Lab Report Density vs. Concentration of Na Cl Solutions PDF

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Density vs. Concentration of NaCl Solutions By: Jonathan Pilafas (performed on 9/10/2018) Purpose: The objective of this lab is to determine the average density of sodium chloride (NaCl) at a variety of different concentrations of NaCl in order to find a reliable trend that can be found through graphing.

References: 1. “Laboratory Experiments for Chemistry 121” - Harper College 2. http://dept.harpercollege.edu/chemistry/msds1/Sodium%20chloride%20ScienceLab.pdf 3. http://dept.harpercollege.edu/chemistry/msds1/Deionized%20Water%20ScienceLab.pdf

Reagents:

Name

Chemical Formula

Molecular Weight

Density

Concentration(s)

Deionized Water

H2O

18.02 g/mole

1 g/mL

55.555 moles

Sodium Chloride

NaCl

58.44g/mole

2.16 g/mL

5%, 10%, 15%, 20%, Unknown A, Unknown B

Safety: Deionized water - Health 0, Fire 0, Reactivity 0 Sodium chloride - Health 1, Fire 0, Reactivity 0

Methods: To begin the experiment, collect the essential and prepared NaCl solutions needed for the lab, which are the 5%, 10%, 15%, and 20% concentrations of NaCl, as well as Unknown A and Unknown B. The procedure in my lab notebook says to prepare these solutions, but that did not occur during this lab because Dr. Weiss had prepared them already. Next, complete three trials of each concentration using the volumetric pipet so that the density values for each solution of known concentration are reliable. This device differs from the one listed in my procedure in my lab notebook, which says to use the volumetric buret. Additional tests might be necessary if there is a glaring outlier found while measuring. Be aware of the significant figures in measurements and calculations. While testing, record the glassware used, amounts of water and sodium chloride, how calculations of the solution concentrations are made, how solution densities are measured, etc. in lab notebook. Next, choose and unknown solution (Unknown A or Unknown B) and record what was selected. Measure the density of this unknown solution by following the same procedure used for the solutions of known concentration. Plot the average density (g/mL) vs. the percent by mass concentration (% NaCl) on a graph using the data from each of the solutions of known concentration that have been prepared. After graphing the data, determine the best-fit line equation (y=mx+b) and coefficient of determination (R² value) and include them both on the graph. If any points are grossly out of line, remake the solution, repeat the density measurements for it, enter the new data, and run the Excel “best fit” determination again. Using the best-fit equation and the mean density of the unknown solution, solve the equation for the percent by mass concentration of the unknown solution. Then, record the % by mass of the unknown solution in notebook. Lastly, plug the unknown solutions into the graph to

conclude the experiment. The end of these listed directions differs from my procedure, which tells us to find the percent error of the unknown concentration we find. There was no instruction during the lab to include these pieces of data, so they are not found in this lab as a result.

Instruments: -

Electronic balance

Glassware: -

10 mL volumetric pipet

-

50 mL beaker

Data: Data Table: % NaCl Solutions % NaCl Solution

Mass (g)

Volume (mL)

Density (g/mL)

5

9.936

10.0

0.9936

10

10.733

10.0

1.0733

15

10.907

10.0

1.0907

20

11.377

10.0

1.1377

Unknown A

10.423

10.0

1.0423

Unknown B

10.737

10.0

1.0737

Graph: SEE NEXT PAGE FOR GRAPH

Calculations:

Calculating the density of each solution: EXAMPLE USED: 15% NaCl Solution 1. (Mass beaker + solution (g)) - (Mass beaker (g)) = Mass solution (g) EX: -

Trial 1: (37.054 g) - (26.164 g) = 10.890 g

-

Trial 2: (37.167 g) - (26.264 g) = 10.903 g

-

Trial 3: (37.205 g) - (26.227 g) = 10.928 g

2. (Mass solution #1 + Mass solution #2 + Mass solution #3) / 3 = Avg mass of solution EX: -

(10.890 g + 10.903 g + 10.928 g) / 3 = 10.907 g

3. (Average mass of solution (g)) / (Volume solution (mL)) = Density solution EX: -

