Units of Measurement

Chemistry and You

Using SI Units

* All metric units are based on multiples of 10. As a result, you can convert between units easily.

Content Background

Si Units of distance and time-In 1790, with the establishment of the metric system, the French became the 1st to adopt measurement standards that were close to being precise. The meter was defined as one ten-millionth of the distance fom the equator to the North Pole along the meridian that passes through Paris. The second was defined as /86,400 of the averagge day. These have since become more precise. The meter is now defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second. The second is now defined i terms of the number of cycles of radiation given off by a specific isotope of the element cesium.

**Chapter 3.2 Units of Measurement**

Stair Step Method

Kilo=km, kl, kg 10 (3) =1,000

Hecto=hm,hl,hg 10 (2)=100

Deka=dkm,dkl,dkg 10 (1)=10

Base= Meter-Length, Liter-Volume, Gram-Mass =1

deci=dm,dl,dg 10(-1)=0.1 or 1/10

centi=cm,cl,cg 10(-2)=0.01 or 1/100

milli=mm,ml,mg 10 (-3)=0.001 or 1/1000

Does the forecast show measurements?

No, the forecast shows only numbers. A measurement contains both a number and a unit.

The International System of Units (SI), after the French name Le Systeme d'Unites.

There are 7 SI base units, from these all other SI units of measurement can be derived.

1ml=1cc=1cm (3), commonly used when prescribed medicine for infants.

King Henry Died By Drinking Chocolate Milk

What does the prefix kilo mean?

1,000

What does the prefix milli mean?

0.001 or 1/1000

What is the largest unit shown?

Kilo

Temperature Scales

Temperature: a measure of how hot or cold an object is.

*Scientists commonly use two equivalent units of temperature, the degree Celsius and the Kelvin

Celsius Scale: sets the freezing point of water at 0 degrees Celsius and the boiling point of water at 100 degrees Celsius.

Kelvin Scale: the freezing point of water is 273.15 Kelvins (K) and the boiling point is 373.15 degrees celsius. A change of 1 degree on the Celsius scale are equivalent to 1 Kelvin on the Kelvin scale.

The zero point on the Kelvin scale, 0 K, or absolute zero is equal to -273.15 degrees C.

SOOOO....

K=degrees C + 273.15

degrees Celsius= K-273.15

Example Problems

Normal human body temperature is 37 degrees Celsus. What is this temperature in Kelvins?

K= C + 273.15

K= 37+273.15=310.15K

The element silver melts 960.8 degrees C and boils at 2212 degrees celsius. Express these temperatures in Kelvins.

K= 960.8 + 273.15= 1233.95 K

K= 2212 + 273.15 = 2485.15 K

Liquid Nitrogen boils at 77.2K. What is this temperature in degrees Celcius?

Degrees C= 77.2 K-273.15=-196.15 degrees C

Do These on Your Own

At 3 kilometers above sea level, ater boils at 90 degrees Celsius. What is this temperature in Kelvins?

The warmest temperature ever recorded on Earth is 58 degrees C, recorded on Libya in 1972. What is this temperature in Kelvins?

The coldest temperature ever recorded on Earth is -89 degrees C, recorded in Antartica in 1983. What is this temperature in Kelvins?

The effective surface temperature of the sun is 5778 K. What is this temperature in degrees Celsius?

Answers

K=C+273

K=90C+ 273=363 K

K= 58 C+ 273= 331K

K=-89 C+ 273= 184 K

C=K-273

C=5778-273=5505 degrees C

Density

Density: the ratio of the mass of an object to its volume. Because density is a ratio and does not depend on the amount of matter, it is an intensive property.

Density = Mass/Volume

Units:

D=Density=gram/liter

M=Mass=grams

V=Volume=Liters

*Density is an intensive property that depends only on the composition of a substance, not on the size of a sample.

Green Chemistry

Density Practice Problems

A copper penny has a mass of 3.1g and a volume of 0.35 cm(3). What is the density of copper?

D=3.1g/0.35cm (3)= 8.86 g/cm(3)

A student finds a shiny piece of metal that she thinks is Aluminum. In the la she finds the metal has a volume 245 cm (3) and a mass of 612g. Calculate the density.

D=612g/ 245 cm(3)=2.50g/cm(3)

M=DV

V=M/D

A bar of silver has a mass of 68.0g and a volume of 6.48 cm(3). What is the density of silver?

D=68.0g/6.48cm(3)=10.5g/cm(3)

Chemsytery Ending

Why is it important for scientists to use standard units to report measurements?

It allows scientists to understand measurements that other scientists have made.

To measure the volume of a solid use LxWxH