There are over a hundred different chemical elements in nature, exhibiting not only different physical but also chemical properties. Under normal conditions, some atoms are gases while others are solids; some exhibit an acidic environment in aqueous solutions while others have a low pH. However, the Periodic Table allows us to systematize all the elements into groups and periods in which changes in the physicochemical properties of materials have a regular pattern (Helmenstine). This paper determines the difference of these properties for the three alkali metals: lithium, potassium, and sodium. Substances constructed from these elements are located in the same group, which means that it is likely that there is some pattern to the hydration reaction.
Hypothesis
The working hypothesis of the experiment is that the greater the atomic number of the element — that is, the lower it is located in the group in the Periodic Table — the more active it reacts with water. In addition, this position is expected to correlate with its physical properties: luster and softness.
Research Question
Does the alkali metal’s position on the Periodic Table influence its activity in reacting with water and its physical properties?
Variables
The independent variable was the type of metal that varied during the experiment. The dependent variables were the physical properties of the metals (luster and softness) and the chemical properties, reaction activity with water: these were subjective data based on personal observations. Finally, the control variables were the physical conditions of the laboratory room, the instruments used, the time, and the person performing the experiment.
Materials
- Beaker, Berzelius (tall-form), Pyrex®, 500-mL, 2
- K, precut piece
- Li, precut piece
- Na, precut piece
- Petri dishes, 3
- Phenolphthalein, 1% solution, 2 mL
- Stationery knife
- Tweezers
- Water, distilled, 600 mL
Procedure
Three metals previously placed in tubes of gasoline were cut in turn, and a small fragment of the metal was carefully placed using tweezers into an appropriately labeled Petri dish. Careful observation of the reaction of the metal with water preceded the dissolution of the metal; drops of phenolphthalein were then placed in the Petri dish. The color change and its intensity were recorded for further analysis.
Results
Processing and Evaluating: Data Processing
The results of the experiment revealed that the three metals reacted differently with water in Petri dishes. At a time when there was not a substantial difference between Lithium and Sodium, Potassium reacted most intensely with water: there was an explosion, which not only broke the metal apart but was also scattered around the area around the Petri dish. This is not surprising since the hydration of Potassium is an exothermic reaction, and the heat released is enough to cause Potassium to ignite (“Potassium and Water”). The fact that combustion did occur is confirmed by the color of the sparks: the metal emitted a purple flame, which is characteristic of Potassium (“Flame Tests”). For Sodium and Lithium, no strong difference was noticeable, although Sodium moved slightly faster across the Petri dish, and the effervescence was subjectively slightly more intense. Interestingly, the addition of the phenolphthalein indicator resulted in slightly different colors: the density and intensity of the fuchsia color increased from Lithium to Potassium.
In terms of physical properties, it was found that the metals did differ. Although the metals were generally similar to each other, a close look (and then a replay of the video recording of the experiment) showed that Lithium cut the softest, while Sodium required the most effort. This correlates well with information about metal densities: Lithium has the lowest density of the three metals, while Sodium has the highest (Clark). This is probably why Lithium was the easiest to cut since its density is the lowest.
Patterns
Correlating the results discussed with the position of the three alkali metals in the Periodic Table reveals some patterns. Thus, the activity of metals in reaction with water increases with the atomic number of the metal: consequently, the chemical activity of these metals in hydration grows in the group from top to bottom. In addition, the metallic luster of substances and their smoothness increases in the same direction. The amount of gas released in the reaction with water also increases, which confirms the increase in the chemical activity of metals in the series Li<Na<K.
Evaluation of the Hypotheses
Both working hypotheses were fully confirmed.
Suggesting Improvement
The experiment performed could be improved by adding more metals. However, since the remaining alkali metals are highly active, it is possible to extend the hypotheses to the alkaline earth metals and the medium activity metals, including the second and third groups. In addition, the reaction of the three alkali metals with acids can be tested, and the titration method with indicators can be used to trace the activity of the acid substitution reactions.
Works Cited
Clark, Jim. “Group 1: Properties of Alkali Metals.” LibreTexts, 2020. Web.
“Flame Tests.” LibreTexts, 2020, Web.
Helmenstine, Anne Marie. “Periodic Table Definition in Chemistry.” ThoughtCo, 2020, Web.
“Potassium and Water.” Lenntech, n.d., Web.