You have two beakers. one contains a solution of hcl at ph = 1.0. the other contains a solution of naoh at ph = 13. into a third beaker, you slowly and cautiously pour 20 ml of the hcl and 20 ml of the naoh. after complete stirring, the ph of the mixture will be
a) 2.0.
b) 12.0.
c) 7.0.
d) 5.0.
e) 9.0

The final pH will be 7.0 (C)

Explanation:

The pH is a scale to measure the concentration of protons in a solution. The followiing equation shows the mathematical definition of pH:

Another important equation is the one correlating the values of pH and pOH, which regards the concentration of hidroxide ions in solution;

, with pKw = 14

Finally, it is necessary to know that when an acidic and an basic solutions are mixed quantitatively, menaing with no excess of hydrogen or hydroxide ions, a neutralization reaction occurs:

HCl + NaOH → NaCl + H₂O

Now, lets calculate the H⁺ and OH⁻ concentrations in both solutions:

HCl: pH = 1.0, which means pH = -log[H⁺] ∴ [H⁺]  = 1 x  10⁻¹ mol/L

NaOH: pH = 13.0, which means pOH = 1.0  pOH = -log[OH⁻] ∴ [OH⁻]  = 1 x  10⁻¹ mol/L

Since the concentrations of H⁺ and OH⁻ are the same and equal volumes of each solutions were used, a neutralization reaction will happen and the final pH will be equal to the pH of water (pKw) which is 7.0.

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.