Name_ Chem 305 Partner_ Lab Section (Circle) M Tu W Th F Date_ MEASUREMENTS Materials: Ice, sodium chloride, metal samples, urine solution, Tums, aspirin tablets Equipment: Hot plate, thermometers, graduated cylinders, weigh boats Purpose: In this lab you will become familiar with some of the equipment commonly used in the chemistry lab. You will use a thermometer to measure temperature, a balance to measure mass, and a graduated cylinder to measure volume. From the measurements of mass and volume, you will determine the density of water and a urine solution made of salt water with food coloring. You will also determine the specific gravity of a urine solution using a hydrometer and your density measurements. It is important that each instrument be used carefully so that your measurements are as accurate as possible. Hazards: All reagents are non-toxic. Use caution with hot plates and boiling water baths. Your instructor will demonstrate the use of balances and accurate reading of volumetric equipment and thermometers. INTRODUCTION: Mass Mass is measurement of how much matter is in a given object or substance. Physicists use the term weight to characterize the force of gravity on matter. In Chemistry 305 you can use the terms weight and mass interchangeably. There are several different balances in the Chemistry 305 laboratory. Some give measurements to 0.01 g while others give measurements to 0.001 g or 0.0001 g. When using these balances, be sure to record all of the digits on the balance in the measurement. General Directions: 1. Before weighing something, be sure that balance reads zero (0.00g to 0.0000g). This process is called tareing the balance. 2. Place the object on the balance. Wait until the numbers do not change. 3. Record the mass. Record all of the digits presented by the balance. Never round your mass measurement. Record the numbers directly onto your report sheet. Do not rely on your memory. Don t forget the units! 4. Clean up any spilled materials on or around the balance. 5. Weigh all chemicals in a weighing boat or in a container. Never place chemicals directly on the balance pan. 3-1
Volume When careful measurements of volume are required in Chemistry 305, you will use a graduated cylinder. General Directions: 1. In order to obtain an accurate reading, the graduated cylinder must be on a flat surface. Be sure your eye is lined up with the level of the liquid in the graduated cylinder. Sometimes it is easier to see against a black background. 2. You will notice that the liquid forms a curved surface (called a meniscus). When reading the level of the liquid, find the place on the scale that coincides with the bottom of the meniscus. 3. When reading the level of liquid in the cylinder, estimate the volume to the nearest 0.1mL as shown below. The volume in the graduated cylinder above could be read as 41.9 ml, 42.0 ml, or 42.1 ml. Notice, all of these values are reported to the nearest 0.1 ml. Temperature In the Chemistry 305 laboratory, temperature is measured in degrees Celsius (º C) and recorded to the nearest 0.1 degree. General Directions: 1. Hold the thermometer by the attached plastic triangle or with a paper towel to prevent transfer of heat from your hand. 2. When measuring the temperature of a liquid, place the thermometer in the middle of the container up from the bottom and away from the walls and bottom of the container. 3-2
3. It takes a while for the thermometer to reach the temperature of the liquid. Carefully observe the temperature and record when the reading no longer changes. 4. The thermometer is marked in Celsius degrees. Estimate the temperature between the marks to the nearest 0.1 º C. This means that all of your temperature measurements should be expressed to the tenths place. For example, 0.5 º C, 13.6 º C, and 99.0 º C are all temperature measurements expressed to the tenths place. PROCEDURES: You will work with one other person in this experiment but you and your partner will make separate measurements. You will record your own and your partner s measurements and then compare results. Report all results, answer all questions, and turn in your report before your leave lab today. I. MASS Part A Mass of Everyday Objects 1. Obtain two small everyday objects (coin, pen, key, etc). Your lab partner should obtain three different objects. 2. Read the general directions above for obtaining the mass of an object. 3. Obtain the mass of each of the objects. Record the mass of each object in the data table below. Do not round your mass measurement. Don t forget the units! 4. Write down the mass of your partner s objects. Don t forget the units! Your Objects Mass Partner s Objects Mass (1) (2) Part B Grams and Milligrams A unit of mass commonly used in the health professions, nutrition, and science is the milligram, abbreviated mg. For example, an Advil tablet (an NSAID ) contains 200 mg of the active ingredient ibuprofen. The milligram is a metric unit: the milli prefix means one thousandth and the gram is the base metric unit of mass. 3-3
