01Chem01Sep Mixture 2019 Spring PDF

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Exp #1 Separation and Analysis of a Ternary Mixture

Chem 01

Pre-laboratory Assignment Before coming into the laboratory, put the following information into your laboratory notebook. a. Title of Experiment b. Purpose of Experiment Also, draw Table 2 in your laboratory notebook (this will be completed during the experiment). Introduction Mixtures are defined as material consisting of two or more substances mixed together with each component retaining its original properties and separable by physical means. In a homogeneous mixture, the composition is uniform throughout the sample. In a heterogeneous mixture, the composition is not uniform throughout the sample. If one component in the mixture has greater prevalence than the others, this would be called an impure substance with the other called the impurities. There are many laboratory techniques that exploited the differences in physical and chemical properties of the components of the mixture and allow for the separation of the individual components (as shown in Fig 1). Fig 1 Separation Techniques: Decanting and Filtering

Decanting

Filtering

Decantation: The process of separating a liquid substance from a settled solid substance by carefully pouring the liquid from the solid without disrupting the solid. Dissolution:

The molecular dispersion of a solid in a liquid substance; for example, the process of dissolving sugar in water.

Evaporation: The process of converting a liquid into a vapor leaving only the dry solid portion. Filtration:

The process of separating a heterogeneous mixture in which the mixture is poured into a funnel equipped with filtering paper. The solid is retained in the filter paper while the liquid is collected in a separate container.

Sublimation: The direct transformation of a solid into a gaseous state without passing through the liquid state.

In this lab, a mixture of solid sodium chloride (NaCl), ammonium chloride (NH Cl), and silicon 4

dioxide (SiO , sand) will be separated into individual components. The differences in their physical and chemical properties will be used in the separation process (see Table 1). The techniques of sublimation, extraction, and decantation will be used to separate the components of the mixture (see 2

Fig 2).

Table 1 Chemical and Physical Properties Substance

Soluble in H O (25 C)

Sublimes (1 Atm)

SiO (sand)

No

No

NaCl

0.34 g/mL

No

NH Cl

0.28 g/mL

Yes

2

4

2

o

2

Fig 2 Separation of a Ternary Mixture

Mixture: SiO2 (s), NaCl (s), NH4Cl (s)

sublimation

heat with Bunsen burner flame (> 500 oC) in hood

solid

SiO2 (s), NaCl (s)

NH4Cl (g)

evaporating dish #1

vaporized

extraction

insoluble in water

SiO2 (s) evaporating dish #1

vapor

add water and decant

soluble in water

NaCl (aq) evaporating dish #2

gently evaporate water using hotplate

NaCl (s) evaporating dish #2

Procedure In the hood, heat a clean evaporating dish using a Bunsen burner (and the clay triangle and iron ring apparatus, as shown in Fig 3), removing any contaminates from the outside of the dish. Let the dish cool and carefully weigh the dish to the nearest 0.001 g. Measure 2-3 g of the unknown mixture into the evaporating dish. Record (see Table 2) the weight of the dish and mixture to the nearest 0.001 g.

In the hood, place the evaporating dish containing the mixture on the clay triangle (see Fig 3). Carefully, heat the evaporating dish with the burner and continue until no more white vapor is 3

produced (approximately 15 min). Stir occasionally with a glass stirrer to be sure all of the NH Cl has vaporized. Once the sublimation is complete allow the dish to cool on a cooling pad on the lab bench 4

top. With the dish at room temperature, weigh the evaporating dish containing the remaining mixture. Record (see Table 2) the weight to the nearest 0.001 g. Fig 3 Sublimation Apparatus

Add 5.0 mL of deionized water to the mixture in the evaporating dish and stir gently for 5 min. Obtain another evaporating dish. Clean, heat, cool, and weigh the dish as done previously. On the bench top, use a hotplate to heat water in a beaker. If using a 9-cm evaporating dish, use a 400-mL beaker about 3/4 full of water. If using a 10-cm evaporating dish, use a 600-mL beaker about 3/4 full of water. Check to be sure that the evaporating dish fits securely at the top of the beaker before continuing (as shown in Fig 4).

Fig 4 Evaporation of Water Decant or pipet the solution from the first evaporating dish into the second dish. Again, add 5.0 mL of deionized water to the mixture in the first evaporating dish, stir gently for 5 min, and again decant into the second dish. Repeat with an additional 5 mL of water. With the extraction steps complete, place the evaporating dish containing the aqueous sodium chloride solution on top of the beaker of boiling water (as shown in Fig 4). Gently, evaporate all of the water from the dish and take care to avoid spattering. Occasionally stir with a glass stirrer. Once the sample is dry, allow the dish to cool on a cooling pad on the lab bench top. With the dish at room temperature, 4

weigh the evaporating dish containing the sodium chloride. Record (see Table 2) the weight to the nearest 0.001 g. Place the evaporating dish containing the sand directly on the hotplate and gentle evaporate any remaining water. Occasionally stir with a glass stirrer. Once the sample is dry, allow the dish to cool on a cooling pad on the lab bench top. With the dish at room temperature, weigh the evaporating dish containing the sand. Record (see Table 2) the weight to the nearest 0.001 g. Questions 1. What distinguishes a mixture from an impure substance? 2. Define the process of sublimation. 3. How do decantation and filtration differ? Which should be faster? 4. Why does one never weigh a hot object? 5. How does this experiment illustrate the principle of conservation of matter? 6. A mixture was found to contain 3.10 g of SiO , 0.38 g of cellulose, and 6.72 g of calcium 2

carbonate. What is the percentage of CaCO in this mixture? 3

5

Table 2 Separation and Analysis of a Ternary Mixture Data Table Weight of evaporating dish #1 and original sample

g

Weight of evaporating dish #1

g

Weight of original sample

g

Weight of evaporating dish #1 after subliming NH Cl

g

Weight of NH Cl

g

4

4

Percent of NH Cl (show calculations) 4

%

g g

100% =

% NH4Cl

Weight of evaporating dish #2 and NaCl

g

Weight of evaporating dish #2

g

Weight of NaCl

g

Percent of NaCl (show calculations)

g

100% =

g

% % NaCl

Weight of evaporating dish #1 and SiO

g

Weight of evaporating dish #1

g

Weight of SiO

g

2

2

Percent of SiO (show calculations) 2

%

g 100% = g

% SiO2

Weight of original sample

g

Weight of determined sample (NH Cl + NaCl + SiO )

g

Differences in these weights

g

4

2

Percent recovery of matter (show calculations)

g matter recovered g original sample

100% =

% recovery of matter

%

Before leaving the laboratory, submit the copy pages from your laboratory notebook to your teaching assistant.

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