Fundamentals of Chemistry. Unit One Scientific Method and Measurement. Scientific Method. Scientific Method : A way to Solve Problems. Steps of the Scientific Method Step 1: Identify the problem To begin the scientific process, a problem must be clearly and specifically identified.
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Fundamentals of Chemistry
Scientific Method and Measurement
Steps of the Scientific Method
Step 1:Identify the problem
To begin the scientific process, a problem must be clearly and specifically identified.
Step 2:Gather Information
Before setting out to find the answer to a scientific question, information must be gathered in the form of preliminary research.
Sources such as journals and scientific papers could be checked for existing information on the problem at hand.
Step 3: Form a Hypothesis
Once a problem or question has been recognized, a hypothesis or educated guess is constructed.
In an experiment, hypotheses are not “correct” or “incorrect”, they are supported or not supported by the data collected.
if a hypothesis has be tested repeatedly and not disproven it is known as a theory or postulate.
Theory answers the question “Why?”
(a theoryexplains what happened)
A rule of nature is known as a law.
Ex. Law of attraction and repulsion, Law of universal gravitation.
Lawanswers the question “what?”
(Law tells what happens)
Step 4: Experimentation and Observation – Used to test your hypothesis.
Data collected during this step needs to be organized and analyzed.
-2 types of data: Qualitative & Quantitative.
▪Qualitative made using the five senses
▪Quantitative made using instruments
**Think about qualitative as “what” and quantitative as “how much”
A controlled experiment contains only 1 experimental variable.
-Variable any factor affecting the outcome of an experiment.
▪Independent variable is set and controlled by the experimenter
(such as time)
▪Dependent variable changesbased on what is done to the experimental variable.
(such as plant growth)
Properly set-up experiments provide a control group as well as an experimental group.
-Control groups are set-up under “normal” conditions and are used to compare to the experimental groups.
Step 5: Draw Conclusions
interpretations of experimental results.
reference should be made to the original hypothesis.
Questions to think about in the conclusion may include:
*Was the hypothesis supported or not supported by the data?
*What were possible sources of error in the lab?
*What are some ways to improve the experiment?
*What are some questions yet to be addressed?
Sometimes an experiment
that “goes wrong” opens the
doorway to a new discovery.
Measurements and calculations should ALWAYS be recorded to the correct number of significant figures!
Example: Room temperature 25.4ºC
Suppose you were given temperature data for various points in Frederick from a variety of sources and the data looked like this: 23.232ºC, 25.2ºC , 26.1746ºC , 27.12ºC. When you calculate the average, how many sig figs should keep?
3 significant figures (25.4ºC)
1)Every Nonzero digit in a reported measurement is significant
• 56.6, 2.34 and 978 all have 3 sig. figs.
2)Zeroes between nonzeroes are significant.
• 6007, 50.89 and 5.708 all have 4sig. figs.
3)Leadingzeros appearing in front of nonzero digits are placeholders and not considered significant.
• 0.000091, 0.042 and 0.42 all have 2 sig.figs.
4) Zeros at the end & to the right of a decimal point are ALWAYS significant.
• 57.00, 2.030 and 7.000 all have 4 sig. figs.
5) Zeros at the end & to the right without a decimal point are NOT significant unless a careful measurement was actually made (which will have a decimal point after - 10.)
• 400, 4000 and 30000 all have 1 sig. fig.
When calculating the correct number of sig figs in an answer, perform all of the calculations first then round the final answer.
round to the same number of decimal places as the measurement with the least number of decimal places.
3.451 + 1.41 + 2.072 = 6.933
6.93 (2 dec.)
7.982 + 1.02 + 2.1 = 11.102
11.1 (1 dec. )
3.45 – 1.1 = 2.35
2.4 (1 dec.)
round the answer to the same number of significant figures as the measurement with the least number of significant figures.
2.1 x 1.301 = 2.7321
2.7(2 sig figs)
4.02 x 2.945 = 11.8389
11.8(3 sig figs)
0.034 x 3.223 = 0.109582
0.11(2 sig figs)
A number written in scientific notation has two components:
-a coefficient and 10 raised to a power
must be greater than or equal to 1 and less than 10.
