Transcript Measuring with Precision

How Do You Measure Precisely in the Lab?
• When using equipment in the lab, you should
always estimate one digit past the shown
increments.
estimated
2.54 cm
What is the length of this block? _______
Important Information
 Unit 3: Measuring up Matter: Scientific
Measurement Quiz on 9/24 (A) or 9/25 (B)
 Unit 3: Measuring up Matter: Scientific
Measurement Test on 9/26 (A) or 9/27 (B)
 Homework: Data Analysis and Graphing Notes (due
9/20 (A) or 9/23 (B))
How Do I Round My Values When
I Am Doing Calculations in the Lab
There are rules about calculations, rounding,
and significant figures. First, you must
determine the number of significant figures in
your measurements.
43.5
3 significant figures
______
(all non-zero numbers are significant)
8022
4
______
significant figures
(sandwiched zeros are significant)
0.0006
1
______
significant figure
(lefty zeros aren’t significant – sorry lefties )
1000
1
______
significant figure
(righty zeros ONLY COUNT IF THERE’S A DECIMAL)
100.00
5
______ significant figures
(righties count because there is a decimal)
6.022 x
23
10
4
______
significant figures
(only consider the front number in scientific notation)
Tip: If an answer is ambiguous, convert it to scientific notation.
Answer: 1066  need to round to 2 sig figs  1.066 x 103  1.1 x 103
How Do I Round My Values
When I Am Doing Calculations in the Lab
Now you try!
Write how many significant figures are in each of these
values:
4 0.0052 g ____
2 82000 s ____
2 6.19 x 101 years ____
3
3.705 mL ____
200.0 kg ____
3 0.0309 m ____
3 7.01 x 1023 atoms ____
4 60500 L ____
3
0.7410 km ____
4 2100 mg _____
2 2.09 x 10-5 g ____
3 3090.0 ⁰C ______
5
How Do I Round When
I Am Multiplying and Dividing?
When measurements are multiplied or divided, the answer
can contain no more SIGNIFICANT FIGURES than the least
accurate measurement.
Example:
21 (2 sig figs)
x 4.50 (3 sig figs)
94.5  Round to 2 sig figs (least number)  95
How Do I Round When I Am Adding and
Subtracting?
When measurements are added or subtracted, the answer
can contain no more DECIMAL PLACES than the least
accurate measurement.
Example:
38.0
(1 decimal place)
+ 6.56 (2 decimal places)
44.56  Round to 2 DECIMAL PLACES (least number)  44.6
Now You Try!
98.0 x 0.05 = ________
4.98 x 108 x 3.1 = 1.5
___________
5
43.9
x 109 54.2 – 10.32 = ________
52
569
40.4
7300/140.0 = _______ 567 + 1.782 = ______________
102 x 0.396 = _________
-4
-9
4 x 10 6.32 x 10-4 / 2.0 = 3.2
x 10-4
0.62 – 10 = ________
0.0004 x 1.002 = __________
________
5
2 x 10
9000 / 0.043 = ______________
604
10789 x 0.0560 = _____________