Answer:
The pH does not decrease drastically because the HCl reacts with the <u>sodium azide (NaN₃)</u> present in the buffer solution.
Explanation:
The buffer solution is formed by 0.26 moles of the weak acid, hydrazoic acid (HN₃), and by 0.26 moles of sodium azide (NaN₃). The equilibrium reaction of this buffer solution is the following:
HN₃(aq) + H₂O(l) ⇄ N₃⁻(aq) + H₃O⁺(aq)
The pH of this solution is:
![pH = pka + log(\frac{[N_{3}^{-}]}{[HN_{3}]}) = -log(2.5 \cdot 10^{-5}) + log(\frac{0.26 mol/1 L}{0.26 mol/1 L}) = 4.60](https://tex.z-dn.net/?f=%20pH%20%3D%20pka%20%2B%20log%28%5Cfrac%7B%5BN_%7B3%7D%5E%7B-%7D%5D%7D%7B%5BHN_%7B3%7D%5D%7D%29%20%3D%20-log%282.5%20%5Ccdot%2010%5E%7B-5%7D%29%20%2B%20log%28%5Cfrac%7B0.26%20mol%2F1%20L%7D%7B0.26%20mol%2F1%20L%7D%29%20%3D%204.60%20)
When 0.05 moles of HCl is added to the buffer solution, the following reaction takes place:
H₃O⁺(aq) + N₃⁻(aq) ⇄ HN₃(aq) + H₂O(l)
The number of moles of NaN₃ after the reaction with HCl is:
Now, the number of moles of HN₃ is:
Then, the pH of the buffer solution after the addition of HCl is:
![pH = pka + log(\frac{[N_{3}^{-}]}{[HN_{3}]}) = -log(2.5 \cdot 10^{-5}) + log(\frac{0.21 mol/V_{T}}{0.31 mol/V_{T}}) = 4.43](https://tex.z-dn.net/?f=%20pH%20%3D%20pka%20%2B%20log%28%5Cfrac%7B%5BN_%7B3%7D%5E%7B-%7D%5D%7D%7B%5BHN_%7B3%7D%5D%7D%29%20%3D%20-log%282.5%20%5Ccdot%2010%5E%7B-5%7D%29%20%2B%20log%28%5Cfrac%7B0.21%20mol%2FV_%7BT%7D%7D%7B0.31%20mol%2FV_%7BT%7D%7D%29%20%3D%204.43%20)
The pH of the buffer solution does not decrease drastically, it is 4.60 before the addition of HCl and 4.43 after the addition of HCl.
Therefore, the pH does not decrease drastically because the HCl reacts with the sodium azide (NaN₃) present in the buffer solution.
I hope it helps you!
Answer:
- <em>He realized that some elements had not been discovered.</em>
Explanation:
Some scientists that tried to arrange the list of elements known before Mendeleev include Antoine Lavoisier, Johann Döbereiner, Alexandre Béguyer de Chancourtois, John Newlands, and Julius Lothar Meyer.
<em>Dimitri Mendeleev</em> was so succesful that he is recognized as the most important in such work.
Mendeleev by writing the properties of the elements on cards elaborated by him, and "playing" trying to order them, realized that, some properties regularly (periodically) repeated.
The elements were sorted in increasing atomic weight (which is not the actual order in the periodic table), but when an element did not meet the pattern discovered, he moved it to a position were its properties fitted.
The amazing creativity of Mendeleev led him to leave blanks for what he thought were places that should be occupied by elements yet undiscovered. More amazing is that he was able to predict the properties of some of those elements.
When years after some of the elements were discovered, the genius of Mendeleev was proven because the "new" elements had the properties predicted by him.
