chemistry

CH3NH2(aq)+H2O(l)=>CH3NH3+(aq)+OH-(aq) Kb=4.4 x 10^-4
Methylamine, CH3NH2, is a weak base that reacts with water according to the equation above. A student obtains a 50.0 mL sample of a methylamine solution and determines the pH of the solution to be 11.77.
(a) Write the expression for the equilibrium constant, Kb, for methylamine.
(b) Calculate the molar concentration of OH- in the 50.0 mL sample of the methylamine solution.
(c) Calculate the initial molar concentration of CH3NH2(aq) in the solution before it reacted with water and equilibrium was established.
The 50.0 mL sample of the methylamine solution is titrated with HCl solution of unknown concentration. The equivalence point of the titration is reached after a volume of 36.0 mL of the HCl solution is added. The pH of the solution at the equivalence point is 5.98.
(d) Write the net-ionic equation that represents the reaction that takes place during the titration.
(e) Calculate the concentration of the HCl solution used to titrate the methylamine.
(f) using the axes provided, sketch the titration curve that results from the titration described above. On the graph, clearly label the equivalence point of the titration.

  1. 👍
  2. 👎
  3. 👁
  1. a) Kb=[CH3NH3][OH-]/[CH3NH2][H20]
    b) -log[H+]=pH=11.77
    pH+pOH=14.00
    14.00-11.77=2.23=pOH
    [OH-]=10^-pOH=10^(-2.23)=.0058M

    1. 👍
    2. 👎
  2. Everything Christina did is correct.
    Starting with C
    4.4E-9=[OH-]^2/x x=.078

    d. Ch3Nh2 + H+ -> CH3NH3+

    e.(30)(x)=(50)(.078) since moles are equal at equivalence.
    x=.13 Molar

    1. 👍
    2. 👎
  3. Why is the [] of the CH3NH3 the same as the [OH-]?

    1. 👍
    2. 👎
  4. in your equilibrium constant expression do not include water because it is a liquid

    1. 👍
    2. 👎
  5. 142

    1. 👍
    2. 👎

Respond to this Question

First Name

Your Response

Similar Questions

  1. CHEMISTRY!!!=0

    Determine pH of each solution: b) 0.20 M CH3NH3I I did.... CH3NH3^+ +H2O -> CH3NH2 + H3O^+ 0.20 ---------------0--------------0 0.20-x--------------x------------x so i got... ? =x^2/0.20-x i looked up in the back of the book and

  2. Buffer solution

    Solve an equilibrium problem (using an ICE table) to calculate the pH. a solution that is 0.205 M in CH3NH2 and 0.110 M in CH3NH3Br. i used th Ka of CH3NH2 and set up the problem as Ka=[H3O][CH3NH2]/[CH3NH3Br], but that was wrong.

  3. AP Chemistry

    Write the expression of for the base dissociation constant for hydrazine, N2H4, a weak base. Hydrazine reacts with water to form the N2H5+ ion.

  4. chemistry

    Use bond energies to determine the enthalpy for the following reaction HCN(g) + H2(g) → CH3NH2(g)

  1. chem

    I am trying to figure out how to calculate the ratio of CH3NH2 to CH3NH3Cl required to create a buffer with pH of 10.26, I'm not sure where to start.

  2. chem

    Arrange the following amines in order of decreasing base strength. NH3, NH2Br, CH3NH2, (CH3)2NH

  3. chemistry

    Calculate the pH at the equivalence point for the titration of 0.210 M methylamine (CH3NH2) with 0.210 M HCl. The Kb of methylamine is 5.0×10−4.

  4. chemistry

    What ratio [CH3NH3+]/[CH3NH2] is needed to prepare a buffer solution with a pH of 8.60 from methylamine, CH3NH2, and methylammonium chloride, CH3NH3Cl? Kb of CH3NH2 = 3.7e-4.

  1. Organic Chemistry

    what is the name of the amide that is formed by the following reaction: Butanoic acid + Methylamine? - CH3CH2CH2COOH + CH3NH2 ---> product + H2O? i put n-methylbutyramide and they counted it wrong.

  2. Chemistry

    I am stumped on this one...Please help!!! Write a balanced base ionization reaction for methylamine (CH3NH2) in water. Identify all species as acids and bases and identify the conjuate acid-base pairs.

  3. Chemistry

    Calculate the pH at the equivalence point for the titration of 0.200 M methylamine (CH3NH2) with 0.200 M HCl. The Kb of methylamine is 5.0× 10–4.

  4. chem 2

    indictae the reactant that is a bronsted lowry acid. HCN(aq) +H2O (l)---> H3O+(aq)=CN-(aq) HCN CN- H20 H30 i think it is HCN the weak acid substance which acts as a proton (H+) donor and CN the weak base? You are right. The HCN

You can view more similar questions or ask a new question.