Density lab report PDF

Preview

Summary

This report includes data collected from the lab....

Description

Chemistry Lab Report Experiment 1: Density

February 5, 2021 Spring 2021

LABORATORY REPORT Experiment 1 Density Name:

Date: 2/4/21

I. Introduction Density is a standard physical property of a liquid or solid. The density of a subject is expressed as a ratio of the subject’s mass to its volume in the following which is the density equals the mass divided by the volume of the object. Therefore, the mass and the volume of the unknown object must be measured beforehand. At any specified temperature and pressure, the density of a sample is constant. Given the specific density of water at various temperatures and solving the density formula for the volume, we can simply determine the volume of our container. The mass of the unknown samples is accurately obtained by weighting and using the measuring by difference method. Once the mass and the volume are obtained for the unknown sample, the density of that unknown liquid or solid can also be calculated. The experiment will provide us the data necessary to calculate the density of the unknown liquid or solid. Therefore, the density is useful and to find characteristics or identify the characteristics of an unknown substance. The importance of learning the density is to what substances float or what substances will shrink based on each substance once these are placed in liquid. Also, it is important to convert the mass to volume when the quantity is measured of a substance. Substances are expected to float if the density is less than the liquid and they are expected to shrink if the density is denser than the liquid. Now, density is an intensive property of matter because density has an independent amount of substance while extensive properties do depend on the amount of substance. The purpose of this experiment was to understand and how to identify some substances, when their identity is unknown by simply finding the density of that substance-using

1

its mass and the volume. Also, the same way as the identity of the weight of the unknown liquid with a fixed volume, this was accomplished by using a volumetric flask which is useful for measuring exact values of liquid. However, the major objective of this experiment was to identify the unknown concentration of a solution. The measurements that are necessary to calculate the density of a sample is the mass and the volume of the sample. The way the density was calculated as stated above was the mass over the volume, and the density was expressed as two significant figures and the reason for that was because the volume of the density had two significant figures. One of the techniques that were learned when doing this experiment was the displacement technique, this technique was learned in part one of the experiment when determining the density of the solid which was used to measure the volume of the amount of solid that was given that had an irregular shape. Another technique that was learned while doing this experiment was when determining the density of a liquid by using the flask, this was basically to measure the exact volumes of a liquid, and last but not least, a technique that was gained by determining a solution. In this part of the experiment, the density of known concentration was determined as well as one unknown solution that was accomplished by plotting the density in the y-axis against the concentration. This was calculated by rearranging the equation of a trend line. However, while doing this experiment some precautions had to be taken, in the first part of the experiment, the walls of the cylinder had to be free of droplets, or else they had to be carefully removed with a paper towel. Also, do not make any big error, the level of the water inside the cylinder had to be as precise as possible. What were the laboratory hazards and safety precautions in this experiment?

2

For the usage of ethanol, the hazards might be Highly flammable liquid and vapor. May cause damage to organs. For tin Causes serious eye irritation. H335 May cause respiratory irritation For NaCl there are no known hazards. II. Procedure and materials Note: THE LAB PROCEDURE AND MATERIALS WHERE TAKEN FROM THE LAB MANUAL. Part I Materials: Top-loading balance, weighing boat, 10 mL graduated cylinder, unknown metal, and DI water 1. Using a top-loading balance, weigh 5 g (record the mass to the nearest 0.001 g) of unknown metal using a small plastic weighing boat (clean and return the weighing boat for reuse by other sections). Record the mass (D.1, refer to Part I Data below). 2. After carefully studying the readability of a 10 mL graduated cylinder, fill it with DI water, about two-thirds full. Ensure that the inner walls of the cylinder are free of droplets, otherwise, carefully remove it with a paper towel. 3. With your eye in line with the bottom of the meniscus, determine the level of water inside the cylinder as precisely as possible. Record the initial volume (D.2) to the nearest decimal place you can read, based on your readability check in Step 2. 4. Tilt the cylinder and slowly slide the unknown metal to avoid water splashing and breaking of Glassware. 5. Carefully return the cylinder to the upright position and precisely read the new volume at the lower meniscus (D.3). Record the final volume on your datasheet. 6. Determine the water volume displaced by metal (which is the volume of unknown metal) by subtracting the volume of the water (initial volume) from the volume of water with the metal in it (final volume) (C.1 – refer to the DataSheet). 7. Calculate the density of the unknown metal using its mass and volume (C.2). Express the density in the proper unit and correct the number of significant figures. 8. Obtain the unknown metal density from your instructor and calculate the percent error (C.3) using the formula below. Record all data and calculations in the DataSheet. % Error = x 100 9. Pour out the water in a beaker and place the wet metal in the labeled container provided by the instructor for drying. Do not dump the wet metal in the sink nor place it back in the original container containing the dry metal. Part II Materials: Top-loading balance, 10 mL volumetric flask, thermometer, unknown liquid 1. Using the same balance from Part A, weigh an empty and dry 10-mL volumetric flask (wipe the outside with a dry paper towel). Record the mass to the nearest 0.001 g (D.4). 2. Familiarize yourself with how you can read the volume of a clear liquid on a volumetric flask column white ring mark.

