Calculate the mass (in g) of each sample. a. 3.87 ×10^21 SO3 molecules b. 1.3 ×10^24 H2 O molecu

Calculate the mass (in g) of each sample. a. 3.87 ×10^21 SO3...

Key Concepts

Mole Concept and Avogadro's Number

The mole is a fundamental unit in chemistry that represents an amount of substance containing Avogadro's number (approximately 6.02×10^23) of particles, whether they are atoms, molecules, or ions. Understanding this concept is essential for converting between the number of individual particles and the amount in moles, which is directly related to measurable mass.

Molar Mass

Molar mass is the mass of one mole of a substance and is usually expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all atoms in a molecule. This concept is crucial for converting the amount of a substance in moles to its mass in grams.

Dimensional Analysis

Dimensional analysis is a method used in chemistry to convert units and solve problems involving multiple conversion factors. In the context of this problem, it involves converting the given number of molecules to moles using Avogadro's number, and then converting moles to grams using the molar mass, ensuring that all units cancel appropriately throughout the calculation.

Transcript

0:00 All right.

00:01 So for this question, we are working now on number 67 of chapter 3.

00:07 It asks us to calculate the mass in grams of each sample.

00:12 So that is what we're working on doing.

00:14 So again, the way i always like to start these problems is to figure out what are we given and where are we trying to go.

00:21 So for each of these problems, we are given the number of molecules and we are trying to get to the number of grams.

00:36 So the question is how can we get there? just like we looked at with a previous problem, there is no straight way to get from molecules to grams.

00:44 However, we can use moles to get there.

00:47 So the first thing we need to do is use avagadro's number, so that would be 6 .022 times 10 to the 23rd.

01:04 That's avagodgadro's number, and that is the number of molecules per mole.

01:16 And we put that on the bottom because, again, we need to get rid of our molecules.

01:21 So that is the only way to get rid of molecules.

01:24 Then we need to figure out how are we going to get from moles to grams? so in that instance, then we're going to multiply it by our molar mass, which is the number of grams per mole of each substance.

01:38 So that gets us out and that leaves us with our grams, which is what we're looking for.

01:43 So for each problem, we're going to follow this basic formula.

01:47 Take the number of molecules were given, divide by avagadra's number, multiply it by the molar mass, and that gives us the number of grams of each substance.

01:58 So let's start with letter a.

02:02 We are given 5 .94 times 10 to the 20th of so3, and those are molecules.

02:20 So what do we need to do? we need to multiply it by moles over, so divide it by, right? 6 .022 times 10 to the 23rd.

02:37 Keep in mind when you're plugging these things into your calculator, you are going to have to put when you divide.

02:44 So what you're going to end up putting in your calculator is the 5 .94 times 10 to the 20th, divide that by in parentheses 6 .022 times 10 to the 23rd, because if you don't put it in parentheses, it's not going to work.

03:01 So you have to put it in parentheses.

03:04 And then you're going to multiply that.

03:06 I prefer personally to do these all step by step.

03:08 So i do one thing, then i do the next one, and then i do the next one.

03:12 That way i don't, my calculator doesn't get confused...

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