Question

In the production of printed circuit boards for the electronics industry, a \(0.60-\mathrm{mm}\) layer of copper is laminated onto an insulating plastic board. Next, a circuit pattern made of a chemically resistant polymer is printed on the board. The unwanted copper is removed by chemical etching, and the protective polymer is finally removed by solvents. One etching reaction is \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}(a q)+4 \mathrm{NH}_{3}(a q)+\mathrm{Cu}(s)\) \(\longrightarrow 2\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}(a q)\) a. Is this reaction an oxidation-reduction process? Explain. b. \(A\) plant needs to manufacture 10,000 printed circuit boards, each \(8.0 \times 16.0 \mathrm{~cm}\) in area. An average of \(80 . \%\) of the copper is removed from each board (density of copper \(=8.96\) \(\mathrm{g} / \mathrm{cm}^{3}\) ). What masses of \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}\) and \(\mathrm{NH}_{3}\) are needed to do this? Assume \(100 \%\) yield.

Short answer

The given reaction is not an oxidation-reduction process since there are no changes in oxidation numbers. To manufacture 10,000 printed circuit boards, the required masses of \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}\) and \(\mathrm{NH}_{3}\) can be calculated by first finding the mass of copper removed and then determining the moles of each reactant required. After these calculations, the mass of \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}\) and \(\mathrm{NH}_{3}\) needed are found by multiplying the moles of each reactant by their respective molar masses.

Step-by-step solution

Identify Oxidation-Reduction process

To identify if it is an oxidation-reduction process, we can check the oxidation numbers of all elements. Remember that in a redox reaction, there will be a change in the oxidation number for at least one element in the reactants and products. The balanced chemical reaction is: \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}(a q)+4 \mathrm{NH}_{3}(a q)+\mathrm{Cu}(s)\) \(\longrightarrow 2\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}(a q)\) Oxidation numbers: For \(\mathrm{Cl}\) in the reactants: -1 (as in all ionic compounds) For \(\mathrm{Cl}\) in the products: -1 (as in all ionic compounds) For \(\mathrm{N}\) in the reactants: -3 (in ammonia) For \(\mathrm{N}\) in the products: -3 (in ammonia) For \(\mathrm{Cu}\) in the reactants (Cu in complex and solid): 0 For \(\mathrm{Cu}\) in the products (Cu in complex): 0 As there are no changes in oxidation numbers, this reaction is not a redox process.

Calculate mass of copper to be removed

We are given that \(80\%\) of the copper layer is removed from each board. The area of each board is \(8.0 \times 16.0\,\mathrm{cm}^2\), and the copper layer is \(0.60\,\mathrm{mm}\) thick. We can calculate the volume of copper removed from each board and then multiply by the given density of copper to find the mass of copper to be removed. Volume of copper removed per board: \(= A \times t = (8.0\,\mathrm{cm} \times 16.0\,\mathrm{cm}) \times (0.60\,\mathrm{mm}) \times (80\%)\) \(= (8.0\,\mathrm{cm} \times 16.0\,\mathrm{cm}) \times (0.60\,\mathrm{mm}) \times 0.8\) Note that we need to convert 0.60 mm to cm: \(1\,\mathrm{mm} = 0.1\,\mathrm{cm}\) The volume of copper removed per board is: \(= (8.0\,\mathrm{cm} \times 16.0\,\mathrm{cm}) \times (0.06\,\mathrm{cm}) \times 0.8\) Now calculate the mass of copper removed per board: \(= \text{volume} \times \rho = (8.0\,\mathrm{cm} \times 16.0\,\mathrm{cm} \times 0.06\,\mathrm{cm} \times 0.8) \times 8.96\,\frac{\mathrm{g}}{\mathrm{cm}^3}\) Finally, calculate the mass of copper removed for 10,000 boards: \(= (8.0 \times 16.0 \times 0.06 \times 0.8 \times 8.96) \times 10{,}000\)

Calculate moles of copper removed

To determine the mass of \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}\) and \(\mathrm{NH}_{3}\) required, we first need to calculate moles of copper removed. Calculate the moles of copper removed using the molar mass of Cu (63.5 g/mol): \(n_{\mathrm{Cu}} = \frac{\text{mass of Cu removed}}{\text{molar mass of Cu}}\)

Calculate moles of reactants required

Now, we can determine the moles of each reactant required by observing the coefficients in the balanced chemical equation. For \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}\): From the balanced equation, 1 mole of \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}\) reacts with 1 mole of \(\mathrm{Cu}\). Therefore, we need the same moles of \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}\) as moles of \(\mathrm{Cu}\) removed. For \(\mathrm{NH}_{3}\): From the balanced equation, 4 moles of \(\mathrm{NH}_{3}\) reacts with 1 mole of \(\mathrm{Cu}\). Therefore, we need 4 times the moles of \(\mathrm{NH}_{3}\) as moles of \(\mathrm{Cu}\) removed.

