Decoding an Unknown Mixture of Solids
By Nicole Escamilla, Daniela Garcia, Itzel Espino, Victoria Robles
Chemistry
September 3, 2017
INTRODUCTION
In this lab we explore the concepts of pure substances and mixtures, the different types of separation methods, and how to physically separate a mixture of unknown components. A mixture is the "combination of two or more substances such that each retains its separate chemical identity (e.g., salt and flour)", there can be heterogeneous or homogeneous mixtures, the difference is that in a homogeneous mixture the components are uniformly distributed throughout the mixture (ex.coffee,milk), whereas in a heterogeneous mixture components are not uniform or have localized regions with different properties (ex.salad dressing,spaghetti sauce). Mixtures can undergo chemical or physical changes, a chemical change is a "process by which one or more substances are altered to form new substances.", and a physical change is a "a change that alters a substance's appearance without changing its chemical composition". From a chemical change a solute results which is a "substance that is dissolved in a chemical solution"; the maximum amount of solute that can be dissolved from a solute is the solubility, and the solvent is the "component of a solution present in the greatest proportion". From the solubility we can precipitate which is "to form an insoluble compound by reacting salts or altering a compound's solubility", and the result of this reaction would be the supernatant or "the liquid result of a precipitation reaction", the matter remaining from a reaction can be the residue, which can be defined as the,"matter remaining after evaporation or distillation or an undesirable reaction byproduct or a recognizable portion of a larger molecule". In contrast to the resulting matter of what is a residue, a filtrate refers to "a liquid that has passed through a filter" and in similar; the volatility also relates to the component undergoing a separation process as it is, "a substance that readily vaporizes". Now, the density is important to the analytics of both compounds and mixtures, and it is the mass per unit volume, while the percentage composition is also an attribute to the analytics while it refers to the "percent by mass of each element in a compound."
Throughout the lab we continued our extension of learning regarding the concepts of pure substances and mixtures and the different types of separation methods, we accomplished this by physically separating a mixture of unknown components; from this experience we became more aware of the importance of the separation processes not only inside the laboratory, but outside in the real-world as well. The purpose of the different separation processes is to change a mixture into two or more different mixtures, and it is important to understand them because we can be aware that there are different methods to separate mixtures/substances, which could benefit us to know which process would be more adequate for which element.
Before starting the actual procedure consisting of separating the mixtures, we constructed different hypothesis to help guide us to more accurate and effective results through the use of the scientific method and moving towards following a procedure in the most correct way we knew.
METHODS
The methods we used to separate each substance from the mixture were magnetic separation process and filtration. When we saw the mixture, we came up with some ideas of what might be in the mixture, the substances we saw were metal, rice, sand and sugar. The first process that started with was the magnetic, before starting the process we put the mixture on the scale. Once we were done we flattened the mixture to see where the pieces of metals where, when we saw the metal we were passing the magnet over the mixture so that we can collect all the pieces of metal. When we finished we put the pieces of metal that we separated on the scale, the metal weighed 1 gram.
The second process that we continued with was filtration, we used the process to separate the rice from the rest of the mixture. We put the mixture in a beaker, once we got the beaker we put a piece of filter paper on top and poked a couple holes. Then we secured it with a rubber band around the breaker. After we finished those steps we we flipped the beaker over and put another one at the bottom, we started to shake the beaker and the sand and sugar started to fall out of the holes. While in the middle of this process some of the sand and sugar was falling out of the beaker, due to that it could have affected the weight of the sand and sugar. When finishing that process we put the separated rice on the scale, the mass was 1.5 gram.
We weren't able to finish the lad or all of the separating processes, but one of the other processes that we wanted to accomplish was evaporation and crystallization. Evaporation would have helped us separate the sugar from the sand. The spets we would have done in this process would be to pour the mixture in a beaker and add water to the beaker with the mixture, after we would turn on the hot plate to medium. This would have evaporated the sugar with the water and leave the sand in the beaker, after we would have poured out the water and leave the sand. We weren't able to find the mass of the sand when it was separated, even though the hot plate would have helped us go a little faster with this process it still would have been time consuming.
Crystallization would have helped us with the water and the sugar, we weren't able to do this process because we did not have the right equipment. The way it would have worked would be, pouring the substances into the machine which would have heated the water, and that helps with separating the liquid from the solid.
