Problem 53 - Chemistry The Central Science

Question

Write balanced molecular and net ionic equations for the reactions of (a) manganese with dilute sulfuric acid, (b) chromium with hydrobromic acid, (c) tin with hydrochloric acid, (d) aluminum with formic acid, HCOOH.

Step-by-Step Solution

Answer

The short version of the answer is as follows: a) Balanced molecular equation: Mn + H2SO4 -> MnSO4 + H2 Net ionic equation: Mn(s) + 2H+(aq) -> Mn^2+(aq) + H2(g) b) Balanced molecular equation: 2Cr + 6HBr -> 2CrBr3 + 3H2 Net ionic equation: 2Cr(s) + 6H+(aq) -> 2Cr^3+(aq) + 3H2(g) c) Balanced molecular equation: Sn + 2HCl -> SnCl2 + H2 Net ionic equation: Sn(s) + 2H+(aq) -> Sn^2+(aq) + H2(g) d) Balanced molecular equation: 2Al + 6HCOOH -> 2Al(HCOO)3 + 3H2 Net ionic equation: 2Al(s) + 6H+(aq) -> 2Al^3+(aq) + 3H2(g)

Step 1: Reaction a: Manganese with dilute sulfuric acid

First, identify the products of the reaction: Mn + H2SO4 -> MnSO4 + H2 Now, balance the equation: Mn + H2SO4 -> MnSO4 + H2 (already balanced) The balanced molecular equation for the reaction of manganese with dilute sulfuric acid is: Mn + H2SO4 -> MnSO4 + H2 To find the net ionic equation, split all species into their ions: Mn(s) + 2H+(aq) + SO4^2-(aq) -> Mn^2+(aq) + SO4^2-(aq) + H2(g) Canceling out the spectator ions (SO4^2-), we get: Mn(s) + 2H+(aq) -> Mn^2+(aq) + H2(g) The net ionic equation for the reaction of manganese with dilute sulfuric acid is: Mn(s) + 2H+(aq) -> Mn^2+(aq) + H2(g)

Step 2: Reaction b: Chromium with hydrobromic acid

First, identify the products of the reaction: Cr + HBr -> CrBr3 + H2 Now, balance the equation: 2Cr + 6HBr -> 2CrBr3 + 3H2 The balanced molecular equation for the reaction of chromium with hydrobromic acid is: 2Cr + 6HBr -> 2CrBr3 + 3H2 To find the net ionic equation, split all species into their ions: 2Cr(s) + 6H+(aq) + 6Br^-(aq) -> 2Cr^3+(aq) + 6Br^-(aq) + 3H2(g) Canceling out the spectator ions (Br^-), we get: 2Cr(s) + 6H+(aq) -> 2Cr^3+(aq) + 3H2(g) The net ionic equation for the reaction of chromium with hydrobromic acid is: 2Cr(s) + 6H+(aq) -> 2Cr^3+(aq) + 3H2(g)

Step 3: Reaction c: Tin with hydrochloric acid

First, identify the products of the reaction: Sn + HCl -> SnCl2 + H2 Now, balance the equation: Sn + 2HCl -> SnCl2 + H2 The balanced molecular equation for the reaction of tin with hydrochloric acid is: Sn + 2HCl -> SnCl2 + H2 To find the net ionic equation, split all species into their ions: Sn(s) + 2H+(aq) + 2Cl^-(aq) -> Sn^2+(aq) + 2Cl^-(aq) + H2(g) Canceling out the spectator ions (Cl^-), we get: Sn(s) + 2H+(aq) -> Sn^2+(aq) + H2(g) The net ionic equation for the reaction of tin with hydrochloric acid is: Sn(s) + 2H+(aq) -> Sn^2+(aq) + H2(g)

Step 4: Reaction d: Aluminum with formic acid

First, identify the products of the reaction: Al + HCOOH -> Al(HCOO)3 + H2 Now, balance the equation: 2Al + 6HCOOH -> 2Al(HCOO)3 + 3H2 The balanced molecular equation for the reaction of aluminum with formic acid is: 2Al + 6HCOOH -> 2Al(HCOO)3 + 3H2 To find the net ionic equation, split all species into their ions: 2Al(s) + 6H+(aq) + 6HCOO^-(aq) -> 2Al^3+(aq) + 6HCOO^-(aq) + 3H2(g) Canceling out the spectator ions (HCOO^-), we get: 2Al(s) + 6H+(aq) -> 2Al^3+(aq) + 3H2(g) The net ionic equation for the reaction of aluminum with formic acid is: 2Al(s) + 6H+(aq) -> 2Al^3+(aq) + 3H2(g)

Key Concepts

Balancing Chemical Equations

Balancing chemical equations is a crucial step in any chemical reaction process. A balanced equation has equal numbers of each type of atom on both sides of the reaction. This mirrors the Law of Conservation of Mass - matter is neither created nor destroyed, but merely rearranged. To balance an equation, begin by writing the unbalanced equation showing all reactants and products.
Next, adjust the coefficients to balance the number of atoms for each element on both sides of the equation. Coefficients are whole numbers placed in front of the chemical formulas. For example, the reaction of chromium with hydrobromic acid, initially written as: Cr + HBr → CrBr₃ + H₂, becomes 2Cr + 6HBr → 2CrBr₃ + 3H₂ when balanced. Here, we balanced chromium, hydrogen, and bromine atoms one by one.
It's essential always to double-check each element to ensure they are balanced. Remember, the smallest whole-number ratios in which reactants combine to form products are required.

Spectator Ions

Spectator ions are ions that remain unchanged on both sides of a chemical reaction. They do not participate in the actual chemical change but appear in the full ionic equation. Identifying spectator ions is important when writing net ionic equations, which highlight only the species that undergo a change.
In the example of manganese reacting with sulfuric acid, the balanced molecular equation is: Mn + H₂SO₄ → MnSO₄ + H₂. Breaking this into ions, we get: Mn(s) + 2H⁺(aq) + SO₄²⁻(aq) → Mn²⁺(aq) + SO₄²⁻(aq) + H₂(g). The sulfate ions (SO₄²⁻) are spectator ions as they appear identically on both sides.

• They can be canceled out to simplify the reaction to the net ionic form:
Mn(s) + 2H⁺(aq) → Mn²⁺(aq) + H₂(g)

Identifying spectator ions helps in understanding the essence of the chemical change occurring during the reaction.

Acid-Metal Reactions

Acid-metal reactions are a common type of redox reaction where an acid reacts with a metal to produce a salt and hydrogen gas. These reactions illustrate basic principles of chemistry, such as the release of hydrogen gas and formation of ionic compounds.
Let's examine the reaction of tin with hydrochloric acid as an example: Sn + 2HCl → SnCl₂ + H₂. Here, tin (Sn) reacts with hydrochloric acid (HCl), resulting in the formation of tin chloride (SnCl₂) and diatomic hydrogen gas (H₂).
Such reactions can be categorized as redox reactions, where the metal loses electrons (oxidation) and the hydrogen ions gain electrons (reduction). The general form of a metal-acid reaction is: Metal + Acid → Salt + Hydrogen gas Acid-metal reactions are not only essential in academic discussions of basic chemistry but also have numerous practical applications, such as metal refining, energy storage in batteries, and in various forms of analytical chemistry.