Problem 136

Lead(Il) chromate $\left(\mathrm{PbCrO}_{4}\right…

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Problem 136

Lead(Il) chromate $\left(\mathrm{PbCrO}_{4}\right)$ is used as the yellow pigment for marking traffic lanes but is banned from house paint because of the risk of lead poisoning. It is produced from chromite (FeCr_a $\mathrm{O}_{4} )$ an ore of chromium:
$$
4 \mathrm{FeCr}_{2} \mathrm{O}_{4}(s)+8 \mathrm{K}_{2} \mathrm{CO}_{3}(a q)+7 \mathrm{O}_{2}(g) \longrightarrow
$$
$$
2 \mathrm{Fe}_{2} \mathrm{O}_{3}(s)+8 \mathrm{K}_{2} \mathrm{CrO}_{4}(a q)+8 \mathrm{CO}_{2}(g)
$$
Lead(II) ion then replaces the $\mathrm{K}^{+}$ ion. If a yellow paint is to have 0.511$\% \mathrm{PbCrO}_{4}$ by mass, how many grams of chromite are needed per kilogram of paint?

Problem 137

Ethanol $\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\right),$ the intoxicant in alcoholic beverages, is also used to make other organic compounds. In concentrated sulfuric acid, ethanol forms diethyl ether and water:
$$
2 \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}(l) \longrightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3}(l)+\mathrm{H}_{2} \mathrm{O}(g)
$$
In a side reaction, some ethanol forms ethylene and water:
$$
\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}(l) \longrightarrow \mathrm{CH}_{2} \mathrm{CH}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)
$$
(a) If 50.0 g of ethanol yields 35.9 g of diethyl ether, what is the percent yield of diethyl ether? (b) If 45.0$\%$ of the ethanol that did not produce the ether reacts by the side reaction, what mass (g) of
ethylene is produced?

Problem 138

When powdered zinc is heated with sulfur, a violent reaction occurs, and zinc sulfide forms:
$$
\mathrm{Zn}(s)+\mathrm{S}_{8}(s) \longrightarrow \mathrm{ZnS}(s)[\text { unbalanced }]
$$
Some of the reactants also combine with oxygen in air to form zinc oxide and sulfur dioxide. When 83.2 $\mathrm{g}$ of $\mathrm{Zn}$ reacts with 52.4 $\mathrm{g}$ of $\mathrm{S}_{8}, 104.4 \mathrm{g}$ of $\mathrm{ZnS}$ forms.
(a) What is the percent yield of ZnS?
(b) If all the remaining reactants combine with oxygen, how many grams of each of the two oxides form?

Problem 139

Cocaine $\left(\mathrm{C}_{17} \mathrm{H}_{21} \mathrm{O}_{4} \mathrm{N}\right)$ is a natural substance found in coca leaves, which have been used for centuries as a local anesthetic
and stimulant. Illegal cocaine arrives in the United States either as the pure compound or as the hydrochloride salt $\left(\mathrm{C}_{17} \mathrm{H}_{21} \mathrm{O}_{4} \mathrm{NHCl}\right)$
At $25^{\circ} \mathrm{C},$ the salt is very soluble in water $(2.50 \mathrm{kg} / \mathrm{L}),$ but cocaine is much less so $(1.70 \mathrm{g} / \mathrm{L})$
(a) What is the maximum mass $(\text { g) of the salt that can dissolve in }$ 50.0 $\mathrm{mL}$ of water?
(b) If this solution is treated with NaOH, the salt is converted to cocaine. How much more water (L) is needed to dissolve it?

