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3 years ago

A gallon of water has a mass of 3.79 kg. how many moles of water (18.02 g/mol) is this?

2 answers:

6 0

<span>210. moles To determine the number of moles of a substance you have, simply divide the mass of the substance you have by its molar mass. So 3.79 kg / 18.02 g/mol = 3790 g / 18.02 g/mol = 210.3218646 mol Since we only have 3 significant figures, the answer should be rounded to 3 figures, giving 210. as the result. Notice that the decimal point is required. If you state the number of moles is 210, then that answer will only have 2 significant figures. But the value of 210. has 3 significant figures.</span>

garik1379 [7]3 years ago

3 0

First, we will convert the mass of the gallon to grams:
a gallon of water has a mass of 3.79 * 1000 = 3790 grams of water

number of moles can be calculated using the following rule:
number of moles = mass / molar mass
Therefore,
number of moles = 3790 / 18.02 = 210.32 moles

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Explanation:

First of all calculate the mass of hydrated compound as,

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Mass of Sulfur = S × 1 = 32.06 × 1 = 32.06 g

Mass of Oxygen = O × 14 = 16 × 14 = 224 g

Mass of Hydrogen = H × 20 = 1.01 × 20 = 20.2 g

Mass of Na₂S0₄.10H₂O = 322.24 g

Secondly, calculate mass of water present in hydrated compound. For this one should look for the coefficient present before H₂O in molecular formula of hydrated compound. In this case the coefficient is 10, so the mass of water is...

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%H₂O = Mass of H₂O / Mass of Hydrated Compound × 100

Putting values,

%H₂O = 180.2 g / 322.24 g × 100

%H₂O = 55.92 % ≈ 56%

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