Fill in the line or circle the appropriate word: 1. Since there are mg in one gram, one should (multiply or divide) by 1000 to convert g to mg. For example a 1.5 g dose of aspirin is equivalent to mg of aspirin. 2. On the other hand, if you wanted to convert mg to g, you would (multiply or divide) by 1000. For example, one of the Advil tablets discussed above contains 200. mg of ibuprofen which is equivalent to g ibuprofen. 3. Weigh one aspirin tablet. Record your data in the table below. Read the label on the aspirin bottle and record the mass of active ingredient (aspirin) in each tablet. 4. Weigh one Tums tablet. Record your data in the table below. Read the label on the Tums bottle and record the mass of the active ingredient (calcium carbonate) to 3 sig figs in each tablet. 5. Data Milligrams Tablet Mass of Tablet (g) Mass of Active Ingredient (mg) Aspirin Tums 6. What is the mass of the aspirin tablet in mg? Show your work. 7. What is the mass of the Tums tablet in mg? Show your work. 8. Calculate the percent (by mass) of active ingredient in each of the tablets. Show your work. [ Percent = mass of active ingredient x 100] total mass of tablet 3-4
II. TEMPERATURE Record all temperatures to the nearest 0.1º C (Refer to page 2). This means that all of your measurements must have a digit in the tenths place. 1. Fill a medium-sized beaker full of tap water. Place your thermometer in the beaker and record the temperature when it no longer changes. Your partner will also read the temperature, independently. In the spaces provided below, record your own reading and that of your partner. Be sure to include your units. Your reading: Partner: 2. Fill a 250-500mL beaker half-full of deionized water. Place it on a hot-plate. Heat the water to boiling and record the temperature of the boiling water. Do NOT let the thermometer touch the bottom of the beaker! In the spaces provided below, record your own reading and that of your partner. Be sure to include your units. Your reading: Partner: 3. While waiting for the water to boil, fill your 100-150 ml beaker 3/4-full with ice and add 5 ml of water. Stir gently with the thermometer for a while, and record the lowest temperature obtained (with the thermometer bulb in the middle of the mixture). Your reading: Partner: 4. Together with your partner, weigh out approximately 10 grams of sodium chloride. To do this, obtain the mass of a weighing boat and record the mass. Then add about 10 g of sodium chloride and record the mass again. The difference in the two masses is the mass of the sodium chloride. This procedure is called weighing by difference. Note: It is not necessary (or even desirable) to weigh out exactly 10 grams, but you must be accurate in your measurement! Don t forget the units! Mass of weigh boat + NaCl Mass of weigh boat Mass of NaCl 5. Now add the NaCl to the ice-water mixture, stir gently with a stirring rod for several minutes until the NaCl dissolves, then read and record the lowest temperature observed. Your reading: Partner: 3-5
III. DENSITY In this part of the experiment you and your partner will determine the density of water and the density of a solid metal object. Density is an easily measured physical property of a substance, often used for identifying materials Density = mass (in grams = m volume (in ml) v Example: A section of a femur bone weighs 25.968 g and occupies a volume of 13.5 ml. The density of the bone fragment would be calculated as follows: D = m = 25.968 g = 1.92 g V 13.5 ml ml A. Density of water 1. One of the partners will weigh a clean dry 25 ml graduated cylinder and record its mass on line b). 2. Fill the graduated cylinder with deionized water to about 20 ml and record the volume to 0.1 ml on line d). This means that your volume measurement will have a digit in the tenths place. 3. Weigh the cylinder again on the same balance and record the mass on line a). Be sure to record units. 4. Calculate the density of the water, taking care to properly account for units and sig figs. 5. The other partner will repeat the experiment using 10 ml of deionized water in a 10mL graduated cylinder. 20 ml trial 10 ml trial a) Mass of graduated cylinder + water b) Mass of empty graduated cylinder c) Mass of water* d) Volume (read from cylinder) e) Density of water* *Show the setup for both calculations below. Don t forget to include all units. Watch your sig figs! Box your final answers. 3-6
