chem lab of Solutions – Concentration

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Chemistry 147 Data Template Solutions Instructions: Data goes in yellow boxes; for results, complete calculations in blue. Lab Section Group Members ali rajeh Sodium Chloride Experiment NaCl Stock Solution (Group) Mass NaCl Volume L 21.99 Moles NaCl moles 0.25 Concentration NaCl Stock Solution moles/L,M 0.38 1.51 NaCl Dilution (Individual) Name: ali rajeh Pipet (Vol) L Dilution (Vol) moles 0.025 0.025 Evaporation of NaCl (Individual) Name: ali rajeh Average 0.01 0.01 0.01 0.01 mol/L 0.025 0.025 Mass Evap Dish g Volume L Concentration of Diluted NaCl Solution 44.253 44.254 44.398 44.399 0.15 0.15 Mass Dish + Salt g Predicted NaCl (mass) g 44.334 44.309 44.482 44.436 0.08796 0.08796 0.08796 0.08796 Actual NaCl (mass) g 0.081 0.055 0.084 0.037 0.064 % Error % 26.07 -14.40 30.74 -42.41 Dye Experiment Dye Used blue#1 Dye Stock Solution (Group) Mass Dye Volume L 0.015 Moles Dye moles 0.1 Concentration Dye Stock Solution mol/L 1.89203E-05 Dye Dilution (Individual) Name: ali rajeh Average Pipet (Vol) L Predicted Conc. Diluted Dye Soln Dilution (Vol) L 0.001 0.001 0.001 0.001 0.0002 Absorbance mol/L 0.1 0.1 0.1 0.1 0.000002 0.000002 0.000002 0.000002 0.10 0.003 0.10 0.005 Calculated Conc % Error from absorbance 1.1147E-06 3.34411E-08 1.1147E-06 5.57351E-08 5.79646E-07 245.038462 245.038462 245.038462 245.038462 Goals 1. Students will understand concentration 2. Students will understand dilutions Objectives 1. Students will be able to make a solution of known concentration 2. Students will be able to carry out a dilution 3. Students will be able to safely handle chemicals Introduction You are applying for a job as a laboratory technician in a forensics lab. There are four of you competing for one job, and as part of the laboratory’s quality control monitoring you are required to prepare a set of solutions that will be tested to check your laboratory technique. The laboratory director will hire one of you based on your experimental technique. For the first part of the experiment you will make a sodium chloride solution, dilute this solution and evaporate the water. The amount of sodium chloride remaining will be used to check if your dilutions were correct. For the second part of the experiment, you will prepare and then dilute a dye solution. The absorption spectrum of this solution will be used to check if your dilutions were correct. Equipment: 1. 100.00 mL volumetric flask with stopper (x5) 2. 250.00 mL volumetric flask with stopper (x5) 3. 1.00, 10.00, and 25.00-mL pipet (x2 each) 4. Pipet bulb (x4) 5. Cuvette (x5) 6. Spec 20 Spectrophotomer 7. Hot plate Reagents: 1. Sodium chloride (solid) 2. FD&C Red 40 (solid) 3. FD&C Yellow 5, Tartrazine (solid) 4. Indigo Carmine (solid) 5. FD&C Blue 1 (solid) Resources: 1. http://science.widener.edu/svb/video/ 2. NIOSH Pocket Guide to Chemical Hazards (NPG) - http://www.cdc.gov/niosh/npg/ 3. SIRI MSDS Database - http://siri.org/msds/index.php 4. Comprehensive Guide to Chemical Resistant Best Gloves - http://www.chemrest.com/ 5. 12 Principles of Green Chemistry – http://bit.ly/1zV7h5c Procedure Prepare a procedure to make the following solutions: 1. Salt Water a. Group – Prepare 250.0 mL of a 1.5 M NaCl solution b. Individual – (1 replicate each) i. Use 1.5 M NaCl stock solution to make 250.0 mL of 0.15 M NaCl. ii. Evaporate 10.0 mL from 0.15 M NaCl solution and determine the mass of NaCl. 2. Dye a. Group – Prepare 100.0 mL of one of the following stock solutions i. 5.0 x 10-4 M FD&C Red 40 ii. 1.0 x 10-3 M FD&C Yellow 5, Tartrazine iii. 5.0 x 10-4 M Indigo Carmine iv. 2.0 x 10-4 M FD&C Blue 1 b. Individual - Use the stock solution to prepare 100.0 mL of one of the following solutions (1 replicate each). i. 5.0 x 10-6 M FD&C Red 40 ii. 1.0 x 10-5 M FD&C Yellow 5, Tartrazine iii. 5.0 x 10-6 M Indigo Carmine iv. 2.0 x 10-6 M FD&C Blue 1 c. Determine the absorbance for each of the individual dye solution (1 replicate each) 3. Your procedure should include step-by-step detail for the following: a. Information on how you will prepare the NaCl and dye solutions and dilutions. b. Detail on what substances you use, the quantities you use and how you measure them, what glassware you use, etc c. A graph using the equation below for the absorbance of your dye. You should plot Absorbance vs Concentration. The absorbance should cover a range from 0 to 1. FD&C Red 40 (λ = 502 nm) Absorbance = Molarity * 42400 FD&C Yellow 5, Tartrazine (λ= 425 nm) Absorbance = Molarity * 24340 Indigo Carmine (λ = 610 nm) Absorbance = Molarity * 21072 M FD&C Blue 1 (λ = 630 nm) Absorbance = Molarity * 89710 d. Numbered references for all external information you use. e. Safety and waste disposal information. f. Detail should be sufficient for another student to reproduce your experiment using nothing but your procedure. Grading 1. Procedure (15 pts, group). a. Submit Word document prior to the deadline to Campus Cruiser for approval. Use the ASSIGNMENTS feature of Campus Cruiser. Do not e-mail the procedure to your instructor. See page 12 of lab manual for instructions. b. Revise procedure ahead of time based on your instructor’s feedback. Each member of your group must write the procedure in your notebook before coming to lab. You must have the procedure in your notebook or you will not be allowed to do the experiment and will receive a zero! Also bring a copy of the revised procedure to lab for your group. c. Submit one copy of the revised procedure to Campus Cruiser before the lab period. This copy will be graded. 2. Notebook (20 pts, individual). a. Before you come to lab you must write, in your own words, the purpose of the experiment in your laboratory notebook. b. You must write steps for the revised procedure before lab. You will not be allowed to perform the experiment if you do not have the purpose and procedure written in your notebook before you enter lab. c. During the experiment, record all your data and observations in your laboratory notebook. Include all masses, volumes, temperatures, unknown numbers, and any other data (including units) you acquire, along with pertinent observations and descriptions. d. Record any changes in procedure you make during the experiment that differ from the procedure you wrote in your notebook. e. Submit carbon copies of laboratory notebook to instructor before leaving lab. 3. Results/Presentation (35 pts, group). a. Datasheet. Use template from shared files in Campus Cruiser to prepare a datasheet. b. Process data and prepare tables. Use Excel for the calculations. One person in each group should submit the Excel file with the calculations via Campus Cruiser before leaving lab. c. A portion of your grade will be based on the accuracy of your results. d. Presentation. Each group will give a brief presentation of their results to the class in the next lab period. Submit electronic version to campus cruiser and bring a hard copy, three slides per page format, for instructor. Remember, you are a technician in a forensics lab validating your technique. You should support your claims with evidence. Be sure to include the following: i. Make a claim ii. Tabulate data and results for NaCl and dye and include percent error. Tables should be succinct and easy to read. (1) Predicted Results. (a) Predicted mass of NaCl after the evaporation. (b) Predicted concentration of diluted dye solution. (2) Actual Results. (a) Mass of sodium chloride. (a) Concentration of dye. iii. Show sample calculations so that the audience knows how you got your results. iv. Sources of error. (compare your results with the expected results and with other students in your group) 4. Discussion (30 pts, individual). Completed by individual. Submit completed discussion to Campus Cruiser by due date. In your discussion you should make a conclusion and then explain how your experimental results and observations support your conclusion. The points below should help you identify the information you have available from this experiment to support your conclusion. Be sure to include: a. A claim. Based upon the purpose of your experiment, what claim can you make using your experimental evidence? b. A table of your results. Include; expected, experimental, and % error in mass of NaCl; expected concentration, absorbance, experimental concentration and % error in concentration of the dye solution c. Discussion of your results. i. Explain how your experiment results support your claims. ii. Explain discrepancies between expected and experimental results f. Uncertainty and Error in measurements. i. Identify at least three (3) possible sources of uncertainty and error in this experiment. ii. Use evidence from your laboratory notebook to evaluate the validity of these sources of uncertainty. iii. Discuss the error sources you have evaluated. iv. Discuss how the direction of each source of error affects the results. g. Supporting references that demonstrate the validity of your method.
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LAB REPORT
DILUTION

