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Question: State whether the given statement is true or false \({K_3}[Fe{(CN)_6}]\) is used as an external in...

State whether the given statement is true or false
K3[Fe(CN)6]{K_3}[Fe{(CN)_6}] is used as an external indicator vsvs K2Cr2O7{K_2}C{r_2}{O_7} titration.
(A) True
(B) False

Explanation

Solution

We know that external indicators are those indicators that are not present in a chemical reaction and have to be added externally. K3[Fe(CN)6]{K_3}[Fe{(CN)_6}] is called Potassium ferricyanide. In titration, potassium dichromate oxidises ferrous ions into ferric ions.

Complete step-by-step answer: We know that indicators in titration are substances that change color when a chemical reaction occurs. One such indicator is an external indicator. External indicators are those indicators that are not present in a chemical reaction and have to be added externally. K3[Fe(CN)6]{K_3}[Fe{(CN)_6}] is called an external indicator. It is called Potassium ferricyanide. It is used as an external indicator in titration . Titration is a method of volumetric analysis. In this Potassium dichromate is also used. It is a good oxidizing agent and oxidized ferrous ions into ferric ions. Following reactions occurs
[Fe+2→Fe+3+e−]×6[F{e^{ + 2}} \to F{e^{ + 3}} + e - ] \times 6
Cr2O7−2+14H+++6e−→2Cr+3+7H2OC{r_{2}}{O_7}^{ - 2} + 14{H^ + } + + 6{e^ - } \to 2C{r^{ + 3}} + 7{H_{2}}O
When ferrous ions are oxidized to ferric ions, it releases six electrons which help reduce dichromate ions to chromium ions. Here Potassium dichromate is acidified with dilute H2SO4{H_2}S{O_4} . Potassium ferrocyanide reacts with ferrous ions to form Fe3[Fe(CN)6]2F{e_3}{[Fe{(CN)_{6}}]_2} .This product is called Ferro ferricyanide. Greenish blue color is because of the formation of Ferro ferricyanide.
3Fe+2+2[Fe(CN)6]−3→Fe3[Fe(CN)6]23F{e^{ + 2}} + 2{[Fe{(CN)_{6}}]^{ - 3}} \to F{e_3}{[Fe{(CN)_{6}}]_2}

Therefore the statement becomes True and thus the correct option is AA.

Note: It is important to note that ferrous sulphate is present in Mohr Salt. The chlt chemical formula of Mohr salt is ferrous ammonium sulphate. This type of titration can be used to determine the strength of Mohr salt. Also sulphuric acid is used to acidify potassium dichromate because it is necessary to make the reaction move quickly.