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Question

Chemistry Question on Expressing Concentration of Solutions

A solution contains 4 g of NaOH and 16.2 g of water. The mole fraction solute and solvent are respectively

A

0.1, 0.9

B

0.2, 0.8

C

0.5, 0.5

D

0.4, 0.6

Answer

0.1, 0.9

Explanation

Solution

Answer (A) 0.1, 0.9

To calculate the mole fraction of a solute and solvent in a solution, we need to determine the number of moles of each component.

Given: Mass of NaOH = 4 g Mass of water = 16.2 g

To find the number of moles of NaOH, we divide the given mass by the molar mass of NaOH. Molar mass of NaOH = 22.99 g/mol (for Na) + 16.00 g/mol (for O) + 1.01 g/mol (for H) = 39.99 g/mol Number of moles of NaOH = 4 g / 39.99 g/mol ≈ 0.1 mol

To find the number of moles of water, we divide the given mass by the molar mass of water. Molar mass of water (H₂O) = 1.01 g/mol (for H) + 1.01 g/mol (for H) + 16.00 g/mol (for O) = 18.02 g/mol Number of moles of water = 16.2 g18.02 g/mol\frac {16.2\ g }{18.02\ g/mol} ≈ 0.9 mol

Now, we can calculate the mole fraction of solute (NaOH) and solvent (water).

Mole fraction of solute (NaOH) = Moles of NaOHTotal moles\frac {Moles\ of \ NaOH}{Total \ moles }= 0.1 mol(0.1 mol+0.9 mol)\frac {0.1\ mol}{(0.1\ mol + 0.9\ mol) } = 0.1

Mole fraction of solvent (water) = moles of waterTotal moles\frac {moles \ of \ water}{Total \ moles} = 0.9 mol(0.1 mol+0.9 mol)\frac {0.9 \ mol}{(0.1\ mol + 0.9\ mol) }= 0.9

Therefore, the mole fraction of solute (NaOH) and solvent (water) in the given solution are approximately 0.1 and 0.9, respectively. So the correct option is 0.1, 0.9.