Problem $1$:

$(02$ marks$)$

What is the theoretical COD of samples containing $600m\frac{g}{L}$ of

$($a$)$ ethanol $(C_2{H}_{5}OH)$

$($b$)$ phenol $(C_6{H}_{5}OH)$

Problem $2$:

$(02$ marks$)$

A $300c{m}^3$ sample of water was collected and tested for dissolved oxygen concentration immediately. A $15\mathrm{.}20c{m}^3$ of $0\mathrm{.}002mo\frac{l}{d}{m}^{3}N{a}_2{S}_2{O}_{3(aq)}$ was required to react with $I_2$ produced. Calculate the dissolved oxygen content of the water in ppm $(m\frac{g}{L}).$ Reactions involved in the Winkler method are illustrated below.

Step $12M{n}_{(aq)}^{2+}+4O{H}_{(aq)}^{-}+O_{2(aq)}2Mn{O}_{2(s)}+2H_2{O}_{(l)}$

Step $2Mn{O}_{2(s)}+2I_{(aq)}^{-}+4H_{(aq)}^{+}M{n}_{(aq)}^{2+}+I_{2(aq)}+2H_2{O}_{(l)}$

Step $32S_2{O}_3^{2-}{?}_{(aq)}+I_{2(aq)}{S}_4{O}_6^{2-}{?}_{(aq)}+2I_{(aq)}^{-}$

Problem $3$:

$(03$ marks$)$

The following information is available for a seeded $5-$day BOD test conducted on a wastewater sample. $25mL$ of the waste sample was added directly into a $300-$mLBOD incubation bottle and then the bottle was filled with dilution water. The initial DO of the diluted sample was $10m\frac{g}{L}$ and the final DO after $5$ days was $2m\frac{g}{L}.$

The corresponding initial and final DO of the seeded dilution water was $8m\frac{g}{L}$ and $6m\frac{g}{L},$ respectively.

What is the $5-$day BOD of wastewater sample and ultimate BOD?

Problem $4$:

$(03$ marks$)$

Determine the $3-$day BOD and ultimate first$-$stage BOD for a wastewater whose $5-$day $20$CBOD is $500m\frac{g}{L}.$ The reaction constant $k($base e$)=0\mathrm{.}23d^{-1}.$ What would have been the $5-$day BOD, if the test had been conducted at $30C?$