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Viefleur [7K]
3 years ago
12

An element has ccp packing with a face-centered cubic unit cell. its density is 8920 kg/m3 and the unit cell volume is 4.72 x 10

-26 l. calculate the molar mass (g/mol) of the element to three significant figures.
Chemistry
1 answer:
ziro4ka [17]3 years ago
5 0
<span>63.4 g/mol
   First, let's determine how many atoms per unit cell in face-centered cubic. There is 8 corners, each of which has 1 atom, and each of those atoms is shared between 8 other unit cells. So 8*1/8 = 1 atom per unit cell. Additionally, there are 6 faces, each of which has 1 atom that's shared between 2 unit cells. So 6*1/2 = 3 atoms per unit cell. So each unit cell has the mass of 1+3 = 4 atoms. Since there is 1000 liters per cubic meter, the mass per liter is 8920 kg/1000 = 8.920 kg/L. Now the mass per unit cell is 8920 g * 4.72x10^-26 = 4.21024x10^-22 g per unit cell. The mass per atom is 4.21024x10^-22 g / 4 = 1.05256x10^-22 g/atom, Finally, multiply by Avogadro's number, getting 1.05256x10^-22 g/atom * 6.0221409x10^23 atom/mol = 63.38664625704 g/mol.
   Rounding to 3 significant digits gives 63.4 g/mol.</span>
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Explanation:

we know that

P_{sol}=\chi_{solvent}P^0_{solvent}

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P sol  - the vapor pressure of the solution

χ  solvent - the mole fraction of the solvent

P ∘ solvent  - the vapor pressure of the pure solvent

This means that in order to be able to calculate the mole fraction of sodium chloride, you need to know what the vapor pressure of pure water is at  

25 ° C  You can use an online calculator to find that the vapor pressure of pure water at  25 C  is equal to about  23.8 torr .

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