**Scientific Measurement**

**Significant Figures!**

**Accuracy**

Adding and Subtracting with sig figs

Measurement

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.

**Precision**

A measure of how close a series of measurements are to one another

Bullseye!

Follow the Rules!

**1**

**2**

**3**

**4**

**5**

**6**

Sometimes you’ll be asked to write your numbers to a particular number of sig figs.

**Error**

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

**Example**

True value = 42 cm

You got = 41.5 cm

**41.5-42 = -0.5**

**% Error**

**l error l**

accepted value

**x100%**

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

counting

exactly defined quantities

22 people in class (not 21.98)

Multiplying and dividing with sig figs

24.7

1 2 3

0.0071

1 2

40.79

1 2 3 4

43.00

1 2 3 4

27,210

1 2 34

(Experimental)

Use scientific notation! Don't leave off numbers!

578492 g written to 3 sig figs is:

5.78 x 10 g NOT 578 g

5

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

14.12+ 7.3=21.42

=21.4

100cm=1m

Round the answer to the same number of sig figs as the measurement with the lower number of sig figs

7.55

x0.34

_______

2.567=2.6

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)

Table 3.1

Length

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)

Volume

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)

1mL=1cc

Mass

SI unit=kg

gram (g) is the base;

1 kg = 1000 g

Weight

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

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

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