Respuesta :
Considering a mass m of 127 grams of iodine, a molecular weight M = 253.8, and moles number n = 0.5, the number of iodine molecules is 3.011x10²³.
Before answering the question, we need to know a few concepts.
What is a mole?
A mole is a quantity unit. It measures how many particles -atoms or molecules- there are in a substance.
One mole is equivalent to a huge number of particles. This number is 6.022x10²³ and it is a constant.
One mole is always equivalent to 6.022x10²³ particles, no matter the substance species. But when referring to this number, we need to identify the particle if we are talking about atoms or molecules.
For instance,
- 1 Helium molecule is monoatomic, which means it is composed of one He atom.
So, one helium mole = 6.022x10²³ He atoms.
- 1 Hydrogen molecule is diatomic, meaning that it is composed of two H atoms.
In this case, one hydrogen mole = 6.022x10²³ H₂ molecules = 2(6.022x10²³) H atoms.
We use the letter n to identify it.
What is the Avogadro number?
The Avogadro number is a constant equivalent to 6.022x10²³ and was determined by Amedeo Avogadro.
This is the number used to determine how many particles there are in a mole.
We use the letters AN to identify it.
What is the molecular weight?
The molecular weight is the value obtained by adding the atomic masses of all the atoms composing the molecule.
It depends on the type of atom and the number of times it appears in the molecule -subindex-.
We use the letters M to identify it.
Now, we need to get the number of molecules present in 127 grams of iodine, I₂.
Available data:
- m = weight in grames = 127 grams ⇒ given data
- atomic mass = 126,9 ⇒ we look for it in the periodic table.
- M = 253.8 ⇒ This is because I₂ is diatomic. Two atoms are composing this molecule, so 126,9 x 2 = 253.8
Now, first we need to calculate how many moles there are in 127 gr of I₂.
The way to calculate it is by using the following formula,
n = m/M
n = 127 / 253.8 = 0.5 There are 0.5 moles in 127 gr of I₂.
Now we need to know how many molecules there are in 0.5 moles of I₂.
We know that 1 mole of I₂ has 6.022x10²³ molecules of I₂. So, how many molecules are in 0.5 moles? X = (0.5 x (6.022x10²³)) / 1
1 mol ------------ 6.022x10²³ molecules of I₂
0.5 moles ------ X = (0.5 x (6.022x10²³)) / 1 = 3.011x10²³ molecules
Answer: In 127 grams of iodine -I₂- there are 3.011x10²³ iodine molecules.
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