Tag: pollution of water

Questions Related to pollution of water

Clean water would have Biochemical oxygen demand (BOD) value of less than:

chemistry water too little to waste pollution of water water pollution planet earth

  1. 17 ppm

  2. 5 ppm

  3. 200,000 ppm

  4. 10 ppm

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Correct Option: B
Explanation:
A water supply with a BOD level of 3-5 ppm is considered moderately clean. In water with a BOD level of 6-9 ppm, the water is considered somewhat polluted because there is usually organic matter present and bacteria are decomposing this waste.
Hence, clean water would have a BOD value of less than 5.

Hence, the correct option is $\text{B}$

Biological Oxygen Demand (BOD) can be defined as:

chemistry water too little to waste pollution of water water pollution planet earth

  1. the amount of oxygen required by bacteria to break down the organic matter of a sample of water

  2. the amount of chemicals required to break down the organic matter of a sample of water

  3. the amount of phosphate required to oxidise the organic matter of a sample of water

  4. the amount of organic matter present in the given sample of water

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Correct Option: A
Explanation:

BOD refers to the dissolved oxygen that the microorganisms like bacteria need to oxidize, means to break down inorganic and organic matter in water. It is a measure of water quality. 

What does $BO{D} _{5}$ represent?

chemistry water too little to waste pollution of water water pollution planet earth

  1. Biological oxygen demand in five days

  2. Dissolved oxygem left after five days

  3. Dissolved oxygen consumed in five days

  4. Microorganisms killed by ozone in sewage treatment plants in five hours

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Correct Option: A
Explanation:

$BO{ D } _{ 5 }$ stands for 5-day Biochemical Oxygen Demand. The BOD test measures, oxygen is used as microbes breathe as they eat the contaminants  in wastewater.

10 mL of water required 1.47 mg of $K _{2}Cr _{2}O _{7}$ (M. wt. = 294) for oxidation of dissolved organic matter in presence of acid. Then the C.O.D of water sample is:

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  1. 2.44 ppm

  2. 24 ppm

  3. 32 ppm

  4. 1.6 ppm

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Correct Option: B
Explanation:

$ Number \  of   \ milliequivalent $ = $\dfrac{weight \ in \ mg}{Equivalent\  weight}$


= $\dfrac{1.47}{294/6}$ = $0.03meq$

$\therefore$COD of sample is:

$\dfrac{0.03}{10}\times 1000$ =  $3meq/L$

In terms of Oxygen COD is :

$3 meq/L \times  (8 mg O _2/meq)$ = $24 mg/L= 24ppm$

Option B is correct.