Problem 88 - Chemistry Matter and Change

Question

Write chemical equations for the following single-replacement reactions that might occur in water. If no reaction occurs, write \(NR\) in place of the products. a. nickel + magnesium chloride \(\rightarrow\) b. calcium \(+\) copper \((11)\) bromide \(\rightarrow\) c. potassium \(+\) aluminum nitrate \(\rightarrow\) d. magnesium \(+\) silver nitrate \(\rightarrow\)

Step-by-Step Solution

Answer

a. Ni + MgCl_2 \(\rightarrow\) NR b. Ca + CuBr_2 \(\rightarrow\) CaBr_2 + Cu c. 3K + Al(NO_3)_3 \(\rightarrow\) 3KNO_3 + Al d. Mg + 2AgNO_3 \(\rightarrow\) Mg(NO_3)_2 + 2Ag

Step 1: Identify the elements and consult the activity series

Nickel (Ni) and magnesium (Mg) are the elements involved in this reaction. Let's consult the activity series: Ni (less active) < Mg (more active) According to the activity series, Ni is less active than Mg. Therefore, no reaction will occur.

Step 2: Write the chemical equation

Since no reaction will occur, we write NR in place of the products: Ni + MgCl_2 \(\rightarrow\) NR b. Calcium + copper (II) bromide

Step 1: Identify the elements and consult the activity series

Calcium (Ca) and copper (Cu) are the elements involved in this reaction. Let's consult the activity series: Ca (more active) > Cu (less active) Since Ca is more active than Cu, a reaction will occur.

Step 2: Write the chemical equation

The more active metal (Ca) will replace the less active metal (Cu) in the compound: Ca + CuBr_2 \(\rightarrow\) CaBr_2 + Cu c. Potassium + aluminum nitrate

Step 1: Identify the elements and consult the activity series

Potassium (K) and aluminum (Al) are the elements involved in this reaction. Let's consult the activity series: K (more active) > Al (less active) Since K is more active than Al, a reaction will occur.

Step 2: Write the chemical equation

The more active metal (K) will replace the less active metal (Al) in the compound: 3K + Al(NO_3)_3 \(\rightarrow\) 3KNO_3 + Al d. Magnesium + silver nitrate

Step 1: Identify the elements and consult the activity series

Magnesium (Mg) and silver (Ag) are the elements involved in this reaction. Let's consult the activity series: Mg (more active) > Ag (less active) Since Mg is more active than Ag, a reaction will occur.

Step 2: Write the chemical equation

The more active metal (Mg) will replace the less active metal (Ag) in the compound: Mg + 2AgNO_3 \(\rightarrow\) Mg(NO_3)_2 + 2Ag

Key Concepts

Activity Series

The activity series is a helpful tool in chemistry that predicts the reactivity of metals. It is a sequence listing metals (and some non-metals) in order of their reactivity from highest to lowest. In a single-replacement reaction, a more reactive metal can replace a less reactive metal in a compound. The activity series essentially ranks metals based on their ability to displace other metals in solution.
For example:

• Potassium (K)
• Calcium (Ca)
• Magnesium (Mg)
• Aluminum (Al)
• Nickel (Ni)
• Silver (Ag)

Using the activity series simplifies the task of predicting whether a reaction will occur. If a metal is higher on the list than another metal present in a compound, it will likely replace the less reactive metal.

Chemical Equations

Chemical equations succinctly represent chemical reactions using symbols for elements and formulas for compounds. They are the shorthand of chemical reactions and are used to convey a considerable amount of information quickly.
In a single-replacement reaction, one element replaces another in a compound. The general form is: \[ A + BC \rightarrow AC + B \]Where:

• \( A \) is the more reactive metal.
• \( BC \) is the compound containing a less reactive metal.
• \( AC \) is the new compound formed.
• \( B \) is the displaced metal.

Balances equations are important to comply with the law of conservation of mass, signifying that atoms are neither created nor destroyed. This ensures the same number of each type of atom appears on both sides of the equation.

Metal Reactivity

Metal reactivity determines how vigorously a metal reacts with other substances. This concept is crucial when predicting the outcomes of chemical reactions. More reactive metals easily lose electrons and participate in reactions faster and more energetically. Less reactive metals are more subdued.
For instance, potassium is highly reactive and can even react vigorously with water, whereas metals like nickel react more sluggishly. Understanding a metal's reactivity helps predict whether it will displace another metal in a compound.
In the activities we discussed:

• Potassium in potassium + aluminum nitrate is more reactive than aluminum.
• Magnesium in magnesium + silver nitrate is more reactive than silver.

This reactivity principle lets us know which metal will replace which in a chemical reaction.

Reaction Prediction

Predicting single-replacement reactions involves determining whether one element will displace another from a compound. This prediction is heavily reliant on the activity series and the relative reactivity of the metals involved.
To predict if a reaction will occur:

• Check the activity series to see if the free element is more reactive than the metal in the compound.
• Consider the reactivity of the element prepared to displace; if it is higher, a reaction will proceed.
• If a metal is less reactive than the metal in the compound, it cannot replace it, so no reaction (NR) occurs.

For example, since calcium is more active than copper, calcium will replace copper in copper (II) bromide. However, nickel will not replace magnesium in magnesium chloride as it is less reactive. These predictions are logical conclusions drawn from the activity series and metal reactivity.