Anions Lab

Purpose: The purpose of this lab is to identify the presence of cations and anions in four unknown solutions by identifying whether they are copper, silver, iron, or chloride ions which is done by adding sodium hydroxide, solid copper, silver nitrate, and potassium thiocyanate to the solutions and analyzing the chemical reactions.

Introduction: Chemical change, unlike physical change is the change in the composition of a substance rather than simply its shape, size, or state (Marie, 2015). Signs that a chemical change has taken place can include a change in state that is not a result of temperature change, for example the forming of precipitates, a change in colour, smell, or taste, the formation of bubbles, and if heat or light is produced
(Marie, 2015). Cations and anions are two different types of ions (Helmenstine, 2015). The difference between the two ions are that cations are atoms (of metals) that have lost electrons in their shells and therefore have a positive charge, while anions are atoms (of non-metals) that have gained electrons in their shells and thus have a negative charge (Helmenstine, 2015). In this lab, different unknown solutions are tested to see if they contain cations or anions based on the specific elemental ions that is present in the solution which can be determined by testing the solution’s chemical reaction with known solutions. It is very important to be able to determine what types of ions, whether anions or cations, as well as the specific elements present in solutions. In the real world, chemists often have to do this in forensics, to test whether a person’s drink has been poisoned or identifying potentially harmful solutions/residue at crime scenes, such as analyzing inorganic salts, acids, and other components of explosives (FBI, 2011).

Hypothesis: If the unknown solutions contain chloride ions which are anions, then a white precipitate will form when silver nitrate is added because when chlorine comes into contact with silver nitrate, white precipitates are formed. If the unknown solutions contains silver ions which are cations, then the solid copper pieces which are added will turn black, because solid copper turns black when it comes into contact with silver. If the unknown solutions contain copper ions which are cations, then the solution would turn gelatinous and blue and precipitates will form, because when solutions containing copper ions is mixed with sodium hydroxide, it will turn gelatinous and blue, and precipitates will form. Lastly, if the unknown solutions contain iron ions which are cations, then it will turn a dark blood red when potassium thiocyanate is added because solutions containing iron ions will turn a dark blood red when it comes into contact with potassium thiocyanate.

Conclusion: My hypothesis was correct, because the first solution was copper nitrate and which contained copper ions (cations) did in fact turn a gelatinous blue and formed precipitates when sodium hydroxide was added. When pieces of solid copper were added to the second solution which was silver nitrate and contained silver ions (cations), the pieces of solid copper did turn black. The third solution which was barium chloride and contained chloride ions (anions) did form white precipitates when silver nitrate was added. Lastly, the fourth solution which was in fact iron nitrate and contained iron ions (cations), turned a dark blood red when it was mixed with potassium thiocyanate. This activity was instructive and illustrated that one can determine the type of ions and the elements present in solutions through analyzing the chemical reactions of the solutions when combined with other solutions/materials. This is possible because different ions whether they are cations or anions, and ions of different elements will react differently when combined with various other matters.

Sources of Error: There were several sources of error that could have affected the results of this lab that could be improved if the lab was conducted a second time. The first being that there may have been a change in the room’s temperature that could have perhaps affected factors such as the time or speed of the reactions that took place. This could be avoided the next time by perhaps regulating the room’s temperature more strictly. Another source of error could be unclean equipment that could have contaminated the chemicals that were being experimented with. This could be avoided by thoroughly cleaning the equipment before conducting the experiment. Also, the size of the droppers were different, and this could have affected the amount of each solution that were being experimented with, meaning that there may have been more of one substance than another. This could be avoided the next time by using droppers that were all the same size.

Analysis:
1. The only solution that had anions was solution #3 because it contained chloride ions. There are two ways to determine whether an ion is a cation or anion. If the element is a non-metal, meaning it is on the right side of the staircase on the periodic table and it is not a noble gas, than its ions will be anions. Chlorine is a non-metal. The other method is to look at the number of electrons in the atoms outer shell. Chlorine has seven electrons in its outer shell, therefore it needs to gain another electron in order to have a full outer shell. After it gains an electron, it will have more electrons than protons, meaning that the chloride ion will have a negative charge making it an anion.
2. The solutions that have cations are #1, #2, and #4 because they each contained copper, silver, and iron ions respectively. Because all three elements are metals, as they are located on the left side of the staircase on the periodic table, their ions must be cations. The reason is because metal atoms give away electrons, as a result their charges become positive because their ions have more protons than they do electrons.
3. The chemical formulae for all the solutions are Cu(NO₃)₂ for copper nitrate, AgNO₃ for silver nitrate, BaCl₂ for barium chloride, Fe(NO₃)₃ for iron nitrate, NaOH for sodium hydroxide, and KSCN for potassium thiocyanate.
Applications and Extensions .
Medical results can be categorized into two major categories, results that give direct yes or no answers and results that give relative results (Torrey, 2016). When an individual is talking about “testing positive” for something they are referring to the results of tests that give yes or no answers (Torrey, 2016). These tests are usually diagnostic tests, and are used to show whether a certain disease or condition is present in your body by giving a “positive” or “negative” result (Torrey, 2016). If the test result is positive, it means that the subject that the test was looking for was found in your body, and if negative, then the test subject was not found in your body (Torrey, 2016). A common misconception is that positive and negative refer to whether the result is good or bad, but that is not always necessarily the case (Torrey, 2016). For example, if the test was used to find tumours in a certain part of your body, and the test result showed “positive”, that means that the tumour(s) was/were in fact found in your body, and in that specific case, the result of the test is “positive” although the patient may consider it a negative or bad result (Torrey, 2016). Likewise, if the test was used to look for STIs in your body, and the test result comes back “negative”, it will probably be considered to be a good or positive result to the client even though the test result itself said “negative” (Torrey, 2016). Career choices in which this knowledge would be useful in are doctors because they need to know the terms in order to explain the results to the patients and ultrasound/x-ray/CT/MRI technicians as well as chemists who analyze the samples (of solutions such as blood or urine) collected from patients because they need to know the terms in order to be able to write the test results which are then sent to doctors, who then inform the
patients.