Weak acid HA is 2% ionized (dissociated) at 0.20 M
the solution. What is Ka for this acid? Ka What is the pH of this solution?
general orientation
Concepts and reason
Equilibrium: Equilibrium is a state in which the concentration of reactants is equal to the concentration of products. It can also be defined as the state in which the rate of the forward reaction is equal to the rate of the reverse reaction.
Ion Balance: Ion balance is a state where equilibrium exists between an ionic compound and its ions.
Fundamentals
The steady state is shown below:
The ion balance is shown below:
Suppose AB is an ionic compound
Equilibrium constant: The equilibrium constant is defined as the ratio between the concentration of the products and the concentrations of the reactants.
pH is the scale of acidity or basicity of a molecule. Acidic solutions will have a lower pH and basic solutions will have a higher pH.
It can be calculated by the formula:
O
Where,
is the concentration of hydrogen ions present.
Step by step
Step 1 of 2
The given reaction condition is written below:
The weak acid HA is ionized at 2% in a 0.20M solution.
The equilibrium reaction for the above reaction is given below:
The expression for the equilibrium constant is given below:
Since 2% is ionized in a 0.20 M solution upon dissociation.
Therefore, the concentration of 0.004 M is ionized during the reaction.
The ion balance equation has been given based on the reaction conditions, since HA is a weak acid, it is only ionized to 2%, i.e. 0.004 M concentration of 0, 20 M.
Be careful when giving the ionized concentration.
Example:
To correct:
The ionized concentration during the equilibrium reaction is 0.004 M
Incorrect:
The ionized concentration during the equilibrium reaction is 0.04 M
Build an ICE table to find the value of the equilibrium constant for the reaction.
Step 2 of 2
The ICE table for the given equilibrium reaction is drawn below:
The value of the equilibrium constant is calculated below.
The PH value is calculated below:
Therefore, the value of Ka for the given equilibrium is .
The pH of the solution is
The value of Ka for the given equilibrium is
The pH of the solution is
The equilibrium constant value and pH of the reaction were calculated using the ICE table and the pH formula.
Be careful when giving the Ka and PH balance value.
Example:
To correct
The value of Ka for the given equilibrium is
The PH value of the solution is.
Incorrect;
The value of Ka for the given equilibrium is
The pH of the solution is 23.95.
Answer
The value of Ka for the given equilibrium is
The pH of the solution is
answer only
The value of Ka for the given equilibrium is
The pH of the solution is
reactive equilibrium products
ABAA*+B
K-[A+][B] [AB]
pH=-log[H]
ΗΑ Η* +Α’
_[h*[A] K-THA]
Ionized concentration = _x0.20 100 =0.004M
initial equilibrium concentration HA 2 H+ 0.2 0 -0.004 +0.004 0.2-0.004 +0.004 + A 0 +0.004 +0.004
[h*][A] (AH) [0.004)(0.004] [0.2-0.004] =8.163×10-5
p”=-log[H] p”=-log[0.004] = 2397
8163×10
_[h*[A] K-THA]
p”=-log[ht]
8163×10.
8163×10
8.163×105.
8163×10.
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