Lab Report on Solubility

The analyses of the mixture were to distinguish and identify homogeneous mixture by using the techniques of decantation and sublimation. By performing these techniques, we examined our solutions such as SiO2 (sand), NH4Cl (ammonium coloride), and NaCl (sodium chloride) and mixed H2O (water) with each solution after being heated. After examining our solutions, we made calculations by finding the percent mass of each solution once the experiment was completed. In our findings, we were able to determine the mass of the determined and the percent recovery of matter.

The outcome of the experiment was that we made the correct calculations which gave us the confidence to know how to analyze the mixture.

Introduction

A mixture is a material that is not uniform in composition, and it is a combination of two or more substances in which each substance retains its own chemical identity. Mixtures are characterized by how each of the substances in the mixture retains its chemical integrity, and that mixtures are separable into these components by physical means.  The substances we see in life are mixtures or compounds.

Compounds differ in that the elements come together in definite proportions, whereas mixtures, as previously stated, are not uniform.  There are 2 types of mixtures, heterogeneous and homogenous. A heterogeneous mixture is one “in which the composition varies from one region of the mixture to another. ”2(p7) This differs from homogenous, where the composition is the same. In this experiment, the components of the mixture were separated by physical means, and consequently, the components underwent physical changes. A physical change is a change, such as a phase change, that occurs with no change in chemical composition.

The main concept being applied and studied in this lab was the separation of components of mixtures by physical means, familiarizing ourselves with the methods of separating substances from another substance using the technique of decanting, filtration, extraction, and sublimation. In the Pearson Education lab manual, decantation is “separating from a liquid from a solid by gently pouring the liquid from the solid so as not to disturb the solid”.  An example of this is separating sand and water by pouring the water into another container.  Filtration is using a filter to separate a solid from a liquid.

Making morning coffee requires the use of a paper filter to separate the solid coffee grounds from liquid water. Extraction is “separating a substance from a mixture by preferentially dissolving that substance in a suitable solvent” or separating the soluble from the insoluble. Sublimation is the process of a “solid passing directly to the gaseous state and back to solid without the appearance of a liquid”. The process of separating the components of a mixture, whether homogenous or heterogeneous, is necessary for the laboratory setting for isolating a particular component for further study.

Research has been made on the uses of ferrofluids in NASA as a “method for controlling fluids in space” and its medical uses for an “implantable artificial heart”. Ferrofluids are colloidal suspensions of magnetic material in a liquid medium, which respond to an external magnetic field. They document the proper procedure for preparing ferrofluid, including decanting a FeCl2 and NH3 solution to isolate magnetite, a black precipitate, from the liquid. Although the process of separating mixtures into various states is performed rudimentary, further research is still conducted to make certain the precision of the separation.

Despite the complex apparatus used in research, basic procedures are still followed, similar to the following procedures that will be presented in this report. Decanting, filtration, extraction, and sublimation have practical applications in a variety of settings. In this lab, a mixture of NH4Cl, NaCl, and SiO2 will be heated, where NH4Cl will be sublimed. The remaining NaCl and SiO2 will be combined with H2O, where NaCl will be extracted. The residue will be SiO2, where it will be heated.

Materials and Methods

Materials

1. Evaporating dish
2. Beakers
3. Test tube
4. Hotplate
5. Scale
6. Spatula
7. Funnel
8. Filter Paper
9. Components of mixture
10. Stirring rod

Methods

Preliminary Steps:

1. Obtain a sample of the mixture. The mixture you will separate contains three components: NaCl, NH4Cl, and SiO2. Their separation will be accomplished by heating the mixture to sub-lime the NH4Cl, extracting the NaCl with water, and drying the remaining SiO2.
2. Obtain an evaporating dish and carefully weigh it to the nearest 0. 01g on top of the loading scale and record its mass on the datasheet.
3. Place about 3g of the mixture into the evaporating dish and carefully weigh it to the nearest 0.01g with the top-loading scale and record its mass on the datasheet.
4. Determine the mass of the mixture by subtracting the mass of the empty evaporating dish from the mass of the evaporating dish containing the mixture and record the calculated mass onto the datasheet.

