Hello!
The partial pressure of helium to keep the partial pressure of oxygen at 0,21 atm in a scuba-diver tank is
8,09 atmTo solve this question, we can use the
Dalton's Law, which states that the total pressure in a container with a mixture of gases is the sum of the partial pressures o each individual gas. For the case of this mixture the Dalton's Law is as follows:

In this equation, we need to clear for PHe, knowing that the PO₂ should be 0,21 atm, to find the required pressure of Helium:

Have a nice day!
2Al + 6HCl -> 2AlCl3 + 3H2
Answer: 12.0 milliliters of 6.50 M HCl ( aq ) are required to react with 2.55 g Zn.
Explanation:
moles =
moles of zinc =
The balanced chemical equation is :

According to stoichiometry:
1 mole of zinc reacts with = 2 moles of HCl
Thus 0.0390 moles of zinc reacts with =
moles of HCl
To calculate the volume for given molarity, we use the equation:
.....(1)
Molarity of
solution = 6.50 M
Volume of solution = ?
Putting values in equation 1, we get:


Thus 12.0 ml of 6.50 M HCl ( aq ) are required to react with 2.55 g Zn
Hello there,
Your correct answer would be 8.<span> There are </span>8 valence electrons<span> available for the Lewis structure for NH</span>3<span>.
Hope this helps
~Hottwizzlers</span>