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Aleks04 [339]
4 years ago
10

If a liter of solution is needed, how many grams of ethanol, C2H6O will be added when a scientist creates a 0.25 molal solution?

Chemistry
1 answer:
Dafna11 [192]4 years ago
5 0

Answer:

11.52g of ethanol

Explanation:

Molality is an unit of concentration defined as ratio between moles of solute (In this case, ethanol) and kg of solvent.

As solvent is water, 1 liter of water weights 1kg.

That means to create a 0.25molal solution it is necessary to have 0.25 moles of ethanol.

Molar weight of ethanol (C₂H₆O) is:

C: 12.01g/mol × 2 = 24.02g/mol

H: 1.01g/mol × 6 = 6.06g/mol

O: 16g/mol × 1 = 16g/mol

24.02g/mol + 6.06g/mol + 16g/mol = 46.08g/mol

As you need 0.25 moles, there is necessary to weight:

0.25 moles × (46.08g/mol) = <em>11.52g of ethanol</em>

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What is the mass of KOH found in a 785 mL of a 1.43 M solution of KOH
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Molarity is defined as the ratio of number of moles to the volume of solution in litres.

The mathematical expression is given as:

Molarity = \frac{Number of moles}{volume of solution in litres}

Here, molarity is equal to 1.43 M and volume is equal to 785 mL.

Convert mL into L

As, 1 mL = 0.001 L

Thus, volume = 785\times 0.001 = 0.785 L

Rearrange the formula of molarity in terms of number of moles:

Number of moles =molarity\times volume of solution in litres

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= 1.12255 mole

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mass in g = 1.12255 mole\times 56.10 g/mol

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Hence, mass of KOH = 62.97 g



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