ACIDS AND BASES Acid Base Titration A very accurate method to measure concentration. Acid + Base ...
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Transcript of ACIDS AND BASES Acid Base Titration A very accurate method to measure concentration. Acid + Base ...
ACIDS AND BASES
Acid Base Titration
A very accurate method to measure concentration.
Acid + Base Salt + Water
H+ + OH- H2O
Moles H+ = Moles OH-
Buret
Solution with Indicator
Acid-Base Titrations The amount of acid or base in a solution
is determined by carrying out a neutralization reaction; an appropriate acid-base indicator (changes color in specific pH range) must be used to show when the neutralization is complete.
This process is called a TITRATION: the addition of a known amount of solution to determine the volume or concentration of another solution.
3 steps… Add a measured amount of an acid
of unknown concentration to a flask.
Add an appropriate indicator to the flask (i.e. phenolphthalein)
Add measured amounts of a base of known concentration using a buret. Continue until the indicator shows that neutralization has occurred. This is called the end point of the titration.
Example: A 25-mL solution of H2SO4 is neutralized by 18 mL of 1.0 M NaOH using phenolphthalein as an indicator. What is the concentraion of the
H2SO4 solution?
Equation: 2NaOH + H2SO4 2H2O + Na2SO4
How many mol of NaOH are needed for neutralization?
NaOH mol 018.0L 1
mol 1 NaOH L 0.018
Example: A 25-mL solution of H2SO4 is neutralized by 18 mL of 1.0 M NaOH using phenolphthalein as an indicator. What is the concentraion of the
H2SO4 solution?
Equation: 2NaOH + H2SO4 2H2O + Na2SO4
How many moles of H2SO4 were neutralized?
4242 SOH mol 0090.0
NaOH mol 2
SOH mol 1 NaOH mol 0.018
Example: A 25-mL solution of H2SO4 is neutralized by 18 mL of 1.0 M NaOH using phenolphthalein as an indicator. What is the concentraion of the
H2SO4 solution?
Equation: 2NaOH + H2SO4 2H2O + Na2SO4
Calculate the concentration of the acid:
L
mol M
M 0.36 solution L 0.025
SOH mol 0.0090 M 42
Titration Curve: a graph showing how the pH changes as a function of the amount of added titrant in a titration.
Data for the graph is obtained by titrating a solution an measuring the pH after every drop of added titrant.
Titration Curve: a graph showing how the pH changes as a function of the amount of added titrant in a titration.
Equivalence point: the point on the curve where the moles of acid equal the moles of base; the midpoint of the steepest part of the curve (the most abrupt change in pH) is a good approximation of the equivalence point.
Titration Curve: a graph showing how the pH changes as a function of the amount of added titrant in a titration.
Knowledge of the equivalence point can then be used to choose a suitable indicator for a given titration; the indicator must change color at a pH that corresponds to the equivalence point.
Calculations of Titrations
1) The Mole Method of Molarity:
Calculate the molarity of a sulfuric acid solution if 23.2 mL of it reacts with 0.212 g of Na2CO3.
H2SO4 + Na2CO3 Na2SO4 + CO2 + H2O
32
42
32
3232 CONa mol 1
SOH 1mol
CONa 106.0g
CONa 1molCONa 0.212g
42SOH mol 0.00200
M 0.0862 L 0232.0
mol 0.00200
L
mol M
2) Normality:
The normality (N) of a solution is defined as the (M) x (total positive oxidation)
oxidation positive totalMolarityNormality
Examples:
HCl H+ + Cl-
H2SO4 2H+ + SO42-
NaOH Na+ + OH-
Ba(OH)2 Ba2+ + 2OH-
+ ox = 1
+ ox = 2
+ ox = 1
+ ox = 2
Example: Calculate the molarity and normality of a solution that contains 34.2 g of Ba(OH)2 in 8.00 L of solution.
mol 6199.0g 171.3
mol 1Ba(OH) g 34.2 2
M 5002.0L 00.8
mol 0.1996M
N 0005.02L 1
mol 0.0250N
In titration problems, you can use this equation:
base) base)(vol. (norm. acid) acid)(vol. (norm.
VNVN bbaa
Example: 30.0 mL of 0.0750 N HNO3 required 22.5 mL of Ca(OH)2 for neutralization. Calculate the normality and molarity of the Ca(OH)2 solution.
N 0.100N
mL) )(22.5(NmL) N)(30 (0.0750
VNVN
b
b
bbaa
M 0.0500M
)2(MN100.0
ox)(MN