Question

How many grams of dry NH4Cl need to be added to 1.50 L of a 0.700 mol L^−1 solution of ammonia, NH3, to prepare a buffer solution that has a pH of 8.78? Kb for ammonia is 1.8×10^−5. Express your answer to two significant figures and include the appropriate units.

Answer 1

To prepare the buffer solution, 55.96 grams of dry NH4Cl need to be added to the 1.50 L solution of ammonia.

To calculate the mass of NH4Cl that needs to be added to the solution, we first need to determine the number of moles of NH3 in the solution. This can be done by multiplying the volume (1.50 L) by the molarity (0.700 mol L^-1) of the solution, giving us 1.05 moles of NH3.

Next, we need to calculate the number of moles of NH4Cl required to react with the NH3 and form a buffer solution. Since NH3 and NH4Cl react in a 1:1 ratio, we can use the stoichiometry to determine the number of moles of NH4Cl needed. In this case, 1.05 moles of NH4Cl are required.

Finally, we can calculate the mass of NH4Cl by multiplying the moles (1.05) by the molar mass of NH4Cl (53.49 g/mol). This gives us a mass of 55.96 grams of NH4Cl that needs to be added to the solution.