3

3. Place the volumetric flask on a level surface. Fill it with the unknown liquid up to the 10-mL white ring mark. You may use a plastic dropper to carefully add the last few drops of liquid so the lower meniscus sits on the white ring mark on the long narrow neck of the flask. Read the volume using the curved (lower meniscus) surface of the water inside it, by bringing your eyes even with the lowest point (concave) on the curve of the liquid. Record the 10- mL volume on your data sheet (D.5). 4. Dry the outside of the volumetric flask using a paper towel. 5. Using the same top-loading balance, weigh and record the mass of the volumetric flask with unknown liquid (D.6) 6. The mass of the liquid is found by subtracting the weight of the empty volumetric flask from the weight of the filled volumetric flask (C.4). Calculate the mass of the liquid using the equation below. mass of liquid = (mass of volumetric flask + liquid) – a mass of the empty volumetric flask ● Calculate the density of the unknown liquid (C.5) and record it in the Datasheet. Express the density value with the correct number of significant figures and proper unit. ● Compare it with the unknown liquid identity that will be provided by your instructor. Calculate the percent error (C.6). Record all data and calculations in the Datasheet. ● Carefully pour the used unknown liquid in a scintillation vial, and measure and record its temperature. Pour out the used unknown liquid in a labeled container (Used Unknown Liquid) provided by the instructor. Part III Materials: Top-loading balance, 10 mL graduated cylinder, thermometer, NaCl solutions (4% 8%, 12%, and 16% in DI water), unknown NaCl solution, and DI water. 1. Weigh a clean dry 10 mL graduated cylinder as precisely as possible. Record its mass to the nearest 0.001g (D.7). 2. Carefully measure 10mL DI water in the graduated cylinder and record the volume on the datasheet (D.8). 3. Wipe the outside of the cylinder and the water on the inner walls of the cylinder (ask the instructor how to do it) that is not part of the 10-mL volume. Weigh the cylinder with the water and record the mass to the nearest 0.001 g (D.9). Calculate the mass of water (C.7) and record it in the Datasheet. 4. Calculate the density of water (this represents 0% NaCl) (C.8). 5. Pour the water inside the graduated cylinder in a beaker and measure and record the temperature (D.10). Dry the cylinder with a paper towel rolled to fit it. Be careful when drying with a paper towel as paper might get stuck in the narrow body of the cylinder. 6. Rinse the graduated cylinder with about 2 mL of 4% NaCl. Collect the rinsing in a beaker in step. 7. Using the proper technique, measure exactly 10 mL of 4% NaCl solution inside a graduated cylinder. Record the 10 mL volume on the datasheet (D.8).

4

8. Weigh the graduated cylinder with 4% NaCl to the nearest 0.001 g (D.11). Record on your datasheet. 9. Calculate the mass of the 4% NaCl and record. 10. Using the mass and volume calculate and record the density of 4% NaCl. 11. Repeat steps 5 to 10 for 8%, 12%, 16% and unknown NaCl solutions.

III. Results Analysis Part I Density of a Solid

Group C Measured (D) and Calculated Data (C)

a. Mass of metal sample (D.1)

5.004g

b. The volume of water + metal simple in a graduated cylinder (D.3)

7.30mL

c. The volume of water in the Two methods are graduated cylinder (D.2)

6.60mL

d. The volume of water displaced (b-c)(C.1)

7.30mL-6.60mL= 0.70mL e. The density of metal (C.2) (a / d ) or

𝑚𝑎𝑠𝑠 𝑜𝑓 𝑚𝑒𝑡𝑎𝑙

( 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑚𝑒𝑡𝑎𝑙 𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑑 ) f.

The probable identity of the metal**

g.

