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During titration of $\ce{KMnO4}$, we use Mohr's salt instead of ferrous sulphate salt to prepare the standard salt solution. Is it done to prevent oxidation of $\ce{Fe^2+}$ to $\ce{Fe^3+}$ before the titration itself? But to prevent that sulphuric acid is used. So why we do not use ferrous sulphate salt instead?

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closed as off-topic by Mithoron, airhuff, Jon Custer, Geoff Hutchison, bon Feb 5 '18 at 12:01

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    $\begingroup$ en.wikipedia.org/wiki/Ammonium_iron(II)_sulfate#Applications $\endgroup$ – Mithoron Feb 4 '18 at 18:26
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    $\begingroup$ To put an answer, and prevent link rot, quoting Wikipedia with my emphasis, "Mohr's salt is the preferred source of ferrous ions as the solid has a long shelf life, being resistant to oxidation. This stability extends somewhat to solutions reflecting the effect of pH on the ferrous/ferric redox couple. This oxidation occurs more readily at high pH. The ammonium ions make solutions of Mohr's salt slightly acidic, which slows this oxidation process" $\endgroup$ – Gaurang Tandon Feb 13 '18 at 5:42

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