Chemistry: The Molecular Nature of Matter and Change
Chemistry: The Molecular Nature of Matter and Change
8th Edition
ISBN: 9781259631757
Author: Martin Silberberg Dr., Patricia Amateis Professor
Publisher: McGraw-Hill Education
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Chapter 4, Problem 4.137P

(a)

Interpretation Introduction

Interpretation:

The mass percentage of Mg in a magnesium-aluminium alloy that has a mass of 0.263 g is to be determined.

Concept introduction:

Mass percent is employed to determine the concentration of one compound in a mixture of the compound. The formula to calculate mass percent is as follows:

Mass percent of compound=(mass of the compoundmass of mixture)

(a)

Expert Solution
Check Mark

Answer to Problem 4.137P

The mass percentage of Mg in a magnesium-aluminium alloy is 22.7%.

Explanation of Solution

Consider the mass of Mg is xg and mass of Al is (0.263x)g.

The formula to calculate the volume of the alloy is as follows:

Volume of alloy=(mass of alloydensity of alloy) (2)

Consider 0.263 g the mass of alloy and 2.40g/cm3 for the density of alloy in the equation (2).

Volume of alloy=(0.263 g2.40g/cm3)=0.10958cm3

The formula to calculate the volume of Mg is as follows:

Volume of Mg=(mass of Mgdensity of Mg) (3)

Consider xg the mass of Mg and 1.74g/cm3 for the density of Mg in the equation (3).

Volume of Mg=(xg1.74g/cm3)

The formula to calculate the volume of Al is as follows:

Volume of Al=(mass of Aldensity of Al) (4)

Consider (0.263x)g the mass of Al and 2.70g/cm3 for the density of Al in the equation (4).

Volume of Al=((0.263x)g2.70g/cm3)

The formula to calculate x is as follows:

Volume of alloy=Volume of Mg+Volume of Al (5)

Substitute 0.10958cm3 for the volume of alloy, (xg1.74g/cm3) for the volume of Mg and ((0.263x)g2.70g/cm3) for the volume of Al in the equation (5).

0.10958cm3=(xg1.74g/cm3)+((0.263x)g2.70g/cm3)x=0.05957g

The expression to calculate the mass percent of Mg is:

mass %ofMg=(massof Mg(g)mass of alloy sample(g))(100) (6)

Substitute 0.05957g for the mass of Mg and 0.263 g for the mass of alloy sample in the equation (6).

Mass %ofMg=(0.05957g0.263 g)(100)=22.6502%22.7%

Conclusion

The mass percentage of Mg in a magnesium-aluminium alloy is 22.7%.

(b)

Interpretation Introduction

Interpretation:

The mass percentage of Mg in a magnesium-aluminium alloy that reacts with excess aqueous HCl and forms 1.38×102molH2 is to be determined.

Concept introduction:

Stoichiometry of a reaction is utilized to determine the amount of any species in the reaction by the relationship between the reactants and products.

Consider the general reaction,

A+2B3C

One mole of A reacts with two moles of B to produce three moles of C. The stoichiometric ratio between A and B is 1:2, the stoichiometric ratio between A and C is 1:3 and the stoichiometric ratio between B and C is 2:3.

(b)

Expert Solution
Check Mark

Answer to Problem 4.137P

The mass percentage of Mg in a magnesium-aluminium alloy is 21.6%.

Explanation of Solution

The reaction of Mg and Al with HCl is as follows:

Mg(s)+2HCl(aq)MgCl2(aq)+H2(g)2Al(s)+6HCl(aq)2AlCl3(aq)+3H2(g)

Consider the mass of Mg is xg and mass of Al is (0.263x)g.

The formula to calculate moles of H2 from Mg is as follows:

moles of H2=(mass of Mgmolar mass of Mg)(1mol H21mol Mg) (7)

Substitute xg for the mass of Mg and 24.31g/mol for molar mass of Mg in the equation (7).

moles of H2=(xg24.31g)(1mol H21mol Mg)

The formula to calculate moles of H2 from Al is as follows:

moles of H2=(mass of Almolar mass of Al)(3mol H22mol Al) (8)

Substitute (0.263x)g for the mass of Al and 26.98g/mol for molar mass of Al in the equation (8)

moles of H2=((0.263x)g26.98g)(3mol H22mol Al)

The formula to calculate x is as follows:

moles of H2 produced=moles of H2 from Mg+moles of H2from Al (9)

Substitute (xg24.31g/mol)(1mol H21mol Mg) for moles of H2 from Mg, 1.38×102mol for moles of H2 produced and ((0.263x)g26.98g/mol)(3mol H22mol Al) for moles of H2 from Al in the equation (9).

