Which of the following can we predict from an equilibrium constant for a reaction?
1 The extent of a reaction
2 Whether the reaction is fast or slow
3 Whether a reaction is exothermic or endothermic
a. 1 only
b. 2 only
c. 3 only
d. 1 and 2 only
e. 1 and 3 only
2. (Points: 1)
Carbonic acid is a diprotic acid, H2CO3, with Ka1 = 4.2 ´ 10-7 and Ka2 = 4.8 ´ 10-11. The ion product for water is Kw = 1.0 ´ 10-14.
What is the H3O+ concentration in a saturated carbonic acid solution that is 0.037 molar?
a. 3.7 ´ 10^-2
b. 7.4 ´ 10^-2
c. 6.5 ´ 10^-4
d. 1.2 ´ 10^-4
e. 4.2 ´ 10^-7
3. (Points: 1)
When all the following solutes act as acids, the one with the weakest conjugate base is
a. H2SO3.
b. H2CO3.
c. HClO4.
d. HClO.
e. HF.
4. (Points: 1)
A sample of ammonia (Kb = 1.8 * 10^-5) is titrated with 0.1 M H2SO4. At the equivalence point, the pH is approximately
a. 1.
b. 5.
c. 7.
d. 9.
e. 11.
Too many questions. Pick one or two that represent all the others and re-post.
3.7 ´ 10^-2
1. The answer is e. 1 and 3 only.
To predict the extent of a reaction, we can use the equilibrium constant (K) of the reaction. The equilibrium constant gives us information about the ratio of the concentrations of the products to the reactants at equilibrium. If the equilibrium constant is large, it indicates that the products are favored and the reaction proceeds to a greater extent. If the equilibrium constant is small, it indicates that the reactants are favored and the reaction proceeds to a lesser extent.
To predict whether a reaction is exothermic or endothermic, we can use the equilibrium constant. If the equilibrium constant (K) is greater than 1, it indicates that the products have a higher energy and the reaction is endothermic. If the equilibrium constant is less than 1, it indicates that the reactants have a higher energy and the reaction is exothermic.
2. The H3O+ concentration in a saturated carbonic acid solution can be calculated using the given Ka values and the ion product for water (Kw).
First, we need to determine the concentration of H2CO3 that dissociates to form H3O+. Since carbonic acid is a diprotic acid, it can dissociate in two steps:
H2CO3 ⇌ H+ + HCO3- (Ka1)
HCO3- ⇌ H+ + CO3^2- (Ka2)
Let's assume x is the concentration of H3O+ from the first dissociation step (Ka1). This means the concentration of HCO3- is also x.
From the equation of the first dissociation step, we can write the expression for the equilibrium constant:
(Ka1) = [H+][HCO3-] / [H2CO3]
Since the concentration of H2CO3 is given as 0.037 M, we can substitute the values and solve for x. This will give us the concentration of H3O+ from the first dissociation step.
Next, we need to consider the second dissociation step. Since Ka2 is much smaller (indicating a weaker acid) than Ka1, we can assume that x (the concentration of HCO3-) is much larger than the concentration of H3O+ from the second dissociation step. This allows us to neglect the contribution from the second dissociation step and assume that the concentration of H3O+ from the first dissociation step is the same as the total concentration of H3O+.
Finally, we can convert the concentration of H3O+ to the H3O+ concentration:
[H3O+] = x M
Using the values of Ka1, Ka2, and Kw, and solving the equations using the method described above, we get the answer.
3. The answer is c. HClO4.
The strength of a conjugate base is determined by the stability of the negative charge on the conjugate base. The weaker the conjugate base, the more stable the negative charge.
Among the given options, HClO4 has the weakest conjugate base because ClO4- is highly stable due to its negative charge being spread across four oxygen atoms. This stability makes the conjugate base weaker compared to the other options.
4. The answer is d. 9.
When ammonia (NH3) reacts with H2SO4, it undergoes a neutralization reaction to form ammonium sulfate (NH4)2SO4.
The balanced equation for the reaction is:
2 NH3 + H2SO4 → (NH4)2SO4
In this reaction, ammonia acts as a base, and H2SO4 acts as an acid.
To find the pH at the equivalence point, we can calculate the concentration of ammonium ions (NH4+) in the solution.
At the equivalence point, moles of NH3 = moles of H2SO4.
Given the concentration of H2SO4 as 0.1 M and assuming we add equal volumes of H2SO4 and NH3, we have moles of NH3 = 0.1 M * volume of NH3.
The volume of NH3 can be calculated using the stoichiometry of the reaction. Since the stoichiometric ratio of NH3 to H2SO4 is 2:1, the volume of NH3 is half the volume of H2SO4.
Equating the moles of NH3 to moles of H2SO4 and solving for volume:
0.1 M * volume of NH3 = 0.1 M * volume of H2SO4 / 2
Now, we can calculate the concentration of NH4+ ions in the solution using the balanced equation.
Since the concentration of NH4+ ions is equal to that of OH- ions (formed from the reaction of NH3 with water), we can calculate the pOH using the concentration of NH4+ ions.
pOH = -log [NH4+]
pH + pOH = 14 (at 25°C)
Finally, we can calculate the pH at the equivalence point by subtracting the pOH from 14.