Problem 55 - Chemistry The Central Science

Question

Using the activity series (Table 4.5 ), write balanced chemical equations for the following reactions. If no reaction occurs, simply 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(s) + Cu(NO₃)₂(aq) -> Fe(NO₃)₂(aq) + Cu(s) (b) NR (no reaction) (c) NR (no reaction) (d) H₂(g) + 2NiCl₂(aq) -> 2HCl(aq) + 2Ni(s) (e) 2Al(s) + 3CoSO₄(aq) -> Al₂(SO₄)₃(aq) + 3Co(s)

Step 1: Refer to the activity series

To solve this problem, we will first need to refer to the activity series for metals. The series is given in Table 4.5, but for convenience, here is a list of the metals relevant to this exercise, in decreasing order of reactivity: Aluminum (Al) > Zinc (Zn) > Iron (Fe) > Cobalt (Co) > Nickel (Ni) > Copper (Cu)

Step 2: Determine if a reaction will occur

For each pair of substances given, we have to determine if a reaction occurs. A reaction will occur if the metal in its elemental form is more reactive than the metal cation in the compound. After determining if a reaction will occur or not, we can write balanced chemical equations for the reactions. (a) Iron (Fe) with Copper(II) Nitrate (Cu(NO₃)₂): Iron is more reactive than copper, so a reaction will occur between iron and copper(II) nitrate. (b) Zinc (Zn) with Magnesium Sulfate (MgSO₄): Zinc is less reactive than magnesium, so no reaction will occur between zinc and magnesium sulfate. We will write NR for this case. (c) Hydrobromic Acid (HBr) with Tin (Sn): Comparing tin with hydrogen in the series, tin is less reactive than hydrogen, so no reaction will occur between hydrobromic acid and tin metal. We will write NR for this case. (d) Hydrogen gas (H₂) with Nickel(II) Chloride (NiCl₂): Hydrogen is more reactive than nickel, so a reaction will occur between hydrogen gas and nickel(II) chloride. (e) Aluminum (Al) with Cobalt(II) Sulfate (CoSO₄): Aluminum is more reactive than cobalt, so a reaction will occur between aluminum and cobalt(II) sulfate.

Step 3: Write balanced chemical equations for the reactions

Now, we write balanced chemical equations for the reactions determined in step 2. (a) Iron (Fe) with Copper(II) Nitrate (Cu(NO₃)₂): Fe(s) + Cu(NO₃)₂(aq) -> Fe(NO₃)₂(aq) + Cu(s) (b) Zinc (Zn) with Magnesium Sulfate (MgSO₄): NR (no reaction) (c) Hydrobromic Acid (HBr) with Tin (Sn): NR (no reaction) (d) Hydrogen gas (H₂) with Nickel(II) Chloride (NiCl₂): H₂(g) + 2NiCl₂(aq) -> 2HCl(aq) + 2Ni(s) (e) Aluminum (Al) with Cobalt(II) Sulfate (CoSO₄): 2Al(s) + 3CoSO₄(aq) -> Al₂(SO₄)₃(aq) + 3Co(s)

Key Concepts

Chemical Reactions

Chemical reactions are processes where substances, known as reactants, interact to form new substances, known as products. These reactions involve changes in the chemical structure and can either release or absorb energy. Understanding chemical reactions is essential as they are the building blocks of many natural processes, such as photosynthesis in plants or metabolism in living organisms.

Common indicators of chemical reactions include:

• Change in color
• Formation of a precipitate
• Evolution of gas
• Temperature change

Chemical reactions play a significant role in our exercise, as we determine whether a reaction occurs based on the activity series.

Reactivity of Metals

The reactivity of metals refers to how easily a metal will lose electrons to form positive ions. Metals that are more reactive are more likely to participate in chemical reactions by displacing less reactive metals from their compounds.

In our activity series, aluminum is more reactive than metals like iron, cobalt, and copper. This is why aluminum can displace these metals in a chemical reaction, forming compounds with their ionic counterparts. The activity series is a useful tool in predicting whether a displacement reaction will take place. For example, iron can displace copper from copper(II) nitrate as described in the exercise.

When analyzing reactivity, consider the following:

• A more reactive metal can displace a less reactive metal from a compound.
• A metal's placement in the series indicates its ability to act in a competitive reaction.
• Reactivity can affect the stability and formation of new compounds.

Balanced Chemical Equations

A balanced chemical equation accurately represents a chemical reaction by showing the number of reactant and product molecules. This balance follows the law of conservation of mass, which states that matter cannot be created or destroyed in an isolated system.

In the given exercise, writing balanced chemical equations ensures that we follow the conservation law, meaning that the number of each type of atom on both sides of the equation is equal. For instance, when balancing the reaction between aluminum and cobalt(II) sulfate, we made sure that the number of aluminum, cobalt, and sulfur atoms are equal on both sides:
2Al(s) + 3CoSO₄(aq) -> Al₂(SO₄)₃(aq) + 3Co(s)

It's helpful to create balanced equations by:

• Counting each type of atom in the reactants and products.
• Adjusting coefficients to balance atoms without altering subscripts.
• Rechecking the balance to ensure atoms and charges are equal.

Balanced equations not only adhere to physical laws but also help in making precise chemical calculations.