1.38×102mol=(xg24.31g/mol)(1mol H21mol Mg)+((0.263x)g26.98g/mol)(3mol H22mol Al)8.22×104=0.014462xx=0.05684g

Substitute 0.05684g for the mass of Mg and 0.263 g for the mass of alloy sample in the equation (6).

Mass %ofMg=(0.05684g0.263 g)(100)=21.6122%21.6%

Conclusion

The mass percentage of Mg in a magnesium-aluminium alloy is 21.6%.

(c)

Interpretation Introduction

Interpretation:

The mass percentage of Mg in a magnesium-aluminium alloy that reacts with excess O2 and forms 0.483g of oxide is to be determined.

Concept introduction:

Stoichiometry of a reaction is utilized to determine the amount of any species in the reaction by the relationship between the reactants and products.

Consider the general reaction,

A+2B3C

One mole of A reacts with two moles of B to produce three moles of C. The stoichiometric ratio between A and B is 1:2, the stoichiometric ratio between A and C is 1:3 and the stoichiometric ratio between B and C is 2:3.

(c)

Expert Solution
Check Mark

Answer to Problem 4.137P

The mass percentage of Mg in a magnesium-aluminium alloy is 22.9%.

Explanation of Solution

The reaction of Mg and Al with O2 is as follows:

Mg(s)+O2(aq)2MgO(s)4Al(s)+3O2(aq)2Al2O3(s)

Consider the mass of Mg is xg and mass of Al is (0.263x)g.

The formula to calculate the mass of MgO from Mg is as follows:

mass of MgO=(mass of Mgmolar mass of Mg)(2mol MgO2mol Mg)(molar mass of MgO) (10)

Substitute xg for the mass of Mg, 24.31g/mol for molar mass of Mg and 40.31g/mol for the molar mass of MgO in the equation (10).

mass of MgO=(xg24.31g/mol)(2mol MgO2mol Mg)(40.31g/mol)

The formula to calculate the mass of Al2O3 from Al is as follows:

mass of Al2O3=(mass of Almolar mass of Al)(2mol Al2O34mol Al)(molar mass of Al2O3) (11)

Substitute (0.263x)g for the mass of Al, 26.98g/mol for molar mass of Al and 101.96g/mol for the molar mass of Al2O3 in the equation (11).

mass of Al2O3=((0.263x)g26.98g/mol)(2mol Al2O34mol Al)(101.96g/mol)

The formula to calculate x is as follows:

mass of oxide produced=mass of MgOfrom Mg+mass of Al2O3from Al (12)

Substitute (xg24.31g/mol)(2mol MgO2mol Mg)(40.31g/mol) for the mass of MgO from Mg, 0.483g for moles of oxide produced and ((0.263x)g26.98g/mol)(2mol Al2O34mol Al)(101.96g/mol) for moles of Al2O3 from Al in the equation (12).

0.483g=[(xg24.31g/mol)(2mol MgO2mol Mg)(40.31g/mol)+((0.263x)g26.98g/mol)(2mol Al2O34mol Al)(101.96g/mol)]0.01359=0.2315xx=0.060298g

Substitute 0.060298g for the mass of Mg and 0.263 g for the mass of alloy sample in the equation (6).

Mass %ofMg=(0.060298g0.263 g)(100)=22.927%22.9%

Conclusion

The mass percentage of Mg in a magnesium-aluminium alloy is 22.9%.

