1 Zinc reacts with acids to produce H 2 gas.Zinc reacts with acids to produce H 2 gas. Have 10.0 g of ZnHave 10.0 g of Zn What volume of 2.50 M HCl is

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• Zinc reacts with Zinc reacts with acids to produce acids to produce HH22 gas. gas.

• Have 10.0 g of ZnHave 10.0 g of Zn

• What volume of What volume of 2.50 M HCl is 2.50 M HCl is needed to convert needed to convert the Zn completely?the Zn completely?

SOLUTION SOLUTION STOICHIOMETRYSTOICHIOMETRY

Section 5.10Section 5.10

2GENERAL PLAN FOR GENERAL PLAN FOR STOICHIOMETRY CALCULATIONSSTOICHIOMETRY CALCULATIONS

GENERAL PLAN FOR GENERAL PLAN FOR STOICHIOMETRY CALCULATIONSSTOICHIOMETRY CALCULATIONS

Mass zinc

StoichiometricfactorMoles

zincMoles HCl

Mass HCl

VolumeHCl

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Step 1: Step 1: Write the balanced equationWrite the balanced equation

Zn(s) + 2 HCl(aq) --> ZnClZn(s) + 2 HCl(aq) --> ZnCl22(aq) + H(aq) + H22(g)(g)

Step 2: Step 2: Calculate amount of ZnCalculate amount of Zn

10.0 g Zn • 1.00 mol Zn65.39 g Zn

= 0.153 mol Zn10.0 g Zn • 1.00 mol Zn65.39 g Zn

= 0.153 mol Zn

Zinc reacts with acids to produce HZinc reacts with acids to produce H22 gas. If you gas. If you have 10.0 g of Zn, what volume of 2.50 M HCl is have 10.0 g of Zn, what volume of 2.50 M HCl is needed to convert the Zn completely?needed to convert the Zn completely?


Step 3: Step 3: Use the stoichiometric factorUse the stoichiometric factor

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Step 3: Step 3: Use the stoichiometric factorUse the stoichiometric factor

0.153 mol Zn • 2 mol HCl1 mol Zn

= 0.306 mol HCl0.153 mol Zn • 2 mol HCl1 mol Zn

= 0.306 mol HCl

0.306 mol HCl • 1.00 L

2.50 mol = 0.122 L HCl0.306 mol HCl •

1.00 L2.50 mol

= 0.122 L HCl



Step 4: Step 4: Calculate volume of HCl req’dCalculate volume of HCl req’d

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ACID-BASE REACTIONSACID-BASE REACTIONSTitrationsTitrations

ACID-BASE REACTIONSACID-BASE REACTIONSTitrationsTitrations

HH22CC22OO44(aq) + 2 NaOH(aq) --->(aq) + 2 NaOH(aq) --->

acidacid basebase

NaNa22CC22OO44(aq) + 2 H(aq) + 2 H22O(liq)O(liq)

Carry out this reaction using a Carry out this reaction using a TITRATIONTITRATION..

Oxalic acid,Oxalic acid,

HH22CC22OO44

6Setup for titrating an acid with a baseSetup for titrating an acid with a base

CCR, page 186

7

TitratioTitrationn

TitratioTitrationn

1. Add solution from the 1. Add solution from the buret.buret.

2. Reagent (base) reacts 2. Reagent (base) reacts with compound (acid) in with compound (acid) in solution in the flask.solution in the flask.

3. Indicator shows when 3. Indicator shows when exact stoichiometric exact stoichiometric reaction has occurred.reaction has occurred.

4. Net ionic equation4. Net ionic equation

HH++ + OH + OH-- --> H --> H22OO

5. At equivalence point 5. At equivalence point

moles Hmoles H++ = moles OH = moles OH--

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1.065 g of H1.065 g of H22CC22OO44 (oxalic (oxalic

acid) requires 35.62 mL acid) requires 35.62 mL

of NaOH for titration to of NaOH for titration to

an equivalence point. an equivalence point.

What is the concentra-What is the concentra-

tion of the NaOH?tion of the NaOH?

