Calculate the number of moles of the indicated substance...

Calculate the number of moles of the indicated substance present in each of the following samples. a. $1.28 \mathrm{g}$ of iron(II) sulfate b. $5.14 \mathrm{mg}$ of mercury(II) iodide c. $9.21 \mu g$ of tin(IV) oxide d. 1.26 lb of cobalt(II) chloride e. $4.25 \mathrm{g}$ of copper(II) nitrate

Calculate the number of moles of the indicated substance present in each of the following samples.
a. $1.28 \mathrm{g}$ of iron(II) sulfate
b. $5.14 \mathrm{mg}$ of mercury(II) iodide
c. $9.21 \mu g$ of tin(IV) oxide
d. 1.26 lb of cobalt(II) chloride
e. $4.25 \mathrm{g}$ of copper(II) nitrate

Key Concepts

Mole Concept

The mole is a fundamental unit in chemistry that represents a specific quantity (6.022×10^23 entities) of a substance. It bridges the gap between the atomic scale and the macroscopic amounts used in the laboratory, enabling chemists to relate measurable masses to the number of atoms or molecules present.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all atoms in the compound’s formula, and it serves as a critical conversion factor for converting between the mass of a substance and the number of moles.

Unit Conversion

Unit conversion involves translating the mass of a substance from one unit to another (e.g., milligrams, micrograms, pounds to grams) to ensure consistency in calculations. This step is essential for correctly applying the molar mass conversion factor when converting a given mass into moles.

Dimensional Analysis

Dimensional analysis is a systematic method that uses conversion factors to ensure that calculations yield the correct units. By multiplying by appropriate ratios, it helps in verifying that the units cancel out properly, leading to a consistent and accurate result in the conversion process.

Transcript

00:01 We have five different compounds and we need to find a number of moles given a particular mass.

00:09 So if we recall, the formula for number of moles is equivalent to mass divided by molar mass.

00:27 All right.

00:28 So now that we have mass, all that we need to find is molar mass.

00:32 And to find the molar mass of a compound.

00:34 All we do is sum up the individual molar masses of each atom, taking into account the number of each atom.

00:44 Right? so i've already gone ahead and calculated all of the molar masses, so this could go a little bit more quicker.

00:52 So for here, this first question, we have iron sulfate.

00:57 I calculated the molar mass as being 151 .9.

01:04 Grams per mole.

01:12 Right, so then once we do the division, we get 8 .426 times 10 to the exponent negative 3 moles.

01:32 And here this e negative 3 means 10 to the exponent negative 3.

01:37 All right.

01:40 Next up we have mercury iodide.

01:44 5 .4.

01:46 5 .14 times 10 to the exponent, negative 3 grams of it.

01:52 So the molar mass of mercury iodide is 454 .4 grams per mole.

02:14 And once we do this division, we get a number of moles being 1 .13 times 10 to the exponent, negative 5 moles.

02:35 Next up, we have 10 oxide.

02:39 And here we have micrograms.

02:41 So we need to do a unit conversion.

02:46 So the way this works is we multiply this quantity by a quantity that is equivalent to one, where we have micrograms in the denominator to cancel out.

02:56 And we have the desired unit grams in the numerator.

02:59 So, we know that 1 gram is equivalent to 1 times 10 to the 6 micrograms.

03:11 So because it's equivalent, everything in this bracket is equivalent to 1.

03:16 So we're not changing this quantity.

03:20 If we run through this division, we get.

03:27 Let me bring my calculator out, 9 .26 divided by 1e6.

03:35 So, yep, it's 9 .26e negative 6, which i should have known.

03:50 Grams...