Measurement in Chemistry Factor-Label Method

The Factor-Label Method At the conclusion of our time together, you should be able to: 1.Recognize a problem that can be solved with the factor label method 2.Transform a statement of equality into a conversion factor 3.Use the appropriate conversion factor in the correct way so that the labels cancel and the correct conversion is found

A way to solve math problems in chemistry Used to convert km to miles, m to km, mol to g, g to mol, etc. To use this we need: 1) desired quantity 2) given quantity 3) conversion factors Conversion factors are valid relationships or equalities expressed as a fraction and equal to one! The Factor label Method

Equalities State the same measurement in two different units length 10.0 in cm

Conversion Factors Fractions in which the numerator and denominator are EQUAL quantities expressed in different units but always equal to one. You can always multiply any equation by this equality and not change the quantity, just the units. Example: 10 in. = 25.4 cm Factors: 10 in. and 25.4 cm 25.4 cm 10 in.

For example: 1 km = 0.6 miles the conversion factor is Write conversion factors for 1 foot = 12 inches What conversion factors can you think of that involve meters?

Conversion Factors Conversion factors for 1 ft = 12 in There are almost an infinite number of conversion factors that include meters:

The Steps to Follow Now we are ready to solve problems using the factor label method. The steps involved are: Write down the given quantity and put it over Determine what conversion factors you will use to turn the given label into the needed label Multiply the given quantity by the appropriate conversion factors to eliminate units you don’t want and leave the units you do want Complete the math

How many kilometers are in 47.0 miles? (note: 1 km = miles) Factor label Example

The Steps to Follow Now we are ready to solve problems using the factor label method. The steps involved are: Complete the math with no rounding Make certain the sig figs are correct by rounding to the correct number of sig figs at the very end Don’t forget the order of operations when you complete the math: “Please Excuse My Dear Aunt Sally”!

How many kilometers are in 47.0 miles? (note: 1 km = miles) The final answer is 75.7 km # km = 47.0 x 1 km = 75.7 km Factor label Example

Summary The previous problem was not that hard In other words, you probably could have done it faster using a different method However, for harder problems the factor label method is easiest

More Examples 1. You want to convert U.S. dollars to Canadian dollars. If the exchange rate is 1 Can$ = 0.65 US$, how much will it cost? # Can$ = 100 US$ x 1 Can$ 0.65 US$ = Can$

The Factor-Label Method Let’s see if you can: 1.Recognize a problem that can be solved with the factor label method 2.Transform a statement of equality into a conversion factor 3.Use the appropriate conversion factor in the correct way so that the labels cancel and the correct conversion is found

Write conversion factors that relate each of the following pairs of units: 1. Liters and mL 1 Liter = 1000 mL 2. hours and minutes 1 hour = 60 minutes 3. meters and kilometers 1000 meters = 1 kilometer Learning Check

How many minutes are in 2.5 hours? Conversion factor Conversion factor 2.5 hr x 60 min = 150 min 2.5 hr x 60 min = 150 min 1 hr 1 hr By using dimensional analysis/factor-label method, the UNITS ensure that you have the conversion right side up, and the UNITS are calculated as well as the numbers!

Learning Check You have $7.25 in your pocket in quarters. How many quarters do you have? 7.25 dollars 4 quarters 1 dollar X = 29 quarters

Measurement in Chemistry Factor-Label Method Part 2

The Factor-Label Method At the conclusion of our time together, you should be able to: 1.Recognize a problem that can be solved by moving the decimal point. 2.Use the appropriate conversion factor in the correct way so that the labels cancel and the correct conversion is found with two changes of labels or labels that are squared or cubed.

Convert km/h to m/s km x 1000 m x 1 h___ = h 1 km 3600 s h 1 km 3600 s m/s Dealing with Two Units

A patient requires injection of g of a pain killer available in a 15 mg/mL solution. How many milliliters should be administered? ? mL = g of drug g drug  mL solnmg drug  ? mL = g of drug g drug mg drug mg drug mL soln 15 1 = 0.80 mL soln When you see a number with two units like 15 mg/mL, it can be used as a conversion factor. What it really says is that 1 ml of the solution contains 15 mg of the drug.

