Experiment 1 Introduction to Density INTRODUCTION The purpose of this experiment is to understand the meaning and significance of the density of a substance. Density is a basic physical property of a homogeneous substance; it is an intensive property, which means it depends only on the substance's composition and does not vary with size or amount. The determination of density is a nondestructive physical process for distinguishing one substance from another. Density is the ratio of a substance's mass to its own volume. Density = Ошибка! In the metric system the unit of density for a liquid or solid is measured in g/mL or g/cm 3. The cm3 volume unit used with solids is numerically equal to mL volume unit used with liquids. That is, 1 mL = 1 cm3. In this experiment you will determine the density of several liquids and compare the physical properties of those liquids. Which is heavier, a pound of aluminum or a pound of lead? The answer, of course, is neither, but many people confuse the words "heavy" and "dense" "Heavy" refers to mass only. Density is the mass of a substance contained in a unit of volume. Lead is a very dense metal and contains a large quantity of matter in a small volume, while aluminum, being much less dense, contains a smaller quantity of matter in the same volume. The volume of 20.0 grams of lead is 1.77 mL. The mass of lead contained in each mL is its density. Density of lead = Ошибка! = 12.3 g/mL The volume of 20.0 g of aluminum is 7.41 mL. Density of aluminum = Ошибка! = 2.70 g/mL From the definition of the gram and the milliliter, we can see that one mL of water at 4 oC would have a mass of exactly one gram. The density of water, then, is 1 g/mL at 4 oC. Since the volume occupied by one gram of water varies slightly with temperature, the density also varies slightly with changes in temperature. The mass of any object is determined by comparing its mass with the mass of known object or objects (i.e., it is weighed). The volume of a liquid is measured using a graduated cylinder, a pipet, or some other apparatus. The volume of a regular solid (e.g. a cube or a sphere) may be determined by measuring its dimensions and then calculating it using the correct mathematical formula. The difficulty in determining the volume of an irregular solid in this manner is obvious. The method commonly used is to measure the change in the volume of water 1 Experiment 1 when the object is immersed in the water. The object displaces a volume of water equal to its own volume. If the solid material is soluble in water, another liquid, in which the solid is insoluble, is used (e.g. carbon tetrachloride for salt). PROCEDURE Part 1: DENSITY OF WATER In any chemistry experiment, it is always advisable to calibrate your instruments and to practice any new technique. The density of water can be found in the CRC Handbook of Physics and Chemistry. You will learn the technique for measuring the density of any liquid by experimentally determining the density of water then comparing it to the actual value obtained from the CRC Handbook. You will need to pay close attention to the proper use of a graduated cylinder and a balance. 1. 2. 3. 4. 5. 6. Open Beyond Labz and go to the Physical Science lab and select the Density Laboratory. Weigh a clean, dry beaker. Fill a graduated cylinder with water. Take a volume measurement of the water being sure to read the bottom of the meniscus. Place the empty beaker on the balance and tare it. Now pour the contents of the graduated cylinder into the beaker and record the mass show on the balance. Calculate the density of the water using the equation, d = m/V. As with any experiment, you should always check how accurate your experimentally obtained value is compared to the "true" or accurate value. This experimental error is also known as percent error and it describes the percentage the experimental value is off from the actual value. Percent error = Ошибка! x 100% If you used the graduated cylinder and balance correctly, you should have an experimental error of less than 1%. If your error is greater that 2% repeat the above experiment until you have a small percent error. 2 Experiment 1 Part 2: DENSITY OF VARIOUS LIQUIDS 1. Repeat the procedure in Part 1 of this experiment for the following liquids. a. Ammonia b. Bromine c. Car Oil d. Honey e. Gasoline f. Acetone g. Ethanol h. Maple syrup i. Jet fuel j. Mercury k. Milk l. Olive Oil m. Phenolphthalein n. Sea water o. Soda p. Tar q. Turpentine r. Virtual fluid A s. Virtual fluid B t. Virtual fluid C 2. Determine the densities of all the liquids and rank them in order of most dense to least dense. Be sure to use the proper number of significant figures in your final values and do not forget to include water when ranking the liquids. 3. Determine the density of an unknown liquid and identify what the liquid is based on its density. (Go to the clipboard and choose “Find density of the unknown fluid”) Part 3: DETERMINATION OF THE DENSITY OF SOLIDS 1. Obtain a metal ball from the stockroom and record what the metal is. 2. Place the metal ball on the balance and record the mass in the Laboratory record book. The mass should be read on the balance to three places past the decimal. Eventually, you will round off in your final number, but keep the places until after you have done your calculations. 3. Fill your graduated cylinder half-way with water. With your eye at the approximate level of the top of the water in the cylinder, read the volume of water in the cylinder to 1 place past the decimal (e.g. 68.4 mL). Record this number as V o in your laboratory record book. 4. Gently slide the # 1 piece of metal into the water, being careful not to lose any water. Make sure the object is completely submerged. 5. Read the volume, recording it as V1. 6. The difference between V1 and V0 is the volume of the metal ball. 3 Experiment 1 7. Calculate the density of the sample. 8. Repeat steps 1- 7 for the following metal samples. a. Al b. Ag c. Fe d. Sn e. Ti f. Ni g. Zn h. Cu i. Au j. Brass 9. Look up the actual densities of these substances and determine your percent error for each sample. 10. Select 3 solids of your choice from the experiment wall and determine their densities. 4 Experiment 1 Scientist: __________________ Lab Report: Introduction to Density Part 1: DENSITY OF WATER Actual density of water _________ Volume of water added to graduated cylinder __________ Mass of water in the beaker __________ Density of the water __________ Show your work here: Calculate your experimental error 5 Experiment 1 Part 2: DENSITIES OF LIQUIDS Liquid 6 Volume (mL) Mass(g) Density(g/mL) Experiment 1 In the table above be sure to list your liquids in order of increasing density. Show a sample calculation here (be sure to indicate what sample you are showing): Unknown Liquid Mass Liquid _____________ Volume Liquid _____________ Density Liquid _____________ Identity of Liquid _____________ Show your calculation here: 7 Experiment 1 Part 3: DENSITY OF SOLIDS Solid Volume (mL) Show a sample calculation here: Conclusion: 8 Mass(g) Density(g/mL) % error