Is it possible for the equivalence point of a titration to not be at pH 7? Explain your answer.

2 answers:

5 0

The reason it will be 7 for some titrations is that when you titrates a strong acid with a strong base for example HCl and NaOH the salt formed is conjugate base of strong acid and will be a very weak base
That means that it cannot produce any OH^-1 and all the H+ has been converted to water.The only source of H+ or OH is water with a Ka of 10^-14 so the pH = -log [H+]=-log 10^-7 = 7
second reason is
When you titrates a weak acid with strong base at equivalence point
only a water solution of the conjugate base exists

CH3COOH + NaOH ----- Na+ CH3COO^-1 + H2O
Since the conjugate base is the conjugate base of a weak acid it will hydrolyze in water like so
for instance Na+ CH3COO^-1 + HCl---- CH3COOH + NaCl the equivalence point will be way BELOW 7 and in the case of above will be less than 5. So pH of 7 at equivalence point is only reached in strong acid strong base titrations.
hope this helps

DENIUS [597]4 years ago

3 0

PH is 7 in case the strength of the acid and base are the same ( i.e. either weak or strong). In case of strong acid weak base or weak acid strong base titrations, buffer solutions can be formed which result in a pH other than 7

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A particular oral contraceptive contains 0.038 mg of ethinyl estradiol in each pill. The formula of this compound is C20H24O2. H

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Answer: The number of molecules of ethinyl estradiol present in one pill are $7.71\times 10^{16}$

Explanation:

To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$

Given mass of ethinyl estradiol = 0.038 mg = $3.8\times 10^-5}g$ (Conversion factor: 1 g = 1000 mg)

Molar mass of ethinyl estradiol $(C_{20}H_{24}O_2)=[(20\times 12)+(24\times 1)+(2\times 16)]=296g/mol$

Putting values in above equation, we get:

$\text{Moles of ethinyl estradiol}=\frac{3.8\times 10^{-5}g}{296g/mol}=1.28\times 10^{-7}mol$

According to mole concept:

1 mole of a compound contains $6.022\times 10^{23}$ number of molecules

So, $1.28\times 10^{-7}mol$ of ethinyl estradiol will contain = $(1.28\times 10^{-7}\times 6.022\times 10^{23})=7.71\times 10^{16}$ number of molecules