Futhermore... (1 Viewer)

[Jaserius]

Hey guys,

When drops of a strong acid, say sulfuric acid are added to a solution every 5 seconds, howcome the Ph drops after the first drop, and then stays down and doesnt change.

I thought that as more and more drops of sulfuric acid were added, the ph would keep decreasing, as the hydrogen ion concentration would keep increasing...

However, I know I am wrong, because I got a multiple choice quesiton based on this principle wrong...

please help me understand,

thanks,
Jason.

 

[Sirius Black]

hmm, would you plz post up the original question?

I think that might be a buffer solution as first drop results in great decrease in pH but then it'll actually goes up (slightly lower than initial pH)

 

[Jaserius]

Sure, its just that it has graphs as the answers, which I cant really draw or anything so ill describe them instead.

A beaker of water has a pH of 7. When drops of sulfuric acid are added the pH changes. Which graph most accurately shows the pH of the solution as sulfuric acid is added to water?

[in all the graphs pH is the vertical axis, and drops added is horizontal]

A. A straight diagonal line eventually reaching pH 0.
B. Looks like a hyperbola, going down initially and then staying down (might rise very slightly) [Correct Answer]
C. A horizontal line for a while which then drops very suddenly and reaches 0.
D. A wavy line which stays horizontal, goes down, then stays horizontal, then goes down to pH 0.

Hmmm.

 

[meLoncoLLie]

equilibrium?

(a random guess)

 

[Sirius Black]

Sure, its just that it has graphs as the answers, which I cant really draw or anything so ill describe them instead.

A beaker of water has a pH of 7. When drops of sulfuric acid are added the pH changes. Which graph most accurately shows the pH of the solution as sulfuric acid is added to water?

[in all the graphs pH is the vertical axis, and drops added is horizontal]

A. A straight diagonal line eventually reaching pH 0.
B. Looks like a hyperbola, going down initially and then staying down (might rise very slightly) [Correct Answer]
C. A horizontal line for a while which then drops very suddenly and reaches 0.
D. A wavy line which stays horizontal, goes down, then stays horizontal, then goes down to pH 0.

Hmmm.

I'd say it is B too. coz pH=-log[H⁺] just use your simple maths knowledge, you will get a logrighmic funtion(y=-logx, as x-->1-, y-->0)- and the it does look like a branch of a hyperbola altho not exactly(In fact, after u add something like 1L of 10M sulfuric acid, teh graph will keep going down to negative...
Hope this helps
:uhhuh:

 

[Jaserius]

thanks mate

 

[KungPow]

Well think about it for a second there. Say the pH of Sulfuric acid is 2 and your water is 7. If you keep adding sulfuric acid, the pH will keep dropping, but will it go lower than 2?

 

[xiao1985]

yes, but the pH of sulfuric acid can go well beyond 2...

 

[BlackJack]

Okay, if you have a solution of sulfuric acid that is at a pH of 2 and you add that, then the water solution will never go below 2 (you're adding an equivalent amount of water). Pure sulfuric acid has a theoretical pH below -1.. keep adding this and it'll go closer to that value.

(Yeah, the rising bit at the end is a big mistake.)

 

[xiao1985]

18M sulfuric acid should already have a pH of less than -1... and much to my surprize, they actually allow first yr'er to handle it ... =p

 

[richz]

lol, our teacher let us use 18M H2SO4 last week when we were doing a reflux

 

[xiao1985]

lol, our teacher let us use 18M H2SO4 last week when we were doing a reflux

very unorthodox... u guys must be highly disciplined...
the worst we gotta use is 4M HCl...