9/10 Volume, Density, Sig-Figs, P v A

Volume:

  • 1 cm3 = 1 mL - this is a one to one conversion

  • 1 L = 1000cm3=1000mL

  • Look at slides of equations did in class

Density:

  • Allows conversion between mass and volume of a substance

    • D= M/V

  • Most commonly used units are g/ml for liquids and solids, and g/L for gases

  • Matter with higher density settles at the bottom and matter with lower density floats

    • Solid water is less dense than liquid, usually liquids are less dense than solids

  • Look at slides for in class problems

Significant Figures:

  • The certainty in measurement is limited by the instrument to make the measurement

    • not all instruments are created the same

    • ex: An orange is weighed and it weighs 249g on the grocery scale but 249.201g on a laboratory scale

    • There is uncertainty in both measurements

  • The last number is always uncertain so 9 and 1 in the oranges

  • The digits in measurement both certain and uncertain are call significant figures

Rules of Sig Figs

  1. All non-zero digits and zeros between non-zero digits are significant

    • ex: 1005 (4 sig-figs) 7.03 (3 sig-figs)

  2. Zeros at the beginning of a number are never significant (leading zeros)

    • 0.02 (1 sig-fig) 0.0026 (2 sig-figs)

  1. Zeros at the end of a number are significant if the number has a decimal point and are no significant if the number has no decimal point (trailing zeros)

    • 0.0200 (3 sig-figs) 3.0 (2 sig-figs) 560 ( 2 sig-figs)

Sig-Figs:

    Adding and Subtracting:

  • When adding or subtracting values, your answer should have the same number of decimal places as the value that has the fewest decimal places

  • When the answer contains more than the correct number of sig-figs, it must be rounded off

    • 20.42+1.322+83.1=104.843 → 104.8

    Multiplying and Dividing:

  • When multiplying or dividing values, your answer should have the same number of sig-figs as the value that has the fewest sig figs

  • When the answer contains more than the correct number, it must be rounded off

    • (6.221 cm)(5.2 cm)= 32. 3495 cm2 → 32 cm2

Precision vs Accuracy:

  • Precision: How close a set of measurements are to each other

    • The closer they are the more precise

  • Accuracy: How close a measurement is to the true value