Red Cabbage as an Acid-Base Indicator
Statement of Purpose
In chemistry, acids and bases are two major categories of substances. Acids have hydrogen ions (H+) as functional groups while bases have hydroxyl ions (OH–) as functional groups. These functional groups react to form water, which has neither hydrogen ions nor hydroxyl ions. Chemists have established a pH scale that measures the degree of acidity or basicity of a substance on a scale ranging from 0 to 14. The pH of 7 is neutral while acidity increases as pH approach zero and basicity increases as pH approaches 14. Chemists use acid-base indicators to measure the degree of acidity or basicity based on the color changes of these indicators. In this view, the experiment demonstrates the use of extracts of red cabbage as an acid-base indicator. The following are the fundamental concepts that the lab abstract will use in elucidating the change of pH.
Acids – These are substances with hydrogen ions as their functional groups.
Bases – These are substances with hydroxyl ions as their functional groups.
Acid-base indicator – It is a substance that can change colors in response to different degrees of pH.
Summary of Procedure
A leaf of red cabbage was obtained, cut into pieces, and then placed in a beaker. Water was added and boiled for two minutes to extract the dye. The extract, which is the blue solution obtained from cabbage, was poured into another beaker and the pieces of the boiled cabbage were discarded. Diluted ammonia solution was added gradually until the color of the extract changed to emerald green from deep blue. A small portion of the solution was poured into another beaker and straw was put to test breath. Several lungfuls of breaths were blown into the test solution until it turns color from emerald green to distinct blue. Vinegar solution was then poured into the distinct blue solution and the color changed to brilliant pink.
Methods Used to Complete Investigation
In the experiment, extracts from the red cabbage represent an acid-base indicator. The ammonia solution is basic, and thus, when added to the acid-base indicator they turned its color to emerald green. The breath changed the color of the indicator from emerald green to distinct blues because it is slightly acidic owing to the carbonic acid. Moreover, the addition of vinegar, which is an acid, changed the color of the indicator to brilliant pink.
Summary of Results
The results demonstrate that extract from red cabbage can change color in response to changes in pH. According to Rosa, Alvarez-Parrilla, and González-Aguilar (2009), extracts from plants are used as indicators because they contain compounds called anthocyanin, which changes the chemical structure and consequently colors in response to pH changes. In this case, anthocyanins in cabbage extract turned from deep blue to emerald green when ammonia solution was added. Ammonia solution is a base, and hence, it changes the molecular structure of anthocyanin in cabbage extract. Several lungful breaths blown through the solution changed the solution to distinct blue because it is acidic. Exhaled breath is slightly acidic because it has carbon dioxide that reacts with moisture to form carbonic acid (Snyder, 2007). Furthermore, the addition of vinegar (acetic acid) changes the distinct blue color of the solution to brilliant pink. The color change occurs because the acetic acid considerably reduces the pH of the solution.
Significance of the Findings
The findings are significant because they demonstrate how pH changes and how cabbage extracts can act as pH indicators. The important concepts that reinforced the results are acids, bases, and acid-base indicators. In the experiment, ammonia solution represents a base while exhaled breath and vinegar represent acids. The cabbage extracts contain anthocyanin, which are compounds that change their molecular structure and consequently colors in response to pH change. The experimental errors that might have negatively influenced the outcomes are a poor extraction of dye and an excess amount of ammonia.
Galvanized Tacks, Drugstore Iodine, and Household Bleach
Statement of Purpose
The transfer of electrons among atoms is the center of chemistry and the generation of electricity. The movement of electrons from one atom to another is dependent on the effective nuclear charge, electronic configuration, and the nature of valence electrons. The number of valence electrons determines if an atom can lose or gain an electron for it to stabilize (Sarker & Nahar, 2013). Fundamentally, oxidation and reduction occur when there is a transfer of electrons from one atom to another. In this case, the experiment of ‘Galvanized Tacks, Drugstore Iodine, and Household Bleach’ demonstrates how the transfer of electrons among atoms occurs when different substances react against each other. The following are fundamental concepts that the lab abstract will use in elucidating the transfer of electrons.
