Which has more molecules, a teaspoon of water that has a mass of 1.25 grams or a teaspoon of alcohol, C2H5OH, that has a mass of 0.890 grams?
To know which compound has more in terms of content, we can simply convert them to molecules using Avogadro's number.
Molecules of water
`1.25 grams water *(1 mol e water)/(18.0 grams water) * (6.022x10^23 mol e c u l es water)/(1 mol e water)`
= 4.18x10^23 molecules of water
Molecules of ethanol, C2H5OH
`0.890 grams ethanol * (1 mol e ethanol)/(46.0 grams) * (6.022x10^23 mol e c u l e s of ethanol)/(1 mol e ethanol)`
= 1.17x10^22 molecules of ethanol
Looking at the results we can say that there are mole water molecules than ethanol molecules.
**ethanol is an alcohol
Notice that the atoms making up alcohol contain those which make up water, plus 2 carbons and 4 extra hydrogens, so the alcohol has the greater molecular mass. The number of molecules in each teaspoon equals its mass divided by the mass of each molecule. The teaspoon of water has a greater mass, while each molecule has a smaller mass than the alcohol.
(1.23/mwater) is a larger number than (0.89/malcohol)
First let the molar masses of the two substances:
M(H2O) = 2 + 16 = 18 g/mol
M(C2H5OH) (12*2) + 5 + 16 + 1 = 46 g/mol
The next step - to find the amount of substance of both substances:
n = m/M
n (H2O) = 1.25 g / 18 g/mol = 0.069 mol
n (C2H5OH) = 0.89 g / 46 g/mol = 0.019 mol
Number of molecules of a substance can be calculated by the formula:
N (molecules) = N a * n
N a = 6.02 * 10^23 mol^-1 - Avogadro's number
N (molecules Н2О) = 6.02 * 10^23 mol^-1 * 0.069 mol = 4.15 * 10^22 molecules
N (molecules C2H5OH) = 6.02 * 10^23 mol^-1 * 0.019 = 1.14 * 10^22 molecules
N (molecules Н2О)/N (molecules C2H5OH) = 4.15 * 10^22 molecules/1.14 * 10^22 molecules = 3.64
Answer: Of water molecules more than the alcohol molecules in 3.64 times.