B. Density of a solid metal object 1. Obtain a solid metal object. Record the type of metal in the table below. Weigh the object and record the mass. 2. To determine the volume of the object, fill a 25 ml graduated cylinder with water to about 15 ml and record the volume to 0.1 ml. Tip the graduated cylinder sideways and slowly and carefully slip the solid into the graduated cylinder. Record the new volume. The difference in the volume is the volume of the metal object. 3. Each partner should select a different metal object made of a different metal. Check each other as you do your measurement. Record all results. Type of Metal a) Mass of metal object b) Volume in cylinder with metal inside c) Volume in cylinder before inserting metal d) Volume of metal object (by subtraction)* e) Density of metal object* *Show the setup for both calculations below. Don t forget to include all units. Watch your sig figs! Box your final answers. Some Typical Density Values (g/cm 3 ): Steel: 7.87, Brass: 8.6, Al: 2.7, Cu: 8.96 3-7
C. Specific Gravity A measurement that is closely related to density is specific gravity. The specific gravity of a liquid can characterize the amount of dissolved solids in a solution. The specific gravity of a liquid is a comparison of the density of that liquid with the density of water, which is 1.00 g/ml (4 C). The formula for determining the specific gravity of a substance is shown below. Notice that the units cancel making specific gravity unit-less. This is one of the few measurements in chemistry without any units. Specific Gravity = Density of substance (g/ml). Density of water at the same temperature (g/ml) Specific gravity measurements are used in many fields including winemaking, automotive technology, athletics, and medicine. In winemaking, the stages of fermentation are followed by measuring the specific gravity of the wine. The amount of dissolved sugar and/or alcohol in wine can be characterized by specific gravity measurements. In medicine, the amount of dissolved solids in urine is indicated by a specific gravity measurement. A high specific gravity of urine could indicate dehydration, improper functioning of the kidneys, glucose and/or protein in the urine, etc. The specific gravity of a fluid is determined by using a hydrometer. Small hydrometers (urinometers) are used in medical labs to determine the specific gravity of urine. The specific gravity of urine can be approximated using special test strips. A hydrometer placed in liquid is spun slowly to keep it from sticking to the sides of the container. The scale on the hydrometer is read at the lowest (center) point of the meniscus of the fluid. Read the specific gravity on the hydrometer to 0.001. 3-8
1. Determine the specific gravity of the urine by first determining its density. Weigh a clean and dry 25 ml graduated cylinder and record the mass. Fill with the urine solution to about 20 ml and record the volume to the nearest 0.1 ml. Be sure to record the units. 2. Weigh the graduated cylinder again and record the mass. (a) Mass of graduated cylinder + urine (b) Mass of empty graduated cylinder (c) Mass of urine (d) Volume of urine 3. Calculate the density of the urine. Watch your sig figs and don t forget the units. Show your calculation set-up and work below (e) Density of urine 4. Calculate the specific gravity of the urine using the density of the urine and the density of water (0.998g/mL). Show your calculation set-up and work below. Specific gravity of urine 5. Use a hydrometer to determine the specific gravity of the urine as demonstrated by your instructor. (Fill a 100 ml graduated cylinder to 85 90 ml of urine. Gently place the hydrometer into the graduated cylinder and gently spin it in the urine. Read the hydrometer at the point where the meniscus interfaces with the hydrometer scale.) Specific gravity of urine (hydrometer reading) 3-9
D. Density and Specific Gravity Problems 1. Ammonium chloride is used as an expectorant in cough medicine. It has a density of 1.53 g/cm 3. What is the mass of 26.0 L of this substance in kg? 2. Jacy bought a gold necklace weighing 21.3 grams from a flea market. She filled a 10mL graduated cylinder with water to the 5.0 ml mark and dropped her necklace in. The level in the graduated cylinder rose to 7.4mL Is her necklace real or fake? If not, identify the possible composition of her necklace. Gold: 19.3 g/cm 3 Copper: 8.86 g/cm 3 Bronze: 9.87 g/cm 3 3. Diesel fuel has a density of 0.839g/mL. What is the volume, in gallons, of 2.3 kg of diesel? [ 1 gallon = 3.79 L] 3-10
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