1. Chapter-2: Analyzing Data (measurements) Dr. Chirie Sumanasekera
CHEMISTRY Lecture_2
Dr. Chirie Sumanasekera
8/21/2018
TOPICS covered today:
Qualitative vs. Quantitative measurements
SI- units (Why do Scientists use SI Units?)
SI- Prefixes
Precision vs. Accuracy of measurements
Temperature measurements (Kelvin to Celcius conversions)

2. 1. Scientific Measurement
Quantitative
Qualitative
Use numbers to describe
Use description w/o
numbers
“Scientific”
(exact, unbiased, measurable, accurate)
“artsy”
(subjective, includes personal bias)
4 meters (m)
quite long
98°F
very hot
80 miles/per hour (MPH)
Driving fast

3. Table of Basic SI-Units:
2. Base units of SI System
In 1960, the International System of units was created and is known as the SI system.
Base Unit = A standard unit of measurement for a specific physical quantity
Table of Basic SI-Units:
Physical Quantity
Base Unit name
Abbreviation
Mass
kilogram kg
Length
meter m
Time
second s
Temperature
kelvin K
Electric current
ampere A
Amount of substance
mole
mol
Luminous intensity
candela cd

4. 3. SI Prefixes of Base Units
Symbol
Numerical value in Base Units
Power of 10 Equivalent

5. 4. Precision & Accuracy of Quantitative Measurements
It is of great importance that scientists measure their data with both PRECISION and ACCURACY!
Why?
If you do not have BOTH of these, you will get inaccurate data that will lead to a collection of errors in your analyses and and wrong conclusions.
Basically, everything you do will be MESSY and no one will be able to replicate your results from experiment, to experiment- including, you!

6. Good scientific measurements are both precise and accurate
Precision & Accuracy of Measurements
Good scientific measurements are both precise and accurate
Precision
Accuracy
How closely can a measurement be reproduced
How close the measurement is to the actual value
(1) Low accuracy
Low precision
(2) Low accuracy
High precision
(3) High accuracy
(4) High accuracy
Examples:

7. Ways to Increase Precision & Accuracy
Pay close attention to detail (be meticulous)
Take each measurement multiple times
Use equipment that is properly calibrated, functional and clean.
Use measuring instruments properly
Increase your sample size
Use the appropriate instrument for the measurement

8. Which measuring cylinder is best for each measurement?
Questions:
Which measuring cylinder is best for each measurement?
100ml A
50ml B
25ml C
10ml D
Answers: D A C
For measuring 8 ml?
For Measuring 72ml?
For measuring 18 ml?

9. Q: Which is the correct way to read the liquid volume in the measuring cylinder? What is the volume of liquid?
Answer: Is the correct way. The liquid volume is 87.5 ml

10. 5. Measuring Temperature _Base unit: Kelvin (K)
0F = 1.8(°C) +32
K = °C + 273
°C = (°F - 32)
We never use 0F scale in Chemistry but use Kelvin and Celcius. Remember the K = 0C equation

11. Q1: Convert 32°C in to Kelvin
Use the Equation below and plug in the numbers:
K = °C + 273
K =
K = 305
Q2: Convert 30°K in to Celcius (Centigrade)
K = °C + 273
30 = °C
30 – 273 = °C
– = °C
So, 30K is equal to -243 °C