Group Members
Ali
Rajeh

OBJECTIVE
The objective of the experiment is to prepare two solutions:
a. sodium chloride solution
b. dye solution
The sodium chloride solution is then evaporated and the mass of sodium chloride is measured.
The dye solution is prepared and its absorption spectrum is obtained.
THEORY
Sodium chloride (NaCl) is an ionic compound of positive sodium ions and negative chloride ions.
When positive molecules of water attract negative chloride ions and when negative water molecules
attract positive sodium ions, water dissolves sodium chloride in it. When such a solution is formed,
sodium chloride is called the solute and water is the solvent. To such a solution, when more solvent is
added to decrease the concentration, the process is called dilution. The number of moles of a solute per
litre of solution is called as molarity or molar concentration, M, of the solute.
𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦, 𝑀 =

𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠, 𝑛
𝑉𝑜𝑙𝑢𝑚𝑒 𝑖𝑛 𝑙𝑖𝑡𝑟𝑒𝑠, 𝑉

When this NaCl solution is evaporated, water in the solution evaporates and we obtain the solute, NaCl.
If dilution is proper, the molarity of concentrated solution will be equal to the molarity of diluted
solution.
When dye solution is diluted, absorption spectrum of the dye solution is obtained using a
spectrophotometer. Absorbance is the amount of light blocked by the molecules of a solution. From the
absorption spectrum, molarity of the diluted dye solution is calculated. If dilution is proper, according to
Beer Lambert’s law, the Absorbance Vs Concentration graph will be linear.
PROCEDURE
Dilution of NaCl solution
1. Number of moles of NaCl required to prepare 250mL of 1.5M NaCl solution was calculated as
per below given formula.
250 mL ×

1.5𝑀
1𝐿

= 0.375 mol of NaCl

2. 1 mol of NaCl weighs 58.43g or molar mass of NaCl = 58.43g. Thus, Mass of NaCl required is then
calculated as follows:
0.375moles × 58.43 g/ moles = 21.99 g

3. Take exactly 21.91g of NaCl for the experiment using a weighing machine, record it and
carefully transfer it to a 250mL volumetric flask.
4. Add water to it and stir well to dissolve NaCl in the water completely.
5. Add more water to make up 250mL of the solution. Be careful to add water drop by drop when
the level of water is near the 250mL mark in the neck of the volumetric flask so that the level of
water doesn’t exceed the 250mL mark.
6. The actual concentration of this ...


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