Help Required

[TWJian]

I need help making boric acid. I have borax decahydrate(Na2B4O7) and sulphuric acid(2 mol/litre). Can anyone help me? Please include ratios. I also need help making propyl formate from propanol and formic acid(ratio please again). What kind of solvent should I use to extract scents and pheromones from ants? Apparently alcohol don't work well since it will react with formic acid.

[BenSon]

Here's the first one you wanted

2Na2B4O7 + 2H2SO4 + 10H2O = 8H3BO3 + 2Na2SO4

I think thats right but ive never done the reaction before.

About the ratios you can work that out with this formula...

Mass(g) = Number of moles X Molecular mass

I'm not sure how much chem you've done before but just write back if theres a problem. As for propyl formate i'm too tired to do both 2nite...

 

~Scott

[TWJian]

So I suppose borax decahydrate has a molecular weight of 202 right?So I need to dissolve 404g of borax decahydrate with 1 litre of water right to obtain a 2 mol solution?By the way, how can I separate boric acid from sodium sulphate?Incidentally, sodium sulphate is also a decahydrate.

[BenSon]

I got 382 for the molecular mass?... But everything else you said was right i'll have to think about that separation.

 

~Scott

[raivo]

H3BO3 can be separated from Na2SO4 by fractional cristallisation. If temperature is higher than 32C then Na2SO4 crystallises without water molecules and at 35C has solubility of 49g in 100ml water. Boric acid is far less soluble 7.6g for 100ml water at 35C. You need to evaporate such amount of water that all Na2SO4 remains in solution. 35C seems to be best temperature for collecting your boric acid.

[TWJian]

How do you calculate molecular mass? I added the atomic weights of Na2B4O7,which is 23x2+11x4+16x7=202. Is it correct?

 

Oh, What colour is propyl formate? I got some amber liquid with an oily liquid UNDERNEATH(odd) by heating 9ml of propan-1-ol with 5 ml formic acid.When the liquid cools down,the oily layer seems to become dirty. I used a makeshift reflux condenser to do this.(conical flask, wet cloth wrapped around the cork and a glass tube leading from it to another test tube immessed in water.Vaccumn will suck the liquid collected at the test tube back for futher reaction)

[BenSon]

You had the way to find the molecular mass right but you said it was borax decahydrate. That is Na2B4O7.10H2O you need to add the weight of 10 H2O's as well then you'll have it right.

 

As far as the Propyl formate thing goes i've been trying to reseach it but i havn't come up with anything yet i could have a stab at the equation but i have a feeling that it would be wrong...

H2CO2 + C3H8 = C4H8O2 + H2

however in your secong post you said propanol not propane so that would be

H2CO2 + C3H7OH = C4H8O2 + H2O

But like i said before these equations could be bogus i can't find any reference to them online so yeah...

 

Anyhow you said you got amber liquid on top of and oily layer well i dont know whats up with that i could find about as much info of the colour of C4H8O2 as i could about making it. sorry i couldn't be of more help...

 

~Scott

[TWJian]

You had the way to find the molecular mass right but you said it was borax decahydrate. That is Na2B4O7.10H2O you need to add the weight of 10 H2O's as well then you'll have it right.

 

As far as the Propyl formate thing goes i've been trying to reseach it but i havn't come up with anything yet i could have a stab at the equation but i have a feeling that it would be wrong...

H2CO2 + C3H8 = C4H8O2 + H2

however in your secong post you said propanol not propane so that would be

H2CO2 + C3H7OH = C4H8O2 + H2O

But like i said before these equations could be bogus i can't find any reference to them online so yeah...

 

Anyhow you said you got amber liquid on top of and oily layer well i dont know whats up with that i could find about as much info of the colour of C4H8O2 as i could about making it. sorry i couldn't be of more help...

 

~Scott

Thanks for your help. I couldn't find the information on the Internet either(colour and preparation). I neglected to mention that I added 5 drops of H2SO4 to the mixture as a catalyst. Regarding borax decahydrate, I suspect the compund is amorphous since it s a fine white powder. Commercial sources seems to be dehydrates but should I factor that into account since I'm adding water to it soon? By the way, H2CO2 + C3H7OH = C4H8O2 + H2O seems rather plausible to me since it resemble a lot of esterfying processes.

