Chem 100: Chemistry and Units- measurements and calculations

I'd recommend still reviewing notes!

Parameter

• Length

• Mass

• Time

Unit

• Metre

• Kilogram

• Second

Symbols

• Metre (m)

• Kilogram (Kg)

• Second (s)

• Amount of substance mole (Mol)

Temperature

• Celsius (°C)

• Fahrenheit (°F)

• Kelvin (K)

Prefixes

Used to adapt the size of a unit to the size of an object.

Precision

Refers to variability among repeated measurements of the same quantity

Accuracy

Closeness of measured valued to the correct value.

% Error

Difference between the measured and known value.

What are the basic rules in assigning numbers of Sig. Figs.?

1. All non-zero digits are significant (1.23)

2. Zeros between non-zero digits are significant. (2.04)

3. Constants of numbers used for counting have an infinite number number of sig. figs. (132.000)

4. Zeros to the left of the first non-zero digit are not significant (0.0054) 2 sig.fig.

5. Zeros that fall both at the end of a number and to the right of the decimal point are significant (0.0200) 3 S.F.

6. When a number ends in zeros that are to the right of a number they are significant only if the number is written with a decimal point.

   • Without a decimal point, it’s not significant

7. Certain values used in conversion factors which are exact have an infinite number of Sig. Figs. (1L=1000mL ; 1in=2.54cm)

Steps to determine the correct number of sig. figs. in mathematical operations.

1. For Multiplication/Division the result should have the same number of Sig. Figs. as the number with the least number of Sig. Figs.

2. For Addition/Subtraction there should be the same number of decimal places in the answer as there are in the number with the least number of decimal places.

3. Exact Conversion Factors in a mathematical operation do not affect the number of Sig. Figs. of the result of the operation.