LAB PROBLEM #1: Standardize a LAB PROBLEM #1: Standardize a solution of NaOH — i.e., accurately solution of NaOH — i.e., accurately determine its concentration.determine its concentration.

LAB PROBLEM #1: Standardize a LAB PROBLEM #1: Standardize a solution of NaOH — i.e., accurately solution of NaOH — i.e., accurately determine its concentration.determine its concentration.

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1.065 g of H1.065 g of H22CC22OO44 (oxalic acid) requires 35.62 (oxalic acid) requires 35.62 mL of NaOH for titration to an equivalence mL of NaOH for titration to an equivalence point. What is the concentration of the NaOH?point. What is the concentration of the NaOH?


Step 1: Step 1: Calculate amount of HCalculate amount of H22CC22OO44

1.065 g • 1 mol

90.04 g = 0.0118 mol1.065 g •

1 mol90.04 g

= 0.0118 mol

0.0118 mol acid • 2 mol NaOH1 mol acid

= 0.0236 mol NaOH

Step 2: Step 2: Calculate amount of NaOH req’dCalculate amount of NaOH req’d

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Step 1: Step 1: Calculate amountCalculate amount of Hof H22CC22OO44

= 0.0118 mol acid= 0.0118 mol acid

Step 2: Step 2: Calculate amount of NaOH req’dCalculate amount of NaOH req’d

= 0.0236 mol NaOH= 0.0236 mol NaOH

Step 3: Step 3: Calculate concentration of NaOHCalculate concentration of NaOH

0.0236 mol NaOH0.03562 L

0.663 M0.0236 mol NaOH

0.03562 L 0.663 M

[NaOH] = 0.663 M[NaOH] = 0.663 M

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LAB PROBLEM #2: LAB PROBLEM #2: Use standardized NaOH to determine Use standardized NaOH to determine the amount of an acid in an unknown.the amount of an acid in an unknown.

LAB PROBLEM #2: LAB PROBLEM #2: Use standardized NaOH to determine Use standardized NaOH to determine the amount of an acid in an unknown.the amount of an acid in an unknown.

Apples contain malic acid, CApples contain malic acid, C44HH66OO55..

CC44HH66OO55(aq) + 2 NaOH(aq) --->(aq) + 2 NaOH(aq) --->

NaNa22CC44HH44OO55(aq) + 2 H(aq) + 2 H22O(liq)O(liq)

76.80 g of apple requires 34.56 mL of 0.663 76.80 g of apple requires 34.56 mL of 0.663

M NaOH for titration. What is weight % of M NaOH for titration. What is weight % of

malic acid?malic acid?

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76.80 g of apple requires 34.56 mL of 76.80 g of apple requires 34.56 mL of 0.663 M NaOH for titration. What is 0.663 M NaOH for titration. What is weight % of malic acid?weight % of malic acid?


Step 1: Step 1: Calculate amount of NaOH used.Calculate amount of NaOH used.

C • V = (0.663 M)(0.03456 L) C • V = (0.663 M)(0.03456 L)


Step 2: Step 2: Calculate amount of acid titrated.Calculate amount of acid titrated.

0.0229 mol NaOH • 1 mol acid

2 mol NaOH


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Step 3: Step 3: Calculate mass of acid titrated.Calculate mass of acid titrated.

0.0115 mol acid • 134 gmol

= 1.54 g

Step 1: Step 1: Calculate amount of NaOH used. Calculate amount of NaOH used.


Step 2: Step 2: Calculate amount of acid titratedCalculate amount of acid titrated


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Step 1: Step 1: Calculate amount of NaOH used. Calculate amount of NaOH used.


Step 2: Step 2: Calculate amount of acid titratedCalculate amount of acid titrated


Step 3: Step 3: Calculate mass of acid titrated.Calculate mass of acid titrated.

= 1.54 g acid= 1.54 g acid

Step 4: Step 4: Calculate % malic acid.Calculate % malic acid.1.54 g76.80 g

• 100% = 2.01%

Documents

1 Zinc reacts with acids to produce H 2 gas.Zinc reacts with acids to produce H 2 gas. Have 10.0 g of ZnHave 10.0 g of Zn What volume of 2.50 M HCl is