Sublimation Steps:

1. Place the beaker containing the mixture on the hot plate and heat until the white fumes no longer form (about 15 minutes) during the sublimation process.
2. Allow the beaker to cool until it reaches room temperature; then weigh the beaker with the contained solid. The loss in mass represents the amount of NH4Cl in your mixture. Calculate this.
3. Add 15ml of water to the solid in this beaker and stir gently for 5 minutes. Decant the liquid carefully into the second beaker, which you have weighed, being careful not to transfer any of the solid into the second beaker.
4. Add 15ml more of water to the solid in the first beaker, stir, and decant this liquid into the second beaker as before. This process extracts the soluble NaCl from the sand. You now have two beakers-one containing wet sand, and the other containing a solution of sodium chloride.
5. Weigh the filter paper and record it on the data sheet.
6. Fold filter paper into halves until it is folded small.
7. Place the folded filter paper inside a funnel. The paper will need to be wetted with water, once wet adjust the filter paper so that it lies flat on the walls of the funnel.
8. Place the funnel into a beaker for gravity filtration.
9.  Pour the mixture contained in the test tube into the gravity filtration beaker and collect filtrate into the beaker.
10. Set filter paper aside with residue.
11. Place the beaker on the hotplate and heat. As the amount of liquid reduces, the NaCl dissolved will start to precipitate as a white solid. When the liquid is fully evaporated, allow the beaker to cool down to room temperature.
12. Weigh the beaker with the dry NaCl, and record the mass on the datasheet.
13. Determine the mass of the recovered NaCl by subtracting the mass of the empty beaker. Once calculations are done record the mass of the recovered NaCl on the datasheet.

Drying the Sand Sample for Recovery Calculations

1. Transfer the wet sand from the filter paper to the beaker.
2. Place the beaker with the wet sand on the hotplate and heat the sand to dry. When the sand is completely dry, the sand should be free-flowing.
3. Allow the sand to cool to room temperature. Weigh the beaker containing the dry sand to the nearest 0. 01g and record this mass onto the datasheet.
4. Determine the mass of the recovered sand by subtracting the mass of the empty beaker from the mass of the beaker containing the dry sand. Record the mass of the recovered sand on the datasheet. Results The experiment was conducted in four parts (parts A, B, C, and D). In part A, the mass of the evaporating dish and original sample was taken. The mass was 80.892 g. Next, the mass of the evaporating dish was taken and found to be 77.886. The mass of the original sample was determined by subtracting the mass of the evaporating dish from the mass of the evaporating dish and original sampled. After sublimation, the mass of the evaporating dish of NH4Cl was found to be 80.713 g. The mass of NH4Cl was found by subtracting the mass of the evaporating dish after sublimation from the mass of the evaporating dish and the original sample. The result was 0. 179 g. The percent of NH4Cl was calculated by dividing the mass of the NH4Cl by the molar mass of NH4Cl (2.783) and multiplying it by 100. The % of NH4Cl was found to be 6.43%. Results from Part A are outlined in Table 1 below.

Table 1

In Part B of the experiment, the mass of a 250 mL beaker and NaCL was taken. The mass was 110.09 g. Next, the mass of the 250 mL was taken and found to be 109 g. Extraction was used to remove the NaCl from the water. Then, the mass of NaCl was calculated by subtracting the mass of the 250 mL beaker from the mass of the beaker and NaCl which was 1.09 g. Finally, the percent of NaCl was calculated by dividing the mass of NH4Cl (0.179 g) by the molar mass of NH4Cl (2.783) and multiplying it by 100. Results from Part B are outlined in Table 2 below.

Table 2

 In Part C of the experiment, SiO2 was found by using decanting. First, the mass of the evaporating dish and SiO2 was taken. The mass was 79.400 g. Next, the mass of the evaporating dish was taken and found to be 77.886 g.

The mass of SiO2 was determined by subtracting the mass of SiO2 from the mass of the evaporating dish and determined to be 1.514 g. The percent of SiO2 was calculated by taking the mass of SiO2 and dividing it by the molar mass of SiO2 (2.783) and multiplying by 100. This calculation resulted in 54.40%. Results from Part B are outlined in Table 3 below.

