1. Chapter 2 Advanced Honors Chemistry
Measurements and Calculations

2. “How do scientists measure things?
Units of Measurement
“How do scientists measure things?
The use standard units of measure called the International System of Units, SI Units.

3. Units of Measurement There are seven base units… Length – meter, m
Mass – kilogram, kg
Time – second, s
Temperature – kelvin, K
Electric current – ampere, A
Amount of substance – mole, mol
Luminous intensity – candela, cd
Derived Units: combinations of base units.
- speed (meters per second, m/s)
- density (kg per cubic meter, kg/cm3)
P. 34 – 35

5. Scientific Notation Answer has to have 1 digit before the decimal.
Use exponents to show the number of digits after the decimal.
1.54 x 10-2
2.002 x 103
4.1 x 10-4
7.023 x 101

6. What’s the difference between…?
Mass is the measure of how much matter is present. It does not depend on gravity.
Weight is the measure of the gravitational pull on matter.
“The weight of an object is different on the moon than on the earth…but the mass does not change.”
Volume is the amount of space occupied by an object.
Density is the ratio of mass to volume.

7. ***Test: Density of Water: 1.00 g/cm3
What is Density?
Density: a measurement of how much matter is contained in a certain volume.
Calculate Density
D = Mass
Volume M V D
***Test: Density of Water: 1.00 g/cm3

8. Precision vs. Accuracy
Accuracy: how close a measurement is to the correct answer.
Precision: how close each measurement is to one another.

9. Precision vs. Accuracy

10. Used to evaluate how accurate your measurements were.
Percentage Error
% Error = | EXP – ACT | x 100
ACT
Used to evaluate how accurate your measurements were.

11. Estimations and Errors in Measuring
What is the smallest interval?
Go one more digit past the smallest interval.

12. Estimations and Errors in Measuring
What is the smallest interval? 0.0 cm
Go one more digit past the smallest interval cm

13. Estimations and Errors in Measuring
What is the volume of the liquid?
What is the smallest interval? 0.0 mL
Go one more digit past the smallest interval mL

14. Estimations and Errors in Measuring
What is the volume of the liquid?
6.62 ± 0.01 mL

15. Rounding

16. Try these: Round to 3 decimal places.      

17. Try these: Round to 3 decimal places.
 4.222  
 0.013
 3.145
 8.000 

18. Significant Figures (Sig Figs)
Conversion factors do not affect significant digits b/c conversion factors are EXACT.

19. Significant Figures (Sig Figs)
How many
sig figs?
804.05
1002
400
30000.

20. Significant Figures (Sig Figs)
How many
sig figs?
804.05
1002
400
30000.

21. Significant Figures (Sig Figs)
How many
sig figs?
804.05
1002
400
30000.

22. Adding and Subtracting Sig Figs
When adding or subtracting decimals, the answer must have:
- the same number of digits to the right of the decimal point as there are in the measurement having the fewest digits to the right of the decimal point.
- In other words: Round to the fewest number of decimal places.
Express each answer to the correct number of significant figures.
* 5.44 m m =
* 1.22 mL mL =

23. Adding and Subtracting Sig Figs
When adding or subtracting decimals, the answer must have:
- the same number of digits to the right of the decimal point as there are in the measurement having the fewest digits to the right of the decimal point.
- In other words: Round to the fewest number of decimal places.
Express each answer to the correct number of significant figures.
* 5.44 m m =  8.05 mL
* 1.22 mL mL =  17.0 mL

24. Multiplying and Dividing Sig Figs
For multiplication or division, the answer:
can have no more significant figures than are in the measurement with the fewest number of significant figures.
In other words: Round to the fewest number of significant digits.
Express each answer to the correct number of significant figures.
* 4.22 m x m =
* 2.4 g/mL  mL =

25. Multiplying and Dividing Sig Figs
For multiplication or division, the answer:
can have no more significant figures than are in the measurement with the fewest number of significant figures.
In other words: Round to the fewest number of significant digits.
Express each answer to the correct number of significant figures.
* 4.22 m x m =  4.47 m (3 SF’s)
* 2.4 g/mL  mL =  38 mL (2 SF’s)

26. Direct Proportion
As one variable increases, the other variable also increases.

27. Inverse Proportion
As one variable increases, the other variable decreases.