Dealing with Two Units, Your Turn If your pace on a treadmill is 65 meters per minute, how many seconds will it take for you to walk a distance of 8450 feet? 1 meter = 3.28 feet 2380 seconds # s= 8450 ftx 1 m 3.28 ft x 1 min 65 m x 60 s 1 min

What about Square and Cubic units? Use the conversion factors you already know, but when you square or cube the unit, don’t forget to cube the number also! Best way: Square or cube the Entire conversion factor Example: Convert 4.3 cm 3 to mm cm 3 10 mm 3 1 cm 1 cm ( ) = 4.3 cm mm cm cm 3 = 4300 mm 3

Learning Check A Nalgene water bottle holds 1000 cm 3 of dihydrogen monoxide (DHMO). How many cubic decimeters is that?

Solution 1000 cm 3 1 dm 3 10 cm 10 cm ( ) = 1 dm 3 So, a dm 3 is the same as a Liter! A cm 3 is the same as a milliliter.

Converting Metric to Metric A rattlesnake is 2.44 m long. How long is the snake in cm? a) 2440 cm b)244 cm c)24.4 cm

Solution A rattlesnake is 2.44 m long. How long is the snake in cm? b)244 cm 2.44 m x 100 cm = 244 cm 1 m

Converting Units of Length Made Easy 0.5 kilometer (km) = 500 meters (m) 0.5 kilometer (km) = 500 meters (m) 2.5 meter (m) = 250 centimeters (cm) 2.5 meter (m) = 250 centimeters (cm) 1 centimeter (cm) = 10 millimeter (mm) 1 centimeter (cm) = 10 millimeter (mm) 1 nanometer (nm) = 1.0 x meter 1 nanometer (nm) = 1.0 x meter O—H distance = 9.4 x m 9.4 x cm nm O—H distance = 9.4 x m 9.4 x cm nm

An Easier Way A rattlesnake is 2.44 m long. How long is the snake in cm? G _ _ M _ _ k h da _ d c m _ _ μ _ _ n 1. A move from 1 meter to centimeters is two places right 2. Move the decimal place of the number two places right cm

Another Example: How many millimeters are there in 4.5 cm? G _ _ M _ _ k h da _ d c m _ _ μ _ _ n 1. A move from cm to mm is one place right 2. Move the decimal place of the number one place right mm

Another Example: How many kilometers are there in 4.5 cm? G _ _ M _ _ k h da _ d c m _ _ μ _ _ n 1. A move from cm to km is five places left 2. Move the decimal place of the number five places left km

The Factor-Label Method Let’s see if you can: 1.Recognize a problem that can be solved by moving the decimal point. 2.Use the appropriate conversion factor in the correct way so that the labels cancel and the correct conversion is found with two changes of labels or labels that are squared or cubed.

Learning Check: 2 kilometers is the same as how many millimeters G _ _ M _ _ k h da _ d c m _ _ μ _ _ n 1. A move from km to mm is six places right 2. Move the decimal place of the number six places right mm, 2 x 10 6 mm

Metric Conversions #1: Write 550 mm as meters. G _ _ M _ _ k h da _ d c m _ _ μ _ _ n 1. A move from mm to m is 3 places left 2. Move the decimal place of the number 3 places left m

A person’s blood contains 185 mg of cholesterol per deciliter of blood. How many grams of cholesterol are there in 1 liter of this blood? A g B g C.1.85 g D.18.5 g E.1850 g Learning Check Learning Check

English and Metric Conversions If you know ONE conversion for each type of measurement, you can convert anything! You must use these conversions: Mass: 454 grams = 1 pound Length: 2.54 cm = 1 inch Volume: L = 1 quart

Learning Check Learning Check An adult human has 4.65 L of blood. How many gallons of blood is that? Unit plan: L qt gallon Unit plan: L qt gallon Equalities:1 quart = L 1 gallon = 4 quarts 1 gallon = 4 quarts Your Setup: gal = 4.65 L x 1 quart x 1 gallon L 4 quarts L 4 quarts = 1.23 gallons

Exit Quiz There are 12 inches in a foot, inches in a centimeter, and 3 feet in a yard. How many centimeters are in yard? # cm = 1 yd x 3 ft 1 yd = cm x 12 in 1 ft x 1 cm x 1 cm in

Exit Quiz #6 on WS Change 9.4 miles to km (1 mile = 1.6 km) # km = 9.4 mi = 15 km x 1.6 km 1 mi

With a U.S. dollar you can buy 1.1 Euros, 130 Yen, or 25 Rubles. How many Yen can you buy with one Ruble? # Yen = 1 Rublex 1 US $ 25 Rubles = 5.2 Yen x 130 Yen 1 US $ Exit Quiz

Calculate how many feet are in 1 meter. (use 1 cm = in) # ft= 1 mx 100 cm 1 m = 3.28 ft x in 1 cm x 1 ft 12 in Exit Quiz