RESULTS
Substance
Separation method
Mass(g)
Mass composition %
Rice
Filtration process- What we did to separate the rice from the sand was that we poured the mixture (without the metals) in a beaker and put a paper with holes on top. Then, we turn the beaker over, letting the rice drop to a bigger beaker so that the sand and salt would stay in the first beaker and the rice would be in another.
1.5g
% = mass substance / mass mixture * 100
15 %=1.5 / 4.5 * 100
Salt
N/A
N/A
N/A
Metal elements
Magnetic process- What we did to extract the tiny metal elements from the mixture using the magnetic process was that we passed a magnet over the mixture, which attracted the metal pieces.
1g
% = mass substance / mass mixture * 100
22%= 1/ 4.5 * 100
Sand
N/A
N/A
N//A
Comparing mass (g) and Mass composition (%)
Discussion
Out of all of the methods we used, the easiest was definitely the magnetism method to remove the small pieces of copper. All that is needed for this method is a strong magnet. It was quick, easy, and did not take much time. We passed the magnet half an inch above the mixture and all of the copper pieces stuck to the magnet which then made weighing the metal much easier. The hardest or most difficult method we had to use was the evaporation and crystallization of the sand and sugar. The thing about evaporation is that it's very time consuming and we had only a limited amount of time. For this method we had to wait for the water to come to a boil and for the salt to evaporate. Once that was over we could weigh the sand. The same thing goes for crystallization, we had to wait until the process was done to weigh the substance.
Some challenges that we faced during the lab are, we weren't able to finish some of the processes that we wanted to do, also during the processes that we did accomplish in the middle of one of them some of the substances were falling out of the beakers so we thought it could have affected the mass of some of the substances. If we were given the chance to do the lab over again something we would have done different would be to do the processes in the right order and also one major thing we would want to change would be to manage are time better.
Conclusion
To begin the lab we were given a mixture of solids in a cup that we had to separate using different separation processes. The mixture contained sand, salt/sugar, small pieces of copper, and dry rice. The correct separation process was to separate the rice, either by hand or using the filtration process, then to use the magnetism method to separate the copper pieces from the mixture, third was to evaporate the salt from the sand, and finally to obtain the salt by using the crystallization method. We began out of order by separating the copper pieces using the magnetism method. By passing a strong magnet over the mixture we were able to collect most of the magnetic pieces. We then weighed the copper which ended up being 1 gram. We then proceeded to separate the rice using the filtration method. We took a beaker, secured a piece of filter paper to the top with a rubber band, and poked small holes that would allow the sand and salt pass through. Once we had all of the rice we weighed it and the end weight was 1.5 grams. This is where we, unfortunately, had to end our experiment due to time management. We would have proceeded with the evaporation method to separate the salt from the sand. In this method we had to pour water into the beaker and use the hot plate to heat it up until the salt were to evaporate. Then we would have dumped the remaining water and weighed the sand. The final step would be to obtain the salt using the crystallization method. Our lab does not have access to the proper equipment to have conducted the crystallization method so it is unclear how it is done or what are results could have been.
At the beginning of the lab, we made four hypotheses about how we would separate the substances. Our first hypothesis is if there is a mixture of rice and sand that has not been dissolved in a liquid, then we can use the filtration process. After completing the lab we can now say that to separate the salt and sand, we would need to use the evaporation and crystallization methods. Therefore, we would disagree with our first hypothesis. Our second hypothesis is if there are tiny magnetic elements in the mixture, then we can use the magnetic separation process. We can agree with this hypothesis because it worked exactly like we predicted it would. Our third hypothesis is if there are sand particles in the substance, then we can use the filtration method to separate them. This method also worked, so we agree with this hypothesis as well. Our final hypothesis is if there are no more sand particles in the mixture, then we will use the filtration method to separate the salt. This method would not work because to separate the salt we had to use the evaporation method and the crystallization method. In the end, we did not agree with this hypothesis.
ABSTRACT
The main objectives of conducting the Unknown Mixture Lab Practicum, were to be able to physically separate a mixture of unknown components, to review the concepts of pure substances and mixtures, and to recognize and know the different types of separation processes.