Which are valid ways to make an ammonia/ammonium buffer for use in the laboratory?

See the explanation below, please.

Explanation:

A buffer solution (also called buffer / regulatory solution) corresponds to a mixture of high concentrations of an acid with its conjugate base, which allows maintenance of the pH when amounts of strong acids or strong bases are added. A buffer solution can be NH3 / ClNH4 (ammonia which is the base, and ammonium chloride, the acid).

  For example, to prepare said buffer, X volume of deionized water is placed, the ammonium chloride to be used is measured on an analytical scale, then dissolved in water, using a stirrer. On the other hand, ammonium hydroxide is added in volume X of deionized water. Both solutions are combined, increasing the flask. The pH is measured using a pH meter.

when 25.0 ml of 0.700 mol/l naoh was mixed in a calorimeter with 25.0 ml of 0.700 mol/l hcl, both initially at 20.0 °c, the temperature increased to 22.1 °c. the heat capacity of the calorimeter is 279 j/°c.

the equation for the reaction is:

naoh + hcl → nacl + h₂o

moles of hcl = 0.0250 l hcl ×

0.700

mol hcl

1 l hcl = 0.0175 mol hcl

volume of solution = (25.0 + 25.0) ml = 50.0 ml

mass of solution = 50.0 ml soln ×

1.00

ml soln

= 50.0 g soln

δt=t2-t1

= (22.1 – 20.0) °c = 2.1 °c

the heats involved are

heat from neutralization + heat to warm solution + heat to warm calorimeter = 0

q1+q2+q3=0

nδh+mcδt+cδt=0

0.0175 mol ×

δh

+ 50.0 g × 4.184 j·g⁻¹°c⁻¹ × 2.1 °c + 279 j°c⁻¹ × 2.1 °c = 0

0.0175 mol ×

δh

+ 439.32 j + 585.9 j = 0

0.0175 mol ×

δh

= -1025.22 j

δh=1025.22j0.0175 mol= -58 600 j/mol = -58.6 kj/mol

it's all four options.