Answer:

Explanation:
Hello!
In this case, according to the chemical reaction by which HBr reacts with Ba(OH)2:

We can see there is a 2:1 mole ratio between the acid and the base; thus, at the equivalent point we can write:

Therefore, for is to compute the volume of the used base, we proceed as shown below:

And we plug in to obtain:

Best regards!
Answer: Thus the volume of the balloon at this altitude is 419 L
Explanation:
Combined gas law is the combination of Boyle's law, Charles's law and Gay-Lussac's law.
The combined gas equation is,

where,
= initial pressure of gas = 751 mm Hg
= final pressure of gas = 495 mm Hg
= initial volume of gas = 340 L
= final volume of gas = ?
= initial temperature of gas = 
= final temperature of gas = 
Now put all the given values in the above equation, we get:


Thus the volume of the balloon at this altitude is 419 L