Find the mass of Ca(oh)2 precipitated out

Question

Given ksp at 25degrees is 4.42*10^-5. A 500ml of saturated solution of Ca(oh)2is mixed with equal volume of 0.4M NaOH

Answer 1

Ionisation eqn. of Ca(Oh)2: Ca(OH)2 = Ca2+ + 2OH– 

ksp of Ca(OH)2=[Ca 2+] [OH-]2=s*(2s)²=4s³ 

=>s=cube-root(ksp/4)=sqrt(4.42*10^-5 /4)=2.23*10^-2 M Ca 2+ ions in 500 ml  soln.=(2.23*10^-2)/2 =0.011 500 ml soln+500 ml NaOH=1000ml,molarity of OH- in new solution=0.2M 

[Ca]2+ =ksp/[OH-]² = (4.42*10^-5)/(0.2*0.2)=0.0011M no. of moles of Ca2+ ppt=0.011-0.0011=0.0102M. Mass of Ca(OH)2= 0.0102*74.