The number of hydroxyl ions in 10cm3 of 0.2M HCl solution is 1)5×10^-4 2)3×10^8 3)3×10^12 4)5×10^-12

Dear Student,

To solve this, we need to find the number of moles of hydroxyl ions. To find that, we need to find the concentration of hydroxyl ions.

Now,

HCl is a strong acid. So it dissociates completely.

So, H+=0.2 MpH = -logH+=0.6989pKw=pH+pOHpOH=14-0.6989pOH=13.3012=-log[OH-]So, [OH-]=antilog[-13.3012]=4.98 x 10-14 MNow, Molarity of OH-ions = 4.98 x 10-14 MVolume = 10 cm3=10 ml=0.01 LSo,Number of moles = Molarity x Volume =  4.98 x 10-14  x 10-2=4.98 x 10-12 So, number of ions = number of moles x NA=4.98 x 10-12 x6.022 x 1023=29.989x 1011=2.99 x 10123 x 1012
Thus, the number of hydroxyl ions is 3 x 1012.
Thus, the correct answer is option (3)

Hope it helps.

Regards

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