Calculate the ph of a 0.170 m nh3-0.187 m nh4cl buffer when a.20.0 ml of 0.100 m hcl, b.20.0 ml of 0.100 m naoh, are added to 200 ml of buffer. ka nh4 + = 5.69 x 10-10

(a) 9.11; (b) 9.26

pH of original buffer

Step 1. Write the chemical equation for the equilibrium

Acid + H_2O ⇌ base + H_3O^(+) ; K_a = 5.69 × 10^(-10)  

Step 2. Calculate the pH of the buffer

The Henderson-Hasselbalch equation is pH = pK_a + log([base]/[acid]).

pH = -log[5.69 × 10^(-10)] + log[(0.170 mol)/L)/(0.187 mol/L)] = 9.24 + log0.1091

= 9.24 – 0.0414 = 9.20

(a) pH after adding HCl

Step 1. Calculate the moles of acid and base in the buffer

Moles of acid = 200 mL × (0.187 mmol/1 mL) = 37.4 mmol

Moles of base = 200 mL × (0.170 mmol/1 mL) = 34.0 mmol

Step 2. Calculate the moles of HCl  added

Moles of HCl added = 20.0 mL × (0.100 mmol/1 mL) = 2.00 mmol

Step 3. Calculate the new moles of acid and base

New moles of acid = (37.4 + 2.00) mmol = 39.4 mmol

New moles of base = (34.0 – 2.00) mmol = 32.0 mmol

Step 4. Calculate the new pH

pH = 9.20 + log[(32.0 mmol)/(39.4 mmol)]) = 9.20 + log0.8122 = 9.20 - 0.0903   = 9.11

(b) pH after adding NaOH

Step 1. Calculate the moles of NaOH added

Moles of NaOH added = 20.0 mL × (0.100 mmol/1 mL) = 2.00 mmol

Step 2. Calculate the new moles of acid and base

Moles of acid = (0.187 - 0.0200) = 0.167 mol

Moles of base = (0.170 + 0.0200) = 0.190 mol

Step 3. Calculate the new pH

pH = 9.20 + log[(0.190 mol/L)/(0.167 mol/L)]) = 9.20 + log1.138 = 9.20 + 0.0560   = 9.26

answer

i think the answer is a) as air pressure in an area increases, the density of the gas particles in that area decreases.

hope it

most historians agree that gabriel mouton, the vicar of st. paul’s church in lyons, france, is the “founding father” of the metric system. he proposed a decimal system of measurement in 1670. mouton based it on the length of one minute of arc of a great circle of the earth (now called a nautical mile, 1852 meters). he also proposed the swing-length of a pendulum with a frequency of one beat per second as the unit of length (about 25 cm). a pendulum beating with this length would have been fairly easy to produce, thus facilitating the widespread distribution of uniform standards. over the years, his work was revised, improved, and extended by a number of french scientists.

the political sponsor of weights and measures reform in the french revolutionary national assembly was the bishop of autun, better known as talleyrand. under his auspices, the french academy appointed several committees to carry out the work of developing a usable system of weights and measures for france. one of the committees recommended a decimalized measurement system based upon a length equal to one ten-millionth of the length of a quadrant of the earth’s meridian (i.e., one ten-millionth of the distance between the equator and the north pole).