Problem 140

High-temperature superconducting oxides hold great promise in the utility, transportation, and computer industries
(a) One superconductor is $\mathrm{La}_{2-x} \mathrm{Sr}_{x} \mathrm{CuO}_{4}$ . Calculate the molar
masses of this oxide when $x=0, x=1,$ and $x=0.163$
(b) Another common superconducting oxide is made by heating a mixture of barium carbonate, copper(II) oxide, and ytrium(III) oxide, followed by further heating in $\mathrm{O}_{2}$ :
$$
4 \mathrm{BaCO}_{3}(s)+6 \mathrm{CuO}(s)+\mathrm{Y}_{2} \mathrm{O}_{3}(s) \longrightarrow
$$
$$
2 \mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{65}(s)+4 \mathrm{CO}_{2}(g)
$$
$$
2 \mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{6.5}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{7}(s)
$$
When equal masses of the three reactants are heated, which reactant is limiting?
(c) After the product in part (b) is removed, what is the mass $\%$ of each reactant in the remaining solid mixture?

Katherine M.

University of Maine

Problem 135

The rocket fuel hydrazine $\left(\mathrm{N}_{2} \mathrm{H}_{4}\right)$ is made by the three-step
Raschig process, which has the following overall equation:
$\mathrm{NaOCl}(a q)+2 \mathrm{NH}_{3}(a q) \longrightarrow \mathrm{N}_{2} \mathrm{H}_{4}(a q)+\mathrm{NaCl}(a q)+\mathrm{H}_{2} \mathrm{O}(l)$
What is the percent atom economy of this process?

Answer

29,5 percent

Stoichiometry of Formulas and Equations

CHEMISTRY: The Molecular Nature of Matter and Change 2016

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Video Transcript

percent. Adam Economy is described as the massive Adams in the desired product, divided by the massive Adams in all reactive. So in this reaction, the desired product is hydrazine and to age for and are to reactant are these compounds here? So we simply use the periodic table to find the massive each Adam multiplying by any coefficients present to find the percent Adam economy. So we have in our product to nitrogen ins plus four hydrogen ins divided by one sodium plus one oxygen, plus the chlorine plus two nitrogen plus six hydrogen, which gives US 29.4% adam economy.

Recommended Questions

Problem 131

The industrial production of hydrazine $\left(\mathrm{N}_{2} \mathrm{H}_{4}\right)$ by the Raschig process is the topic of the Focus On feature for Chapter 4 on www.masteringchemistry.com. The following chemical equation represents the overall process, which actually involves three consecutive reactions.
$2 \mathrm{NH}_{3}(\mathrm{aq})+\mathrm{Cl}_{2}(\mathrm{g})+2 \mathrm{NaOH}(\mathrm{aq}) \longrightarrow$
$$\mathrm{N}_{2} \mathrm{H}_{4}(\mathrm{aq})+2 \mathrm{NaCl}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})$$
(a) Use the definition of percent atom economy (AE) from exercise 130 to calculate, to the nearest percent, the percent AE for the Raschig process.
(b) Propose a reaction for the synthesis of $\mathrm{N}_{2} \mathrm{H}_{4}$ that has percent AE of $100 \%$.

Problem 57

Hydrazine, $\mathrm{N}_{2} \mathrm{H}_{4}$ , emits a large quantity of energy when it reacts with oxygen, which has led to hydrazine's use as a fuel for rockets:
$$\mathrm{N}_{2} \mathrm{H}_{4}(l)+\mathrm{O}_{2}(g) \rightarrow \mathrm{N}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(g)$$
How many moles of each of the gaseous products are produced when 20.0 g of pure hydrazine is ignited in the presence of 20.0 g of pure oxygen? How many grams of each product are produced?

Problem 66

Rocket Fuel The exothermic reaction between liquid hydrazine $\left(\mathrm{N}_{2} \mathrm{H}_{2}\right)$ and liquid hydrogen peroxide $\left(\mathrm{H}_{2} \mathrm{O}_{2}\right)$
is used to fuel rockets. The products of this reaction are nitrogen gas and water.
a. Write the balanced chemical equation.
b. How much hydrazine, in grams, is needed to produce 10.0 mol of nitrogen gas?

