   Chapter 16, Problem 87GQ

Chapter
Section
Textbook Problem

A 2.50 g sample of a solid that could be Ba(OH)2 or Sr(OH)2 was dissolved in enough water to make 1.00L of solution. If the pH of the solution is 12.61, what is the identity of the solid?

Interpretation Introduction

Interpretation:

The identity of the solid has to be determined when the 2.50 g sample of a solid that could be Ba(OH)2 or Sr(OH)2 was dissolved in enough water to make 1.00L of solution. If the pH of the solution is 12.61.

Concept introduction:

The concentration of compound can be calculated by using the following formula.

Concentration = Mass of given compoundMolar mass of given compound × 1Volume in Litres

Explanation

Let’s calculate the hydroxide ion concentration by using pH value.

Given pH =12.61

pH  =  - log[H3O+]12.61 =-log[H3O+][H3O+]=10-12.61[H3O+]=2.455×10-13MAt 250CKW=[H3O+][OH-]=1.0×10-141.0×10-14=(2.45×10-13)[OH-][OH-]=4.1×10-2M

Therefore, hydroxide ion concentration is 4.1×10-2M

Assumed the solid to be Ba(OH)2

The dissociation of Ba(OH)2 is as follows.

Ba(OH)2Ba2++2OH-

Let’s calculate the concentration of Ba(OH)2

Given mass of solid = 2.50g

Molar mass of Ba(OH)2=171.327g/mol

Volume = 1L

Concentration of Ba(OH)2=Mass of Ba(OH)2Molar mass of Ba(OH)2×1V2

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