Effective nuclear charge – This concept refers to the sum of protons in the nucleus
Valence electrons – These are the electrons that exist in the outermost energy level in an electronic configuration.
Electronegativity and electropositivity – These concepts explain the ability of an atom to gain or lose valence electrons respectively.
Oxidation and reduction – These concepts explain the process of losing electrons or gaining electrons respectively.
Summary of Procedure
Galvanized tacks were placed in a beaker and pressed to cover the bottom surface. Iodine solution was poured into the beaker to the level where it covered most of the galvanized tacks. The mixture of iodine and galvanized tacks was swirled until the dark-purple-violet color of iodine faded to pale yellow. The solution was poured into another beaker leaving galvanized tacks. A few drops of household bleach were added to the solution until the dark-purple-violet color returned. Subsequently, a few drops of vinegar were added to the solution to dissolve formed clumps.
Methods Used to Complete Investigation
In the illustrated experiment, galvanized tacks contain zinc, which protects them from corrosion. Iodine solution was added so that zinc could react with iodine in a redox reaction, which entailed oxidation of zinc and reduction of iodine. The color change from dark-purple-violet to pale-yellow solution indicates the occurrence of a redox reaction. Household bleach contains hypochlorite anion that reverses the redox; hence, restoring the color of iodine to dark-purple-violet. Vinegar solution represented an acidic solution that enhances the solubility of zinc hydroxide.
Summary of Results
During the experiment, it was evident that the color of iodine changed from dark-purple-violet to pale-yellow indicating that zinc reacted with iodine solution. The chemical equation for the reaction is:-
Zn (s) + I2 (aq) → Zn2+ (aq) + 2I– (aq)
(Dark-purple-violet solution) (Pale-yellow solution)
Hypochlorite anion oxidized iodide anion into iodine leading to the restoration of the dark-purple-violet color (Kaiho, 2015).
2ClO– (aq) + 2H+ (aq) + 2I– (aq) → Cl2 (aq) + H2O (I) + I2 (aq)
Zinc cations react with water to form zinc hydroxide, which is insoluble in water.
Zn2+ (aq) + H2O → (l) Zn(OH)2 (s)
The addition of acetic acid dissolved the clumps formed leading to the formation of the dark-purple-violet solution, which resembles iodine solution.
Zn(OH)2 (aq) + 2CH3-CO2H (aq) → Zn2+ (aq) + 2H2O (l) + 2CH3– CO2– (aq)
Overall, the above chemical equations illustrate the reduction of iodine by zinc and the oxidation of iodide anion by hypochlorite anion.
Significance of Findings
The findings of the experiment are significant because they illustrate how electrons transfer from one substance to another during chemical reactions. The results reinforce the concepts of electronegativity, electropositivity, reduction, and oxidation. Zinc is electropositive because it easily loses its two valence electrons while iodine is electronegative because it easily gains an electron. Essentially, zinc loses a reducing agent because it donates two electrons to iodine hence reducing its net positive charge while iodine is an oxidizing agent because it gains electrons from zinc hence increasing its net positive charge (Joule & Mills, 2009). The experimental errors that might have negatively influenced the findings are the amounts of iodine solution, hypochlorite solution, and acetic acid.
References
Joule, A., & Mills, K. (2009). Heterocyclic chemistry. Hoboken: John Wiley & Sons.
Kaiho, T. (2015). Iodine chemistry and applications. New York: John Wiley & Sons.
Rosa, A., Alvarez-Parrilla, E., & González-Aguilar, A. (2009). Fruit and vegetable phytochemicals: Chemistry, nutritional value, and stability. Iowa: Wiley-Blackwell.
Snyder, C. (2007). The Extraordinary Chemistry of Ordinary Things (4th ed.). New York: John Wiley & Sons.
Sarker, S., & Nahar, L. (2013). Chemistry for pharmacy students: General, organic, and natural product chemistry. New York: John Wiley & Sons.