Water's Chem Questions

[Water]

Hey Guys, just got two questions atm, pretty basic but just need clarity on it.


a) Once a titration is completed, can the substance with unknown concentration, which its concentration been found, be called a standard solution?


b) In a titration, where HCL has known concentration and NaOH  has unknown concentration, why is methyl orange neccessary in the experiment?

[pi]

Don't understand part a), but I'm pretty sure part b) is because it produces a sharper endpoint (and has a very distinct colour change).

[Water]

a) Say, your titrating NaOH with HCL, which has a known concentration. When you find the concentration of NaOH, would it be called a standard solution then?


and for a) I wrote, NaOH would be considered a standard solution because it is a solution which has a known concentration, therefore fits the requisites of a standard solution.





For b , i wrote) We already have known c(HCL) and are trying to find C(NaOH), thus by using methyl orange , on HCL, when NaOH is titrated against HCL, the end point will color shift from acidic to base, pink to yellow. Thus being a neccessary indicator.


Would b, for valid?

[Andiio]

a) Say, your titrating NaOH with HCL, which has a known concentration. When you find the concentration of NaOH, would it be called a standard solution then?


and for a) I wrote, NaOH would be considered a standard solution because it is a solution which has a known concentration, therefore fits the requisites of a standard solution.





For b , i wrote) We already have known c(HCL) and are trying to find C(NaOH), thus by using methyl orange , on HCL, when NaOH is titrated against HCL, the end point will color shift from acidic to base, pink to yellow. Thus being a neccessary indicator.


Would b, for valid?

I think your answer for a) would be viable if you were to perform another titration with the 'standard solution' you've obtained. Otherwise, no.

[Water]

But why not? if we consider that NaOH is pure during the process of titration. What would it make different from one completed titration, to applying it in another?

[Mao]

a) Yes, it can be considered a 'standard solution' for precisely the reason you have stated: the concentration is known, and thus can be used in other analysis. Standard solutions are not limited to titrations only (all sorts of spectrophotometry, etc)

b) The titration of HCl vs NaOH is quite sharp, most indicators would work. Since the equivalence point is pH~7, we ideally want bromothymol blue, however that indicator is not that common (i.e. expensive). Other indicators would work equally as well though, as the transition is sharp (i.e. is large), capturing the end point at a slightly higher/lower pH would still give an end point close to the equivalence point.

For weak acid this is not true, as the transition isn't sharp and capturing a higher/lower pH would give a volume significantly (statistically speaking) different to the equivalence point.

I think I misunderstood the question, we use the indicator to capture the equivalence point. Having an indicator that changes colour allow us to visually determine whether or not we have reached the equivalence point. (you are again correct.) The blurb above discusses why methyl orange is a suitable indicator.

[Water]

Thankyou very much

[Water]

Can this exist as an partial, assuming that partial = ionic, equation.

3Ag+ (aq) + Cl3- (aq) -> 3AgCl (s)  


The Cl3 was derived from C8H8Cl3 with the addition of Silver Nitrated.

The problem is. My Cl3, is a small 3 beneath the l, and it has negative in it, shud there be a negative in it? to look like Cl3-. It looks right, but not sure if it "is" right. lol >_<


or would it be just Ag+ + Cl- -> AgCl (s) (I think this is wrong though)

Cuz the question asks  A 2.0g sample leads to 0.478g of precipitate. Calculate the % purity by mass of the organic compound (C8H15Cl3) in the sample.


---> And we are meant to create  a partial equation for the process before completing the above

The partial equation which is the above, is what I am concerned about, to ensure that my working out is 100% legit >;

[schnappy]

It isn't a standard solution because its cocentration is constantly changing because of evaporation. If you used it immedietely after finding its concentration, the error would be negligible but I don't believe it constitutes a primary standard.

A primary standard has a fixed and known concentration.

[cltf]

Can this exist as an partial, assuming that partial = ionic, equation.

3Ag+ (aq) + Cl3- (aq) -> 3AgCl (s) 


The Cl3 was derived from C8H8Cl3 with the addition of Silver Nitrated.

The problem is. My Cl3, is a small 3 beneath the l, and it has negative in it, shud there be a negative in it? to look like Cl3-. It looks right, but not sure if it "is" right. lol >_<


or would it be just Ag+ + Cl- -> AgCl (s) (I think this is wrong though)

Cuz the question asks  A 2.0g sample leads to 0.478g of precipitate. Calculate the % purity by mass of the organic compound (C8H15Cl3) in the sample.


---> And we are meant to create  a partial equation for the process before completing the above

The partial equation which is the above, is what I am concerned about, to ensure that my working out is 100% legit >;

I don't think Cl3- actually exists.

It's more likely to be:

3Ag+ + 3Cl- --> 3AgCl

And the second question is kinda confusing.

[cltf]

It isn't a standard solution because its cocentration is constantly changing because of evaporation. If you used it immedietely after finding its concentration, the error would be negligible but I don't believe it constitutes a primary standard.

A primary standard has a fixed and known concentration.

Standard solution: a solution of known concentration
Primary standard: Safe, not volatile, cheap etc.

"If you used it immedietely after finding its concentration, the error would be negligible" in this case yes it can be the standard solution.

[Water]

Can this exist as an partial, assuming that partial = ionic, equation.

3Ag+ (aq) + Cl3- (aq) -> 3AgCl (s)  


The Cl3 was derived from C8H8Cl3 with the addition of Silver Nitrated.

The problem is. My Cl3, is a small 3 beneath the l, and it has negative in it, shud there be a negative in it? to look like Cl3-. It looks right, but not sure if it "is" right. lol >_<


or would it be just Ag+ + Cl- -> AgCl (s) (I think this is wrong though)

Cuz the question asks  A 2.0g sample leads to 0.478g of precipitate. Calculate the % purity by mass of the organic compound (C8H15Cl3) in the sample.


---> And we are meant to create  a partial equation for the process before completing the above

The partial equation which is the above, is what I am concerned about, to ensure that my working out is 100% legit >;

I don't think Cl3- actually exists.

It's more likely to be:

3Ag+ + 3Cl- --> 3AgCl

And the second question is kinda confusing.

I thought about it as well Anywayz I"ll type the entire question..


An organic compound has a formula C8H15Cl3. The purity of a sample of this compound is to to be checked by teh addition of silver nitrated to precipitate the chlorine atoms as silver chloride. It is difficult to write a completed, balanced equation for this reaction but fortunately only a partial equation is required.

a) Write a partial equation for this process
a) I cheated abit and checked google to just have clarity
C8H15Cl3 + 3 AgNo3 = 3 AgCl + C8H15 + 3 No3

for the full equation, and this is what i got.

So then, what would the ionic equation be for for the ahove,

I cant understand how it would be
3Ag+ + 3Cl- --> 3AgCl

Cause then the mole ratio between AgCl and Cl- from C8H15Cl3 would be 1 : 1


Therefore, wouldn't this be plausible .. ?

3Ag+ (aq) + Cl3- (aq) -> 3AgCl (s)  







b) A 2.0g sample leads to 0.478g of precipitate. Calculate the % purity by mass of the organic compound in the sample.


I used the my ionic equation to find the answer to this question. So if a) was wrong, b) is most likely wrong as well



PS: SOLVED

[cltf]

I googled it, Cl3- doesn't exist. So that answers that.

[Water]

Indeed, It was Ag+    +     Cl-