Density + Sig Figs

Exact Numbers

• counted numbers

• unit conversions in the same system (ex: 1 kg-1000g)

• not considered when trying to figure how many sig figs should have

Measured Numbers

• use measuring devices

• device used → how many digits we record

• thermometer (temp)

• graduated cylinder (vol)

• burette (vol)

• scale (mass)

4 rules of 0’s in sig figs

1. non zero numbers are ALWAYS significant

2. Leading zeros are NEVER significant

3. Captive Zeros are ALWAYS significant

4. Trailing zeros are significant when there’s a decimal point

5. All digits in the coefficient of a scientific notation are significant

Rules for significant figures in adding + subtracting

• calculated answer should have the same # of digits after decimal point as the # in the calculation with the LEAST digits after the decimal

Rules for significant figures in multiplying + dividing

• calculated answer must contain the same # of SF as the # in the calculation w. the LEAST SF’s

Rules for significant figures in Averages

• Apply rule of Addition for averages because counting numbers are not significant

Intensive property

• only depends on the type of property but not on how much there is

ex: density…iron’s density is the same regardless of shape/size

when volume changes, mass changes proportionally

Extensive Property

• depends on the amount

ex: mass, volume

how would you get the volume of an object like metal

• measure the volume of water in a cylinder or other tool

• measure the amount of volume after the object is put in

Subtract water w. metal - water

Accuracy/Percent Error

• compare experimental value to known value (true value: provided or easily looked up)

• 0-100 |experimental-true|/true x 100

• use rule of division

• expressed as a %

precision

• compare closeness of your values to one another

• how repeatable are data points to one another

• average deviation/average value x 1,000 (ppt: parts per thousand)

• 0 (little deviation) - 1,000 ( a lot of deviation)

• to find deviation: density of each trial-average density

Physical property

• The composition of the substance does not change in measuring either the
  mass or the volume and hence the density

is temperature intensive or extensive

• extensive because heating causes expansion and cooling causes contraction

if a series of liquids are places on top one another, what liquid is the most dense

• the one at the bottom