[springgy]

 

[azmanam]

Not a very well worded question, I must say.  What if it were reworded thusly:

How many grams of potassium hydrogenphthalate will be required to react completely with 20 mL of a (WHAT MOLARITY???) sodium hydroxide solution.

You need the molarity of the sodium hydroxide solution to do this problem.

Look at the units for M_KHP.  Have you seen those units before?

Can you write a balanced equation for this reaction?

[springgy]

Not a very well worded question, I must say.  What if it were reworded thusly:

How many grams of potassium hydrogenphthalate will be required to react completely with 20 mL of a (WHAT MOLARITY???) sodium hydroxide solution.

You need the molarity of the sodium hydroxide solution to do this problem.

Look at the units for M_KHP.  Have you seen those units before?

Can you write a balanced equation for this reaction?

It isn't well worded is it. The molarity of the NaOH is 0.1. mol L-1.

I haven't seen units of M_KPH before. I tried searching on google, but nothing related came up.

I would write a balanced equation, but I'm not exactly sure what it is making. I get KHC8H4O4 + NaOH ---> ?

[azmanam]

Read up a bit on potassium hydrogenphthalate (wikipedia - http://en.wikipedia.org/wiki/Potassium_hydrogen_phthalate).  Look at the structure and see if that gives you any hints on what products you might be making.  The page may also help you with your M_KHP dilemma. 

For complex organic acid/base reactions, the formulas can look confusing and overwhelming.  Knowing a bit about the structure can sometimes help.  In this case, it may be easier to visualize what is going on by writing the formula of potassium hydrogen phthalate as KH(Phthalate), instead of KHC₈H₄O₄.

[springgy]

Would I get KHP + NaOH --> KPNa + H20?

And for working the amount I need. Would I do:

204.22g x 0.1 x 20
1000 x 1.0

That along the right lines, or is that not even the right equation.

[azmanam]

You have the correct chemical equation. I don't know if you went through and tried to balance it or not, but the equation - in this one example - happened to self-balance.

I'm not following your mathematical equation.  Walk me through your thought process, and please write out your units.

pay no attention to the following test.

Code: [Select]

testing1
2check

[springgy]

I have no idea what that equation means really. I just was searching on google and it came up, and I thought it looked about right. Obviously not.

If its a 1:1 reaction, and I am using 20mL of NaOH, does that mean I could just use 20mL of KHP. So I could do: moles = concentration x voulme

the do mass = moles x Mr?

[Borek]

Lets try with something more obvious - neutralization of KHSO₄:

KHSO₄ + NaOH -> KNaSO₄ + H₂O

Got it? Now - phthalic acid is rather unpleasant molecule to write its formula down when balancing chemical reactions, so we abbreviate its dissociated form with P^2-. Thus neutralization of KHP is very similar to neutralization of KHSO₄. The main difference is that KHP is a compound that can be easily prepared in high purity, so it is a good primary subtance for acid/base titrations.

[azmanam]

I have no idea what that equation means really. I just was searching on google and it came up, and I thought it looked about right. Obviously not.

See my signature

Phthalic acid (wikipedia - http://en.wikipedia.org/wiki/Phthalic_acid) is a 'diprotic' acid.  Note the two COOH functional groups in the molecule, the carboxylic acid functionalities.  The 'H' part of the COOH is the acidic proton - exactly analagous to the 'H' in HCl.  If the reaction were HCl + NaOH --> NaCl + H₂O, the reaction would probably look more like ones you may be used to seeing.  Phthalic acid is also analogous to H₂SO₄ - sulfuric acid is also a diprotic acid.

Because the 'H' is the acidic proton, and because there are two of them, it can be written as H₂C₈H₄O₄, or less commonly as H₂(Phthalate). It is written as H₂(Phthalate) in order to appear to the reader more like a typical diprotic acid, similar to HCl or H₂SO₄.

But we're dealing with potassium hydrogen phthalate.  Someone has already come along and reacted phthalic acid with some potassium base (probably KOH).  That leaves us with a monopotassium salt, KH(Phthalate).  It is now analogous to sodium bicarbonate, NaHCO₃, or NaHSO₄.  The compound has had one acidic hydrogen atom removed, but it still has one acidic hydrogen atom remaining.  That's where NaOH comes in.

NaOH acts as a base to remove the final acidic proton from KH(Phthalate).  That will leave us with the same products from all protic acid base reactions: a salt and water.  Specifically, this example will leave us with sodium potassium phthalate, KNa(Phthalate) and water, as you're chemical equation noted.

If its a 1:1 reaction, and I am using 20mL of NaOH, does that mean I could just use 20mL of KHP.

No.  Balanced chemical equations give you mole ratios, and nothing else.  The only way to convert between one chemical in a chemical equation and another is to convert moles to moles.

moles = concentration x volume

That is a true statement.

[springgy]

See my signature

No.  Balanced chemical equations give you mole ratios, and nothing else.  The only way to convert between one chemical in a chemical equation and another is to convert moles to moles.

moles = concentration x volume

That is a true statement.

Yeah, that was kinda a dumb statement by me. 20mL will react with 20mL, lol, been one of those days.

But with that moles to moles thing. Is this now right. No. of Moles NaOH = Concentration x volume = 0.1 x (20/1000) = 0.002moles

then becuase its 1:1, Its the same number of moles for KHP

So, mass = moles x Mr = 0.002 x 204.22 = 0.408g

[azmanam]

Theory looks good to me.  Didn't check your math, though.

Well done.

fyi - Whenever you work with values in chemistry problems, I'd recommend always writing the units immediately after every number.  On these forums, it will be easier to glance at it and see if you're on the right track.  On homework, a stickler could potentially mark it wrong, because 0.1*(20/1000) doesn't equal any number of moles if there weren't any moles on the left side of the equals sign.  Ya know?  It will also help you check-as-you-go.  If your units don't cancel correctly, you probably made a mistake somewhere.  If you don't have the units, you won't know til the end and you'll have no idea where you made your mistake.

happy chemistry
-AA

[springgy]

Theory looks good to me.  Didn't check your math, though.

Well done.

fyi - Whenever you work with values in chemistry problems, I'd recommend always writing the units immediately after every number.  On these forums, it will be easier to glance at it and see if you're on the right track.  On homework, a stickler could potentially mark it wrong, because 0.1*(20/1000) doesn't equal any number of moles if there weren't any moles on the left side of the equals sign.  Ya know?  It will also help you check-as-you-go.  If your units don't cancel correctly, you probably made a mistake somewhere.  If you don't have the units, you won't know til the end and you'll have no idea where you made your mistake.

happy chemistry
-AA

Yeah, you have a great point there. I must remember to do that. Thanks for all your help