[BenSon]

Your right, dehydrated borax is a chalkey white substance. If you measure how much borax you are going to react before you hydrate it then you won't have to factor the water in. However if you plan to hydrate it then measure it out, then you will have to add the water into the molecular mass. Also make sure not to add more water then enough to hydrate the borax or that could effect the amounts.

 

~Scott

[TWJian]

One main problem that I have to face is that borax also forms pentahydrates. Apparently, my chalky white borax has turned into a crystalline fine powder(on the surface) after exposure. So, should I just hydrate the entire thing anyway and treat the borax as a decahydrate? If so, how can I hydrate it? Dissolve it in water and crystallise it out?

[raivo]

If temperature is lower than 58C then borax crystallises as decahydrate. So you may hydrate it by weting it. After that you have to dry it without rising temperature over 58C.

 

In real world amount of water that hydrated salts have differs from theoretical. At least if you do not have nice crystalls. So i think best way is to use excess of sulfuric acid so you know all borax gets used or you may do some kind of titration to determine how much borax your powder actually contains. In that case you do not need to hydrate. You can also determine exact concentration by solubility or specific gravity of solution. I have some tables for this. If you decide to go that way i can share.

[TWJian]

If temperature is lower than 58C then borax crystallises as decahydrate. So you may hydrate it by weting it. After that you have to dry it without rising temperature over 58C.

 

In real world amount of water that hydrated salts have differs from theoretical. At least if you do not have nice crystalls. So i think best way is to use excess of sulfuric acid so you know all borax gets used or you may do some kind of titration to determine how much borax your powder actually contains. In that case you do not need to hydrate. You can also determine exact concentration by solubility or specific gravity of solution. I have some tables for this. If you decide to go that way i can share.

 

Your idea is good. However, I'm using a triple beam scale(smallest unit 0.1g) so it might entail some problems for me. Is it possible for me to use a pH multimeter to determine the pH of the solution and stop adding borax to sulphuric acid as soon the mixture reaches the pH of boric acid? Could you help me determine the correct pH for boric acid if I try adding borax to sulphuric acid with a molarity of 2 mol/dm3 The tables could help me in my calculations. Thanks again for your help.

[BenSon]

Is it possible for me to use a pH multimeter to determine the pH of the solution and stop adding borax to sulphuric acid as soon the mixture reaches the pH of boric acid?

 

I haven't done this for a while but...ravio suggested this already but a titration may be a good idea. I'm not sure if you have the gear for that though anyway here is a pretty through site on it http://www.dartmouth.edu/~chemlab/techniques/titration.html

 

~Scott

[raivo]

I have no ph tables for boric acid at hand but i believe that if endpoint is reached (no free sulfuric acid left) then ph does not change any more (or changes very slowly) by adding borax. There should be sudden rise of ph just before endpoint.

 

Specific gravity depending on concentration is as follows

Na2B4O7 @ 15C

% g/cm3

0.5 1.0042

1.0 1.0084

1.5 1.0131

2.0 1.0179

 

0.1g scale may be good enough if you can take 300ml (or more) of solution.

 

No matter what way you use you may take certain excess of sulfuric acid so you can be sure all borax gets used. Sulfuric acid is so well soluble that your boric acid does not get contaminated and you may recrystallise it if you need still more purity.

[TWJian]

I added 5 ml of sulphuric acid(2 mol/litre) with 3.8 g of borax. I heated the mixture in a beaker until the temp. reaches 50 degrees celcius. The solution was neutral(pH 7 right on the mark) so I suspected I added too much borax. I added several drops of H2SO4(still maintaining same temp.) and suddenly a mass of crystal crystallised up and the temp. rose to 60. I let the mixture( now pH5) cool down to 35C(pH rose to 6.4, presumely some of the boric acid have crystallised out) then filtered it, washed the crystals with a little water, and filtered it again. The white crystals should be mostly boric acid right? Could you calculate its approx. purity based on my methods?( theorically)

[Guest nickorgs]

According to my calculations,

you've produced 2.20 g of broric acid H3BO3.

if you initially had 3.8 g of Na2B4O7*10H20, that means you had 1.8 g of Na2B4O7 and 2 g of 10H20 (just use proportion for calculations). And then a series of very simplified mathematical calculation lead you to the answer of 2.20 grams. But still you should remember that during the heating of your mixture some amount of water could be evaporized and thus the way it makes this answer very unreliable.

