Sodium hypochlorite, NaOCl, is the active ingredient in household bleach. What is the concentration of hypochlorite ion if 20.00 cm3 of bleach requires 25.30 cm3 of 0.500 M HCl to reach the equivalence point?
a. 1.13 M
b. 0.132 M
c. 0.395 M
d. 0.632 M

Respuesta :

Answer : The correct option is, (d) 0.632 M

Explanation : Given,

Concentration of HCl = 0.500 M

Volume of HCl = [tex]25.30cm^3=25.30mL=0.2530L[/tex]

conversion used : [tex]1cm^3=1mL\\1mL=0.001L[/tex]

Volume of hypochlorite ion = [tex]20.00cm^3=20.00mL=0.2000L[/tex]

The chemical reaction will be:

[tex]OCl^-+H^+\rightarrow HClO[/tex]

First we have to calculate the moles of [tex]H^+[/tex] ion.

[tex]\text{Moles of }H^+=\text{Concentration of }H^+\times \text{Volume of }H^+[/tex]

[tex]\text{Moles of }H^+=0.500M\times 0.2530L=0.1265mol[/tex]

From the reaction we conclude that,

Moles of [tex]H^+[/tex] = Moles of [tex]ClO^-[/tex] = 0.1265 mol

Now we have to calculate the concentration of hypochlorite ion.

[tex]\text{Moles of }ClO^-=\text{Concentration of }ClO^-\times \text{Volume of }ClO^-[/tex]

[tex]0.1265mol=\text{Concentration of }ClO^-\times 0.2000L[/tex]

[tex]\text{Concentration of }ClO^-=0.632M[/tex]

Therefore, the concentration of hypochlorite ion is 0.632 M.

The concentration of the base from the calculation is 0.395 M.

The reaction is written as;

NaOCl (l) + 2 HCl (aq) → NaCl (aq) + Cl 2 (g) + H 2O (l).

Using the formula;

CAVA/CBVB = NA/NB

CA = 0.500 M

VA = 25.30 cm3

CB = ?

VB = 20.00 cm3

NA = 2

NB = 1

CAVANB = CBVBNA

CB = CAVANB /VBNA

CB =  0.500 × 25.30 × 1/ 20.00  × 2

CB = 0.395 M

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