In a 1.0× 10–2 M solution of CH3NH3Br(aq), identify the relative molar amounts of these species.
H2O, OH-, CH3NH3+, CH3NH2, H3O+, Br-, HBr
CH3NH3Br ==> CH3NH3^+ + Br^-
Then the CH3NH3^+ is hydrolyzed
..CH3NH3^+ + H2O ==> CH3NH2 + H3O^+
I..0.01...............0........0
C...-x................x........x
E.0.01-x..............x........x
Ka for CH3NH3^+ = (Kw/Kb for CH3NH2) = (x)(x)/(0.01-x).
Solve for x = (CH3NH2) = (H3O)^+.
That will give you CH3NH3^+, CH3NH2, H3O^+; (Br^-) is 0.01, Calculate OH from (H^+)(OH^-) = Kw = 1E-14
You will need to convert these values to the RELATIVE number; I'm not sure what your prof means by that.
To identify the relative molar amounts of the species in the given solution, we need to consider the dissociation of CH3NH3Br in water.
CH3NH3Br dissociates into CH3NH3+ and Br- ions.
CH3NH3+ further reacts with water to form CH3NH2 and H3O+ ions.
Therefore, the species present in the solution are:
- H2O (water)
- OH- (hydroxide ion)
- CH3NH3+ (methylammonium ion)
- CH3NH2 (methylamine)
- H3O+ (hydronium ion)
- Br- (bromide ion)
- HBr (hydrobromic acid)
Now, let's determine the relative amounts of these species.
Since the solution is a 1.0× 10–2 M solution of CH3NH3Br(aq), it means that the concentration of CH3NH3Br is 1.0× 10–2 M.
Since CH3NH3Br dissociates into CH3NH3+ and Br- ions, the concentration of both CH3NH3+ and Br- ions will also be 1.0× 10–2 M.
Now, let's consider the reaction of CH3NH3+ with water. Since CH3NH3+ reacts with water to form CH3NH2 and H3O+ ions, the concentration of CH3NH3+ will decrease while the concentrations of CH3NH2 and H3O+ will increase.
The exact concentrations of CH3NH2 and H3O+ will depend on the extent of the reaction and the equilibrium constant. However, without any additional information, we cannot determine the exact concentrations of CH3NH2 and H3O+.
Lastly, since H2O is a solvent, its concentration remains constant and does not change significantly upon the dissociation of CH3NH3Br. Therefore, the concentration of H2O is the same as the initial concentration of the solution.
To summarize, the relative molar amounts of the species in the given 1.0× 10–2 M solution of CH3NH3Br(aq) are:
- H2O: Same as the initial concentration of the solution
- OH-, CH3NH2, H3O+: Concentrations will be determined by the reaction between CH3NH3+ and water, without additional information, exact concentrations cannot be determined
- CH3NH3+ and Br-: 1.0× 10–2 M (equal to the initial concentration of the solution)
To determine the relative molar amounts of the species in a 1.0×10–2 M solution of CH3NH3Br(aq), we need to consider the dissociation of CH3NH3Br in water.
CH3NH3Br dissociates into CH3NH3+ and Br- ions in water. So, the species present in the solution are:
1. H2O: Water is the solvent in this solution, but it does not dissociate.
2. OH-: Since water does not dissociate, there will be no OH- ions in this solution.
3. CH3NH3+: This is the dissociated form of the CH3NH3+ ion, which is the cation. It will be molarly equal to the original CH3NH3Br concentration, which is 1.0×10–2 M.
4. CH3NH2: This is the non-dissociated form of CH3NH3Br, which is the weak base. Since it does not fully dissociate, its concentration will be lower than that of CH3NH3+. The actual concentration of CH3NH2 can be determined using the expression for the base ionization constant (Kb) and the concentration of CH3NH3+.
5. H3O+: Since CH3NH3Br is a salt, it does not directly produce H3O+ ions. However, H3O+ ions can be generated through the reaction of water with CH3NH2, as CH3NH2 is a weak base. The actual concentration of H3O+ can be determined using the expression for the water dissociation constant (Kw) and the concentration of CH3NH2.
6. Br-: This is the dissociated form of the CH3NH3Br anion. It will also be molarly equal to the original CH3NH3Br concentration, which is 1.0×10–2 M.
7. HBr: This is the non-dissociated form of HBr, but it will not be present in significant amounts because CH3NH3Br is the stronger acid. The concentration of HBr can be calculated using the expression for the acid dissociation constant (Ka) and the concentration of CH3NH3+.
To summarize:
- H2O: Present as the solvent, does not dissociate.
- OH-: Not present in significant amounts.
- CH3NH3+: Molar concentration is 1.0×10–2 M.
- CH3NH2: Present in smaller amounts due to the partial ionization of CH3NH3Br.
- H3O+: Present in smaller amounts due to the partial ionization of CH3NH3Br.
- Br-: Molar concentration is 1.0×10–2 M.
- HBr: Present in smaller amounts due to the partial ionization of HBr.