Problem 79

Hydrazine $\left(\mathrm{N}_{2} \mathrm{H}_{4}\right)$ is used as a fuel in liquid-fueled rockets. When hydrazine reacts with oxygen gas, nitrogen gas and water vapor are produced. Write a balanced equation and use bond energies from Table 8.5 to estimate $\Delta H$ for this reaction.

Problem 85

Hydrazine $\left(\mathrm{N}_{2} \mathrm{H}_{4}\right)$ is a fuel used by some spacecraft. It is normally oxidized by $\mathrm{N}_{2} \mathrm{O}_{4}$ according to the equation:
$$
\mathrm{N}_{2} \mathrm{H}_{4}(l)+\mathrm{N}_{2} \mathrm{O}_{4}(g) \longrightarrow 2 \mathrm{N}_{2} \mathrm{O}(g)+2 \mathrm{H}_{2} \mathrm{O}(g)
$$
Calculate $\Delta H_{\mathrm{rxn}}^{\circ}$ for this reaction using standard enthalpies of
formation.

Problem 88

Hydrazine $\left(\mathrm{N}_{2} \mathrm{H}_{4}\right)$ is used as a rocket fuel because it reacts very exothermically with oxygen to form nitrogen gas and water vapor. The heat released and the increase in number of moles of gas provide thrust. Calculate the enthalpy of reaction.

Problem 82

The hydrazine fuel cell is based on the reaction
$$\mathrm{N}_{2} \mathrm{H}_{4}(\mathrm{aq})+\mathrm{O}_{2}(\mathrm{g}) \longrightarrow \mathrm{N}_{2}(\mathrm{g})+2 \mathrm{H}_{2} \mathrm{O}(1)$$
The theoretical $E_{\text {cell }}^{\circ}$ of this fuel cell is 1.559 V. Use this information and data from Appendix D to calculate a value of $\Delta_{f} G^{\circ}$ for $\left[\mathrm{N}_{2} \mathrm{H}_{4}(\mathrm{aq})\right]$

Problem 76

Hydrazine, $\mathrm{N}_{2} \mathrm{H}_{4},$ decomposes according to the following reaction: $$3 \mathrm{N}_{2} \mathrm{H}_{4}(l) \longrightarrow 4 \mathrm{NH}_{3}(g)+\mathrm{N}_{2}(g)$$ (a) Given that the standard enthalpy of formation of hydrazine is $50.42 \mathrm{kJ} / \mathrm{mol},$ calculate $\Delta H^{\circ}$ for its decomposition. (b) Both hydrazine and ammonia burn in oxygen to produce $\mathrm{H}_{2} \mathrm{O}(l)$ and $\mathrm{N}_{2}(g) .$ Write balanced equations for each of these processes and calculate $\Delta H^{\circ}$ for each of them. On a mass basis (per kg), would hydrazine or ammonia be the better fuel?

Problem 64

Hydrazine, $\mathrm{N}_{2} \mathrm{H}_{4},$ a base like ammonia, can react with an acid such as sulfuric acid.
$2 \mathrm{N}_{2} \mathrm{H}_{4}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \longrightarrow 2 \mathrm{N}_{2} \mathrm{H}_{5}^{+}(\mathrm{aq})+\mathrm{SO}_{4}^{2-}(\mathrm{aq})$
What mass of hydrazine reacts with $250 .$ mL of $0.146 \mathrm{M}$ $\mathrm{H}_{2} \mathrm{SO}_{4} ?$

Problem 22

Hydrazine $\left(\mathrm{N}_{2} \mathrm{H}_{4}\right)$ and dinitrogen tetroxide $\left(\mathrm{N}_{2} \mathrm{O}_{4}\right)$ form a self-igniting mixture that has been used as a rocket propellant. The reaction products are $\mathrm{N}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ . (a) Write a balanced chemical equation for this reaction. (b) What is being oxidized, and what is being reduced? (c) Which substance serves as the reducing agent and which as the oxidizing agent?