High School

Activity #6:

United States quarters, worth 25 cents, are made of 91.67% copper and 8.33% nickel by mass. Each quarter has a diameter of 0.955 inches (2.46 cm) and a thickness of 0.070 inches (0.175 cm).

1. Weigh the quarter: 5.6 g

2. What is the mass of the copper in the quarter? What is the mass of the nickel in the quarter?

3. How many moles of copper are in the quarter? How many moles of nickel are in the quarter?

4. How many atoms of copper are in the quarter? How many atoms of nickel are in the quarter?

5. Based on information found online, an ounce of copper currently sells for around 29 cents, and an ounce of nickel sells for around 44 cents. If you sold the quarter for the price of its metal, would it be worth more or less than twenty-five cents? (You might want to look up the conversion between ounces and grams.)

Answer :

Sure! Let's break down the problem and go through each part step-by-step:

1. Weighing the Quarter:
- The weight of the quarter is given as 5.6 grams.

2. Mass of Copper and Nickel in the Quarter:
- The quarter is composed of 91.67% copper and 8.33% nickel by mass.
- To find the mass of copper:
[tex]\[
\text{Mass of Copper} = 0.9167 \times 5.6 = 5.13352 \, \text{grams}
\][/tex]
- To find the mass of nickel:
[tex]\[
\text{Mass of Nickel} = 0.0833 \times 5.6 = 0.46648 \, \text{grams}
\][/tex]

3. Moles of Copper and Nickel:
- Molar mass of copper = 63.55 g/mol.
- Molar mass of nickel = 58.69 g/mol.
- To calculate moles of copper:
[tex]\[
\text{Moles of Copper} = \frac{5.13352}{63.55} = 0.08078 \, \text{moles}
\][/tex]
- To calculate moles of nickel:
[tex]\[
\text{Moles of Nickel} = \frac{0.46648}{58.69} = 0.00795 \, \text{moles}
\][/tex]

4. Atoms of Copper and Nickel:
- Using Avogadro's number [tex]\(6.022 \times 10^{23}\)[/tex] atoms/mol.
- Number of atoms of copper:
[tex]\[
\text{Atoms of Copper} = 0.08078 \times 6.022 \times 10^{23} = 4.8645 \times 10^{22} \, \text{atoms}
\][/tex]
- Number of atoms of nickel:
[tex]\[
\text{Atoms of Nickel} = 0.00795 \times 6.022 \times 10^{23} = 4.7864 \times 10^{21} \, \text{atoms}
\][/tex]

5. Value of Metals in the Quarter:
- Conversion factor: 1 ounce = 28.3495 grams.
- Current prices: Copper = [tex]$0.29 per ounce, Nickel = $[/tex]0.44 per ounce.
- Value of copper in the quarter:
[tex]\[
\text{Value of Copper} = \left(\frac{5.13352}{28.3495}\right) \times 0.29 \approx 0.05257 \, \text{dollars}
\][/tex]
- Value of nickel in the quarter:
[tex]\[
\text{Value of Nickel} = \left(\frac{0.46648}{28.3495}\right) \times 0.44 \approx 0.00718 \, \text{dollars}
\][/tex]
- Total metal value:
[tex]\[
\text{Total Metal Value} = 0.05257 + 0.00718 = 0.05975 \, \text{dollars}
\][/tex]

6. Comparison with Face Value:
- The face value of a quarter is [tex]$0.25.
- Metal value ($[/tex]0.05975) is less than the face value ($0.25).
- Thus, the quarter is worth more in face value than in metal content. Selling it for its metal would be less than its worth as currency.

This breakdown provides the mass of each metal, the number of moles, the number of atoms, and the monetary comparison of metal value versus face value.