50g of CaCO​3is added in 500mL 5N H2SO4 solution . calculate the normality of given mixture provided that the react with each other in the reaction CaCO3+H2SO4----> CaSO4+H2O when they react we use the formula Nmix= N1V1-N2V2/V1+V2 why is that "minus -" sign n general why when they react we use this formula pls explain in detail

Dear student,

For CaCO3 , N2 = Gm equivalent of solute / Volume of solution (L)
N2 = Mass (gm)Equivalent mass × Volume of solution (L)N2V2 = 50 100 2N2V2 = 1
For H2SO4 : N1V1 = 5 x 500 x 10-3 = 2.5
From the formula: 
Nmix = N1V1 -N2V2 V1+V2Nmix = 2.5 - 1500 × 1000Nmix = 3 

Here Acid and base reacting with each other and neutralising therefore we use N1V1 - N2V2 , if we use a mixture of acids or a mixture of bases then we add N1V1 + N2V2

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