2.3 x 103
7.9 x 10-5
-Number between 1 & 10 = 5.4
-Move the decimal 5 times
5.4 x 105
5.4 x 10 = 54
54 x 10 = 540
540 x 10 = 5,400
5,400 x 10 = 54,000
54,000 x 10 = 540,000
5.4 x 105 = 540,000
positive power of ten, the decimal moves one place to the right.
Examples: 4.67 x 103 = 4670
2.71 x 104 = 27100
negative power of ten, the decimal point moves one place to the left.
Examples: 4.5 x 10-6 = 0.0000045
1.21 x 10-3 = 0.00121
*Remember: 10-1 = (1/10) = 0.1
3.2 x 10-1 = (3.2/10) = 0.32
-Examples of error: incorrectly calibrated equipment or uncertainty of equipment or uncontrollable human error
-all of the known digits in the measurement
(indicated by the markings on equipment)
-plus one digit that is estimated
(how far in between the markings).
-you would be estimating 1 decimal place!!
-the 25degrees in known and the .5is estimated.
(It was marked to the whole degree, so you can only estimate to the tenth.)
**Only estimate 1 place beyond what you can read for sure!!**
-Student 1 measures the length of the block and finds it to be 4.4cm.
-Student 2 measures the block of wood and determines its length to be 5.2 cm.
*Which measurement is more accurate?
Object is more than 12.3cm and just less than 12.4cm.
The smallest marking represents 0.1cm, so you estimate to the nearest 0.01cm.
The length of the object would be accurately and precisely recorded as 12.39cm.
The last digit is estimated, so, 12.31 – 12.39cm would be acceptable.
Object is more than 12cm and less than 12.5cm.
The smallest marking represents 0.5cm, so you estimate to the nearest 0.1cm.
The length of the object would be accurately and precisely recorded as 12.4cm.
The last digit is estimated, so, 12.1 –12.4 cm would be acceptable. (Up to 0.5 cm off)
Which ruler is more precise?
From 200.51g to 200.57g
0.1 gram (you can read it to the tenth’s place!!)
200.5 grams(hundreds, tens, ones, tenths marked)
(If you were buying a gold nugget, how many decimal places would you want to be sure of??)
A) 3.00gB) 3.000gC) 3g
ANSWER: B) 3.000g
A) 6.93kgB) 6.9kgC) 8 kg
Off by: 0.07kg 0.1kg 1kg
(analyzes the accuracy of the data)
Accepted value correct value (what the data should be – based on reliable research)
(What you are told it should be!!)
Experimental value value measured in lab
(what you measure or calculate it to be!!)
% Error =
Experimental value – Accepted valuex 100%
Negative % error Your answer is lower than it should be.
Positive % error Your answer is higher than it should be.
Accepted value – experimental valuex 100%
Experimental value = 4.4 cm (student measured)
Accepted value = 4.3cm (what you’re told it should be)
4.3cm – 4.4cm x 100% = -2.3 % error
Accepted value – Experimental valuex 100%
Experimental value= 15.7 cm (student measured)
Accepted value= 15.8cm(what you’re told it should be)
15.8cm – 15.7cm x 100% = 0.63 % error
Can be determined by three methods:
1. Formula: volume=ℓ x w x h
2. Measuring with a graduated cylinder
(units = mL)
3. Determined by water displacement
(units = mL = cm3)
* What is the volume in cm3 of a metal toy that displaces 7.5mL of water when dropped into a small container?
D = m/V
** Different prefixes are used for different amounts**
_____ ____ ____ 0.4 4 40 400
K h dk U d c m
5 50 500 5000 _____ ______ _____
used to convert from units
1) write down what is known (number & unit)
2) set up a conversion factor with the target end unit on top and one known unit on the bottom (if unit you are canceling is on top)
3) divide the product of the numbers in the numerator by the product of the numbers in the denominator
4) make sure that the final answer has the same number of significant figures as the number given.
#1. How many seconds are in 7 minutes?
known = 7 min.
conversion factor = 60 sec. / 1 min.
7 min x 60 sec = 420 sec = 420 sec
#2. How many cm are there in 5.2 meters?
known = 5.2 m
conversion factor = 1 m / 100 cm
5.2 m x 100 cm = 520 cm = 520 cm
#3. How many hours are there in 3 weeks?
known = 3 wk
conversion factor = 1 wk / 7 days
1 day / 24 hr
3 wk x 7 days x 24 hr = 520 hr = 520 hr
1 wk1 day 1