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Chapter 4 Solutions

Chemistry: The Molecular Nature of Matter and Change

Ch. 4.1 - A chemist dilutes 60.0 mL of 4.50 M potassium...Ch. 4.1 - Prob. 4.6BFPCh. 4.1 - Prob. 4.7AFPCh. 4.1 - Prob. 4.7BFPCh. 4.3 - Prob. 4.8AFPCh. 4.3 - Prob. 4.8BFPCh. 4.3 - Prob. 4.9AFPCh. 4.3 - Molecular views of the reactant solutions for a...Ch. 4.3 - It is desirable to remove calcium ion from hard...Ch. 4.3 - To lift fingerprints from a crime scene, a...Ch. 4.3 - Despite the toxicity of lead, many of its...Ch. 4.3 - Mercury and its compounds have uses from fillings...Ch. 4.4 - How many OH−(aq) ions are present in 451 mL of...Ch. 4.4 - Prob. 4.12BFPCh. 4.4 - Prob. 4.13AFPCh. 4.4 - Prob. 4.13BFPCh. 4.4 - Prob. 4.14AFPCh. 4.4 - Prob. 4.14BFPCh. 4.4 - Another active ingredient in some antacids is...Ch. 4.4 - Prob. 4.15BFPCh. 4.4 - What volume of 0.1292 M Ba(OH)2 would neutralize...Ch. 4.4 - Calculate the molarity of a solution of KOH if...Ch. 4.5 - Prob. 4.17AFPCh. 4.5 - Prob. 4.17BFPCh. 4.5 - Prob. 4.18AFPCh. 4.5 - Prob. 4.18BFPCh. 4.5 - Prob. 4.19AFPCh. 4.5 - Prob. 4.19BFPCh. 4.6 - Prob. 4.20AFPCh. 4.6 - Prob. 4.20BFPCh. 4 - Prob. 4.1PCh. 4 - What types of substances are most likely to be...Ch. 4 - Prob. 4.3PCh. 4 - Prob. 4.4PCh. 4 - Which of the following scenes best represents how...Ch. 4 - Prob. 4.6PCh. 4 - Prob. 4.7PCh. 4 - Prob. 4.8PCh. 4 - Prob. 4.9PCh. 4 - Prob. 4.10PCh. 4 - A mathematical equation useful for dilution...Ch. 4 - Prob. 4.12PCh. 4 - Prob. 4.13PCh. 4 - Prob. 4.14PCh. 4 - Prob. 4.15PCh. 4 - Does an aqueous solution of each of the following...Ch. 4 - Prob. 4.17PCh. 4 - Prob. 4.18PCh. 4 - Prob. 4.19PCh. 4 - Prob. 4.20PCh. 4 - Prob. 4.21PCh. 4 - Calculate each of the following quantities: Mass...Ch. 4 - Prob. 4.23PCh. 4 - Prob. 4.24PCh. 4 - Prob. 4.25PCh. 4 - Prob. 4.26PCh. 4 - Prob. 4.27PCh. 4 - Prob. 4.28PCh. 4 - Calculate each of the following quantities: Volume...Ch. 4 - Prob. 4.30PCh. 4 - Concentrated sulfuric acid (18.3 M) has a density...Ch. 4 - Prob. 4.32PCh. 4 - Muriatic acid, an industrial grade of concentrated...Ch. 4 - Prob. 4.34PCh. 4 - Prob. 4.35PCh. 4 - Prob. 4.36PCh. 4 - Write two sets of equations (both molecular and...Ch. 4 - Why do some pairs of ions precipitate and others...Ch. 4 - Use Table 4.1 to determine which of the following...Ch. 4 - The beakers represent the aqueous reaction of...Ch. 4 - Complete the following precipitation reactions...Ch. 4 - Prob. 4.42PCh. 4 - Prob. 4.43PCh. 4 - Prob. 4.44PCh. 4 - Prob. 4.45PCh. 4 - Prob. 4.46PCh. 4 - Prob. 4.47PCh. 4 - If 25.0 mL of silver nitrate solution reacts with...Ch. 4 - Prob. 4.49PCh. 4 - Prob. 4.50PCh. 4 - With ions shown as spheres and solvent molecules...Ch. 4 - The precipitation reaction between 25.0 mL of a...Ch. 4 - A 1.50-g sample of an unknown alkali-metal...Ch. 4 - Prob. 4.54PCh. 4 - The mass percent of Cl− in a seawater sample is...Ch. 4 - Prob. 4.56PCh. 4 - Prob. 4.57PCh. 4 - Write a general equation for a neutralization...Ch. 4 - Prob. 4.59PCh. 4 - (a) Name three common weak acids. (b) Name one...Ch. 4 - Prob. 4.61PCh. 4 - Prob. 4.62PCh. 4 - How many moles of H+ ions are present in each of...Ch. 4 - Prob. 4.64PCh. 4 - Prob. 4.65PCh. 4 - Complete the following acid-base reactions with...Ch. 4 - Limestone (calcium carbonate) is insoluble in...Ch. 4 - Prob. 4.68PCh. 4 - Prob. 4.69PCh. 4 - How many grams of NaH2PO4 are needed to react with...Ch. 4 - Prob. 4.71PCh. 4 - Prob. 4.72PCh. 4 - Prob. 4.73PCh. 4 - Prob. 4.74PCh. 4 - Prob. 4.75PCh. 4 - Prob. 4.76PCh. 4 - A mixture of bases