How many of the following will turn moist red litmus blue and finally white?

$\ce{Li2O}$, $\ce{KO3}$, $\ce{RbO2}$, $\ce{Cs2O2}$, $\ce{BeO}$, $\ce{MgO}$, $\ce{BaO2}$, $\ce{SrO}$.

Since bleach convert moist red litmus blue and then white, but how we can identify which compound will act as bleach ?


The standard oxides $\ce{Li2O, MgO}$ and $\ce{SrO}$ are water soluble and hydrolyse to form hydroxides and a basic solution. $\ce{BeO}$ is insoluble in water.

$\ce{RbO2}$ is a superoxide which in aqueous solution undergoes disproportionation to $\ce{O2}$ and $\ce{OH-}$ so will give a blue litmus test.

The peroxides $\ce{Cs2O2}$ and $\ce{BaO2}$ react with water to give hydrogen peroxide and the hydroxides, so again a basic solution(source). The hydrogen peroxide produced will bleach the litmus paper.

$\ce{KO3}$(Potassium Ozonide) is highly unstable, decomposes in water to $\ce{O2}$ and $\ce{KOH}$

The oxides which will NOT decolorize litmus are $\ce{Li2O, MgO, BeO}$ and $\ce{SrO}$. The peroxides ($\ce{Cs2O2}$ and $\ce{BaO2}$), the superoxide($\ce{RbO2}$) and the ozonide($\ce{KO3}$) will decolorize litmus.

  • $\begingroup$ KO3 is Potassium Ozonide $\endgroup$ – saket kumar Feb 11 '19 at 8:39
  • $\begingroup$ RbO2 is technically a superoxide. $\endgroup$ – Oscar Lanzi Feb 11 '19 at 10:03
  • $\begingroup$ @OscarLanzi quite correct, my error. I will correct the entry $\endgroup$ – Waylander Feb 11 '19 at 11:20
  • $\begingroup$ @Waylander Can you mention Compound Name clearly which finally turn white ? I am asking this because in my book answer of this question is given as 4 I.e. 4 Compound will turn white finally. A/c to your answer only 3 compound will turn white. $\endgroup$ – saket kumar Feb 11 '19 at 12:55

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