Chem 106 Practical Everyday Chemistry CALCULATIONS Dr. Ron Rusay Diablo Valley College Spring 2004

Unit Conversion

Systematic Problem Solving Dimensional/Unit Analysis (Conversion) How many mL of milk are in a1/2 gallon carton? 0.50 gal ? mL 1 gal = 4 qt 1 qt = 946 mL Or 0.50 gal | 4 qt | 946 mL | 1 gal | 1 qt = ? mL

Complete the following Units & Conversions Number Scientific Notation Named unit 1.3 x 1010 yrs 13,000,000,000 yrs. ________________ __? gigayears 13 gyrs 546 5.46 X 10 2 ___________ mL ______________ mL 0.546 Liters 0.546 L 0.845 ____________ kg __8.45 x 10 -1 kg___ _? grams__ 845 g

Percent A comparison based on normalization to 100. George Washington University, 1995: 64 unsealed addressed envelopes with $10 in each were dropped on campus in different classrooms. In economics 18 of 32 were mailed back, in [business, history and psychology] 10 of 32 were mailed. What is the percent for each of the 2 groups of students? 18/32 x 100 = 10/32 x 100 = 56.25% © Copyright 1998-2004 R.J. Rusay 31.25%

Percent Continued The Professor conducting the study received 43.75% of the original $640 in the mail. How much did he receive? How many of you would mail the envelop presuming no one knows you found it? One student mailed an empty envelop with the return address: Mr. IOU, 1013 Indebted Lane, Bankrupt City, MS (WSJ 1/18/95) 43.75% /100% x $ 640 = $280 © Copyright 1998-2004 R.J. Rusay

Mass and Volume Measurement Mass / Volume (g/ml) = Density Liquid Solid

01-08-01UN Title: Example 1.8 Caption: Calculation of iron density with voice balloon. Note that the units are expressed when given values are substituted into the general equation. The answer is also expressed in the proper units. Notes: Proper units for density are mass per unit volume.

Volume of an object (any shape) by displacement If the mass were 28.8 g, what is the density? 28.8 g/10.5 ml= 2.74 g/ml 60.5 mL -50.0 mL 10.5 mL What is the volume of the jade?

Density http://www.density.com/what.htm Density = Mass / Volume [g/mL or g/cm3; g/L] Least dense man-made solid substance: Aerogel, D = 3.025 x 10-3 g/cm3 http://eande.lbl.gov/ECS/Aerogels/satoc.htm http://stardust.jpl.nasa.gov/spacecraft/aerogel.html Dair = 1.22 x 10-3 g/cm3 (1.22 g/L) Densest known substance: a White Dwarf http://antwrp.gsfc.nasa.gov/apod/ap961203.html © Copyright 1998-2004 R.J. Rusay

Conversion Factor Method (Dimensional Analysis) Qualitative Descriptions vs. Quantitative Use exact numbers / “scale factor” UNITS A Bookkeeping Method: Example ___ ft___in --------> ? m (1 ft = 12 in; 2.54 cm = 1 in; 100 cm = 1 m) ___ft x 12 in/ft + ___in = ___in ___in x 2.54 cm/in x 1 m/100cm = ___m 5 9 5 10 70 1.78 70 © Copyright 1998-2004 R.J. Rusay

Volumes of regular shapes V = s 3 h V = l x w x h V = 4/3  r 3

(1 T = 1,000 kg; 1 kg = 1000g; tsp = 14.8 mL; 1 mL = 1 cm3 ) Calculate the density [D = ? g/cm3 ] of a White Dwarf. 1.0 teaspoon has a mass of 3.0 T (metric tons). (1 T = 1,000 kg; 1 kg = 1000g; tsp = 14.8 mL; 1 mL = 1 cm3 ) Conversion Factors in red are among the ones that you must know from memory.

Popcorn & Science How good is it? Expansion Kernel Size Moisture Content cm3 / g Kernels / 10 g Percent H2O How would you experimentally determine these values?

Popcorn & Science How good is it? Would a single trial be as good as three?

Popcorn & Science How good is it? The average of 3 or more trials is common.

Popcorn & Science How good is it? The average of 3 or more trials is common.

Popcorn & Science How good is it? The average of 3 or more trials is common.

Popcorn & Science How good is it? Calculations: MWVT Number: cm3/g Lite Movie Theater Corn on the Cob 24.8 26 23 Kernel Size: kernels/10g 57.5 52.8 59.1 Percent Water: % 12.0 15.0 14.3 Which would you rate the best and why?