more questions for you guys - urgent!!! (1 Viewer)

[Pace_T]

firstly, i apologise for the many questions within such a small amount of time. I really couldn't prevent this from happening because alot of work has just been set out for us. I am also sorry for creating a new thread, it is really important that i get these done pretty quickly. I hope you can answer these questions for me please

1. Explain the difference between 'end point and 'equivalence point'
(the textbook is totally vague on this point lol!)

2. what is the chemical equation for NH3(aq) reacting with HCl? I know there should be an acidic salt, and i think the product is ammonium chloride but im not sure :S

3. In a sample of vinegar a vinegar company has added some sulfuric acid to increase the acitidity. How could we test for sulfuric acid in vinegar?

4. Also, im not too sure, but if excess phenolphthalein (more than 2/3 drops) was added to a titration would the solution become more acidic, thus affecting the outcome of the titration?

Thanks in advance for any of your help.

 

[BlackJack]

1. If I remember right, the end point of a titration is when that first permanent, observable colour change is noted. This is a purely visual definition. Now, the equivalence point is when there just enough acid to cancel out the base (and vice versa). If you've seen the graphs for the acid/base indicators it's the inflexion in the middle of the steep part.

2. NH₃ + HCl -> NH₄⁺ + Cl^-. All aqueous.

3. Sulphuric acid is hydrogen sulphate. You can use a test for sulphate ions.

4. Phenolphthalein is an acid, I think. It will indeed affect your titration in excess. (Although you usually have bigger problems to worry about.)

 

[jamesy_1988]

for the sulfate test you could used barium nitrate to precipitate out barium sulfate and do a quantitative analysis on the amount present, then calculate the amount of sulfuric acid present in the sample

Jamesy