Video: Applying Knowledge of the Relationship between Amount in Moles and the Masses of Samples of SO₂ and NO₂, and Their Molecular Masses

For statements (I) and (II), state for each if they are true or false. (I) An equal number of moles of SO₂ and NO₂ have different masses. (II) The molecular mass of SO₂ is greater than the molecular mass of NO₂. If both are true, state if (II) is a correct explanation for (I).

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Video Transcript

For statements (I) and (II), state for each if they are true or false. (I) An equal number of moles of SO2 and NO2 have different masses. (II) The molecular mass of SO2 is greater than the molecular mass of NO2. If both are true, state if (II) is a correct explanation for (I).

In the first part of this question, we’re being asked to compare the masses of SO2 or sulfur dioxide and NO2 or nitrogen dioxide. The question tells us that we’re comparing an equal number of moles of these two different chemical species. Since a mole is just 6.02 times 10 to the 23 entities, in this case, molecules of sulfur dioxide or nitrogen dioxide, what we’re really comparing here is the mass of sulfur dioxide molecules and nitrogen dioxide molecules.

If we look at the periodic table for nitrogen, oxygen, and sulfur, the elements in the molecules that we’re interested in for this question, we’ll see that each of these elements have different atomic masses. We could then use these atomic masses to determine the molecular mass of sulfur dioxide or nitrogen dioxide molecules. In a molecule of nitrogen dioxide, there is one nitrogen atom that has an atomic mass of about 14 grams per mole. And we have two oxygens that have an atomic mass of about 16 grams per mole. This means that the molecular mass of nitrogen dioxide is about 46 grams per mole. So, one mole of nitrogen dioxide weighs 46 grams.

Now, let’s determine the molecular mass of sulfur dioxide. We have one atom of sulfur in sulfur dioxide, which has an atomic mass of about 32 grams per mole. And we, again, have two oxygen atoms that have an atomic mass of about 16 grams per mole. So, sulfur dioxide has a molecular mass of 64 grams per mole.

So, as we can see from calculating these molecular masses, if we had one mole of nitrogen dioxide molecules, that would weigh about 46 grams. But if we had one mole of sulfur dioxide molecules, that would weigh about 64 grams. So, statement (I) is true. An equal number of moles of sulfur dioxide and nitrogen dioxide would have different masses.

Along the way, we’ve also answered statement (II), which says that the molecular mass of SO2 is greater than the molecular mass of NO2. So, this statement is true as well. The molecular mass of sulfur dioxide is 64 grams per mole, but the molecular mass of nitrogen dioxide is 46 grams per mole.

Since both statement (I) and statement (II) are true, we have to state if (II) is a correct explanation for (I). That is, if the molecular mass of SO2 being larger than the molecular mass of NO2 is the reason that an equal number of moles of SO2 and NO2 have different masses. This is true as well. Because the molecular mass of SO2 is greater than the molecular mass of NO2, one mole of SO2 molecules will have a greater mass than one mole of NO2 molecules.

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