Problem 55 - Chemistry: The Central Science in SI Units, Global Edition

Question

Using the activity series (Table 4.5 ), write balanced chemical equations for the following reactions. If no reaction occurs, write NR. (a) Iron metal is added to a solution of copper(II) nitrate, (b) zinc metal is added to a solution of magnesium sulfate, (c) hydrobromic acid is added to tin metal, (d) hydrogen gas is bubbled through an aqueous solution of nickel(II) chloride, (e) aluminum metal is added to a solution of cobalt(II) sulfate.

Step-by-Step Solution

Answer

(a) Fe + Cu(NO₃)₂ -> Fe(NO₃)₂ + Cu (b) NR (c) Sn + 2 HBr -> SnBr₂ + H₂ (d) NR (e) 2 Al + 3 CoSO₄ -> Al₂(SO₄)₃ + 3 Co

Step 1: (a) Iron metal with copper(II) nitrate

First, check the activity series to determine whether a reaction will occur. Iron (Fe) is more reactive than Copper (Cu), so a reaction will occur. Write the unbalanced equation: Fe + Cu(NO₃)₂ -> Fe(NO₃)₂ + Cu Now, balance the equation: Fe + Cu(NO₃)₂ -> Fe(NO₃)₂ + Cu.

Step 2: (b) Zinc metal with magnesium sulfate

Check the activity series to determine whether a reaction will occur. Zinc (Zn) is less reactive than Magnesium (Mg), so no reaction will occur. Write NR.

Step 3: (c) Hydrobromic acid with tin metal

Check the activity series to determine whether a reaction will occur. Tin (Sn) is more reactive than Hydrogen (H), so a reaction will occur. Write the unbalanced equation: Sn + HBr -> SnBr₂ + H₂ Now, balance the equation: Sn + 2 HBr -> SnBr₂ + H₂.

Step 4: (d) Hydrogen gas with nickel(II) chloride solution

Check the activity series to determine whether a reaction will occur. Hydrogen (H) is less reactive than Nickel (Ni), so no reaction will occur. Write NR.

Step 5: (e) Aluminum metal with cobalt(II) sulfate

Check the activity series to determine whether a reaction will occur. Aluminum (Al) is more reactive than Cobalt (Co), so a reaction will occur. Write the unbalanced equation: Al + CoSO₄ -> Al₂(SO₄)₃ + Co Now, balance the equation: 2 Al + 3 CoSO₄ -> Al₂(SO₄)₃ + 3 Co.

Key Concepts

Balanced Chemical Equations

When dealing with chemical reactions, it's crucial to write balanced chemical equations. This ensures that the law of conservation of mass is satisfied. In a balanced equation, the number of each type of atom on the reactant side (left) equals the number on the product side (right). We use coefficients, which are numbers placed before compounds or elements, to achieve this balance without altering the chemical formulas.
For example, in the reaction between iron and copper(II) nitrate, we'll start with the unbalanced equation:

• Fe + Cu(NO₃)₂ → Fe(NO₃)₂ + Cu

To balance this, notice that there's one iron and one copper atom on each side, so the equation needs no additional coefficients. In another case, like aluminum reacting with cobalt(II) sulfate, you'll start with:

• Al + CoSO₄ → Al₂(SO₄)₃ + Co

Here, you'll need to balance several atoms:

• 2 Al + 3 CoSO₄ → Al₂(SO₄)₃ + 3 Co

By using coefficients "2" for aluminum and "3" for cobalt(II) sulfate and cobalt, the equation is balanced.

Reactivity of Metals

The reactivity of metals is a crucial concept in chemistry as it determines how metals interact with other substances. The "reactivity series" is a list that ranks metals (and hydrogen) in order of decreasing reactivity. Metals higher in the series are more reactive than those below.
Reactivity often hinges on a metal's ability to lose electrons and form cations. Highly reactive metals, like potassium and calcium, will react vigorously with water and acids. Less reactive metals, such as gold and platinum, barely react or do not react at all under normal conditions.
In our exercise, iron reacts with copper(II) nitrate because it's more reactive. However, zinc does not displace magnesium from magnesium sulfate because it's less reactive. This insight is critical when predicting whether a chemical reaction will occur.

Single Replacement Reactions

Single replacement reactions involve an element reacting with a compound, during which elements switch places. For a successful single replacement reaction, the lone element must be more reactive than the one it replaces in the compound.
Equations for these reactions will typically follow the pattern:

• A + BC → AC + B

In our examples:

• Iron (Fe) replaces Copper (Cu) in copper(II) nitrate, forming iron nitrate and metallic copper.
• Aluminum (Al) replaces Cobalt (Co) in cobalt(II) sulfate, forming aluminum sulfate and metallic cobalt.

If the single element is less reactive, as with zinc and magnesium sulfate, no reaction occurs (written as NR). This distinction is crucial for predicting the outcomes of potential reactions in laboratory or industrial contexts.

Activity Series Table

An activity series table is a helpful tool in predicting the feasibility of single replacement reactions. This table lists metals and hydrogen according to their reactivity, from the most reactive at the top to the least reactive at the bottom.
By consulting an activity series, you can determine whether a metal can replace another in a compound. If the metal in question is above the element it seeks to replace, the reaction will occur. For example, the activity series may show:

• Aluminum above Cobalt, leading to a reaction with cobalt(II) sulfate.
• Zinc below Magnesium, thus causing no reaction with magnesium sulfate.

Using this table not only supports the prediction of reactions but also conserves reagents and time. It's an indispensable tool for chemists and students alike, offering a clear view of what reactions are energetically favorable.