____ atm _____ 22.4 L _____ kPa _____ 5000 mol _____

17. Addition and subtraction with Sig Figs
The answer has only as many decimal places as the measurement having the least number of decimal places.
Procedure:
1. line up all measurements by decimal points
2. perform the calculation on your calculator
3. draw a line down next to the least decimal place
4. round your answer off the answer to the digit to the left of the line

18. Example:
Given: 2 H2 + O2 → 2H2O If g of H2 are combined with 32.0 g of O2, how many grams of H2O are formed? ____

19. Multiplication and Division
Rule: The solution to a multiplication or division problem can only have as many significant figures as the starting measurement with the least number of significant figures.
Procedure:
1. perform the calculation on your calculator
2. count the number of significant figures in the starting measurements
3. round your answer off the answer to the least number of significant figures

20. Example:
A student found the mass of an object to be grams and the volume of the object to be 22.0 mL. What is the density of the object?

21. Example:
Gold has a density of g/mL. If a piece of gold has a volume of mL, what is the mass of the object

22. Example:
What is the mass of 75.2 mL of mercury? (density of mercury is g/cm3)