6B.1

[Chloe Shamtob 2H]

The molar concentration of HCl in hydrochloric acid is reduced to 12% of its initial value by dilution. What is the difference in the pH values of the two solutions?

Can someone help me start this problem?

[Emily Ding 1J]

The way I like to do questions like these is to start off with an arbitrary concentration amount, calculate the pH, and then just take 12% of whatever value you decided to use for the concentration and recalculate the pH with this value to find the difference. I hope this makes sense! I believe the answer key took a different approach, but this is personally the most intuitive for me.

[Praneetha Kakarla 3A]

Hey, you can just do calculations w/ 1M for the initial HCl & then 0.12M for the diluted HCl because we're working with percentages. So, the pH of the initial HCl is -log(1) & the pH of the diluted HCl is -log(0.12). This should give you the difference in pH.

[George Cazares 1E]

To find the initial pH you can find the pH of a 1M concentration by pH= -log[H3O+] which is pH =-log(1)=0. Then to find the concentration reduced to 12% just find plug in .12 into pH=log[H3O+], which is pH=-log(.12)= 0.92. Thus, the difference would be ΔpH=(-log(.12))-(-log(1)).