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Some Basic Concepts of Chemistry question

2010 · Shift 2 · Q2
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Some Basic Concepts of Chemistry question

2010 · Shift 2 · Q2

JEE AdvancedChemistrySome Basic Concepts of ChemistryNumerical+4 / −1
Silver (atomic weight = 108 g mol-1) has a density of 10.5 g.cm-3. The number of silver atoms on a surface of area 10-12 m2 can be expressed in scientific notation as y ×\times× 10x. The value of x is?
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Correct answer: 7

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Problem Analysis

We are given the atomic weight and density of silver, and a specific surface area. We need to find the number of silver atoms that would fit on this surface. The final answer should be expressed in scientific notation y×10xy \times 10^xy×10x, and we need to find the value of the exponent, xxx.

The core of the problem is to determine the area occupied by a single silver atom on a surface.

Step-by-Step Solution

  1. Calculate the volume of one mole of silver (Molar Volume). The molar volume (VmV_mVm​) can be calculated from the atomic weight (Molar Mass, MMM) and the density (ρ\rhoρ). Given:

    • Atomic weight, M=108M = 108M=108 g/mol
    • Density, ρ=10.5\rho = 10.5ρ=10.5 g/cm³

    Vm=Mρ=108 g/mol10.5 g/cm3≈10.286 cm3/molV_m = \frac{M}{\rho} = \frac{108 \text{ g/mol}}{10.5 \text{ g/cm}^3} \approx 10.286 \text{ cm}^3/\text{mol}Vm​=ρM​=10.5 g/cm3108 g/mol​≈10.286 cm3/mol

  2. Calculate the volume occupied by a single silver atom. We can find the volume of a single atom (VatomV_{atom}Vatom​) by dividing the molar volume by Avogadro's number (NA=6.022×1023N_A = 6.022 \times 10^{23}NA​=6.022×1023 atoms/mol).

    Vatom=VmNA=10.286 cm3/mol6.022×1023 atoms/mol≈1.708×10−23 cm3/atomV_{atom} = \frac{V_m}{N_A} = \frac{10.286 \text{ cm}^3/\text{mol}}{6.022 \times 10^{23} \text{ atoms/mol}} \approx 1.708 \times 10^{-23} \text{ cm}^3/\text{atom}Vatom​=NA​Vm​​=6.022×1023 atoms/mol10.286 cm3/mol​≈1.708×10−23 cm3/atom

  3. Estimate the surface area occupied by a single silver atom. To estimate the area an atom occupies on a surface, we can model the volume it occupies as a small cube. If the volume of this cube is VatomV_{atom}Vatom​, its side length 'a' would be a=(Vatom)1/3a = (V_{atom})^{1/3}a=(Vatom​)1/3. The area this atom presents on a surface would be a2a^2a2. Therefore, the area of a single atom (AatomA_{atom}Aatom​) can be estimated as:

    Aatom=(Vatom)2/3=(1.708×10−23 cm3)2/3A_{atom} = (V_{atom})^{2/3} = (1.708 \times 10^{-23} \text{ cm}^3)^{2/3}Aatom​=(Vatom​)2/3=(1.708×10−23 cm3)2/3 Aatom≈6.63×10−16 cm2A_{atom} \approx 6.63 \times 10^{-16} \text{ cm}^2Aatom​≈6.63×10−16 cm2

  4. Convert the given surface area to consistent units. The given surface area is A=10−12 m2A = 10^{-12} \text{ m}^2A=10−12 m2. We need to convert this to cm² to be consistent with our calculation for AatomA_{atom}Aatom​. Since 1 m=100 cm1 \text{ m} = 100 \text{ cm}1 m=100 cm, then 1 m2=(100 cm)2=104 cm21 \text{ m}^2 = (100 \text{ cm})^2 = 10^4 \text{ cm}^21 m2=(100 cm)2=104 cm2.

    A=10−12 m2×104 cm21 m2=10−8 cm2A = 10^{-12} \text{ m}^2 \times \frac{10^4 \text{ cm}^2}{1 \text{ m}^2} = 10^{-8} \text{ cm}^2A=10−12 m2×1 m2104 cm2​=10−8 cm2

  5. Calculate the total number of silver atoms on the surface. The total number of atoms (NNN) is the total surface area divided by the area occupied by a single atom.

    N=AAatom=10−8 cm26.63×10−16 cm2≈0.1508×108 atomsN = \frac{A}{A_{atom}} = \frac{10^{-8} \text{ cm}^2}{6.63 \times 10^{-16} \text{ cm}^2} \approx 0.1508 \times 10^8 \text{ atoms}N=Aatom​A​=6.63×10−16 cm210−8 cm2​≈0.1508×108 atoms

  6. Express the result in scientific notation and find x. The number of atoms is expressed in scientific notation as y×10xy \times 10^xy×10x, where 1≤y<101 \le y < 101≤y<10.

    N=0.1508×108=1.508×107N = 0.1508 \times 10^8 = 1.508 \times 10^7N=0.1508×108=1.508×107 Comparing this with y×10xy \times 10^xy×10x, we can see that y=1.508y = 1.508y=1.508 and x=7x = 7x=7.

Conclusion

The value of x is 7.

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