Unknown Ionic Compound Preliminary Lab
Discussion of Results and Scientific Explanation
The main goal was to identify the unknown compound, which was MgCl2, better known as Magnesium Chloride. Before knowing what the unknown was, we had several test that needed to be done in order to determine the unknown compound. To find the identity of the compound we did various experiments for example, we observed the physical properties, tested the qualitative and quantitative solubility, did a cation and anion test and tested the conductivity of the compound.
First we observed the unknown from its physical properties. It was white and had a rough and grainy feel to it. It was also observed as a solid and did not have a smell. All of these properties suggest that the compound was ionic because ionic compounds do not have a distinct odor and are solid at room temperature because of their high melting points. The unknown compound was then tested for solubility in water, toluene and acetone. The compound was soluble in water, indicating the compound was either a polar or an ionic compound, and not as soluble in toluene or acetone which points to the compound being more ionic.
Once finished observing the unknown, we tested for pH. To do this, we the unknown with water and used litmus paper to determine whether it was an acid, base, or neutral. The litmus paper showed us that the unknown had a pH of 7, so it is a neutral compound.
We then tested the conductivity. To do this we test the solution with a voltmeter in order to determine whether or not the compound can withstand water when it is dissolved. If the compound was to be conductive in water, it would dissolve and then produce an electric current. Once the compound was dissolved, it was then tested with a voltmeter that produced a voltage of -0.20 volts. This is important information because it shows that the compound was ionic since only ionic compound dissolve in water and produce and electric current.
During the quantitative testing, 20.521 grams of unknown was mixed with 17 mL of water and that was then put into an Erlenmeyer Flask and stirred. It was left for one week to see if it would dissolve or have any change at all. Once checked, there was no precipitate, so we performed the test again. This time we used 19.085 grams of unknown and mixed that with 10 mL of water and we are currently in the process of waiting for the results. Checking the mixture before leaving, it seemed to be showing some type of precipitate, so we are hoping that this test works better than the first.
Next to determine one of the elements within the compound we tested for anions and cations. First we tested for cations and in order to do this we performed a flame test and an ammonium test. To start the flame test, the nichrome wire had to be cleaned by heating it over a flame to ensure our results are not contaminated. A solution of water and the element was used to place the nichrome wire in, and then the nichrome wire is placed into the flame. If the flame produces a color it is indicative of a certain metalloid ion or metal. A color is produced in the flame when the heat of the flame changes the metal ions into atoms, which then become excited and produce light that can be seen with the naked eye. Once we tested the unknown in the flame to, it was determined that there was no color change, which lead us to believe that our unknown has to be a compound with Magnesium. 1 mL of the unknown solution was placed into a test tube and 1 mL of NaOH (6 M) was added. A pH paper was placed on a watch glass using water to help it stick. The watch glass was placed on the top of the test tube. If ammonium is present, the water will dissolve resulting in a higher pH.
Going into next lab, we will finish up the quantitative testing. To do this, we will use a process called vacuum filtration. This is done by pouring the mixture of the unknown and water through filter paper and letting the water drain into a funnel and hoping that a precipitate is presents and is collected on the filter paper.
Conclusion:
Although this process takes time and can be confusing at time, it is very simple to do. Figuring out how to determine the unknown with the test preformed here was difficult at one point, but in the end, the test(s) showed that Magnesium Chloride was the unknown solution.