# Chemistry

A 100 milliliter sample of 0.100-molar NH4Cl solution was added to 80 milliliters of a 0.200-molar solution of NH3. The value of Kb for ammonia is 1.79 x 10^-5.

(a) What is the value of pKb for ammonia?

(b) What is the pH of the solution described in the question?

(c) If 0.200 grams of NaOH were added to the solution, what would be the new pH of the solution? (assume that the volume of the solution does not change.)

(d) If equal molar quantities of NH3 and NH4+ were mixed in solution, what would be the pH of the solution?

1. 👍
2. 👎
3. 👁
1. I assume you can do (a).
(b) pH = pKa + log[(base)/(acid)]
Note this is pKa and NOT pKb.

(c)moles NaOH = grams/molar mass NaOH.

Exactly how much of this can you do? What do you not understand?

1. 👍
2. 👎
2. I don't understand C and D

1. 👍
2. 👎
3. The purpose of a buffer is to resist a change in pH. When an acid is added, one of the materials (the base--in this case NH3) neutralizes the acid forming MORE of the salt. So NH4^+ increases and NH3 decreases. When a base is added, it reacts with the acid (in this case NH4^+, thus decreasing NH4+ and increasing NH3.

1. 👍
2. 👎
4. can you help set up the equations i would need to use?

1. 👍
2. 👎
5. NH4^+ + OH^- ==> NH3 + H2O

Set up an ICE chart.
initial:
NH4^+ = mL x M = 100 x 0.1 = 10 millimoles
NH3 = mL x M = 80 x 0.20 = 16 millimoles.

change:
we add 0.2 g NaOH which is 0.2/40 = 0.005 moles or 5 millimoles.
NH3 = +5 millimoles
NH4^+ = -5 millimoles

equilibrium:
NH3 = 16 + 5 = 21 millimoles.
NH4^+ = 10 - 5 = 5 millimoles.

You may substitute millimoles in place of concn (since millimoles/mL = molarity and the mL (180 mL) appears in both numerator and denominator) OR you can divide millimoles/180 mL to arrive at concn for both base and acid and substitute those numbers. Plug those into the HH equation and solve for pH.

For part d, just set up the HH equation and pH = pKa + log (base/acid). The question is asking you to calculate pH if base and acid were equal. So plug in the same number (any number you choose) for base and acid and calculate. Note that the log of 1 = 0.

1. 👍
2. 👎
6. what's the answer

1. 👍
2. 👎

## Similar Questions

1. ### CHEMISTRY

a) Calculate the change in pH when 4.00 mL of 0.100 M HCl(aq) is added to 100.0 mL of a buffer solution that is 0.100 M in NH3(aq) and 0.100 M in NH4Cl(aq). b) Calculate the change in pH when 4.00 mL of 0.100 M NaOH(aq) is added

2. ### chemistry

Calculate the change in pH when 9.00 mL of 0.100 M HCl(aq) is added to 100.0 mL of a buffer solution that is 0.100 M in NH3(aq) and 0.100 M in NH4Cl(aq). Calculate the change in pH when 9.00 mL of 0.100 M NaOH(aq) is added to the

3. ### Chemistry

What mass of NH4Cl must be added to 0.750 L of a 0.100 M solution of NH3 to give a buffer solution with a pH of 9.26? Kb(NH3) = 1.8 x 10^-5. (Hint: Assume a negligible change in volume as the solid is added.)

4. ### Chemistry

If the theoretical molar enthalpy of solution for NH4Cl(aq) is +14.7 KJ/mol, what mass of NH4Cl is needed to decrease the temperature of 100.0g of water by -20.0oC. Write a thermochemical equation for this process, including the

1. ### Chemistry

Consider the titration of 100.0 mL of 0.100 M H2NNH2 (Kb = 3.0 10-6) by 0.200 M HNO3. Calculate the pH of the resulting solution after the following volumes of HNO3 have been added. a)0.0 mL b)20.0 mL c)25.0 mL d)40.0 mL e)50.0 mL

2. ### Chem 1A

A 15.00 g sample of an ionic compound NaA, where A- is the anion of a weak acid, was dissolved in enough water to make 100.0 mL of solution and was then titrated with 0.100 M HCl. After 700.0 mL of HCl was added, the pH was 5.00.

3. ### Chemistry

The solubility of insoluble substances changes depending on the nature of the solution. Below are two solutions in which Cu(OH)2 is dissolved; in each case, the solubility of Cu(OH)2 in those solutions is not the same as it is in

4. ### Chemistry

Which of the following mixtures will result in the formation of a buffer solution if all solutions are 1.0 M before mixing? i) 100. mL of NH3(aq) and 100. mL of HCl(aq). ii) 100. mL of NH3(aq) and 50. mL of HCl(aq). iii) 100. mL

1. ### AP Chemistry

(a) When 300.0 milliliters of a solution of 0.200 molar AgNO3 is mixed with 100.0 milliliters of a 0.0500 molar CaCl2 solution, what is the concentration of silver ion after the reaction has gone to completion? (b)Write the net

2. ### ap chemistry

The ionization constant of HF is 7.2 × 10−4. What is the molar concentration of H+ in a solution which is 0.353 molar in HF and 0.145 molar in KF?

3. ### Chemistry

A 100.0 mL sample of a 0.200 molar aqueous solution of K2CrO4 was added to 100.0 mL of a 0.100 molar aqueous solution of BaCl2. The mixture was stirred and the precipitate was collected, dried carefully, and weighed. How many

4. ### Chemistry

A solution is prepared by pipetting 5.00 mL of 0.0983 molar HCl into a 100.0 mL graduated cylinder, and adding enough water to prepare 50.0 mL of solution. 1.The concentration of this solution is ____________M 2.The pH of this