+ If you have a solution of H2SO4 (2mol/l) and you add 5 ml that means you add totally 0.32 g of H2SO4 (I think yes?).

I suppose that helps you.

[TWJian]

According to my calculations' date='

you've produced 2.20 g of broric acid H3BO3.

if you initially had 3.8 g of Na2B4O7*10H20, that means you had 1.8 g of Na2B4O7 and 2 g of 10H20 (just use proportion for calculations). And then a series of very simplified mathematical calculation lead you to the answer of 2.20 grams. But still you should remember that during the heating of your mixture some amount of water could be evaporized and thus the way it makes this answer very unreliable.

+ If you have a solution of H2SO4 (2mol/l) and you add 5 ml that means you add totally 0.32 g of H2SO4 (I think yes?).

I suppose that helps you.[/quote']

 

Right, I got 2g of white crystals(presumely boric acid)

[YT2095]

a simple test would be to dissolve a little of that "White Powder" in some methylated spirits and then ignite the soln, if it burns with a green flame, it`s Boric acid

[TWJian]

Alright, I just burn that powder on a metal spon. The flame changed into green. By the way, could anyone explain why boric acid is toxic? Please explain what it does to the human body. And why are insects extremely weak against it?

[BenSon]

This is from Here

 

Asking "How toxic is boric acid?" is sort of like asking "How hot is hot?" The answer clearly needs to be qualified...and, yes, scientists have figured out a means to compare one chemical to the next. In fact, on this scale, scientists and/or regulators can compare most anything that can be swallowed, inhaled or put in one's eyes. The scale I am referring to gives a figure known as the LD50 rating - a dose that would cause the deaths of 50 percent of a specific animal population. One method used to determine the LD50 rating for most substances is via laboratory-controlled oral doses to rats. The following table lists the LD50 (oral-rat) for several common substances as published by the Registry of Toxic Effects of Chemical Substances.

 

Substance

LD50

(milligrams of dose

/kg of body weight)

Aspirin 1,000

Boric Acid 2,660

Table Salt 3,000

Boron #10 3,500

Baking Soda 4,200

Grain Alcohol 14,000

 

Insects are so susceptable to it because they are tiny and their small systems are literally flooded by the boric acid quickly leading to toxic levels. In humans thios level takes alot more to reach. I'm not sure exactly what it does to the body to cause death though...

 

~Scott

[YT2095]

Agreed,

 

I use borax (sodium Borate) and sugar mix, around the edges of my raised beds in the garden as an ant killer, it works great

[H2SO4]

I dont know if your just rying to make boric acid for just making chemicals to ad to your collection ( i do this alot) or if you actualy need some real quick . I f you need some real quick , you can go to a drug store, and they should carry some (of reasonable purity) by the glycerin. This is where i get my boric acid.

[H2SO4]

"YT2095 Wrote "Agreed,

 

I use borax (sodium Borate) and sugar mix, around the edges of my raised beds in the garden as an ant killer, it works great :)"

 

What if your dog/cat/watever eats it. Do the ants carry this off to eat because it has sugar in it? It would make sense

[BenSon]

maybe YT has no dog or cat? Also the ants are ment to be attracted by the suger to the boric acid, as a pesticide.

 

~Scott

[YT2095]

this is on my allotment garden, there`s no pets there either, as Benson said, the sugar is the "bait", a bit like warfarin impregnated grain used in rat poison, I live on the 13`th floor and have 3 cats, there`s no garden here

 

as for obtaining it, the local chemist will supply it in small amounts, I bought a kilo of it and that had to be ordered in especialy, I use it as a trace element where I grow cauliflower (it stops the florets from seperating).

 

btw, did you know that if you mixed it with silicone oil, it`ll make Silly Putty? )