Question

Assuming that seawater is a 3.50 mass % aqueous solution of NaCl, what is the molality of seawater?

Answer 1

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Answer 2

To find the molality of seawater, we need to determine the amount of NaCl dissolved in water in moles and then divide it by the mass of water in kilograms.

Given that seawater is a 3.50 mass % aqueous solution of NaCl, this means that for every 100 grams of seawater, 3.50 grams of NaCl is dissolved in it.

Let's assume we have 100 grams of seawater. Then, the mass of NaCl in this 100 grams of seawater is 3.50 grams.

Now, to find the moles of NaCl, we need to divide the mass of NaCl by its molar mass.

The molar mass of NaCl (sodium chloride) can be found in the periodic table:

• Molar mass of Na (sodium) = 22.99 g/mol
• Molar mass of Cl (chlorine) = 35.45 g/mol

Molar mass of NaCl = 22.99 g/mol + 35.45 g/mol = 58.44 g/mol

Now, let's calculate the moles of NaCl in 100 grams of seawater:

Moles of NaCl = Mass of NaCl / Molar mass of NaCl Moles of NaCl = 3.50 g / 58.44 g/mol ≈ 0.0599 mol

The next step is to find the mass of water in the 100 grams of seawater. Since we know that the total mass of the seawater is 100 grams and the mass of NaCl is 3.50 grams, we can calculate the mass of water as follows:

Mass of water = Total mass of seawater - Mass of NaCl Mass of water = 100 g - 3.50 g ≈ 96.50 g

Finally, to find the molality, we divide the moles of NaCl by the mass of water in kilograms:

Molality = Moles of NaCl / Mass of water in kg Molality ≈ 0.0599 mol / (96.50 g / 1000 g/kg) ≈ 0.621 mol/kg

So, the molality of seawater is approximately 0.621 mol/kg.