Consider a sample of helium and a sample of neon, both at 30ºC and 1.5atm. Both samples have a volume of 5.0 liters. Which statement concerning these samples is not true?
a- each weighs the same amount
b- each has the same # of atoms of gas
c- the density of the neon is greater than that of the helium
d- each sample contains the same # of moles of gas
e- none of the above
So what is your thinking? I will be happy to critique it.
Look at it this way.
PV = nRT.
So P is the same, V is the same, R is the same, T is the same; ergo, n (the number of moles) MUST be the same.
So what does that tell you.
Remember # moles = grams/molar mass and you know # moles is th same.
To determine which statement concerning the samples of helium and neon is not true, let's analyze each statement:
a) "Each weighs the same amount":
To compare the weights of the samples, we need to consider the molar mass of each gas. The molar masses of helium and neon are approximately 4 grams/mol and 20 grams/mol, respectively. Since both samples have the same volume and temperature, which are constant for this comparison, the weight of helium sample (with a lower molar mass) will be lighter than the weight of the neon sample. Therefore, statement a is NOT true.
b) "Each has the same number of atoms of gas":
We know that the number of atoms in a sample depends on the number of moles and Avogadro's number (6.022 x 10^23 atoms/mol). Since both samples have the same volume, temperature, and pressure, we can assume they contain the same number of moles of gas. As a result, the number of atoms should also be the same in both samples. Hence, statement b is true.
c) "The density of the neon is greater than that of the helium":
Density is defined as the mass of a substance divided by its volume. As mentioned earlier, the neon sample weighs more than the helium sample due to its higher molar mass. However, both samples have the same volume of 5.0 liters. As a result, the density of the neon sample will be greater than that of the helium sample. Thus, statement c is true.
d) "Each sample contains the same number of moles of gas":
As mentioned before, since both samples have the same volume, temperature, and pressure, we can assume they contain the same number of moles of gas. Therefore, statement d is true.
After analyzing all the statements, we can conclude that statement a, "Each weighs the same amount," is NOT true. So, the correct answer is (a) each weighs the same amount.