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Ch.4 - Reactions in Aqueous Solution
Chapter 4, Problem 109b

A sample of 8.69 g of Zn(OH)2 is added to 155.0 mL of 0.750 M H2SO4. (b) Which is the limiting reactant in the reaction?

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First, write the balanced chemical equation for the reaction between zinc hydroxide (Zn(OH)2) and sulfuric acid (H2SO4). The balanced equation is: Zn(OH)2 + H2SO4 → ZnSO4 + 2H2O.
Calculate the number of moles of Zn(OH)2 using its molar mass. The molar mass of Zn(OH)2 is approximately 99.41 g/mol. Use the formula: moles = mass / molar mass.
Calculate the number of moles of H2SO4 using its concentration and volume. The concentration is given as 0.750 M and the volume is 155.0 mL. Convert the volume to liters and use the formula: moles = concentration × volume.
Determine the stoichiometric ratio from the balanced equation. According to the equation, 1 mole of Zn(OH)2 reacts with 1 mole of H2SO4. Compare the moles of each reactant to find the limiting reactant.
Identify the limiting reactant by comparing the calculated moles of Zn(OH)2 and H2SO4. The reactant with fewer moles than required by the stoichiometric ratio is the limiting reactant.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions based on the balanced chemical equation. It involves using mole ratios derived from the coefficients of the balanced equation to determine how much of each reactant is needed or how much product can be formed. Understanding stoichiometry is essential for identifying limiting reactants, as it allows for the comparison of the amounts of reactants available.
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Limiting Reactant

The limiting reactant is the substance that is completely consumed first in a chemical reaction, thus determining the maximum amount of product that can be formed. Once the limiting reactant is used up, the reaction cannot proceed further, even if other reactants are still available. Identifying the limiting reactant is crucial for calculating yields and understanding the efficiency of a reaction.
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Molarity and Volume Calculations

Molarity (M) is a measure of concentration defined as the number of moles of solute per liter of solution. To determine the amount of a reactant in a solution, one can use the formula: moles = molarity × volume (in liters). In this question, calculating the moles of H2SO4 using its molarity and the given volume is necessary to compare it with the moles of Zn(OH)2 to find the limiting reactant.
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Related Practice
Textbook Question

(b) An elemental analysis of the acid indicates that it is composed of 5.89% H, 70.6% C, and 23.5% O by mass. What is its molecular formula?

Textbook Question
The discovery of hafnium, element number 72, provideda controversial episode in chemistry. G. Urbain, a Frenchchemist, claimed in 1911 to have isolated an elementnumber 72 from a sample of rare earth (elements 58–71)compounds. However, Niels Bohr believed that hafniumwas more likely to be found along with zirconium thanwith the rare earths. D. Coster and G. von Hevesy, workingin Bohr's laboratory in Copenhagen, showed in 1922 thatelement 72 was present in a sample of Norwegian zircon,an ore of zirconium. (The name hafnium comes from theLatin name for Copenhagen, Hafnia). (c) Solid zirconiumdioxide, ZrO2, reacts with chlorine gas in the presenceof carbon. The products of the reaction are ZrCl4 and twogases, CO2 and CO in the ratio 1:2. Write a balanced chemicalequation for the reaction.
Textbook Question

A sample of 8.69 g of Zn(OH)2 is added to 155.0 mL of 0.750 M H2SO4. (c) How many moles of Zn(OH)2, H2SO4, ZnSO4 are present after the reaction is complete?

Textbook Question

In 2014, a major chemical leak at a facility in West Virginia released 28,390 L of MCHM (4-methylcyclohexylmethanol, C8H16O) into the Elk River. The density of MCHM is 0.9074 g/mL. (a) Calculate the initial molarity of MCHM in the river, assuming that the first part of the river is 2.00 m deep, 90.0 m wide, and 90.0 m long.

Textbook Question
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