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Warmup (5 min)

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Have your packet out!

1. 103 / 10-4 =

2. (1019) (102) =

3. Round 5.678 to 3 digits

4. 16 =

3.0

5. (56.8)(6.0) =

All answers will be discussed during lecture, but see if you can do these NOW!

*You will need a calculator today.

Introduction to Quantitative ChemistrySignificant FiguresRoundingScientific Notation

Take notes on Introduction to Quantitative Chemistry Notes/Problems and ALSO on a separate sheet of paper

Quantitative ObservationsQualitative Observations

Involves measured Involves general

values and numbers observations without

examples? measurement

Ex. It is 36.7⁰C outside today

The river is 31.5 m deep

The cheese costs $4.25 per pound

Ex. It is hot today

The building is tall

I do not weigh a lot

What are significant figures? (‘sig figs’)

“Important numbers”?!?!?!

11.818 sec vs 12.000 sec? Who cares?

In swimming/track, the stopwatch is VERY precise

- There is a reason for placing zeros in a measured value when they are not important for calculation purposes. Significant does not mean IMPORTANT.
- The number of sig figs reported in a value implied the degree of precision of the instrument used to make the measurement.

Which digits are significant?

0.00450600

3

2

1) 1908

2) 0.0025

3) 15.9

5

5

1

4) 0.7040

5) 340.06

6) 140. vs 140.0 vs 140

0.00805

100800

4.000100

2000

3

4

7

1

Pick your ocean

Skip zeros, find first 1-9 digit

Count all digits, even the zeros

Round these values to four significant figures:

- 0.0587920b. 1670.48564 c. 3450824
a. 0.05879 b. 1670. c. 3451000

Rules for Rounding:

- If the digit to be removed is < 5, the preceding digit remains unchanged
Ex. 25.44 rounds to 25.4

- If the digit to be removed is ≥ 5, then the preceding digit is increased by 1
Ex. 25.46 rounds to 25.5

16 = b. (56.8)(6.0) =

3.0

c. 590.0 = d. (324.6)(815.991) =

611

340

5.3

0.966

264900

Rules1) To see how many sig figs to use in your answer, look at the # sig figs in the values given to you in the problem.2) If the starting values have different numbers of sig figs, use the lower # of sig figs

7.442

- 7.429

0.013

c. 16.82

+ 3.2257

20.0457

20.05

Perform the indicated calculations on the following measured values, giving the final answer with the correct number of significant figures.

- 2.86
+ 3.4921

+ 1.3

7.6521

7.7

Round to the last digit that they have in common. I will sometimes break this rule for one reason or another…… just go with it.

Scientific notation is used to simplify very small or large numbers. It expresses a number as:

- a number between 1 and 10 and
2) a power of 10

Ex. 6780 6.780 x 103

PART 1: Identifying correct scientific notation

Which of these numbers are/are not written in correct scientific notation?

3.57 x 10-8 4.23 x 10-275.3 x 10-10

2.92 x 109 0.00345 x 104

Gross!

Move the decimal to the right, exponent = negative

0.00032 3.2 x 10-4

PART 2: Changing a value into scientific notation

Move the decimal to the

left, exponent = positive.

32000 3.2 x 104

a. Change 0.00045 to scientific notation

b. Express 1.28 x 10-5 in standard (regular) notation

a. 4.5 x 10-4b. 0.0000128

Put the following values into scientific notation using 3 significant figures:

1) 0.00980 3) 25900.0

2) 10.5 4) 0.043

2.59 x 104

9.80 x 10-3

1.05 x 101

4.30 x 10-2

5 x 10-3

4

0.0015

1 x 106

5.05 x 103

0.00000335

220000

2.5 x 10-4

Take 3 minutes to fill in the missing pieces from this chart

PART 3 Multiplying, dividing numbers in scientific notation

Ex A: (2.5 x 105)(2.0 x10-2)

= 5.0 x 103

Ex B: 6.8 x 107

1.7 x 103

****make sure to group values in your calculator using parenthesis!!!!!!!!!!!!!!

= 4.0 x 104 (add a zero bc you need 2 sig figs)

( )

1.78 x 10-11

7.37 x 103

Do the last 5 on your own. I will give answers in 3 minutes.

1. (8.31 x 10-1)(2.14 x10-11) = 2. (3.51 x 10-3)(2.10 x106) =

3. 9.1 x 104 =4. (5.9 x 104) =

11 x 108 (7.2 x 10-3)

5. (5.5 x 104) (1.1 x106) =

(3.2 x 108)

8.2 x 106

8.3 x 10-5

1.9 x 102