Extraction of Sodium chloride

[Primarygun]

I thought of a method to prepare sodium chloride solid.

First, pour a certain amount of hydrochloric acid into sodium hydroxide, add a few drops of methyl orange with titration, stop when the colour turns from yellow to red. There are some excess acid mixed with a solution of sodium chloride. Evaporate with steam bath and get the filtrate (crystal), wash it with distilled water and dry it. Is it a good method?

 

Moreover, I want to ask why the change of pH value is very little when an acid is adding to an alkali.

[BenSon]

Sounds pretty good to me you may have some methyl orange contamination but that would be very minor. To answer your question there is a very large PH difference when titrating strong acids with strong bases. The curve would look like a slight increase followed by a very steep increase followed by slight increase. The reason you can use a variety of different indicators for strong acid/base titrations is that the equivalence point value is simlilar the value for a large range of PH values.

Hope that made sense.

 

~Scott

[Primarygun]

Would you like to explain the curve? What's the nature of methyl orange?

How about using excess hydrochloric acid? Then the product would not be contaminated.

[YT2095]

excess HCL will indeed work, that way all you`ll need is a bit of litmus paper or universal indicator paper and look for mild Red color, the HCL will evaporate off without a problem.

 

that`s the method I`de employ

[BenSon]

The first two titration curves refer to strong acid/base titrations Here You can see the rapid PH change, you could use an indicator that changes at 7 8 9 6 5 4 you will get the same result even though the exact equivilance point is at 7. For other titration where the equivilance point dosn't have alot of values similar to it you should use a PH meter to determine the equivilance point. The HCl is not reacting with the methyl orange so adding excess HCl is not going to help with contamination by the methyl orange.

 

~Scott

 

Edit: I would also suggest not using litmus it is one of the harder ones to see the colour change. There are other indicators that are easyer to see the colour change.

[YT2095]

he means skipping the meth orange all together I think.

and litmus will be just fine for the red/pink from the blue paper.

 

or as I mentioned the universal indicator paper that does the whole PH range on a scale, you only need a slight red/pink change

[reverse]

How pure is table salt?

 

if purity is not an issue, then there is a tonne of sea water and sunlight out there.

[BenSon]

I think table salt is pretty pure.. but seawater isn't, espechially if you live in a city there is heaps of polutants and substancial amounts of magnesium chloride in sea water too...

 

~Scott

[Primarygun]

Will some other salts be trapped inside crystals of sodium chloride when we evaporate the solution?

[Primarygun]

Why is the change when some acid is added into alkali very small?

Relative to the change around the end point, I can understand it.

But, the pH value really drop very slightly, why?

[BenSon]

Ok i think i get what your asking...Your saying why is the PH change at the biggining of the titration so slight compared to the PH change around the equivalence point. I think it is to do with the concentrations of the solutions at the start of the titration the concentration changes only slightly as it is neutralised. When it is approching the equivalence point the PH varies quickley due to the the fact the concentration is dropping from a small value to zero very quickley.

 

To answer your other question salt devived from the evap of sea water, there will be a mixture of metal chlorides approximately 98% of the will be sodium chloride while the other 2% will be other metal salts like magnesium, calcium, pottassium...Table salt on the other hand is much more pure about 99.9% with small amounts of potassium iodate. So if your looking for pure NaCl then iodised table salt is a fairly good choice.

 

~Scott

 

Edit: did you check out the link i posted in post No5 ?

[Primarygun]

I think that both combination of water molecules fron hydrogen ions and hydroxide ions and the addition of water into the solution speed up the lowering of the pH value. (Acid is adding into a solution of alkali)

[Primarygun]

Edit: did you check out the link i posted in post No5 ?

Yes, but I think I am trapped by a small problem which cannot be answered in that web site though it contains lots of information of titration, such as weak-weak, strong ../

[BenSon]

I think that both combination of water molecules fron hydrogen ions and hydroxide ions and the addition of water into the solution speed up the lowering of the pH value.

 

To me this dosen't make sense maybe you could reword it?

 

~Scott

[Primarygun]

Neutralization + addition of solution which contains water

Dilute the solution

Hence, pH value should drop faster.

[BenSon]

Ah right interesting point, I think that it would maybe effect the values above and below the equivalance point but not at it because when a solution is neutral it cant be diluted make sense? So when you add 1molL of NaOH to 1molL HCl it dosen't matter how much water is present because the amount of acid it take to neutralise base is the same no matter how much water is present...

 

~Scott

[Primarygun]

Doesn't the pH value vary as different molarity though the amount of acid molecules is the same?

[BenSon]

Yes it does that why i said the small dilution effect would change the PH value up untill the equivalence point when the solution is neutralised. Now that the solution is neutralised you cant diluite a neutral solution so the molarity of any acid or base is zero. That is why the end result is the same regaurdless of the dilution effecting the results prior the the equivalence point.

 

~Scott