The overall equation for the reaction between sodium carbonate solution and dilute hydrochloric acid is
`Na_(2)CO_(3)(aq.)+2HCl(aq.)rarrNaCl(aq)+CO_(2)(g)H_(2)O(l)`
If you had the two solutions of the same concentration, you would have to use double volume of HCl to reach the equivalence point.
Indicators change their colours at the end point of the reaction and hence we are able to know the end points (equivalence points of reactions).
25 ml of `Na_(2)CO_(3)` solution requires 100 ml of 0.1 M HCl to reach end point with phenolphthalein indicator. Molarity of `HCO_(3^(-))` ions in the resulting solution is

Options

A. 0.008 M
B. 0.04M
C. 0.16 M
D. 0.08M

Answer

D

Explanation

In presence of phenophthalein indicator valence factor of Hph = 1
Equivalents of HCl = Equivalent of `Na_(2)CO_(3)`
`N_(1)V_(1)=N_(2)V_(2)`
For HCl `N_(1)=M_(1) ` and `Na_(2)CO_(3)N_(2)=N_(2)M_(1)V_(1)=M_(2)V_(2)`
`0.1 xx 100 = N_(2)xx25`
`M_(2)=0.4`
Reaction is `Na_(2)CO_(3) +HCl rarrNaHCO_(3)+NaCl`
in moles of `Na_(2)CO_(3)=MV`
`0.4 018xx25xx10^(-3)`
=moles of `NaCHO_(3)`
molarity of `HCO_(3)^(-)=("Moles of " NaHCO_(3))/("Volume")=(0.4xx25xx10^(-3)xx1000)/(125)=0.08`