Measurement & Conversions

1. Measurement & Conversions Get ready for some math!!!!

2. Scientific Notation • Used for very large or very small numbers • All numbers are represented by a number between 1 and 10 multiplied by a power of 10 • The number of places the decimal point has moved determines the power of 10. • If the power is positive, the decimal point will move to the • If the power is negative, the decimal point will move to the left

3. Measurement • Measurements and calculations allow for some of the properties of substances to be determined (mass, density) • Scientific Notation is often used because measurements in chemistry can be very large or very small

4. Convert the following numbers to scientific notation 24500 356 0.000985 0.222 12200

5. Convert the following scientific notation numbers to regular numbers 4.2 x 103 2.15 x 10-4 3.14 x 10-6 9.22 x 105 9.57 x 102

6. Significant Figures • All measured quantities are generally reported in a way that the last digit is UNCERTAIN. • All other digits are considered SIGNIFICANT.

7. Rules for Sig Figs • Nonzero digits are always significant. 22.6 kg has 3 significant figures 453.9 m has 4 sig figs • Zeros between nonzero digits are significant. 20.3 kg has 3 sig figs 87009 L has 5 sig figs

8. Rules for Sig Figs cont’d • Zeros in front of nonzero digits are not significant (they simply are decimal place holders) 0.0009876 has 4 sig figs 0.0008 has 1 sig fig • Zeros both at the end of a number and to the right of a decimal point are significant 85.00 kg has 4 sig figs 9.0700000000 has 11 sig figs

9. Rules for Sig Figs cont’d • Zeros both at the end of a number but to the left of a decimal point may not be significant. If a zero has not been measured or estimated, it is NOT SIGNIFICANT. A decimal point placed after zeros indicates that the zeros are significant. 2000 m has one significant figure 2000. m has four sig figs

10. Rules for Calculations • Multiplication or Division – • Final answer has the smallest # of sig figs • DO NOT ROUND UNTIL THE VERY END. • Addition or Subtraction – • Result cannot have more decimals places than the unit with the smallest # of decimal places

11. Rules for Calculations • If a calculation has both multiplication (or division) and addition/subtraction, round after each operation. • EXACT VALUES HAVE UNLIMITED SIG FIGS • 2 MOLECULES ARE 2 MOLECULES. = COUNT VALUE

12. SI Units

13. Prefixes

14. Conversion in Metrics K H D M D C M

15. Find the number of m in 2.35 km.

16. Find the number of km in 756 m

17. Conversion Factors • A ratio that is derived from the equality of two different units that can be used to convert from one unit to the other • 5 dozen eggs = how many individual eggs? CONVERSION FACTOR 1 dozen = 12 individual 5 dozen x 12 individual = 60 individual eggs 1 dozen

18. How many g is 8503 mg?

19. How many mm is 0.331 km?

20. Derived Units • Units derived from the seven base units • Volume= l x w x h (m3) • Volume • The most common used unit for volume is cm3. • 1cm3 = 1ml • 1000cm3 = 1dm3 = 1000ml = 1L. • density • Density is the ratio of the mass of an object to its volume • Density = mass volume

21. Precision vs. Accuracy • Accuracy- the accuracy of a measurement is how close the measurement is to the true or actual value • Precision – is how closely several measurements made agree with one another.

23. Percent Error Analysis • % Error = Measured value – Accepted Value Accepted value