Question

What is the molarity of 555 L of a Ba(OH)2 solution if the pH is 10.20?

Answer 1

pH is a symbolic representation of:

`pH=-\log \lbrack H^+\rbrack`

and for water we now that:

`\lbrack H^+\rbrack\lbrack OH^-\rbrack=10^(-14)`

that means the text give us the information to calculate the concentration of protons and therefore the concentration of ions OH-:

`pH=10.2\rightarrow\lbrack H^+\rbrack=10^(-10.2)^{}`

therefore the concentration of OH- can be calculated:

`\lbrack OH^-\rbrack=(10^(-14))/(10^(-10.2))=10^(-3.8)=1.58*10^(-4)\text{ M}`

but they are not asking about the concetration of OH- they ask about concentration of Ba(OH)2 and for that we need to know the disolution stechiometry

`Ba(OH)_2\rightarrow Ba^++2* OH^-`

Whic mean the concentration of Ba(OH)2 is half the concentration of OH-:

`\lbrack Ba(OH)_2\rbrack=(\lbrack OH^-\rbrack)/(2)=7.92*10^(-5)M`