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Equilibrium

Question
CBSEENCH11006620

If 20 ml of 1·5 × 10–5 M BaClsolution is mixed with 40 ml of 0·9 × 10–5MNa2SO4 solution, will a precipitate get formed? Ksp for BaSO4 = 0·1 × 10–10.

Solution

Solubility product of BaSO4 = 0·1 × 10–10
Total volume of the mixture solution = 20 + 40 = 60 ml
(i) Determining Ba2+ ions concentration ; (Before mixing) M1 V1 = M2V2 (After mixing)
           1.5 space cross times space 10 to the power of negative 5 end exponent space cross times space 20 space equals space straight M subscript 2 space cross times space 60
therefore space space space space straight M subscript 2 left parenthesis Molarity space of space BaCl subscript 2 right parenthesis
space space space space equals space fraction numerator 1.5 space cross times space 10 to the power of negative 5 end exponent space cross times space 20 over denominator 60 end fraction equals space 0.5 space cross times space 10 to the power of negative 5 end exponent space mol space straight L to the power of negative 1 end exponent
therefore space space space space open square brackets Ba to the power of 2 plus end exponent close square brackets space space equals space 0.5 space cross times space 10 to the power of negative 5 end exponent space mol space ions space straight L to the power of minus to the power of 1
left parenthesis ii right parenthesis space Determining space SO subscript 4 superscript 2 minus end superscript space ions space concentration colon
left parenthesis Before space mixing right parenthesis space straight M subscript 1 straight V subscript 1 space equals space straight M subscript 2 straight V subscript 2 left parenthesis After space mixing right parenthesis
space space space space space space space 0.9 space cross times space 10 to the power of negative 5 end exponent space cross times space 40 space equals space straight M subscript 2 space cross times space 60
therefore space space space space straight M subscript 2 left parenthesis Molarity space of space Na subscript 2 SO subscript 4 right parenthesis
space space equals space fraction numerator 0.9 space cross times space 10 to the power of negative 5 end exponent space cross times space 40 over denominator 60 end fraction equals space 0.6 space cross times space 10 to the power of negative 5 end exponent space mol space straight L to the power of negative 1 end exponent
As sodium sulphate is fully ionised
space space Na subscript 2 SO subscript 4 space space space rightwards harpoon over leftwards harpoon space space space space 2 Na to the power of 2 plus end exponent space plus space SO subscript 4 superscript 2 minus end superscript
therefore space space open square brackets SO subscript 4 superscript negative 2 end superscript close square brackets space equals space 0.6 space cross times space 10 to the power of negative 5 end exponent space mol space ions space straight L to the power of negative 1 end exponent
(iii) Determining ionic product;
open square brackets Ba to the power of 2 plus end exponent close square brackets space open square brackets SO subscript 4 superscript 2 minus end superscript close square brackets space equals space left parenthesis 0.5 space cross times space 10 to the power of negative 5 end exponent right parenthesis thin space left parenthesis 0.6 space cross times space 10 to the power of negative 5 end exponent right parenthesis
space space space space space space space space space space space space space space space space space space space space space space equals space 0.30 space cross times space 10 to the power of negative 10 end exponent
As the ionic product of BaSO4 (0·30 × 10–10) is more than the Ksp value of the salt, therefore, a precipitate of barium sulphate will be formed.