Problem 57 - Chemistry The Molecular Science

Question

(a) In what groups of the periodic table are the most reactive metals found? Where do we find the least reactive metals? (b) Silver (Ag) does not react with 1-M HCl solution. Will Ag react with a solution of aluminum nitrate, \(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3} ?\) If so, write a chemical equation for the reaction. (c) Lead (Pb) will react very slowly with 1-M HCl solution. Aluminum will react with lead(II) sulfate solution, \(\mathrm{PbSO}_{4}\). Will Pb react with an \(\mathrm{AgNO}_{3}\) solution? If so, write a chemical equation for the reaction. (d) On the basis of the information obtained in answering parts (a), (b), and (c), arrange \(\mathrm{Ag}, \mathrm{Al}\), and \(\mathrm{Pb}\) in decreasing order of reactivity.

Step-by-Step Solution

Answer

(a) Most reactive: Groups 1 and 2; Least reactive: Noble metals. (b) No. (c) Yes, with equation. (d) Order: Al > Pb > Ag.

Step 1: Identify the groups with the most reactive metals

The most reactive metals are found in the alkali metals (Group 1) and alkaline earth metals (Group 2) of the periodic table.

Step 2: Locate the least reactive metals

The least reactive metals are typically found in the transition metals, particularly the "noble" metals such as gold, platinum, and silver, which are located in the later groups (around Groups 10-12).

Step 3: Determine if Ag will react with Al(NO3)3 solution

Silver (Ag) does not react with aluminum nitrate solution, \(\mathrm{Al(NO_{3})_3}\), because aluminum is more reactive than silver. This prevents a single displacement reaction from occurring.

Step 4: Assess reactivity between Pb and AgNO3 solution

Lead (Pb) will react with silver nitrate \(\mathrm{AgNO_{3}}\) because lead is more reactive than silver. The chemical reaction is \(\mathrm{Pb} + 2\mathrm{AgNO_{3}} \rightarrow \mathrm{Pb(NO_{3})_2} + 2\mathrm{Ag}\).

Step 5: Arrange metals by reactivity

Based on previous answers, the order of decreasing reactivity is Aluminum (Al) > Lead (Pb) > Silver (Ag). This is because Al reacts with PbSO4, Pb reacts with AgNO3, and Ag does not react with Al(NO3)3 or 1-M HCl.

Key Concepts

Periodic Table Groups

The periodic table is an organized chart of chemical elements based on atomic number, electron configuration, and recurring chemical properties. It is divided into several groups, each representing elements with similar properties.
Among these, the most reactive metals are usually found in Groups 1 and 2, known as the alkali metals and alkaline earth metals, respectively. These elements tend to lose electrons easily, which is why they are highly reactive.

• **Group 1:** Contains the alkali metals such as lithium (Li), sodium (Na), and potassium (K). These metals have one outer electron, making them very eager to undergo chemical reactions to achieve a stable electron configuration.
• **Group 2:** Contains alkaline earth metals like magnesium (Mg) and calcium (Ca), which have two valence electrons and are somewhat less reactive than alkali metals, but still more reactive than many other metals.

In contrast, the least reactive metals, often referred to as "noble" metals, can be found among the transition metals, particularly in the later groups like 10-12 (e.g., gold, silver, and platinum). These metals are resistant to corrosion and oxidation, which explains their lower reactivity.

Alkali Metals

Alkali metals, located in Group 1 of the periodic table, are notorious for their high reactivity. This reactivity stems from their desire to lose their one valence electron to form a stable electron shell.
These metals are soft, can be cut with a knife, and form alkaline solutions in water. Reactivity increases down the group with francium being the most reactive, though it's rarely encountered due to its rarity and radioactivity.

• **Lithium (Li), Sodium (Na), Potassium (K):** Reactivity increases from lithium to potassium, with reactions becoming more vigorous, notably with water.
• **Characteristics:** They have a characteristic "shiny" appearance when freshly cut, but tarnish quickly as they react with moisture in the air.

Due to their high reactivity, these metals are stored in oil to prevent them from reacting with moisture and oxygen present in the air. Their applications are significant in batteries, heat exchangers, and photoelectric cells due to their unique properties.

Chemical Reactions

Chemical reactions involve the transformation of substances through the breaking of old bonds and the formation of new ones. They can be categorized into several types, including synthesis, decomposition, single displacement, and double displacement reactions.
Reactivity is key in determining the likelihood of a reaction occurring. The more reactive a metal, the more eager it is to participate in these reactions.

• **Displacement Reactions:** These involve a more reactive element displacing a less reactive element from a compound. For example, in the reaction of lead (Pb) with silver nitrate (\(\mathrm{AgNO_3}\)), lead displaces silver, forming lead nitrate and free silver: \(\mathrm{Pb} + 2\mathrm{AgNO_3} \rightarrow \mathrm{Pb(NO_3)_2} + 2\mathrm{Ag}\).
• **Factors Influencing Reactions:** Temperature, concentration, and the presence of catalysts can influence reaction rates.

Understanding chemical reactions and the inherent reactivity of metals helps in predicting reaction outcomes, crucial for many industrial and laboratory processes.

Displacement Reactions

Displacement reactions, often referred to as replacement reactions, occur when a more reactive metal displaces a less reactive metal from its compound.
This type of reaction is common in metals and helps determine the order of reactivity in the reactivity series.

• **Single Displacement:** Here, one element replaces another. For example, lead in a solution of silver nitrate replaces silver due to its higher reactivity.
• **Reactivity Series:** The sequence from most to least reactive helps predict outcomes. For instance, aluminum is more reactive than lead, which in turn is more reactive than silver. This explains why aluminum can displace lead in reactions but not vice versa.

Single displacement reactions illustrate fundamental concepts of reactivity and are integral in processes like metal extraction and electrochemical applications, including batteries.