EXPERIMENT 2: Separation of the Components of a Mixture Materials: Evaporating dish (2) Watch Glass
Magnet
Hot Plate
Unknown mixture
Objective: To learn the use of physical properties such as solubility, density, boiling point, and melting point to identify liquids and solids substances.
INTRODUCTION Elements and compounds are pure substances. The composition of a pure substance is constant, and thus pure substances have characteristic physical properties that do not change. Examples of physical properties that can be used to describe pure substances include solubility, conductivity, magnetism, density, boiling point, and melting point. A mixture results from the combination of two or more pure substances that do not react chemically. The physical properties of a mixture depend on its composition because the amounts of each substance making up a mixture can vary. By taking advantage of the unique physical properties of individual components within a mixture, it should be possible to separate a mixture into its components. Mixtures have the following fundamental properties:
Each component of a mixture retains its chemical identity and hence its own properties. Composition of a mixture may vary while that of its components is fixed. Mixtures can be separated into these components by using physical methods like, decantation, distillation, evaporation, crystallization, sublimation, and filtration.
For example, if one component in a mixture of two solids is soluble in water, whiles a second component is not, adding water to the mixture and filtering the residue can separate the water-soluble component from the insoluble component of the mixture. Subjecting the mixture to such a physical change would change the ratio of components of the mixture. This leads to one of the definitions of a mixture - a substance whose composition can be altered by a physical change. Most common materials in our daily life are examples of mixtures, such as rocks, soil, seawater, cement, and wood. Mixtures can be either homogenous or heterogeneous. This experiment deals with the separation of the components of a heterogeneous mixture. Physical properties like magnetic property, solubility, etc. will be utilized in the separation techniques. In order to determine the percent composition of a mixture, it is necessary to separate the components quantitatively (without loss of material) and then measure the mass of each recovered component. Mass percent composition is a convenient way to express the actual composition of a mixture in terms of the amount of each component. The sum of the mass percentage of all components in a mixture equals 100%. The mass percentage of each component in a mixture is calculated as follows: Mass % of component = (mass of component/total mass of mixture) x 100% A flow chart is often used to illustrate the steps involved in the separation of a mixture. In a flow chart, the substances in the mixture are listed inside boxes and are connected by arrows. The actual physical steps that must be carried out to separate the components are listed next to the arrow.
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Experiment Overview The purpose of this experiment is to study the physical properties of salt (NaCl), sand (SiO2), and iron filings (Fe) and use this information to design and carry out a procedure for separating these three components in a mixture. The flow chart for the separation is given below: Mixture (Fe filings, salt, sand)
Weigh the remaining residue of salt & sand.
Discard the removed Fe into a designated container.
Add 20ml + 10ml + 10ml of water to the evaporating dish, stir and cautiously pour the liquid to a 2nd evaporating dish each time, make sure that no sand particles are transferred to the 2nd dish.
Dry the remaining wet sand in the 1st evaporating dish and let it cool. Weigh dry sand.
Gently evaporate water obtained in the 2nd dish to recover salt. When salt is completely dry, let it cool and weigh.
PROCEDURE 1. Record your unknown number on the data sheet.
2. Carefully weigh a clean and dry evaporating dish. Add about 2g of the unknown mixture to the dish. Weigh the dish containing the sample and calculate the sample weight by subtracting the weight of the empty dish. 3. Wrap a magnet in a piece of paper towel and use the magnet to pick out all of the iron filings from the mixture. Weigh the evaporating dish with the remaining solid. The loss in weight represents the amount of Fe in the sample mixture. 4. Add 20 ml of water to the solid in the evaporating dish and stir gently for a couple of minutes. 5. Weigh a second evaporating dish with a watch glass. 6. Decant the liquid from the first dish into the second dish. Be careful not to transfer any solid into the second dish.
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7. Repeat the decantation process (Steps 4 and 6) for two additional trials using 10 ml of water each time. This rinsing will ensure the extraction of all soluble NaCl from the sand. At this stage of the experiment there are two evaporating dishes – the first one with wet sand and the second one with a solution of NaCl and a watch glass. 8. Place the second evaporating dish with NaCl solution on a hot plate and gently heat the solution to evaporate the water. Towards the end, cover the dish with the previously weighed watch glass and reduce the heat to prevent splattering. When the NaCl is completely dry, no more water will condense on the watch glass and it, too, will be dry. Cool the evaporating dish and watch glass back to room temperature and weigh. Calculate the percentage of NaCl in the sample. 9. Place the first evaporating dish with wet sand on a hot plate and warm to dryness. When the sand is absolutely dry, remove the dish from the heat and cool to room temperature. Weigh the dish and the dry sand in it and calculate the amount of sand in the sample. Calculate the percentage of sand in the sample. Remember: % component =
wt. of component in grams x 100 wt. of sample in grams
Safety Precautions The materials in this lab are considered relatively nonhazardous. Observe all normal laboratory safety procedures. Wear chemical splash goggles whenever chemicals, glassware, or heat are used in the chemistry laboratory. 3
EXPERIMENT 2: Separation of the Components of a Mixture REPORT SHEET Name ___________________________
Instructor ______________________
Date ____________________________
Unknown # _________
PART A. a) Weight of evaporating dish and original sample: b) Weight of 1st evaporating dish: c) Weight of original sample: d) Weight of evaporating dish after removing Fe filing: e) Weight of Fe filings: f) % of Fe (show calculations):
_________g _________g _________g _________g _________g _________%
PART B. a) Weight of evaporating dish, watch glass and NaCl (after drying): b) Weight of 2nd evaporating dish and watch glass: c) Weight of NaCl: d) % of NaCl (show calculations):
_________g _________g _________g _________%
PART C. a) b) c) d)
Weight of evaporating dish and SiO2 (after drying): Weight of 1st evaporating dish: Weight of SiO2: % of SiO2 (show calculations):
_________g _________g _________g _________%
PART D. a) Weight of original sample: b) Weight of determined (Fe + NaCl + SiO2): c) Difference in these weights: % Recovery = g of matter x 100 g of original sample
_________g _________g _________g _________%
Account for errors:
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EXPERIMENT 2: Separation of the Components of a Mixture Name:____________________________ Pre-Laboratory Questions and Exercises Due before lab begins. Answer in the space provided. 1. Draw a flow chart for the separation of iron filings, salt (NaCl), and sand (SiO2) mixture used in the experiment.
2. Define the following techniques used for the separation of mixtures: Decantation -
Filtration -
Distillation -
Sublimation -
3. Define homogenous and heterogeneous mixtures. Give 3 examples of each
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EXPERIMENT 2: Separation of the Components of a Mixture Name:____________________________ Post-Laboratory Questions and Exercises Due after completing the lab. Answer in the space provided. 1. The Department of Transportation uses a mixture of sand and salt to de-ice roadways in the winter. The mixture contains 8.35 tons of salt and 6.28 tons sand. What is the mass percent of each component in the mixture?
2. A bakery needs a mixture of flour and sugar to make cookies. The mixture should contain 62.5%flour and 37.5%sugar. You are in charge of ordering the components to make 275 pounds of mixture. How many pounds of flour and sugar should be ordered?
3. Which substance(s) dissolve in water? Is solubility a physical or chemical property? Explain.
4. Is the combination of salt and sand a new compound or a mixture? Explain.
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