Question

Answer in detail.....!!!​

Answer 1

Question:

10 mL of water required 1.47 mg of K₂Cr₂O₇ (molecular weight =294) for oxidation of dissolved organic matter. C.O.D (Chemical Oxygen Demand) of water is?

Answer:

According to the question,

⇒ 10 mL of water (H₂O) requires 1.47 mg of K₂Cr₂O₇ for oxidation

It can also be written as,

⇒ 10 mL of water (H₂O) requires 1.47 x 10⁻³ g of K₂Cr₂O₇

∵ 1 milligram (mg) =  10⁻³ g

Then,

10⁶ mL of water (H₂O) requires 1.47 g of K₂Cr₂O₇

So Here,

49 g of K₂Cr₂O₇ requires 8 g O₂

147 g of K₂Cr₂O₇ requires $x$ g of O₂

This can be represented as

$\green{\rm 49\;g \implies 8g \;of \;O_2}$

$\orange{\rm 147 g \implies x \;g\;of \;O_2}}$

$\sf Therefore,$

$\red{\implies \rm x = \dfrac{8 \times 147}{49} = 24}$

$\blue{\boxed{\boxed{\bold{\sf x = 24 \;ppm}}}}$

Hence option (b) is correct