CHEM 121 pre-lab - Speech or Presentation Example

______________________________________ Drawer number _________ Lab Day and Time:____________________________ ________________ Experiment 2: PRELAB ASSIGNMENT FOR DENSITY1. The definition of density is ___Mass__________ per __Unit Volume___________.The word "per" indicates the arithmetic operation ___Division________________.2. When using a graduated cylinder you read the volume at the bottom of the__Meniscus_________________. It is ______Less________ accurate than a pipet. (more or less)3.

In an experiment performed as in Part A, the following data were collected: mass of vial 20.0138 g mass of vial + water 29.9368 g volume of water 10.00 mL Then:A. The mass of the water is ___9.923 g_________________B. The density of the water is ___0.9923 g/mL________________C. The temperature of the lab is _40 oC__ (to the nearest degree, determine from density chart on pg. 30)4. An experiment performed as in Part C with a metal other than aluminum gave the following data: volume of water: 3.

72 mL mass of metal bar: 12.8432 g volume of water + metal bar: 9.84 mLThen …A. The volume of the metal bar is ___6.12 mL_____________.B. The density of metal bar is ___2.10 g/mL______________.B. Determination of the Percent Alcohol in a Solution Unknown #_______ 25% 50% 75% 100% unknown 9. Mass of vial (tare weight) 18.75 g 16.23 g 17.11 g 17.91 g 18.12 g 10. Mass of vial + liquid 28.25 g 25.18 g 25.51 g 25.

81 g 26.82 g11. Mass of liquid (#10 – #9) 9.50 g 8.95 g 8.40 g 7.90 g 8.60 g12. Vol. of liquid pipetted 10.00 mL 10.00 mL 10.00 mL 10.00 mL 10.00 mL13. Density (#11 ÷ #12) 0.95 g/mL 0.895 g/mL 0.84 g/mL 0.79 g/mL 0.86 g/mL14. Create a standard curve of Density (y-axis) vs. % alcohol (x-axis) and attach to this worksheet. Percent alcohol of the unknown (Determined from standard curve graph) 66%C. Density of Aluminum15.

Mass of aluminum bar __7.448_____ g16. Volume of water in graduated cyl. __5.45______ mL17. Volume of water + aluminum bar __8.20______ mL18. Volume of aluminum bar (#17 – #16) __2.75______ mL19. Density of aluminum (#15 ÷ #18) __2.7054____ g/mL 20. Literature value for the density of aluminum _2.6989____ g/mL21. Percent difference between your value and literature value (see p. 33) _0.24__D. Thickness of Aluminum Foil 22. Length of foil (≤ 15.0 cm) ___13.

1____ cm23. Width of foil (≤ 10.0 cm) ___9.5_____ cm24. Mass of foil ___9.745___ g25. Thickness of foil (math on p. 34) ___0.02901_ cmuse conversions in Table 3 on p.25 ___0.0002901_ mto convert the thickness of foil in cminto m, m, and nm ___290.1_____ m ___290100___ nmQUESTIONS For Lab #2Write your answers on separate paper and attach to your lab report form. For word problems: Use good scientific expression. Make your sentences short and clear. Neatness counts, as does spelling.

Show your work for numerical problems. If the answer is very large or very small, express your answers in correct exponential notation. Always use the correct number of significant figures.1. What might be done to a bar of soap during manufacturing to make the soap into a floating soap?A bar of soap can be made as a hollow bar during manufacturing so that its density remains less than that of water and therefore, it can become a floating soap. 2. A kilogram of metallic osmium, the densest element known, occupies a volume of 44.5 mL. What is the density of osmium?

Density of Osmium is (1000 g)/(44.5 mL) = 22.47 g/mL. This means Osmium is approximately 22.47 times denser than water. 3. The density of mercury is 13.6 g/mL. What is the density of mercury in pounds/gallon? Density of mercury in pounds/gallon is 113.4975.4. If the density of gasoline is 0.79 g/mL, what mass of gasoline, in kilograms, is in a full 25-gallon tank?Mass of gasoline in a full 25 gallon tank = 25*3.78541178*0.79 kg = 74.762 kg.5. a. Which is heavier, a pound of feathers or a pound of lead?

Both are equally heavy.b. Which is denser, a pound of feathers or a pound of lead?A pound of lead is denser than a pound of feathers.6. In 1989, the supertanker Exxon Valdez spilled 250,000 barrels of crude oil (1 barrel = 42 gallons) off the coast of Alaska. What area of ocean would be polluted if this much oil spread out to a thin film with thickness of 0.10 mm? (Hints: volume = area x thickness. 1 mL = 1 cm3) Express your answer in cm2 and in miles2.The area of the ocean that will be polluted = 3.

975*1012 cm2 which is equal to 153.46 miles2.7. Let’s assume that your secondary education has led you to rob armored cars. In your latest heist, if you were faced with bags of coins that weighed the same, which bag would you take: pennies, nickels, dimes, or quarters? Which bag contains more money? Important data: a penny weighs 3.09 g, a nickel weighs 4.88 g, a dime weighs 2.25 g, and a quarter weighs 5.68 g. (Naturally, show your work for full credit.) Hint: calculate the monetary density of each coin.

Monetary density of different coins is the following:Penny $0.01/3.09 g = $0.003/gNickel $0.05/4.88 g = $0.010/gDime $0.10/2.25 g = $0.0444/gQuarters $0.25/5.68 g = $0.0440/gClearly monetary density of dimes is the highest and therefore, I would take the bag containing dimes as it contains more money. However, if I can afford to take one more bag I will not like to leave the quarters bag as well.8. What would be the effect on your calculated value of the density of water if there was an air bubble in the pipet when you transferred the water into the empty vial?

Would the value be higher or lower or would there be no change? Explain your answerIf there was an air bubble in the pipet while transferring the water in the vial for density measurement, the measured value of density will be lower than the actual value as the volume has been measured on higher side erroneously due to entrapped air bubble.9. What would be the effect on your calculated value of the density of water if “empty” vial had not been completely dried before weighing? Would the value be higher or lower or would there be no change?

Explain your answerThe measured value of density of water will not be affected in this case as the mass of empty vial is deducted to calculate the mass of the measured volume of water. Therefore, whether the vial was completely dry or not will not affect the result.