Calculate pH question (1 Viewer)

[Qudans]

Hi, i need help doing this question as i dont understand what to do -_-

perchloric acid is the strongest of all acids. 2.512 g of solid perchloric acid, HClO4 is dissolved in water to make 1L of solution.

a) calculate the ph of the solution
b) calculate the pH of the solution if 0.2512 g are dissolved to make the litre of solution

 

[shady145]

find how many moles of HClO4 2.512gms is (n=m/mm)
then you will have moles/litre as it dissolves in 1 litre
look at the chemical formula to see how many hydrogen ions it will donate... it will donate 1, therefore concentration of hydrogen ions (protons) is the same as the concentration of HClO4
whack this in you calc using the formula pH=-log(concentration) <----- base 10
then you will get the pH

you can do the same to the second part if you want...

 

[kaz1]

a)n[HClO₄]=2.512/(1+35.45+4(16))=0.025mol
C[HClO₄]=0.025/1=0.025mol/L
C[H⁺]=0.025mol/L
pH=-log(0.025)=1.6

b) Replace the bolded bit with 0.2512

 

[Fortify]

HClO4(s) -> HClO4(aq)

n (HClO4) = m / mm

n (HClO4) = 2.512 / 100.458

n (HClO4) = 0.025 mol

C (HClO4) = 0.025 / 1

C (HClO4) = 0.025 molL^-1

pH = - log [H+]

pH = - log [0.025]

pH = 1.6

Now for (b) the concentration decreases by a factor of 10, so the pH rises 1.

pH = 2.6