Chromium and oxygen combine to form chromium(III) oxide....

Chromium and oxygen combine to form chromium(III) oxide. $(9.2,9.3,9.4,9.5)$ $$ 4 \mathrm{Cr}(s)+3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{Cr}_{2} \mathrm{O}_{3}(s) $$ a. How many moles of $\mathrm{O}_{2}$ react with $4.50 \mathrm{~mol}$ of $\mathrm{Cr}$ ? b. How many grams of $\mathrm{Cr}_{2} \mathrm{O}_{3}$ are produced when $24.8 \mathrm{~g}$ of Cr reacts? c. When $26.0 \mathrm{~g}$ of $\mathrm{Cr}$ reacts with $8.00 \mathrm{~g} \mathrm{of} \mathrm{} \mathrm{O}_{2}$, how many grams of $\mathrm{Cr}_{2} \mathrm{O}_{3}$ can form? d. If $74.0 \mathrm{~g}$ of $\mathrm{Cr}$ and $62.0 \mathrm{~g} \mathrm{of} \mathrm{} \mathrm{O}_{2}$ are mixed, and $87.3 \mathrm{~g}$ of $\mathrm{Cr}_{2} \mathrm{O}_{3}$ is actually obtained, what is the percent yield of $\mathrm{Cr}_{2} \mathrm{O}_{3}$ for the reaction?

Chromium and oxygen combine to form chromium(III) oxide. $(9.2,9.3,9.4,9.5)$
$$
4 \mathrm{Cr}(s)+3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{Cr}_{2} \mathrm{O}_{3}(s)
$$
a. How many moles of $\mathrm{O}_{2}$ react with $4.50 \mathrm{~mol}$ of $\mathrm{Cr}$ ?
b. How many grams of $\mathrm{Cr}_{2} \mathrm{O}_{3}$ are produced when $24.8 \mathrm{~g}$ of Cr reacts?
c. When $26.0 \mathrm{~g}$ of $\mathrm{Cr}$ reacts with $8.00 \mathrm{~g} \mathrm{of} \mathrm{} \mathrm{O}_{2}$, how many grams of $\mathrm{Cr}_{2} \mathrm{O}_{3}$ can form?
d. If $74.0 \mathrm{~g}$ of $\mathrm{Cr}$ and $62.0 \mathrm{~g} \mathrm{of} \mathrm{} \mathrm{O}_{2}$ are mixed, and $87.3 \mathrm{~g}$ of $\mathrm{Cr}_{2} \mathrm{O}_{3}$ is actually obtained, what is the percent yield of $\mathrm{Cr}_{2} \mathrm{O}_{3}$ for the reaction?

Key Concepts

Mole Concept

The mole concept is a fundamental chemical unit that allows scientists to count atoms, molecules, or ions by weighing a substance. It establishes a relation between the mass of a substance and the number of particles it contains by using Avogadro's number, which is approximately 6.022 x 10^23, thereby enabling the conversion between grams and moles.

Stoichiometry

Stoichiometry involves the quantitative relationships between reactants and products in a chemical reaction as dictated by the balanced chemical equation. It uses molar ratios derived from the reaction coefficients to perform conversions between moles of different substances, which is essential for calculating amounts needed or produced in a reaction.

Limiting Reagent

The limiting reagent is the reactant that is completely consumed first during a chemical reaction, thereby limiting the amount of product that can be formed. Identifying the limiting reagent involves comparing the mole ratios of the reactants to determine which one will run out before the others, which is crucial for accurate stoichiometric calculations.

Percent Yield

Percent yield is a measure of the efficiency of a chemical reaction, defined as the ratio of the actual amount of product obtained to the theoretical amount predicted by stoichiometric calculations, multiplied by 100. It provides insight into the practicality of a reaction under given conditions and highlights potential losses or inefficiencies during the process.

Transcript

00:01 In this problem, we'll be looking at the reaction between chromium metal and atmospheric oxygen.

00:07 Chromium metal, and one of our tasks is to write a balanced chemical equation, chromium metal reacts with oxygen to produce chromium -3 oxide.

00:28 I'm going to write that name up here.

00:38 And the chemical formula for chromium -3 oxide is cr -203.

00:47 So this balanced chemical equation will be four, three, and two for the coefficients.

00:55 Here we have written the balanced chemical equation, and that is the answer for part a.

01:05 Part b and part c asks us to use a given of 0 .175 grams of chromium 3 oxide.

01:29 Like chromium -3, chromium metal.

01:38 And my unknown for part b is mass of chromium -3 oxide.

01:49 And for part c, same unknown, or same given, but my unknown will be mass of oxygen consumed.

02:04 Okay, so i'm going to write down my molar masses, our molar masses, right over here.

02:12 And i've got them written down also so i can reference it on a piece of paper.

02:21 So chromium is 52 .00.

02:30 These are in grams per mole.

02:36 Cr203 is 151 .99 and 02 is 32 .00.

02:49 All these are grams per mole.

02:53 Okay.

02:54 Our solving sequence will be mass of the given, to moles of the given, to moles of the unknown, to mass of the unknown...

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