Dimensional Analysis: Lesson 6
Want to know how to convert km/hr to mi/hr?
Just like converting between curencies in Chemistry it is usually necessary to convert between units
This process is called
Dimensional Analysis
Steps:
- Find the unit equality
- Find the conversion factor
- Apply conversion factor
- Cancel units
Example: 3 600s = 1 hour
(2.4 hr) (3600s/ 1hr) = 8640 s
Example:
What is 100km/hr in m/s?
1 km = 1000 m
1 hr = 3600s
(100 km/hr)(1000m/1 km)(1 hr/ 3600s) = 27.8m/s
Example:
How many seconds are in a day?
~ Kelly Bui
LESSON 5 Scientific Notation! (Say whaaat?)
Scientific Notation & S.D.
- Accuracy and precision is very important in science
- Important to communicate this accuracy carefully
- Calculators = not smart enough to decide what is/what is not precise
- Scientists have est. rules for rounding off extra digits; YOU MUST FOLLOW THEM!
(π r^2)(h) -> π (0.8)^2(13.2) = 26.540174... 8 SDs present
Significant Digits
- Non-zero digits are always significant
- If zero is a place keeper, it is generally NOT significant
ie. 0.0031
- Any numbers to the left of a decimal point are SIGNIFICANT
ie. 2.00, 23.05, 13.900
- Zeros after another number are SIGNIFICANT
ie. 3.000, 0.00000120, 3.014, 1.120
- When adding or subtracting round to the least precise number
ie. 7.4212 - 3.54 = 3.8812 -> 3.88
12.3 + 10.771 = 23.071 -> 23.1
- When you multiply or divide, round to the number with fewest SDs
ie. 2.5 x 5.55 = 13.875 -> 14 1.33421 x 19.531 = 26.058434551 -> 26.058
- Constants (π, G, ect) on your data sheet have infinite SDs
Scientific Notation
- Used if we need to write the number 1000 with only 2 SDs
- Used if we want to write the number 22 billion 1 hundred million w/o taking up an entire line
> ie. 22,100,000,000
= 2.21 x 10^10
= 2.2 x 10^10
= 2.210 x 10^10
- Shows really big or really small numbers easily
- Makes use of power of 10
Calculators
- Your calculator has funtions that you can use easily
- EXP, EE, X10 > 3.24 E-5 RIGHT :)
> (3.24)(10^5) WRONG :(
SIGNIFICANT
DIGITS ♥ ✔
(dang they're cool)
~ kim nipp
LESSON 4: SI System and Percent Error
Prefixes Used with SI Units
- We can put a prefix in front of the unit and change the power of it.
- tera (T): 10^12 - femto (fm): 10^-15
-giga (G): 10^9 - pico (pi): 10^-12
-Mega(M): 10^6 - nano (n) 10^-9
-kilo(k): 10^3 - micro :10^-6
- hecto(h): 10^2 - milli (m): 10^-3
- deca (da): 10^1 - centi (c): 10^-2
SI Prefixes
- the SI System uses many prefixes to represent very large or very small numbers
- Don't use scientific notation and prefixes together! It becomes very confusing
Experimental Accuracy
- In general the maximum accuracy of any measurement is one half of the smallest division of the measuring device
- A ruler with measurements of the millimeters has a maximum accuracy of positive or negative 0.5mm
Expressing Error
- Error is a fundamental part of science
- There are usually 3 reasons for error:
> physical errors in the measuring device
> "sloppy" measurements
> changing ambient conditions
Calculating Errors
- Two different possibilities: Absolute Error, Percentage Error
Absolute Error
- Measured value minus accepted value
- Absolute Error = Measured - Accepted
Percent Error
- Most common
- Percent Error = [Measured-Accepted/Accepted] x 100
A Joke and a clip about chemical reaction
LESSON 1 BALANCING & WORD EQUATIONS
WHAT ARE PHASE SYMBOLS?
They are subscripts that indicate the phase of the chemical, such as
eg. Al(s) - solid , H2O(l) - liquid , H2(g) - gas , AgNo(aq) - Aqueous
CHEMICAL EQUATIONS FROM WORD EQUATIONS
(
Solution means something that is dissolved in water and is therefore an
aqueous phase.)
1) In chemical equations it must include phase symbols and a balance of the equation
2)
Diatomic molecules: are elements that when on its own in an equation will always consist of 2
atoms (these elements form a seven on the periodic table)
eg. H2 , N2 , O2 , F2 , CI2 , BR2 , I2
3)
Polyatomic molecules:
P4 , S8
Examples:
1)
A solution of barium phosphate is mixed with aqueous sodium sulphate to yield solid barium sulphate and aqueous sodium phosphate.
Ba3(PO4)2 (aq) + 3 Na2SO4 (aq) ~> 3 BaSO4 (s) + 2 Na3PO4 (aq)
2)
A solution of aluminum chloride , carbon dioxide and water can be prepared mixing pure aluminum carbonate with a solution of hydrochloric acid.
Al2(CO3)3 (s) + 6 HCI (aq) ~> 3 CO2 (g) + 2 AlCI3 (aq) + 3 H2O
9.13.10
Example: 
