Tag: chemistry

Quizzes (490) Questions (9892)

Questions Related to chemistry

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

Pollution of lakes and rivers affects aquatic life. Fish cannot live in water that has oxygen less than $4$ milligrams per liter. Other freshwater aquatic life (including anaerobic bacteria) also cannot survive without adequate oxygen. 'BOD' stands for:

  1. Biological oxygen demand

  2. Bacterial oxygen deficit

  3. Basic oxygen demand

  4. Building oxygen deposits
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
BOD stands for Biological Oxygen Demand is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period.
Multiple choice chemistry water too little to waste pollution of water water pollution planet earth

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

  1. 17 ppm

  2. 5 ppm

  3. 200,000 ppm

  4. 10 ppm
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $\text{B}$
Multiple choice chemistry water too little to waste pollution of water water pollution planet earth

Biological Oxygen Demand (BOD) can be defined as:

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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. 

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

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

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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:

  1. 2.44 ppm

  2. 24 ppm

  3. 32 ppm

  4. 1.6 ppm
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

Multiple choice chemistry mix and separate different types of mixtures homogenous and heterogenous mixtures all about mixtures

Salt, sugar, and many other substances dissolve in water to form :

  1. homogenous mixture

  2. heterogenous mixture

  3. Ionic compound

  4. molecular compound
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A mixture is a material system made up of two or more different substances which are mixed but are not combined chemically. A homogeneous mixture is a type of mixture in which the composition is uniform and every part of the solution has the same properties. Salt, sugar, and many other substances dissolve in water to form homogeneous mixtures.

Multiple choice chemistry mix and separate different types of mixtures homogenous and heterogenous mixtures all about mixtures

Which of the following is a homogeneous solution?

  1. Muddy water

  2. Bread

  3. Concrete

  4. A solution of sugar in water
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The solution in which the concentration of solute is the same in every part of the solution is known as a homogeneous solution, sugar is completely soluble in water and forms homogeneous solution.