Calculate mass of reactants required

Now that we know the moles of each reactant required, we can calculate their masses. For \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}\): Molar mass of \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}\) = 253.0 g/mol. Mass of \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}\) required: \(= \text{moles of} \, \left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2} \times \text{molar mass of} \, \left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}\) For \(\mathrm{NH}_{3}\): Molar mass of \(\mathrm{NH}_{3}\) = 17.0 g/mol. Mass of \(\mathrm{NH}_{3}\) required: \(= \text{moles of} \, \mathrm{NH}_{3} \times \text{molar mass of} \, \mathrm{NH}_{3}\) Now we have the masses of \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Cl}_{2}\) and \(\mathrm{NH}_{3}\) required for the production of 10,000 printed circuit boards.

Key concepts

Oxidation-Reduction

An oxidation-reduction (redox) reaction involves the transfer of electrons between two species, resulting in changes in the oxidation states of the reacting molecules. In any redox reaction:

• Reduction refers to the gain of electrons, leading to a decrease in oxidation number.
• Oxidation involves the loss of electrons, causing an increase in oxidation number.

In the given chemical equation concerned with the etching of copper, it's essential to determine if oxidation numbers change: 1. **Copper** remains with the same oxidation number, neither gaining nor losing electrons. 2. **Chlorine** and **Nitrogen** also retain their oxidation states throughout the reaction. Since there are no changes in the oxidation state for any of the elements involved, this process is not a redox reaction. This distinction is crucial because different chemical processes need different approaches and chemicals.

Copper Removal

In manufacturing printed circuit boards (PCBs), the removal of excess copper is a significant step. To achieve the required circuitry, unnecessary copper layers are chemically etched away, leaving behind the desired pathways. This is accomplished by applying:

• A chemical etching agent that selectively dissolves the exposed copper areas while leaving other areas intact.
• A protective polymer that helps define the circuit pattern and prevent the etching solution from affecting desired copper tracks.

In this exercise, the copper etching involves calculating the actual copper removal as a percentage of the initial copper layer. It’s designed to address real-world challenges like controlling material waste and ensuring precise electrical pathways. Understanding the chemical interactions and consistent application of formulas ensures high-quality PCB production.

Printed Circuit Boards

Printed Circuit Boards, or PCBs, are the backbone of electronic devices. They provide platforms for mounting and connecting various electronic components in a stable and reliable manner. The process of making PCBs involves several critical steps:

• Initially, a copper layer is laminated onto an insulating board.
• A circuit design is then printed onto this copper layer using a resistant polymer.
• Chemical etching removes the extra copper, leaving the circuit pattern intact.
• Finally, the resistant polymer is removed to reveal the circuit paths on the board.

PCBs are crucial as they ensure that components function together effectively, supporting complex circuits and systems. Learning about their production, including copper etching, deepens understanding of modern electronics and their manufacture.

Mass Calculation

Mass calculation is a fundamental part of chemical processes. It helps in determining the quantity of reactants needed and the extent of the reaction. Given step-by-step calculations from the problem, let's see how it unfolds:- **Volume and Mass**: First, calculate the volume of copper to be etched away. This is done using the area of the board and the thickness of the copper layer.- **Density**: Use the known density of copper to find the mass of copper removed. The density formula, \( ext{mass} = ext{volume} imes ext{density}\), is employed here.- **Scaling Up**: Larger manufacturing processes, like producing 10,000 boards, require scaling the calculations, multiplying the mass obtained for one board by 10,000 to provide the total required mass.Understanding and applying these calculations ensures that enough etching agents are prepared for PCB manufacturing, minimizing material wastage and ensuring efficient production.

Chemical Reaction

Chemical reactions describe how substances interact to form new compositions, compositions fundamental to chemical manufacturing processes like PCB etching. - **Understanding the Reaction**: This involves predicting the quantities of each reactant needed for a complete reaction, which is particularly necessary when removing copper from PCBs. - **Balanced Equations**: These are central to determining how much reactant is necessary for removing copper efficiently. By balancing the equation: - You ensure that all atoms are accounted for on each side, signifying that mass is conserved. - Use of stoichiometry to determine how much of each reactant exactly interacts with copper to achieve complete removal. - Calculating the conversion allows for precise preparation, ensuring the created chemical environments are sufficient without excess waste. Balancing chemical reactions and knowing the role each component has in PCB production helps manage chemical reactions efficiently, which is vital for sustainable manufacturing practices.