Rocks in Caves: The stalactites and stalagmites in most caves are made of limest

Question

Rocks in Caves: The stalactites and stalagmites in most caves are made of limestone (calcium carbonate). However, in the Lower Kane Cave in Wyoming they are made of gypsum (calcium sulfate). The presence of CaSO4 is explained by the following sequence of reactions:

H2S(aq) + 2O2(g) --> H2SO4(aq)

H2SO4(aq) + CaCO3(s) --> CaSO4(s) + H2CO3(aq)

Which of these reactions is a redox reaction (circle the correct reaction)? How many electrons are transferred? Which reactant is reduced? Write a net ionic equation for the reaction of H2SO4 with CaCO3.

STEP BY STEP explanation please! I need to fully understand this! Thank you :)

Explanation / Answer

H2S + 2O2 = H2SO4 is a redox reaction .

for sulphur , it changes from -2 state to +6 state ( loss of 8 electrons ) , oxygen changes from 0 state to -2 state (gain of 2 electrons ) . so the total no.of electrons transferred is 10 ,

oxygen is reduced.

In the reaction of H2SO4 and CaCO3 , there is no change in the ionic states of the reactants and products , the ionoic states are , hydrogen = +1 state , sulphur = +6 state , oxygen= -2 state , calcium = +2 state , carbon = +4 state . these states remain the same in the products too..

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