Calculate the number of moles of sulfur atoms present in each of the following samples. a. 2.01

Calculate the number of moles of sulfur atoms present in...

Key Concepts

Mole Concept

The mole is a fundamental unit in chemistry used to count particles, where one mole is equivalent to Avogadro's number (approximately 6.022 x 10^23) of particles. This concept enables chemists to convert between the mass of a substance and the number of atoms or molecules it contains.

Molar Mass

Molar mass is the mass of one mole of a substance measured in grams per mole. It is calculated by summing the atomic masses of all the atoms in the chemical formula, and is used to convert between the mass of a sample and the number of moles present.

Chemical Formulas and Composition

Chemical formulas express the composition of compounds by showing the number and types of atoms present. Understanding the chemical formula allows one to determine how many atoms of a particular element exist in one molecule, which is crucial for performing stoichiometric calculations.

Stoichiometry

Stoichiometry involves the quantitative relationship between reactants and products in a chemical reaction, or within a compound in this context. It is used to deduce the number of moles of a specific element in a sample by applying the mole concept and the molecular composition provided by the chemical formula.

Transcript

00:02 Hi there.

00:04 In this problem, we are trying to determine how many moles of sulfur atoms are in 2 .01 grams of four different substances.

00:13 Our substances are sodium sulfate.

00:24 So the formula for that, let's see, sodium is n -a.

00:31 Sulfate is s -o -4 with a negative 2 charge.

00:35 The sodium only has a one positive charge.

00:38 So the formula for this needs to be.

00:40 The n .a .2 s .04.

00:43 Our second compound that we're going to be looking at is sodium sulfite.

00:53 Writing the formula for that, you're going to have n .a.

00:59 Solphite is s .o .3, but it still has a two negative charge.

01:04 So this needs to be n .a .2.

01:06 S .o .3.

01:08 Our third compound is sodium sulfide.

01:15 That ide ending tells us it is just the element sulfur that has become the negative ion.

01:24 Sulfur is in group six of the periodic table, so it has a two negative charge also.

01:29 So we're going to have an a2s, and then finally they give us the formula for the sodium biosulfate as n .a .2 .03 is the thiosulfate polysulfate.

01:47 Palliotomic ion.

01:48 It has a two negative charge, so again, they have two sodiums with this.

01:52 And the question wants to know moles of sulfur atoms in each of these substances, in 2 .01 grams of each of these.

02:12 All right.

02:12 So this looks like a stoichiometry problem.

02:15 We are going to need to first convert from grams to moles by dividing by the molar mass of each of these substances.

02:23 So four separate problems and then we need to convert to sulfur atoms from moles of the compound we need to convert from moles to sulfur atoms by using the formula so let's go ahead and get started and see what that looks like so in our first problem we have 2 .01 grams of the n .a2 s .4 sodium sulfate and the first thing we're going to need to do is divide by the molar mass.

02:57 So remember, we get molar mass by looking at the periodic table.

03:01 For sodium, the molar mass is 23 .0 grams per mole.

03:08 We have two of those.

03:10 So i'm going to have to multiply that by two.

03:13 For the sulfur on the periodic table, its molar mass is 32 .1 grams per mole.

03:20 And for the oxygen in this formula, there are four oxygens.

03:25 So i'm going to have to take four times the mass of 16 .0.

03:35 When i add these all together, i get 142 .1 grams per mole as the molar mass.

03:44 So that is what i'm going to use in my next step here.

03:48 I'm going to put the 142 .1 grams of na2 -s -4 on the bottom and one mole of na2 -s -4 in the numerator.

04:03 Because these are equal.

04:04 There are this many grams in one mole.