To determine the ammonia concentration in a sample of lake water, three samples are prepared. In sample A, 10.0 mL of lake water

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To determine the ammonia concentration in a sample of lake water, three samples are prepared. In sample A, 10.0 mL of lake water

is mixed with 5 mL of phenol solution and 2 mL of sodium hypochlorite solution, and diluted to 25.0 mL in a volumetric flask. In sample B, 10.0 mL of lake water is mixed with 5 mL of phenol solution, 2 mL of sodium hypochlorite solution, and 2.50 mL of a 5.50×10−4 M ammonia solution, and diluted to 25.0 mL. Sample C is a reagent blank. It contains 10.0 mL of distilled water, 5 mL of phenol solution, and 2 mL of sodium hypochlorite solution, diluted to 25.0 mL. The absorbance of the three samples is then measured at 625 nm in a 1.00 cm cuvet. The results are shown in the table.Sample Absorbance (625 nm)A 0.419B 0.666C 0.045What is the molar absorptivity (????) of the indophenol product?????=M−1cm−1What is the concentration of ammonia in the lake water?[NH3]lake water=M

Chemistry

1 answer:

eduard [2.7K] · Answer 1 · 2026-03-12T09:18:11+03:00

Answer:Sample Absorbance (625 nm)

A 0.536

B 0.783

C 0.045

Thus, I will make use of this information to address your inquiry. If you possess different absorbance values, simply follow my approach and substitute other figures.

Initially, we note that 1 mole of NH3 yields 1 mole of product.

For moles of NH3 in B = moles of NH3 in A + (5.5 x10^-4 x2.5/1000) = 1.375 x10^6 + mA

( mA = moles of NH3 in A) volume of B = 25 = volume of A

Now A = el C = eC (as l = 1cm)

Because the net absorbance due to the complex must account for blank absorbance.

Thus, A(A) = 0.536 - 0.045 = 0.491, A(B) = 0.783 - 0.045 = 0.738

(you can substitute different figures in this stage)

A2/A1 = C2/C1, A(B)/A(A) = (1.375x10^-6 +mA)/(mA) = 0.738/0.491

Thus, mA = 2.733 x 10^-6 = moles of NH3 in A (Lake water)

Consequently, [NH3] water ( 2.733 x10^-6 ) x 1000/25 = 1.093 x 10^-4 M

Volume of lake water = 10 ml out of 25,

Ammonia concentration in lake water = 2.733 x10^-6 x 1000/10 = 2.733 x 10^-4 M