Page 1 1 ACID - BASE REACTIONS Titrations H 2 C 2 O 4( aq ) + 2 NaOH ( aq ) --- > Na 2 C 2 O 4( aq ) +2 H 2 O (l) acid base Carry out this reaction using a TITRATION . Oxalic acid, H 2 C 2 O 4 2 Setup for titrating an acid with a base CCR, page 186 3 Titration 1. Add solution to the buret . 2. Reagent (base) reacts with compound (acid) in solution in the flask. 3. Indicator shows when exact stoichiometric reaction has occurred. 4. Net ionic equation H + + OH - -- > H 2 O 5. At equivalence point moles H + = moles OH -
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ACID-BASE REACTIONSTitrations
H2C2O4(aq) + 2 NaOH(aq) ---> Na2C2O4(aq) +2 H2O(l)
acid base
Carry out this reaction using a TITRATION.
Oxalic acid,
H2C2O4
2Setup for titrating an acid with a base
CCR, page 186
3
Titration1. Add solution to the buret.
2. Reagent (base) reacts with compound (acid) in solution in the flask.
3. Indicator shows when exact stoichiometricreaction has occurred.
4. Net ionic equation
H+ + OH- --> H2O
5. At equivalence point
moles H+ = moles OH-
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4
1.065 g of H2C2O4
(oxalic acid) requires
35.62 mL of NaOH for
titration to an
equivalence point.
What is the concentra-
tion of the NaOH?
LAB PROBLEM #1: Standardize a solution of NaOH — i.e., accurately determine its concentration.
5
1.065 g of H2C2O4 (oxalic acid) requires 35.62 mL of NaOH for titration to an equivalence point. What is the concentration of the NaOH?
Step 1: Calculate amount of H2C2O4
1.065 g • 1 mol
90.04 g = 0.0118 mol
0.0118 mol acid • 2 mol NaOH
1 mol acid = 0.0236 mol NaOH
Step 2: Calculate amount of NaOH req’d
6
1.065 g of H2C2O4 (oxalic acid) requires 35.62 mL of NaOH for titration to an equivalence point. What is the concentration of the NaOH?
Step 1: Calculate amount of H2C2O4
= 0.0118 mol acid
Step 2: Calculate amount of NaOH req’d
= 0.0236 mol NaOH
Step 3: Calculate concentration of NaOH
0.0236 mol NaOH
0.03562 L 0.663 M
[NaOH] = 0.663 M
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LAB PROBLEM #2: Use standardized NaOH to determine the amount of an acid in an unknown.
Apples contain malic acid, C4H6O5.
C4H6O5(aq) + 2 NaOH(aq) --> Na2C4H4O5 (aq)+ 2 H2O (l)
76.80 g of apple requires 34.56 mL of 0.663 M
NaOH for titration. What is weight % of malic
acid?
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76.80 g of apple requires 34.56 mL of 0.663 M NaOH for titration. What is weight % of malic acid?
Step 1: Calculate amount of NaOH used.
C • V = (0.663 M)(0.03456 L)
= 0.0229 mol NaOH
Step 2: Calculate amount of acid titrated.
0.0229 mol NaOH • 1 mol acid
2 mol NaOH
= 0.0115 mol acid
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76.80 g of apple requires 34.56 mL of 0.663 M NaOH for titration. What is weight % of malic acid?
Step 3: Calculate mass of acid titrated.
0.0115 mol acid • 134 g
mol = 1.54 g
Step 1: Calculate amount of NaOH used.
= 0.0229 mol NaOH
Step 2: Calculate amount of acid titrated
= 0.0115 mol acid
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76.80 g of apple requires 34.56 mL of 0.663 M NaOH for titration. What is weight % of malic acid?
Step 1: Calculate amount of NaOH used.
= 0.0229 mol NaOH
Step 2: Calculate amount of acid titrated
= 0.0115 mol acid
Step 3: Calculate mass of acid titrated.
= 1.54 g acid
Step 4: Calculate % malic acid.
1.54 g
76.80 g • 100% = 2.01%
11Normality
• Normality = Molarity multipied by the number of ionizable H+ or OH-
• ionizable H+ or OH- are called “equivalents”
• For neutralizing acids and bases you could use the formula…
NaVa = NbVb
Where N = normality and V = volume and “a” is for acid and “b” is for base
• How many mL of 0.125 M calcium hydroxide are needed to neutralize 25.00 mL of a 0.085 M hydrochloric acid?
8.5 mL of Ca(OH)2
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