Table 3

In Part D of the experiment, the goal was to determine if the percentage of each of the components of the solution totaled 100%. The mass obtained from NH4Cl, NaCl, and SiO2 were subtracted from the mass of the original sample (3.006 g) and the difference in the weights was 0.223 g. The percent recovery of matter formula was used. The formula is as follows: Percent of recover matter = g matter recovered x 100 g original sample The percent of each component of the experiment was found to add to 100%. This indicates the experiment was conducted in such a manner that there was no error. Calculations are indicated below: NH4Cl (6.43%), NaCl (39.17%), and SiO2 (54.40%) (6.43% + 39.17% + 54.40% = 100%)

Discussion

The starting point of this experiment was a mixture of NH4Cl (Ammonium chloride), NaCl (sodium chloride), and SiO2 (sand). Each of these substances retained its own chemical identity throughout this experiment. NH4Cl and NaCl are ionic compounds, in which normally a metal bonds to a nonmetal, based on the charges of the ions. SiO2 is a binary molecular compound, which is a combination of two nonmetals. When measuring the different amounts of the three components of the mixture, all measurements were based on significant figures. Thus, each certain digit plus one uncertain digit was included in all measurements.

The process of sublimation, in which a solid passes directly to the gaseous state and back to the solid-state without the appearance of the liquid state, was used to separate the NH4Cl from the rest of the mixture. The sublimation effectively separated the NH4Cl from the rest of the mixture. The sample contained 0.179 g of NH4Cl after sublimation. The percent of NH4Cl came out to be 6.432%. Later on, the NaCl was separated from the SiO2 because of the solubility of NaCl in water and the insolubility of SiO2 in water. Solubility is the ability of a substance to dissolve when in the presence of a certain solvent (Zumdahl).

The process of extraction, in which a substance is separated from a mixture by dissolving that substance in a suitable solvent, was used to separate the NaCl from the SiO2. The NaCl dissolved in the water, and by decantation, the process of separating a liquid from a solid by gently pouring the liquid from the solid so as not to disturb the solid, the NaCl solution was separated from the SiO2. Heating can cause substances to evaporate, which represents a state change, so when the water evaporated from the NaCl, solid NaCl was left behind. The amount of NaCl in the experiment was measured to be 1.09 g, with the percent of NaCl as 39.17%. Then, the remaining component of the mixture, SiO2, was measured to be 1.514 g once it had dried out. The percent of SiO2 came out to be 54.40%. The comparison between the measured masses of the three different substances in the mixture and the actual masses of the components proved that the substances of mixtures can be separated, yet still retain their chemical and physical properties. After the components of the original sample were successfully separated, their masses were added together to determine whether their added masses equaled their original mass.

The measured total of the three separate components in the mixture was 2.783 g, whereas the mass of the original sample was 3.006 g. Thus, this similar correlation between the masses proves that all three components had relatively the same masses before and after they were separated from the mixture. When the percentages of each component in the mixture were calculated and subsequently added together, the total was 100.00%. Ideally, the total percentage should be 100%, because substances are neither created nor destroyed during these physical separation methods, according to the principle of conservation of matter (Zumdahl).

This total proximity to 100% proves the concept that mixtures can be separated into their components by physical means, and that their components will retain their initial properties.

Conclusion

Mixture of components and their various forms of separation is seen routinely. We see it in foods such as stews, where there is a mixture of vegetables and meats. We witness it at the beach, with sand and water as a heterogeneous mixture, meaning that they do not dissolve within each other to form one instead they exist side by side.

It is also present in the air that surrounds us as it contains carbon dioxide, oxygen, and nitrogen. In all these examples, there is a blending and combining of substances. Even coffee, in its various forms, that university scholars seem to purely subsist on, is a prime example of the chemistry exercises performed in the experiment—the heating of a liquid, to the use of a filter for the separation of a liquid and a solid. Through this lab experiment, we were able to witness the process of separating components within a mixture. This was accomplished by exercising the methods of decantation, filtration, and evaporation.

Ideally, determining the unknown masses were to add to 100%, showing that each step of the process was done correctly. Our group’s ability to successfully add the total masses to 100%, indicated the positive possibility to separate each constituent, while each continuing to keep their original properties in an introductory chemistry setting.

References:

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