Answer:- 0.138 M
Solution:- The buffer pH is calculated using Handerson equation:

acts as a weak acid and
as a base which is pretty conjugate base of the weak acid we have.
The acid hase two protons(hydrogen) where as the base has only one proton. So, we could write the equation as:

Phosphoric acid gives protons in three steps. So, the above equation is the second step as the acid has only two protons and the base has one proton.
So, we will use the second pKa value. The acid concentration is given as 0.10 M and we are asked to calculate the concentration of the base to make a buffer of exactly pH 7.00.
Let's plug in the values in the equation:



Taking antilog:


On cross multiply:
[base] = 1.38(0.10)
[base] = 0.138
So, the concentration of the base that is
required to make the buffer is 0.138M.
The amount of hydrogen chloride that can be made is 1064 g
Why?
The two reactions are:
2H₂O → 2H₂ + O₂ 75.3 % yield
H₂ + Cl₂ → 2HCl 69.8% yield
We have to apply a big conversion factor to go from grams of water (The limiting reactant), to grams of HCl, the final product. We have to be very careful with the coefficients and percentage yields!


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Mass of lead (II) chromate is 51 g. The molecular formula is
and its molar mass is 323.2 g/mol
Number of moles can be calculated using the following formula:

Here, m is mass and M is molar mass.
Putting the values,

Therefore, number of moles of lead (II) chromate will be 0.1578 mol.
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