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# : Lanthanum metal forms cations with a charge of 3+.

ISBN: 9780321809247 1

## Solution for problem 98 Chapter 4

Chemistry: A Molecular Approach | 3rd Edition

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Chemistry: A Molecular Approach | 3rd Edition

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Problem 98

98: Lanthanum metal forms cations with a charge of 3+. Consider the following observations about the chemistry of lanthanum: When lanthanum metal is exposed to air, a white solid (compound A) is formed that contains lanthanum and one other element. When lanthanum metal is added to water, gas bubbles are observed and a different white solid (compound B) is formed. Both A and B dissolve in hydrochloric acid to give a clear solution. When either of these solutions is evaporated, a soluble white solid (compound C) remains. If compound C is dissolved in water and sulfuric acid is added, a white precipitate (compound D) forms, (a) Propose identities for the substances A, B, C, and D. (b) Write net ionic equations for all the reactions described. (c) Based on the preceding observations, what can be said about the position of lanthanum in the activity series (Table)? Table Activity Series of Metals in Aqueous Solution

Step-by-Step Solution:
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Solution: Here, we are going to identify the compounds A, B, C and D and also write the net ionic equations for all the reactions described. Step1: When, lanthanum is exposed to air, lanthanum oxide is formed. The balanced molecular equation for the reaction is: 4Ln(s) + 3O (g) --2--> 2Ln O 2 3 The compound (A) thus formed is Ln O 2 3 Step2: When lanthanum metal is added to water, lanthanum hydroxide is formed. The balanced molecular equation for the reaction is: 2Ln(s) + 6H O(l) -2---> 2Ln(OH) (s) + 3H (g) 3 2 The compound (B) thus formed is Ln(OH) 3 Step3: Both the compounds A and B dissolves in HCl as shown below: Ln O2(s3+ 6HCl(aq) -------> 2LnCl (aq) + 3H O 3 2 Ln(OH) (s) +3HCl(aq) -------> LnCl (aq) + 3H O 3 2 The net ionic equation for the above reactions are: Ln O (s) + 6H ------> 2Ln + 3H O 3+ 2 3 2 Ln(OH) (s) +3H ------> Ln + 3H O 3+ 2 On evaporation of LnCl , solid LnCl3s formed. Thus, t3 compound C is LnCl . 3 Step4: When lanthanum chloride is dissolved in water and sulfuric acid is added, lanthanum sulfate is formed. The reaction involved in the process is: LnCl (s3+ 3H O(l) -2--> Ln(OH) (aq) + 3HCl 3 2Ln(OH) (s) +3H SO ------2 Ln4SO ) (s) + 6H2 4 3 2 The net ionic equation for the above reactions are: LnCl (s) + 3H ------> Ln + 3HCl 3+ 3 2Ln + 3SO 4-------> Ln (SO2) (s4 3 Thus, the compound D is Ln (SO ) . 2 4 3 Step5: c) Since, lanthanum is readily reactive with most of the solvents, so it should be placed high in the reactivity series. -------------------------

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##### ISBN: 9780321809247

Since the solution to 98 from 4 chapter was answered, more than 741 students have viewed the full step-by-step answer. The full step-by-step solution to problem: 98 from chapter: 4 was answered by , our top Chemistry solution expert on 02/22/17, 04:35PM. This full solution covers the following key subjects: lanthanum, compound, white, solid, metal. This expansive textbook survival guide covers 82 chapters, and 9454 solutions. Chemistry: A Molecular Approach was written by and is associated to the ISBN: 9780321809247. This textbook survival guide was created for the textbook: Chemistry: A Molecular Approach, edition: 3. The answer to “98: Lanthanum metal forms cations with a charge of 3+. Consider the following observations about the chemistry of lanthanum: When lanthanum metal is exposed to air, a white solid (compound A) is formed that contains lanthanum and one other element. When lanthanum metal is added to water, gas bubbles are observed and a different white solid (compound B) is formed. Both A and B dissolve in hydrochloric acid to give a clear solution. When either of these solutions is evaporated, a soluble white solid (compound C) remains. If compound C is dissolved in water and sulfuric acid is added, a white precipitate (compound D) forms, (a) Propose identities for the substances A, B, C, and D. (b) Write net ionic equations for all the reactions described. (c) Based on the preceding observations, what can be said about the position of lanthanum in the activity series (Table)? Table Activity Series of Metals in Aqueous Solution” is broken down into a number of easy to follow steps, and 154 words.

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