One way to generate hydrogen gas in the laboratory is to...

Name: Problem 83, Chapter 8: Chemistry Principles and Practice
Uploaded: 2022-02-10T15:44:58-08:00
Duration: 1 min 5 s
Channel: Crystal Wang
Description: One way to generate hydrogen gas in the laboratory is to combine a reactive metal with water. The ensuing chemical reaction produces hydrogen gas as one product. Which element would generate hydrogen gas more vigorously when combined with water: potassium or calcium? Explain your answer. Write the balanced chemical reaction for both processes.

One way to generate hydrogen gas in the laboratory is to combine a reactive metal with water. The ensuing chemical reaction produces hydrogen gas as one product. Which element would generate hydrogen gas more vigorously when combined with water: potassium or calcium? Explain your answer. Write the balanced chemical reaction for both processes.

Key Concepts

Reactivity Series

The reactivity series is an empirical arrangement of metals (and some non-metals) in order of decreasing reactivity. Metals higher in the series, like potassium, react more vigorously with water than those lower, such as calcium. This concept is key to predicting the outcome of reactions between metals and water, particularly regarding the rate and extent of hydrogen gas evolution.

Metal-Water Reaction Mechanism

When a metal reacts with water, the metal atoms lose electrons (oxidation) and water gains electrons (reduction), leading to the formation of metal hydroxides and the release of hydrogen gas. Understanding this mechanism is essential for rationalizing why certain metals, based on their inherent reactivity, produce hydrogen gas more quickly and energetically.

Balanced Chemical Equations

Balanced chemical equations are used to represent the stoichiometry of chemical reactions, ensuring that mass and charge are conserved. For the reactions of metals with water, the balanced equation for potassium is 2K + 2H2O ? 2KOH + H2 and for calcium is Ca + 2H2O ? Ca(OH)2 + H2. These equations demonstrate how the reactants are converted into products in fixed proportions.

Alkali Metals vs. Alkaline Earth Metals

Alkali metals, such as potassium, are found in Group 1 of the periodic table and are characterized by their high reactivity, particularly with water, due to their single valence electron and low ionization energy. In contrast, alkaline earth metals like calcium, located in Group 2, have two valence electrons and are generally less reactive with water. This fundamental difference accounts for the more vigorous hydrogen gas evolution observed with potassium compared to calcium.

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