Lab Density and Dimensional Analysis

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Lone Star College System, Woodlands *

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1402

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Chemistry

Date

Feb 20, 2024

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pdf

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Uploaded by ProfRiver12386

Lab 2: Density and Dimensional Analysis Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu I. Objectives • To learn about the concept and calculation of density • To learn about how different instruments can be used to measure density in the laboratory • To practice dimensional analysis calculations and reporting final answers to correct significant figures II. Introduction Part 1: Density______________________________________________________________________ Density is defined as the mass per unit volume of a substance, and it is a physical property of matter. A physical property can be measured without changing the chemical identity of the substance. Since pure substances have unique density values, measuring the density of a substance can help identify that substance. Density is determined by dividing the mass of a substance by its volume: Density = !"## $%&’!( (2.1) The units of density are commonly expressed as g/cm 3 for solids, g/mL for liquids, and g/L for gases. Density is also an intensive property of matter. This means that the value of density is independent of the quantity of matter present. For example, the density of a gold coin and a gold statue are the same, even though the gold statue consists of the greater quantity of gold. This is in contrast to extensive properties, like volume (the amount of space occupied by matter), which depend of the quantity of mater present. The more matter present, the larger the volume. Even in everyday life, we have a sense of how dense objects are. Even small children will be surprised if they pick something up, and the weight is not what they expected from the size. Being able to measure the density of a material has many practical applications. Density is used to find the thickness of eggshells to see if they are marketable. Engineers can use the density of soil to measure to see how much weight the soil will support. Another example is how oil has a lower density in comparison to water. When oil and water are mixed, their other chemical properties prevent them from mixing successfully and we see that they separate. But what determines why oil is the top layer and water is the lower layer? The answer is density! Water has a greater density which makes it sink, while oil has a lower density and it is able to float. Finding the mass of most things in a chemistry lab is usually easy. The mass can be measured on a balance. There are a variety of instruments used to measure volume. Although you will not be going into the lab, you can still get an idea of what it is like to properly measure density. The instruments we will “use” are below:

Lab 2: Density and Dimensional Analysis Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu Graduated cylinder Buret volumetric flask Graduated cylinders are a quick way to measure the volume of a liquid. The buret is much longer and usually skinnier. You can turn the stopcock at the bottom to release controlled amounts of liquid. The volumetric flask is different in that only a single volume can be measured out. The one shown contains 200.00 mL of liquid when it is filled to the line on the skinny portion of the flask. With a graduated cylinder, the bottom is always zero, so to get a volume measurement, you just read the liquid level. With a buret, you do not fill the liquid to the very top, so you have to take both an initial and a final reading and subtract the initial from the final. With a volumetric flask, you always fill it to the same line. In this lab, you will be solving a blunder that a lab intern accidentally made. You will be measuring the density of two different liquids. Below is the situation you are facing in the virtual lab. You work for a company that has many different research groups, and your group has just developed a new food preservative which has been named “Compound A.” Another group in your company has developed a new neurotoxin, which they have unfortunately also called “Compound A.” An intern was reorganizing the chemical storage stockroom and placed all the bottles labeled “Compound A” on the same shelf. You would like to begin testing the new food preservative, but don’t know which bottle contains the food preservative and which contains the neurotoxin. It would clearly not be a good idea to put neurotoxin into your food products. You have asked a theoretical chemist what to do, and he said that the preservative will have a higher density. It is your job to determine which bottle of Compound A contains the food preservative. Part 2: Dimensional Analysis___________________________________________________________ Dimensional analysis is an essential skill for the entire study of chemistry. For most chemistry problems, you will solve using conversion factors. A conversion factor is a fractional quantity of a unit equation with the units we are converting from on the bottom and the units we are converting to on the top.

Lab 2: Density and Dimensional Analysis Introductory Chemistry – Prof. Martinez All labs written using collective resources shared by numerous Lone Star College System Chemistry Faculty. For more information, please contact me at Esmeralda.Martinez@lonestar.edu In this lab, you will perform dimensional analysis problems in the Applied Exercises. Below are some useful prefixes and conversion factors that may come in handy. Metric prefixes and their meanings are given in the table below. Commonly Used Prefixes in the Metric System - METERS Prefix Symbol Meaning Conversion Factor Alt. Conversion Factor mega M 1,000,000 1Mm = 1 x 10 6 m 1Mm = 1 x 10 6 m kilo K 1,000 1km = 1 x 10³m 1km = 1 x 10³m deci D 0.1 1dm = 1 x 10 -1 m 1 x 10¹dm = 1m centi C 0.01 1cm = 1 x 10 -2 m 1 x 10²cm = 1m milli M 0.001 1mm = 1 x 10 -3 m 1 x 10³mm = 1m micro µ 0.000001 1µm = 1 x 10 -6 m 1 x 10 6 µm = 1m nano N 0.000000001 1nm = 1 x 10 -9 m 1 x 10 9 nm = 1m Commonly Used Prefixes in the Metric System - LITERS Prefix Symbol Meaning Conversion Factor Alt. Conversion Factor mega M 1,000,000 1ML = 1 x 10 6 L 1ML = 1 x 10 6 L kilo K 1,000 1kL = 1 x 10³L 1kL = 1 x 10³L deci D 0.1 1dL = 1 x 10 -1 L 1 x 10¹dL = 1L centi C 0.01 1cL = 1 x 10 -2 L 1 x 10²cL = 1L milli M 0.001 1mL = 1 x 10 -3 L 1 x 10³mL = 1L micro µ 0.000001 1µL = 1 x 10 -6 L 1 x 10 6 µL = 1L nano N 0.000000001 1nL = 1 x 10 -9 L 1 x 10 9 nL = 1L Commonly Used Prefixes in the Metric System - GRAMS Prefix Symbol Meaning Conversion Factor Alt. Conversion Factor mega M 1,000,000 1Mg = 1 x 10 6 g 1Mg = 1 x 10 6 g kilo K 1,000 1kg = 1 x 10³g 1kg = 1 x 10³g deci D 0.1 1dg = 1 x 10 -1 g 1 x 10¹dg = 1g centi C 0.01 1cg = 1 x 10 -2 g 1 x 10²cg = 1g milli M 0.001 1mg = 1 x 10 -3 g 1 x 10³mg = 1g micro µ 0.000001 1µg = 1 x 10 -6 g 1 x 10 6 µg = 1g nano N 0.000000001 1ng = 1 x 10 -9 g 1 x 10 9 ng = 1g English to metric conversions mass 1 pound (lb) = 453.6 grams (g) length 1 inch (in) = 2.54 centimeters (cm) volume 1 quart (qt) = 946.4 milliliters (mL)

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