1.

Calculatethe concentration of Na_(2)S_(2)O_(3) . 5H_(2)Osolution in grams per itre . 10 mL of which just decolourised 15 mL of N/20 iodine solution .

Answer»

SOLUTION :`{:(S_(2)O_(3)^(2-),+ I_(2)to,1/2S_(4)O_(6)^(2-)+I^(-1)),(+4,,+5):}`
Eq. wt of `Na_(2)S_(2)O_(3).5H_(2)O= (" mol.wt")/("change in ON per mole")`
`=(248.2)/1 `
m.e of 10 mL of `Na_(2)S_(2)O_(3) .5H_(2)O ` solution = m.e of IODINE solution
`= 1/20 xx 15 = 0.75`
Equivalent of 10 mL of `Na_(2)S_(2)O_(3). 5H_(2)O = (0.75)/(1000)`
Concentration of hypo in grams per litre` = 0.186 xx 1000/10 g//L `
` = 18.6 g//L `


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