Chemistry July 8, 2008 1st Qtr

SIGNIFICANT NUMBER in CALCULATIONS
> A calculated answer can't be more precise than the measuring tool
> A calculated answer must watch at least precise measurement
> SF - needed for final answers from:
1. Adding/Subtracting
2. Multiplying/Dividing

EXACT NUMBERS in CALCULATION
1000 meters in a kilometre
60 seconds in a minutes

These numbers are examples of exact numbers. These are definite, not measurements. A definite has infinite numbers of significant digits & will NOT affect the significant digits in the final answer.

ADDING & SUBTRACTING
The answer has the same decimal paces as the measurements with the fewer/fewest decimal places.

25.2 (has 1 decimal place) + 1.34 (has 2 decimal places)= 26.54
answer: 26.5 (1 decimal place)


Try it Yourself!
246.213 ml + 79.91 ml + 8786.268 ml= 9112.391 ml
answer: 9112.39 ml

Multiplying & Dividing
When 2 measurements are multiplied (or divided), the answers should contain as many significant digits as the less precise measurements (lower number of significant figures)
eg. 3.06*1.4=4.3 (COPY the LEAST # of significant figures) in this case it's 1.4, which has 2 significant figures

Try it Yourself!
9000*8576=77,184,000
answer: 8*10^7

Rounding Off Numbers
> when the question asks you to estimate
> an answer is different to obtain

Scientific Notation
> way of expressing really big or small numbers
> often used in 'scientific' calculations where the analysis must be very precise

2 parts:
N * 10^x
x - integer, positive (+) or negative (-)
N - Mantissa >=1 & <10

To change standard form to scientific Notation
->
e.g. 5,673,098
5.673098*10^6

Exponent is + -> greater than 1
- -> less than 1

e.g. 289,800,000
2.898*10^9

e.g. 0.000567
5.67*10^-4

To change SN -> SF
e.g. 0.0059*10^5
590
+ -> move to the right
- -> move to the left