01:160:311 Study Guide - Quiz Guide: Solvent, Boiling Point, Miscibility
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Separation of a Mixture Laboratory
In this experiment we will separate the different components of a mixture made up of sand (SiO2) and sodium chloride (NaCl, commonly known as salt). Both of these compounds are solid white crystals, so it is difficult to tell them apart with the naked eye. However, each component exhibits different physical properties that can be used to separate one from the other. There are several physical separation techniques that can be used to determine the percent composition of the original mixture.
Materials & Apparatus:
Sand/salt mixture provided in your Lab Kit
2 - Erlenmeyer Flasks
Scale
Water
Graduated Cylinder
Background:
It is important to know how to separate mixtures because many reactions carried out in the laboratory produce mixtures of different compounds. It is often necessary to separate the components of these mixtures, which can be done using several techniques. We will explore a few of these techniques: sublimation, filtration, evaporation and decantation.
Sublimation is the process of a substance passing from the solid to the gaseous state without first passing through the liquid state. Not all substances possess this characteristic. In fact, most substances to NOT sublime under normal conditions, but must be placed under low pressure and low temperature. Ammonium chloride (NH4Cl) and iodine (I2) are both substances that do sublime under normal conditions.
Filtration is the process used to separate the components of a mixture of solid substances that differ in solubility in a certain solvent. You can separate a mixture of solid substances by adding a liquid to the original mixture in which only some of the components of the mixture will dissolve. The resulting mixture, which contains both the dissolved and undissolved substances, is then poured through a filter paper--a porous paper that allows liquids to pass through while retaining any solids. The liquid that has passed through the filter paper is called the filtrate; the solid on the paper is the residue.
Evaporation can also be used to separate the solvent from the solution. A solution can be slowly heated in an Erlenmeyer flask, and the solute will remain after the solvent has evaporated.
Decantation is the process of separating a liquid from a solid (sediment) by gently pouring the liquid from the solid so as not to disturb the solid.
For this experiment, a practical plan is as follows: First combine the solid mixture of the two compounds, sodium chloride (NaCl) and sand (SiO2), with water. This will dissolve the sodium chloride. The sand will not dissolve into the water. We will "filter" the entire mixture, which allows the water in which the sodium chloride is dissolved to pass through, but not the sand. We will now have separated the sodium chloride and the sand. Then, we must evaporate off the water so that we weigh only the two original solids and not the water we added.
Procedure:
(NOTE: Do NOT dispose of any part of your lab until you are 100% positive you do not need it again. It is good practice to keep all parts of your lab until you are finished.)
Record the letter (A, B, C, or D) of your mixture (on the bag contents label) on the line above Data Table 1 below.
Obtain an Erlenmeyer flask [label it 1] and weigh and record the mass.
Add the entire contents of your unknown mixture bag to the flask and weigh and record the mass of the Erlenmeyer flask and the mixture.
Add 10 mL of water (preferably distilled) to the solid in the Erlenmeyer flask [Erlenmeyer flask 1] and stir gently for 5 minutes.
Weigh a new clean, dry Erlenmeyer flask [Erlenmeyer flask 2].
Decant the liquid from Erlenmeyer flask 1 into Erlenmeyer flask 2. This may work better if you place a utensil against the lip of the pouring flask to encourage a slow steady stream of liquid into the second flask.
Add another 10 mL of water to the solid in Erlenmeyer flask 1, stir for 1-2 minutes, and decant this liquid into the Erlenmeyer flask 2 as before.
Repeat with still another 10 mL of water. This process extracts (dissolves) the soluble sodium chloride from the insoluble sand.
Allow the two flasks to dry. Let them dry until the sand appears dry and freely moves when you shake the Erlenmeyer flask a little and the sodium chloride looks dry.
To speed up the process, you can heat the flasks slowly over a burner set on low on your stove top or in the oven (set at 125-200ËF). I would suggest heating it on top of another pan (NOT nonstick coated) Use a low setting and watch closely as you donât want it to boil over.
Allow the Erlenmeyer flasks to cool to room temperature (if they were heated) and weigh the Erlenmeyer flasks and their contents separately. Record their masses in the appropriate sections of the table.
To ensure that there is no water remaining, heat for another 5-10 minutes oven or 1-2 minutes on the stove. Allow to cool to room temperature and reweigh the Erlenmeyer flask. If it is within 0.3 g of your initial weighing you can stop. If the second weighing is not within 0.3 g of your initial weighing, reheat again, cool, and reweigh. The difference between this mass and the mass of the empty Erlenmeyer flask is the mass of NaCl.
Unknown Mixture Label (A, B, C, or D) ___________
Data Table 1
| Measure or calculate and record the following (in grams): | |
| mass of the empty Erlenmeyer flask 1: | |
| mass of the Erlenmeyer flask 1 plus the mixture sample: | |
| mass of the mixture sample: | |
| mass of the Erlenmeyer flask 1 and the remaining contents after drying of sand: | |
| mass of Erlenmeyer flask 1 and dry sand (2nd weighing) | |
| Subtract (a) from (e) to obtain the mass of sand in the sample: | |
| Measure or calculate and record the following (in grams): | |
| mass of an empty Erlenmeyer flask 2: | |
| mass of Erlenmeyer flask 2 and dry NaCl (1st weighing) | |
| mass of Erlenmeyer flask 2 and dry NaCl (2nd weighing) | |
| mass of Erlenmeyer flask 2 and dry NaCl (3rd weighing) if necessary | |
| measured mass of dry NaCl: |
Assignment Questions (all work must be shown for all calculations):
Using the results of your lab, complete all the questions below.
