UNITS IN CHEMISTRY

TEMPERATURE Farenheit- Scale most commonly used in the US; based on cooling brine and body temperature (100 F was supposed to be about how warm a human body is) Celsius- Scale used in most of the rest of the world; based on water (Freezing is 0°C and boiling is 100°C)

TEMPERATURE Kelvin is another temperature scale! It was based on Celsius; the creator of the scale wanted a point where temperature did not exist, he found this to be at -273 °C. Water freezes at 273 K and boils at 373 K

TO CONVERT FROM K TO °C K= o C You MUST KNOW this one by heart Convert 25°C to K Convert 367K to °C

TO CONVERT FROM °C TO °F F=1.8(C) + 32 You DON’T have to memorize this equation but it is helpful to know Convert 115 °F to °C Convert 12°C to °F

CONVERT K TO °F There is no direct conversion between Kelvin and Fahrenheit You must use both scales or combine both equations! F=1.8(K - 273) + 32

EXAMPLES: Solve the following temperature conversions: 1.) 245°C to K 2.) 45°F to °C 3.) 386K to °C 4.) 102°C to °F 5.) 364°F to K

OTHER UNITS TO KNOW Mass- The amount of matter in an object (similar to weight, weight is based on gravity and the mass of an object) Volume- The amount of space something occupies (think of math!) Pressure- The amount of force acting upon an area

YES, YOU HAVE TO MEMORIZE THESE!! 1 centimeter=1cm=1/100 meter 1 millimeter=1mm=1/1000 meter 1 kilometer=1km=1000 meter Metric prefix review

UNIT CONVERSION A math skill which lets you change measurements in one unit into measurements in another unit You MUST learn it this way. We use it all summer

CONVERTING UNITS A conversion factor is the equivalence statement of two units Example – 1.00 inch = 2.54 cm can be written in two ways 2.54 cm Or 1.00 inch 1.00 inch 2.54 cm The correct choice is the one that allows the cancellation of the unwanted units

1. Put the known number and unit on the left 2. Leave a HUGE space. 3. Put the unknown unit on the right 4. Put an empty fraction in the space 5. Put the known UNITS on the bottom of the fraction. 6. Put the unknown UNITS on the top of the fraction. 7. Plug in numbers from a conversion factor: Solve and circle your answer.

EXAMPLES This is called the factor-labeling method or dimensional analysis Example – convert 9.00 inches to cm 9 in x 2.54 cm = 1 1 in Example – convert 5.00 cm to inches 5cm x 1 in = cm 22.9 cm 1.97 in

EXAMPLES: Convert each of the following: hr to min km to m cm to m x 10 8 min to days L to mL

UNCERTAINTY (COUNT VS. MEASURE..) If you measure the volume of water using a graduated cylinder, you have to ESTIMATE the last 0.1 mL’s. That is a MEASURED number

If you add your 10 nails together, you COUNT the nails and know exactly how many you have. There is no confusion in counting there is always confusion in measurement That confusion is called ‘uncertainty’ in science and ‘sig figs’ represent this uncertainty!