Percent error (C.3)

% error =

𝐷 =

Tin = 7.3g/mL

|𝑒𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙−𝑡ℎ𝑒𝑜𝑟𝑖𝑐𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 | x 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑣𝑎𝑙𝑢𝑒

100

5.004𝑔 𝑔 = 7.2 𝑚𝐿 0.70𝑚𝐿

𝑔

% 𝑒𝑟𝑟𝑜𝑟 =

𝑔 |7.2 𝑚𝐿 −7.3 𝑚𝐿 | 𝑔

7.3 𝑚𝐿

x100

=1.4% * Show all calculations ** Note: Probable Unknown Metal: Aluminum = 2.7 g/mL; Tin = 7.3 g/mL; Nickel = 8.9 g/mL

5

Part II density of a Liquid Measured (D) and Calculated Data (C) a. Volume of unknown liquid (D.4)

10.00mL

b. Mass of volumetric flask + unknown liquid (D.6)

17.642g

c. Mass of empty volumetric flask (D.5)

10.642g

d. Mass of unknown liquid (b – c) (C.4)

17.642g - 10.642g = 7.000g

e. Density of unknown liquid ((C.5) (d/a) f.

D=

7.000𝑔 𝑔 = 0.7000 𝑚𝐿 10.00𝑚𝐿

2-propanol = 0.7854 g/mL

Identity of unknown liquid*

𝑔

𝑔

% 𝑒𝑟𝑟𝑜𝑟 =

|0.7000 𝑚𝐿 −0.7854 𝑚𝐿 |

g. Percent error (C.6)

% error =

𝑔

0.7854 𝑚𝐿

|𝑒𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙−𝑡ℎ𝑒𝑜𝑟𝑖𝑐𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 | x 100 x100 =10.87% 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑣𝑎𝑙𝑢𝑒

Possible identity of unknown liquid:

2-propanol = 0.7854 g/mL; 95% ethanol = 0.8114 g/mL;

toluene = 0.8669 g/mL The identity of the unknown liquid is closer to 2-propanol =0.7854 g/mL therefore the unknown liquid is 2-Propanol Part III Determination of Solution Concentration using the Graphical Trend Line Relationship between Density and Concentration

0 % NaCl

Measured (D) and Calculated Data (C)

a. Mass of graduated cylinder + water (D.9)

36.342 g

b. Mass of graduated cylinder (D.7)

26.625 g

c. Mass of water (a – b) (C.7) d. Volume of water in cylinder (D.8)

36.342 g - 26.625g = 9.717 g 10.00 mL

6

e. Density of water (C.8) f.

D=

Temperature (D.10)

4 % NaCl

9.717𝑔 𝑔 = 0.9717 𝑚𝐿 10.00 𝑚𝐿 25℃

Measured (D) and Calculated Data (C)

a. Volume of NaCl solution (D.8)

10.00mL

b. Mass of graduated cylinder + NaCl solution (D.11)

36.589 g

c. Mass of graduated cylinder (D.7)

26.625 g

d.

Mass of NaCl solution (b – c) (C.9)

e. Density of NaCl solution (C.10)

8% NaCl

36.589 g - 26.625 g = 9.964g D=

9.964𝑔 𝑔 = 0.9964 10.00 𝑚𝐿 𝑚𝐿

Measured (D) and Calculated Data (C)

a. Volume of NaCl solution (D.8)

10.00 mL

b.

36.909 g

Mass of graduated cylinder + NaCl solution D.12)

c. Mass of graduated cylinder (D.7) d.

Mass of NaCl solution (b – c) (C.11)

e. Density of NaCl solution (C.12)

12% NaCl

26.625 g 36.909 g - 26.625 g = 10.284 g D=

10.284𝑔 𝑔 = 1.028 10.00 𝑚𝐿 𝑚𝐿

Measured (D) and Calculated Data (C)

a. Volume of NaCl solution (D.8)

10.00 mL

b.

37.196 g

Mass of graduated cylinder + NaCl solution (D.13)

c. Mass of graduated cylinder (D.7)

26.625 g

d. Mass of NaCl solution (b – c) (C.13)

37.196 g - 26.625 g = 10.571 g

e. Density of NaCl solution (C.14)

D=

16% NaCl a. Volume of NaCl solution (D.8)

10.571𝑔 𝑔 = 1.057 𝑚𝐿 10.00 𝑚𝐿

Measured (D) and Calculated Data (C) 10.00 mL

7

b. Mass of graduated cylinder + NaCl solution (D.14)

37.300 g

c. Mass of graduated cylinder (D.7)

26.625 g

d. Mass of NaCl solution (b – c) (C.15)

37.300 g - 26.625 g = 10.675 g

e. Density of NaCl solution (C.16)