Upload one picture that is representative of your experiment with this report to the appropriate D2L Brightspace Assignments folder.
Complete Data Table 1 located in the Procedure. Make sure to include all your work for all the calculations performed.
The amount of sodium chloride in the original mixture may also be determined indirectly by subtracting the SiO2 mass from the initial sample mass. Calculate the expected mass of NaCl using this method.
Calculate the percent difference of NaCl (Note: This is not % Error, but it is a similar calculation. This is an error calculation that checks precision between the results of the two methods from the following equation: (Note: the unit for this calculation is â% differenceâ)
% difference=measured mass-mass by subtractionmass by subtraction x 100
What is the mass percent of each component in your mixture: SiO2, and NaCl? (Note: the units for this calculation are â% SiO2â and â% NaClâ)
mass percent=mass of componenttotal mass of sample x 100
Error Analysis: Was your % difference from Assignment Question 4 within 10%? Why or why not? Did your two mass percentages in Assignment Question 5 add up to 100%? Why or why not? What were your biggest sources of error in this experiment? What would you do differently if you were to repeat this experiment? Explain.
What type of properties (physical or chemical) are we using to separate the mixture in this laboratory. Explain your answer.
A mixture is found to contain 0.69 g SiO2, 1.05 g of cellulose, and 2.17 g of calcium carbonate. What is the mass percentage of SiO2 in this mixture?
Assume you have a mixture of NH4Cl, sand, and salt and access to a regular chemistry laboratory. How would you separate the three?Write out what your procedure would be in numbered steps. Please research the answer to this question and properly cite your source. It is alright to research using the internet. However, Wikipedia, Yahoo Answers, Ask.com, and other non-scientific sources cannot be used.
Procedure: Setting Up: Add 1.0 g of p-aminobenzoic acid and 10 mL of absolute ethanol to the round-bottom flask containing a stir bar. Stir the mixture until the solid is completely dissolved. Add 1 mL of concentrated [18M] sulfuric acid dropwise to the ethanolic solution of p-aminohenzoic acid, equip the flask with a condenser, and set up the apparatus for heating under reflux using the heating mantle. Reaction: Heat the mixture under gentle reflux for 30 min, stirring all the while. If any solid remains in the flask at this time, remove the flask from the heat source and allow the mixture to cool for 2-3 min. Add an extra 3 mL of ethanol and 0.5 mL of concentrated H2SO4, to the reaction flask and resume heating under reflux. After the reaction mixture becomes homogeneous, continue heating it under gentle reflux for another 30 min. For the experiment to succeed, it is important that all of the solids dissolve during the reflux period. Work-Up and Isolation: Allow the reaction mixture to cool to room temperature and then pour it into a beaker containing 30 mL of water. Basify the mixture to a pH of about 8 by slowly adding 10% aqueous sodium carbonate with stirring. Be careful in this step as frothing occurs during the neutralization. You should calculate beforehand the approximate volume of 10% aqueous sodium carbonate that will be required to neutralize the total amount of sulfuric acid you used. Collect the crude benzocaine that precipitates by vacuum filtration. Use three 10-mL portions of cold water to rinse the solid from the beaker and wash the filter cake. Air-dry the product. Purification: Weigh the crude product and recrystallize from methanol/water pair of solvents: Place the solid in a 50 mL Erlenmeyer flask. Add the minimum amount of hot methanol to dissolve it. Keep on a steam bath. Slowly add hot water to the solution using a disposable pipette just until the solution becomes cloudy and fails to clear up when it is swirled. To the hot solution on the steam bath add hot methanol, drop wise, until the turbidity or crystals just disappear. Allow the solution to cool to room temperature and then cool it in an ice-water bath for 10-15 min to complete crystallization. Isolate the crystals by vacuum filtration, wash them with 5-10 mL of cold water, and allow them to air-dry. Weigh the crystals and calculate the percentage yield.
True or False? When analyzing the IR spectra of starting material and product, a positive indication suggesting that the product was made would be the disappearance of a strong stretch between 1690-1740 cm-1.
|
Why is it important that all of the solids dissolve during the reflux period for you to obtain a good yield of product?
A. Because everything needs to be in solution for the reaction to happen to the fullest extent.
B. Because the product will be impure if the intermediate doesn't dissolve completely.
C. Because the ethanol will evaporate off if it's not dissolved.
D. All of the above
What is the gas that is evolved during neutralization?
A. O2
B. CO2
C. SO2
D. CO3
Why is it necessary to neutralize the reaction mixture to work up the product?
A. Because it is dangerous to work with an acidic solution.
B. Because after the addition of ethanol and sulfuric acid, the benzocaine exists as ammonia and must be protonated so that it becomes insoluble and collectable.
C. Because after the addition of ethanol and sulfuric acid, the benzocaine exists as a soluble carboxylic acid and must be neutralized so that it becomes insoluble and collectable.
D. Because after the addition of ethanol and sulfuric acid, the benzocaine exists as a soluble ammonium salt and must be neutralized so that it becomes insoluble and collectable.
If you end up adding 1.5 mL of concentrated sulfuric acid (18 M), how many mL of 10% aqueous sodium carbonate would be required to neutralize the reaction mixture?
A. 1.5 mL
B. 3 mL
C. 15 mL
D. 29 mL
What is the purpose of the sulfuric acid?
A. To catalyze the reaction.
B. To protonate the intermediate salt.
C. To protonate the ethanol.
D. To increase the pH of the reaction mixture.
What is the theoretical yield of the product?
A. 1.00 g
B. 2.98 g
C. 1.20 g
D. 10 mL