Problem 29 - Chemistry Matter and Change

Question

Zinc chloride \(\left(\mathrm{ZnCl}_{2}\right)\) is used in soldering flux, an alloy used to join two metals together. Determine the moles of \(\mathrm{Cl}^{-}\) ions in 2.50 \(\mathrm{mol} \mathrm{ZnCl}_{2}\) .

Step-by-Step Solution

Answer

There are 5.00 moles of \(\mathrm{Cl}^{-}\) ions in 2.50 moles of \(\mathrm{ZnCl}_{2}\).

Step 1: Understand the Formula

Zinc chloride (\(\mathrm{ZnCl}_{2}\)) consists of one zinc ion (\(\mathrm{Zn}^{2+}\)) and two chloride ions (\(\mathrm{Cl}^{-}\)). This means for each molecule of zinc chloride, there are two chloride ions present.

Step 2: Apply the Mole Concept

Since one mole of a substance contains Avogadro's number of entities and given that 1 mole of \(\mathrm{ZnCl}_{2}\) contains 2 moles of \(\mathrm{Cl}^{-}\) ions, we can find the number of moles of \(\mathrm{Cl}^{-}\) ions in 2.50 moles of \(\mathrm{ZnCl}_{2}\).

Step 3: Calculate the Moles of \(\mathrm{Cl}^{-}\) Ions

Using the relationship, \(\text{moles of } \mathrm{Cl}^{-} = 2 \times \text{moles of } \mathrm{ZnCl}_{2}\), we calculate: \[\text{moles of } \mathrm{Cl}^{-} = 2 \times 2.50 = 5.00 \text{ moles}\]

Step 4: Conclusion

Therefore, in 2.50 moles of \(\mathrm{ZnCl}_{2}\)), there are 5.00 moles of \(\mathrm{Cl}^{-}\) ions.

Key Concepts

Zinc Chloride

Zinc chloride is an important compound represented by the formula \( \text{ZnCl}_2 \). It is often utilized in applications such as soldering flux, where it helps join metals together. Within each molecule of zinc chloride, you will find one zinc ion, which carries a charge of \( \text{Zn}^{2+} \), and two chloride ions, \( \text{Cl}^- \). The presence of these ions gives zinc chloride its chemical properties and plays a crucial role in its functionality. Knowing the composition of zinc chloride allows us to determine the number of ions in various chemical scenarios.

Chemical Formulas

Chemical formulas are the shorthand notations used to represent chemical compounds. They consist of symbols for the elements present in the compound, along with numbers that indicate the ratios of these elements. In the formula \( \text{ZnCl}_2 \), the chemical formula for zinc chloride, the subscript '2' next to chlorine (\( \text{Cl} \)) tells us that each molecule of zinc chloride contains two chloride ions for every one zinc ion.
Understanding chemical formulas is key because they not only communicate the composition of the compound but also allow us to determine the number of atoms or ions present. This is useful in calculating quantities for reactions or in understanding how substances interact.

Avogadro's Number

Avogadro's number is a fundamental concept in chemistry, serving as a bridge between the atomic scale and the macroscopic world. This number, \( 6.022 \times 10^{23} \), is the number of atoms, ions, or molecules in one mole of a substance. Avogadro's number provides a way to translate between the amount of substance and the number of individual particles.
For instance, when we talk about 2.50 moles of \( \text{ZnCl}_2 \), we are referring to \( 2.50 \times 6.022 \times 10^{23} = 1.5055 \times 10^{24} \) formula units of zinc chloride. Since each unit contains two chloride ions, we can use this to further calculate the total number of \( \text{Cl}^- \) ions present.

Ions and Ionic Compounds

Ions are charged particles that form when atoms gain or lose electrons. Positively charged ions are called cations, like \( \text{Zn}^{2+} \) in zinc chloride, and negatively charged ions are called anions, like \( \text{Cl}^- \). Ionic compounds are formed when these ions bond together due to their opposite charges, resulting in a compound that is usually neutral overall.
Zinc chloride is an example of an ionic compound. In \( \text{ZnCl}_2 \), the zinc ion with a \(+2\) charge and the two chloride ions, each with a \(-1\) charge, result in a neutral compound overall. Understanding ionic compounds helps in predicting and explaining the properties and behaviors of substances in reactions and in various applications.