D=

UNKNOWN % NaCl

10.675𝑔 𝑔 = 1.068 𝑚𝐿 10.00 𝑚𝐿

Measured (D) and Calculated Data (C)

a. Volume of NaCl solution (D.8)

10.00 mL

b. Mass of graduated cylinder + NaCl solution (D.15)

37.860 g

c. Mass of graduated cylinder (D.7)

26.625 g

d. Mass of NaCl solution (b – c) (C.17)

37.860 g - 26.625 g = 11.235 g

e. Density of NaCl solution (C.18)

D=

11.235𝑔 𝑔 = 1.124 𝑚𝐿 10.00 𝑚𝐿

% NaCl

0%

4%

8%

12%

16%

Unknown % NaCl

Density (g/mL)

0.9717

0.9964

1.028

1.057

1.068

1.124

8

IV. Discussion Part I Density of a solid In this part of the experiment, we were asked to get the density of an unknown solid. However, in order to get the density of the solid, the mass and the volume of the substance had to be found. There are two methods that are used to find the volume of the object, the first method is used to find the volume of a regular shape whether is cubic or cylindrical we had to measure the appropriate dimensions and then calculate the volume. The other method is used to find the volume of an irregular shape with a given amount of solid. This is the displacement technique and this was the one that was used in this experiment. Now to determine the density of an irregular shape is determined by dividing the mass over the volume, the volume must be in mL. There were some precautions that needed to be done during this part of the experiment. To carefully slide the metal that way, we could avoid breaking the glassware or splashing the water. Another precaution that was taken in this part of the experiment, was the eye in line with a lower meniscus of a clear liquid that way avoiding erroneous while reading the volume. Once the object was submerged the water was used to determine the volume of the solid, first, the solid

9

had to be submerged in the water, and by watching how much the water went up in the beaker. In other words, the displacement of the water in the beaker. Once the experiment was performed, and the density of the unknown solid was obtained, by comparing the density of other known metals, we established that the identity of the unknown metal was Tin. Part II

Density of a liquid

The goal in this part of the experiment was to find the density of the unknown liquid, the density was determined by using the same formula as in part one. Density equals mass over volume. However, to determine the volume of an unknown liquid a volumetric flask is used by measuring exact volumes of liquid. The density of the unknown liquid was 0.7000 g/mL, this was four significant figures due to the fact that that was the least significant figures while subtracting were four. Now, to determine the percent error of the unknown liquid, the theoretical density as well as the experimental value was used. The percent error was 10.9%, the possible causes of the percent error in this experiment could be due to human error while measuring the liquid in the beaker and/or when using the volumetric flask. Now the possible unknown liquid is more likely to be 2-propanol because it is the closest to any other density. Part III Determination of Solution Concentration using Graphical Trend-line Relationship between Density and Concentration The main goal of this part of the experiment was to find the density of five known concentrations which were 0%, 4%, 8%, 12%, and 16% of NaCl solutions, plus another one with an unknown concentration. This was accomplished by measuring the mass and the volume by using the density equation. Now, the unknown concentration of the NaCl solution was determined by using the graphical method. In the graph, the density was plotted against the concentration and a trend line was then drawn. The density of the known concentration was calculated using the density

10

formula which is d = m/v. However, between each measurement, it was important to rinse the graduated cylinder because that way it would remove other concentration solutions that could be in the beaker. Once the density of all known concentrations was collected, then it was plugged into the graph. The density (g/mL) was plugged into the vertical axis while the NaCl concentration was plugged into the horizontal axis. For both the density and the NaCl concentrations the starting points were “0” since we had NaCl of zero concentration. Since the density was plugged into the vertical axis and the concentration into the horizontal the graph was labeled as “Density (m/mL) vs %NaCl” this was important to identify the concentration of the unknown NaCl solution with the trend line. The equation of the trend line basically, ‘density = m (%m/v NaCl) + b’ where m is the slope and b is the y-intercept. Once the density and the concentration was plugged into the graph it was noticed that while the percentage of the concentration was increasing also the density was increasing. If the density was higher, it corresponded to a higher percentage of NaCl. Finally, to find the concentration of an unknown solution, the graph was used. There were two techniques that could be used to identify the concentration of the unknown solution, one of the methods used to determine the concentration of the unknown NaCl is the graphical method and/or the equation of a straight line. To determine the concentration of the unknown solution I used the graph method. Which the unknown concentration was equal to 6%. V. Conclusions By performing this experiment, there were some important concepts that were l...