Lab 9 - Reversible Changes Lab Report PDF

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Reversible Changes Lab Report...

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Lab 9- Reversible Changes Pre Lab 9 1.It is important to know the difference between acids and bases because acids are strong and acidic which can cause burns if it comes in contact with your skin. On the other hand, bases are not as strong or acidic so they will not burn you if it comes in contact with your skin. 2. Ionic bonds are formed when atoms accept the electrons of another atom. Covalent bonds are formed when atoms share electrons. Hydrogen bonds are formed when there is an electromagnetic attraction between molecules. The type of bonding used for matching base pairs of DNA are hydrogen bonds. 3. The chromate ions are acidic and form dichromate ions. The carbon and oxygen single bond will break which will form water when oxygen combines with hydrogen +. The other chromate ion bonds with a C+O3- ion to form dichromate. 4. Temperature can help orm complex ions. For instance, in the reaction in part 2, CoCl2-(H2O)6 is dissolved into methanol and a solution is created as a product of the reaction. The ions react with each other when exposed to new temperatures which create the reaction.

Observations / Meaningful Data Tables / Meaningful Figures / OR Analysis / Conclusion In step one of part one of the experiment, adding several drops of H2SO4 to K2CrO4 turned the solution orange. In step two of part one, adding NaOH to the solution turned it yellow. Then, adding H2SO4 back to the solution turned it orange again. Finally, adding NaOH to the solution turned it back to yellow. During these reactions, the test tube became warm which showed that a reaction was occurring. H2SO4 changes the solution to a dichromate and the addition of NaOH changes it back to a chromate. Adding more acid changes the equilibrium to dichromate and adding more base changes the equilibrium to chromate. In step one of part two of the experiment, by adding four drops of HCl to CoCl2 turned the solution blue. Adding eight drops of water to the CoCl2 turned the solution pink. In step four, adding ten drops of HCl turned the solution purple. In step five, adding water and then six drops of HCl turned the solution pink. When the solution was heated at 330 degrees Celsius, the solution turned purple. Cooling the solution in an ice bath turned the solution back to pink. In part one, we use different concentrations for sulfuric acid and sodium

hydroxide because each concentration has a different level of acids and bases. If too much of one is added, it could affect the reaction that occurs. In part two, the reaction produces and consumes heat. It produces heat in the ninth step and it consumes heat in every other step. You can determine this by looking at the reaction that occurs. For instance, “an endothermic process absorbs heat from the surrounding, while an exothermic process releases heat into the surroundings” (Balter, Sciencing). “Le Chatelier’s principle asserts that a disturbance, when applied to a resting system may drive the system away from its equilibrium state, but will invoke a countervailing influence that will counteract the effect of the disturbance” (Norwich, NCBI). In terms of this experiment, H2SO4 is the acid while NaOH is the base. When you add more of the H2SO4 or the acid to the solution, it changes the equilibrium of the substance to dichromate. When you add more of the NaOH or the base to the solution, it changes the equilibrium of the substance to chromate. In part two of the experiment, you can see that by dissolving CoCl2 in methanol, the solution changes to either a blue, purple, or pink. By adding HCl, the solution turns blue while adding water turns the solution pink. By taking the sample and splitting it into four different test tubes, you can compare the effects of multiple additions to the solution. Adding HCl to the substance changes it to a purple color. Adding water and then HCl back to the solution changes it to a pink. Adding H2SO4 changes it to a light pink. Heating the solution changes it to a purple while cooling that solution changes it back to a pink. All three of these solutions share a common trait: their final color is pink. Because of this, you can conclude that a reaction occurs within all of the solutions. The results from this experiment should be trusted because every step was conducted very carefully with the goal of getting the most accurate results possible. The measurements all seemed to make sense because the desired reaction occurred in every step. My hypothesis is that by adding new solutions to a sample, an exothermic reaction will occur which will cause a physical change in the sample. My hypothesis is supported because in every step of the experiment, the data shows a reaction occuring. Most notably, in step two of part one of the experiment, when touching the test tube, you can feel the temperature increase when the reaction is occuring. This is a perfect example of an exothermic reaction because heat is being released due to the reaction and the physical state changed from an orange color into a yellow. The hypothesis is supported in part two of the experiment as well because when the samples are mixed with other solutions such as HCl or H2SO4, their physical states shift to a pink color and the temperature also increases indicating a reaction is occuring. In part one of the experiment, the independent variable is the amount of K2CrO4. This is the same for every step in part one of the experiment. The dependent variable is the amount of an acid or a base added to the solution. In part one, either H2SO4 or NaOH is added to the solution which changes the reaction that occurs. In part two of the experiment, the independent variable is the amount of CoCl2 used. The dependent

variable is the additive to the CoCl2. The dependent variables in this part are either HCl, H2SO4, temperature, and a control. They relate to each other because the additives to the sample of CoCl2 show a reaction occuring. Acid is more effective than temperature at changing the color of the solution because the acid changes the equilibrium more quickly. Because of this, it takes less time for the reaction to occur. According to Arden and Giddings experiment on chromic acid solutions, “polychromates are removed by means of water, and the dichromate by direct reaction with alkali, neither of these being ion-exchange processes” (Arden and Giddings, Online Library). In terms of the experiment they conducted, they found that chromate is an acidic solution. In our experiment, we found that by adding more acid to a solution, the equilibrium changes to dichromate whereas by adding more base to a solution, the equilibrium changes to a chromate. In our experiment, there were many steps that involved dropping a certain number of a substance into a solution. Because of this, I could have dropped too many drops or not enough drops into the solution. This could make the solution weaker or stronger than it was intended to be. Because of this, the final results could have been inaccurate. In the future, the experiment would be more accurate if the number of drops were specified in each step. The data collected in this experiment supports my hypothesis because the majority of the reactions that occurred in each step were exothermic reactions. Because of this, a physical change occurred in every step. That physical change was a change in the color of the solution. The results show that by adding an acid, the equilibrium will change to a dichromate and that by adding a base, the equilibrium will change to a chromate. In part two of the experiment, the results show that even though different things are added to a substance, a similar result can occur when the substances undergo an exothermic reaction.

Works Cited Arden, T. V., and Giddings, M. (2007, May 4) Anion exchange in chromate solution. Journal of Applied Chemistry. Wiley-Blackwell. Balter, A. How Does One Determine Whether a Reaction Is Endothermic or Exothermic in a Calorimetric Experiment? Sciencing. Norwich, K. H. (2010) Le Chatelier's Principle in Sensation and Perception: Fractal-Like Enfolding at Different Scales. Frontiers in Physiology. Frontiers Research Foundation....