Calculate the number of atoms of each element present in each of the following samples. a. 4.21

Calculate the number of atoms of each element present in...

Key Concepts

Chemical Formula and Composition

A chemical formula provides the types and numbers of atoms in a molecule. Understanding the formula allows one to determine the total number of atoms of each element present in a compound by taking into account the number of atoms of each element within a single molecule.

Stoichiometry

Stoichiometry involves quantitative calculations that relate the amounts of reactants and products in chemical reactions. It relies on balanced chemical equations and allows one to determine the number of atoms or molecules involved in a reaction based on the masses of substances used.

Avogadro's Number

Avogadro's number, approximately 6.022 x 10^23, is a constant that defines the number of particles in one mole of any substance. This constant is crucial for linking the amount of material (in moles) to the actual number of individual atoms or molecules.

Molar Mass

Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). It is calculated by adding the atomic masses of all the atoms in a molecule and is fundamental for converting between the mass of a substance and the number of moles present.

Mole Concept

The mole is a unit in chemistry that represents a specific number (6.022 x 10^23) of particles, whether atoms, molecules, ions, or electrons. It connects the micro-scale world of atoms and molecules to measurable quantities in the macro world, allowing chemists to quantitatively analyze substances through mass and number of particles.

Transcript

00:01 Okay, here we have water and a particular mass of the 4 .21 grams of water.

00:09 And we want to know the number of atoms of each element are present.

00:14 Okay, so first let's derive a formula to find in this.

00:20 So, in order to find number of elements or atoms, we need to find number of molecules.

00:28 And the equation for number of molecules is moles multiplied by avagadro's number and a.

00:50 Right, but we have mass.

00:54 So let's find another way we can represent moles.

00:58 So we know that moles is equivalent to mass over molar mass.

01:04 And we can find molar mass by adding up the...

01:06 Atomic mass of each element present in the compound.

01:13 So now that we have this formula, we could just insert it and substitute it for moles.

01:24 Mass over molar mass.

01:27 Multiply that by an a.

01:31 Okay, so this is our formula.

01:37 Well, this.

01:38 So here we have a mass.

01:40 We can divide it by a molar mass, which is for water, 18 .01 grams per mole, multiplied by avagagos number, which is 6 .022 times 10 to the exponent, 23.

02:09 An e here means times 10 to the exponent.

02:13 And this is units of per mole.

02:20 Okay, so if we carry through with this formula, we at 1 .4 times 10 to the exponent, times 10 to the exponent 23 molecules of water present here.

02:55 Molecules, yes.

02:57 Case, it's a bit tricky.

03:00 E represents times 10 to the exponent, any exponent over here, any exponent.

03:15 It's what e means so quickly here.

03:18 This number is what's in the exponent.

03:23 Okay, so now that we have number of molecules, we want to find number of atoms in each element.

03:31 So if we have one molecule of water, then we have two atoms of hydrogen and one atom of oxygen.

03:42 So it's simple enough, and we're just going to take that logic to apply it for large numbers.

03:52 So if we have so many molecules of water, let's say 10, then we have 20.

04:00 You have twice the number of hydrogen atoms.

04:04 Versus water molecules.

04:07 And then we have always the same number of water molecules as we do have atoms of oxygen.

04:16 Okay, so that's the logic behind what we're about to do.

04:20 So then, now to convert this into atoms of hydrogen, we just take this number multiple by 2.

04:26 So 1 .4 times 2 is 2 .8.

04:29 And let's keep that exponent times 10 to the 23 atoms of hydrogen.

04:37 And then for oxygen it's the same amount of molecules for every one molecule we have the exact same one oxygen atom so yeah and point times t to 23 atoms okay next up you have a couple more so now we have carbon dioxide and 6 .81 grams of it so we take mass divided by molar mass which i have summed up to being 44 grams per mole and we multiply that by the 6 .022 times 10 to the 23 avagadro's constant or n a...

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