Ethanol has a specific gravity of 0.787 and a molecular weight of 46.1 g/mol. Wh
ID: 1022424 • Letter: E
Question
Ethanol has a specific gravity of 0.787 and a molecular weight of 46.1 g/mol. What is the density of ethanol in SI units?
How many gm-moles are in 1.0 lb-moles
Assume that the composition of air is 20% oxygen (MW=32) and 80% nitrogen (MW=28) by volume. What is the mass fraction of oxygen in the air (in percent)
The average 70 kg (150 lb) being has 5.5 L of blood (1.05 g/mL). How many 1 oz drinks of 20% alcohol by volume (40 proof) must be consumed for the blood alcohol content (BAC) to exceed 0.1 (BAC is g alcohol per 100 mLblood)? Assume that all of the alcohol consumed goes directly into the blood.
Explanation / Answer
Ethanol has a specific gravity of 0.787 and a molecular weight of 46.1 g/mol. What is the density of ethanol in SI units?
The specific gravity is given as a ratio of the substances density (D ethanol ) to the density of water (DH20), i.e;
Specific gravity = D ethanol /DH20
Given that Ethanol has a specific gravity of 0.787.
07.87 = (D ethanol ) / (1000 Kg / m³)
D ethanol= 07.87*(1000 Kg / m³)
= 787 (Kg / m³)
How many gm-moles are in 1.0 lb-moles
molecular weight of ethanol = 46.1 g/mol.
1.0 lb=453.592 g
Number of moles = amount in g / molecular weight
= 453.592 g/46.1 g/mol
=9.84 moles
Assume that the composition of air is 20% oxygen (MW=32) and 80% nitrogen (MW=28) by volume. What is the mass fraction of oxygen in the air (in percent)
At the same condition of temperature and pressure volume of gas is depend to the number of moles of gases.
Thus the moles of N2 are 80 and O2 are 20.
Now calculate the mole ratio of gases N2 and O2:
80/20= 4
N2/O2 mole ratio
Mass of O2 and N2:
0.20*32 = 6.4 g O2
0.80*28 = 22.4 g N2
22.4 / 6.4= 3.5 N2/O2 mass ratio
Mole fraction of O2 and N2:
6.4/ (6.4 + 22.4) = 0.22 O2
22.8 / (6.4 + 22.4) = 0.79 N2
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