(10.907 g) / (10.0 mL) = 1.0907 g

Calculating the average density and the standard deviations of each solution: (Density #1 + Density #2 + Density #3) / 3 = Average density EXAMPLE: 15 mL NaCl Solution -

(1.089 g/mL + 1.090 g/mL + 1.093 g/mL) / 3 = 1.090666667 g/mL

(Density #1 distance from the mean + Density #2 distance from the mean + Density #3 distance from the mean) / 3 = Standard deviation (Average distance from the mean) -

| (1.089 g/mL - 1.090666667 g/mL) | + | (1.090 g/mL - 1.090666667 g/mL) | + | (1.093 g/mL - 1.090666667 g/mL) | / 3 = Standard deviation

-

(0.001666667 g/mL) + (0.000666667 g/mL) + (0.002333333 g/mL) / 3 = Standard deviation

-

0.004666667 g/mL / 3 = Standard deviation

-

Standard deviation = 0.0015555557

Calculating the % NaCl concentration in each of the unknowns: Given equation is y = 0.009x + 0.9615 Density of Unknown A = 1.042333333 Density of Unknown B = 1.0736666667 To find % NaCl concentration, plug in both densities as “y”

Unknown A -

Y = mx + b

-

X = (y - b) / m

-

X = 8.981481481

Unknown B -

Y = mx + b

-

X = (y - b) / m

-

X = 12.46296296

Results: To conclude this lab, the concentration of Unknown A was recorded as 12.49296296%, and the concentration of Unknown B was recorded as 8.981481481%.

Discussion: During this lab, I found that the percent by mass for NaCl solutions would increase in density approximately 0.045 per 5% increase in concentration, or 0.009 per 1% increase in concentration, as demonstrated in the given slope-intercept equation y = 0.009x + 0.9615. For instance, the 15% NaCl solution was found to be 1.090666667, and the 20% NaCl solution was

found to be 1.137666667. The difference between these two values is 0.0047 considering its 5% increase in concentration, which means the distance between these two values is 0.0094 per 1% increase in concentration. This is evidently close to the given slope of 0.009, and validates it as a result. The y-intercept of the given equation is 0.9615. The y-intercept is relatively accurate at this point because of the concentrations of the solution. When the solution has a 0% NaCl solution, that means the solution is 100% water. If the solution is 100% water, the concentration will be as close to 1 as possible, therefore validating 0.9615 as the slope-intercept of the given equation. Although most of the points we recorded on our graph were valid, we reached a questionable error while plugging in the data for 20% NaCl concentrated solution. Instead of the density increasing at a reasonable pace, such as a 0.009 per 1% increase like the given equation suggests, the density dropped in half. Thankfully, we retested the measurements and found the appropriate data, and the increase from the 15% NaCl solution to the 20% NaCl solution turned out to be the most accurate change throughout the entire experiment. In addition, there are not any glaring discrepancies in the densities of the unknown solution, and I think our team did an excellent job of ensuring that. I personally the volume of the pipet impacted the calculated density very positively. Since this experiment required a very accurate volumetric device, the volumetric pipet was our best option. Since our group discovered data that was profoundly accurate to one another’s, it was evidently the result of following clear directions, as well as the device achieving nothing but positive results.

Error Analysis: Although most of our experiment went well, there were some issues that must have arisen throughout the experiment, since the data and results on the excel graph were not quite perfect. The volumetric pipet was a phenomenal measuring device, but I genuinely believe that this is where most of our mistakes occur. Since the 10 mL solution’s data point was noticeably higher than the rest of the data points according to the line on the graph, my lab partner clearly must have made a mistake. Since errors during the initial stages of the experiment were very difficult to achieve, the only explanation for the failure during this experiment had to have occurred while measuring.

Conclusion: At the end of this experiment, we concluded that the increase of 1% concentration of NaCl in NaCl solutions increases at a rate of y = 0.009x + 0.9615. This was a simple idea to discover, since my team of four classmates collaborated and discovered data that increased at a steady rate from one anothers data. In addition, this lab goes to show that the data being recorded from volumetric devices is absolutely critical to measure correctly when collecting data....