How do I safely react NaOH with HF to yield H20 and NaF?

[Comeback City]

I have been reading about how NaOH (Sodium Hydroxide) reacting with HF (Hydrofluoric Acid) yields the products H₂0 (Water) and NaF (Sodium Fluoride). If I were to do this, would I need the EXACT same quantity of NaOH as HF to get H₂0 and NaF?

 

[Borek]

Have you heard about limiting reagents?

 

[SteamKing]

I have been reading about how NaOH (Sodium Hydroxide) reacting with HF (Hydrofluoric Acid) yields the products H₂0 (Water) and NaF (Sodium Fluoride). If I were to do this, would I need the EXACT same quantity of NaOH as HF to get H₂0 and NaF?

The first thing to do when trying to find out what happens in a chemical reaction is to write a balanced chemical reaction formula.

Is
NaOH + HF → NaF + H₂O

a balanced chemical reaction formula?

 

[Comeback City]

Have you heard about limiting reagents?

I know that it is the first reactant that is used up in an reaction. But that is pretty much it. Is that how this would work with different amounts?

 

[Comeback City]

The first thing to do when trying to find out what happens in a chemical reaction is to write a balanced chemical reaction formula.

Is
NaOH + HF → NaF + H₂O

a balanced chemical reaction formula?

Yes it is.

 

[SteamKing]

Yes it is.

Count the number of different atoms on each side of the equation. If they're not equal, the reaction equation is not balanced.

 

[Borek]

Is that how this would work with different amounts?

Yes.

 

[SteamKing]

With the reaction:

NaOH + HF → NaF + H₂O

you want to start with an equal number of moles of HF and NaOH, otherwise you'll have either some HF or NaOH left over after everything has reacted.

1 mole of HF = 1.008 + 18.998 = 20.006 grams +
1 mole of NaOH = 22.990 + 15.994 + 1.008 = 39.992 grams

will yield

1 mole of NaF = 22.990 + 18.998 = 41.988 grams +
1 mole of H₂O = 2*1.008 + 15.994 = 18.010 grams

 

[Borek]

you want to start with an equal number of moles of HF and NaOH

Technically yes, but in practice this is unrealistic, so we always use an excess of one reagent. That's why purification of the product is an important part of each synthesis procedure.

 

[Comeback City]

Technically yes, but in practice this is unrealistic, so we always use an excess of one reagent. That's why purification of the product is an important part of each synthesis procedure.

So if I were to have 1 mole of NaOH and 1.01 moles of HF, would the extra 0.01 moles of HF simply be mixed in with the Water and Sodium Fluoride? If so, could I purify it by boiling out the extra HF (which I believe has a boiling point of about 67°F or 19.5°C)?

 

[Borek]

Apart from the fact I don't like the idea of an airborne HF you are right.

Much safer (but also more difficult) approach is to use excess of NaOH, to be sure no HF is left. HF is quite nasty, not only highly corrosive but also pretty toxic. Trick is, while HF can be easily boiled off, getting rid of excess NaOH is not trivial and may require recrystallization. To be on the safe side you can use excess HF and pass the gases through a scrubber which will filter out HF. Or perhaps just distilling off water with excess HF will be safe enough, no idea what is the best approach here.

 

[Comeback City]

Apart from the fact I don't like the idea of an airborne HF you are right.

Much safer (but also more difficult) approach is to use excess of NaOH, to be sure no HF is left. HF is quite nasty, not only highly corrosive but also pretty toxic. Trick is, while HF can be easily boiled off, getting rid of excess NaOH is not trivial and may require recrystallization. To be on the safe side you can use excess HF and pass the gases through a scrubber which will filter out HF. Or perhaps just distilling off water with excess HF will be safe enough, no idea what is the best approach here.

I think the best option would be to distill the water if possible. Thanks for all the help!

 

[Borek]

I think the best option would be to distill the water

Don't forget you are distilling water AND hydrogen fluoride.

 

[Jeff Armstrong]

Mixing what ever quantity of NaOH and HF you want to, the reaction will occur. However, it will only produce the amount of NaF you are seeking that corresponds to the reactant that is in less quantity with respect ratio of the reactants required. For example if you started with 1 gram of NaOH and 1 million grams of HF and mixed them, you would produce about 1.05 grams of NaF. (1 gram of NaOH is 0.025 moles, NaOH and HF react in 1:1 ratio to produce NaF in a 1:1 ratio, thuse 0.025 moles of NaF which is ~ 1.05 grams).

Think of it like your car and gasoline, you car can hold about 10-15 gallons of gasoline, which reacts with oxygen to make among other by products, CO2 and water (gas phase which, with the heat, expand to make your car go). Now, which runs out first your gas tank or all the oxygen on the earth? This is the concept of a limiting reagent.

 

[Jeff Armstrong]

I think the best option would be to distill the water if possible. Thanks for all the help!

Borek is correct, you cannot simply distill water to easily separate it from HF, you will get some fraction of HF. Your best bet was stated above, use enough NaOH to react all the HF. Also, do this reaction in the aqueous phase. I.e. a solution of HF and NaOH. Do not use gaseous HF and solid NaOH. Pure HF is gaseous but it dissolves readily in water as a weak acid. In the aqueous phase this is a pretty easy acid-base reaction.

Don't mess with HF, it is quite harmful. HF does not quickly cause burning sensation on the skin like strong acids (such as HCl or H2SO4) as such you cannot really tell if you have been exposed. HF does absorb through the skin and leaches calcium from your bones. I do not recommend handling it if you are not trained and aware of the dangers.