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Transcript of Scientific Measurement
Adding and Subtracting with sig figs
a quantity that is both a number and a unit
Fundamental to experimental sciences
Helps make very big or small numbers easier to work with.
A measure of how close a measurement comes to the actual or true value of what you are measuring.
A measure of how close a series of measurements are to one another
Follow the Rules!
Sometimes you’ll be asked to write your numbers to a particular number of sig figs.
The difference between what you got and what you were supposed to get.
experimental value - accepted
What you got
What you were supposed to get
True value = 42 cm
You got = 41.5 cm
41.5-42 = -0.5
l error l
If it isn't a zero it's significant.
Every nonzero in a reported measurement is assumed to be significant.
Zeros in between nonseros are significant
zeros appearing between nonzero digits are significant.
Zeros on the far left are just
placeholders (not significant)
Leftmost zeros appearing in front of nonzero digits
are NOT significant.
The zeros at the end of a number, after the decimal point are always significant.
Zeros at the end of a number and to the right of a decimal point are always significant.
Zeros at the end of a number with no decimal point are just placeholders.
Zeros at the rightmost end of a measurement that lie to the left of an understood decimal point are not significant if they serve as place holders to show the magnitude of the number.
2 ways you can have unlimited sig. figs
exactly defined quantities
22 people in class (not 21.98)
Multiplying and dividing with sig figs
1 2 3
1 2 3 4
1 2 3 4
1 2 34
Use scientific notation! Don't leave off numbers!
578492 g written to 3 sig figs is:
5.78 x 10 g NOT 578 g
Add or subtract as normal
Round the number of sig figs to the same number as the one with the least number after the decimal point
Round the answer to the same number of sig figs as the measurement with the lower number of sig figs
Measuring with SI Units
The standard units in science are the metric system (base 10)
The International System of Units (abbreviated SI) is a revised version of the metric system
The 5 SI base units in Chemistry are the meter (m), kilogram (kg), Kelvin (K), second (s), and the mole (mol)
SI unit: meter (m)
For larger or smaller measurements, use prefixes!
Common metric units of length include the centimeter (cm), meter (m), and kilometer (km)
Common unit is the liter (L), a non-SI unit
1 L=the volume of a cube that is 10 cm along each edge (10cm x 10cm x 10cm)
Common metric units of volume are the liter (L), milliliter (mL), microliter (uL), ans cubic centimeter (cc, cm^3)
gram (g) is the base;
1 kg = 1000 g
Weight and mass are two different things entirely, even though they are used interchangeably.
Weight is a force that measures the pull of gravity on a given mass
Mass is the measure of quantity of matter
Temperature is the measure of how hot or cold an object is.
Temp determines the direction of heat transfer. Heat flows from warmer to colder objects
SI unit=Kelvin (K), although the Celsius (C) scale is used often as well
Possible to convert between the two units:
K= C + 273
C= K - 273
Kelvin does not have any negative temperatures
Absolute zero= 0 K
Equal to -273.15 C
Nothing can be colder than absolute zero
Energy is the capacity to do work or produce heat
Common units are the joule (J), which is the SI unit, and the calorie (cal)
1 cal is the quantity of heat needed to raise the temperature of 1 g of pure water by 1C
Conversion between cal and J:
1 J = 0.2390 cal
1 cal = 4.184 J