1. Which tool on the left could you be the most precise with?
1.3 Notes Continued…
buret
How does the precision of measurements affect the precision of scientific calculations?
Which tool on the left could you be the most precise with?
Graduated
cylinder
buret

2. Limits of Measurement Precision
Precision is a gauge of how __________ a measurement is.
Which clock is the most precise…how can you tell?
exact
Digital clock – measuring with more digits!

3. Limits of Measurement
The digits involved in your measurement are called __________________ __________________ (sig figs)
Sig figs are all the digits that are __________ in a measurement, plus the last digit that is _______________.
significant
figures
known
estimated

4. The number of significant digits depends on how the measuring device is calibrated…
The first meter stick can report _____ sig fig
The second meter stick can report _____ sig figs
The third meter stick can report _______ sig figs 1 2 3

5. Sig fig Rules All nonzero digit are considered significant figures…
576 meters =
Zeros in between nonzero digits are considered significant figures…
5007 meters =
Zeros that aren’t shown when a number is in scientific notation do not count as sig figs
5000 meters = 5 x 103 meters =
meters = 7.2 x 10-4 meters=
3 sig figs
4 sig figs
1 sig fig
2 sig fig

6. Sig fig Rules
Zeros at the end of a number with a __________ are there because they were measured…they count as sig figs
Example: You measured 50.0 meters exactly, as opposed to 50.1 meters
50.0 meters = 5.00 x 101 meters =
decimal
3 sig figs

7. Limits of Measurement
The precision of a calculated answer is limited by the _____________ precise measurement used in the calculation.
least
Calculated
answer

8. Limits of Measurement Mass = 34.73 grams (sig figs? ) 4
Volume = 4.42 cubic centimeters (sig figs? )
If the least precise measurement in a calculation has three significant figures, then the calculated answer can only have at most _________ significant figures.
After rounding, our final answer is… 4 3
three
Use this 7 to round
Calculated
answer
Least precise
measurement
7.86 g/cm3

9. Limits of Measurement The same applies for adding and subtracting..
Students measured two masses using two different tools…
1.52 grams (sig figs? )
1.8 grams (sig figs? )
What is the total mass? This should be rounded to…
1.52 g
_+1.8__g
3.32 g (calculated answer)
After rounding, our final answer is… 3 2
Least precise
measurement
3.3 g

10. Limits of Measurement Accuracy
Another important quality in a measurement is its accuracy. Accuracy is the ______________ of a measurement to the expected or __________ value of what is being measured.
For example, suppose a digital clock is running 15 minutes ___________. Although the clock would remain precise to the nearest second, the time displayed would not be accurate.
closeness
true
ahead

11. If the bull’s-eye represents the true value, which dart board represents higher accuracy?
On the left – closer to target

12. Measuring Temperature
A ___________________ is an instrument that measures temperature, or how hot an object is.
thermometer
At what temperature on the celsius scale does….
water boil?
water freeze?
At what temperature on the kelvin scale does…
100°C
0°C
373 K
273 K

13. Practice: Convert 15 °C to kelvin
So both the Kelvin and Celsius scales have _______ divisions between water’s boiling and freezing point
100
°C = K - 273
K = °C
Practice: Convert 15 °C to kelvin
K = 15°C
= 288 K

14. Assessment Questions
A student measures the volume and mass of a liquid. The volume is 50.0 mL and the mass is g. What is the correct calculated value of the liquid’s density? (A calculator reads )
1.6 g/cm3
1.57 g/cm3
1.569 g/cm3
g/cm3

15. Assessment Questions
2. What is the difference between precision and accuracy?
How exact a
measurement is
How close the
measurement
is to the true value

16. 3. How can you convert the temperature of 32 °C to kelvin?
Assessment Questions
3. How can you convert the temperature of 32 °C to kelvin?
add 32
subtract 32
add 273
subtract 273