can sometimes be the active...Ch. 4 - Describe how to determine the oxidation number of...Ch. 4 - Prob. 4.79PCh. 4 - Prob. 4.80PCh. 4 - Why must every redox reaction involve an oxidizing...Ch. 4 - Prob. 4.82PCh. 4 - Identify the oxidizing agent and the reducing...Ch. 4 - Give the oxidation number of carbon in each of the...Ch. 4 - Prob. 4.85PCh. 4 - Give the oxidation number of nitrogen in each of...Ch. 4 - Give the oxidation number of sulfur in each of the...Ch. 4 - Prob. 4.88PCh. 4 - Give the oxidation number of phosphorus in each of...Ch. 4 - Give the oxidation number of manganese in each of...Ch. 4 - Give the oxidation number of chromium in each of...Ch. 4 - Identify the oxidizing and reducing agents in the...Ch. 4 - Identify the oxidizing and reducing agents in the...Ch. 4 - Identify the oxidizing and reducing agents in the...Ch. 4 - Identify the oxidizing and reducing agents in the...Ch. 4 - The active agent in many hair bleaches is hydrogen...Ch. 4 - A person’s blood alcohol (C2H5OH) level can be...Ch. 4 - Which type of redox reaction leads to each of the...Ch. 4 - Why do decomposition redox reactions typically...Ch. 4 - Which of the types of reactions discussed in...Ch. 4 - Are all combustion reactions redox reactions?...Ch. 4 - Give one example of a combination reaction that is...Ch. 4 - Prob. 4.103PCh. 4 - Prob. 4.104PCh. 4 - Prob. 4.105PCh. 4 - Prob. 4.106PCh. 4 - Prob. 4.107PCh. 4 - Predict the product(s) and write a balanced...Ch. 4 - Prob. 4.109PCh. 4 - Predict the product(s) and write a balanced...Ch. 4 - Prob. 4.111PCh. 4 - Predict the product(s) and write a balanced...Ch. 4 - How many grams of O2 can be prepared from the...Ch. 4 - How many grams of chlorine gas can be produced...Ch. 4 - Prob. 4.115PCh. 4 - Prob. 4.116PCh. 4 - A mixture of KClO3 and KCl with a mass of 0.950 g...Ch. 4 - Prob. 4.118PCh. 4 - Before arc welding was developed, a displacement...Ch. 4 - Iron reacts rapidly with chlorine gas to form a...Ch. 4 - A sample of impure magnesium was analyzed by...Ch. 4 - Why is the equilibrium state said to be...Ch. 4 - Prob. 4.123PCh. 4 - Describe what happens on the molecular level when...Ch. 4 - When either a mixture of NO and Br2 or pure...Ch. 4 - Prob. 4.126PCh. 4 - Nutritional biochemists have known for decades...Ch. 4 - Limestone (CaCO3) is used to remove acidic...Ch. 4 - The brewing industry uses yeast to convert glucose...Ch. 4 - A chemical engineer determines the mass percent of...Ch. 4 - Prob. 4.131PCh. 4 - You are given solutions of HCl and NaOH and must...Ch. 4 - The flask represents the products of the titration...Ch. 4 - To find the mass percent of dolomite [CaMg(CO3)2]...Ch. 4 - On a lab exam, you have to find the concentrations...Ch. 4 - Nitric acid, a major industrial and laboratory...Ch. 4 - Prob. 4.137PCh. 4 - In 1995, Mario Molina, Paul Crutzen, and F....Ch. 4 - Sodium peroxide (Na2O2) is often used in...Ch. 4 - A student forgets to weigh a mixture of sodium...Ch. 4 - Prob. 4.141PCh. 4 - Prob. 4.142PCh. 4 - Physicians who specialize in sports medicine...Ch. 4 - Thyroxine (C15H11I4NO4) is a hormone synthesized...Ch. 4 - Over time, as their free fatty acid (FFA) content...Ch. 4 - Prob. 4.146PCh. 4 - Calcium dihydrogen phosphate, Ca(H2PO4)2, and...Ch. 4 - Prob. 4.148PCh. 4 - Prob. 4.149PCh. 4 - Prob. 4.150PCh. 4 - In 1997 and 2009, at United Nations conferences on...Ch. 4 - In a car engine, gasoline (represented by C8H18)...Ch. 4 - Prob. 4.153PCh. 4 - Prob. 4.154PCh. 4 - Prob. 4.155PCh. 4 - Prob. 4.156PCh. 4 - Prob. 4.157P
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