Why would candles burn longer when you add salt (NaCl) to them?

Why would candles burn longer when you add salt (NaCl) to them?

That question just came up in a quiz show and Im puzzled, as it makes no sense at the first glance.

Do they?

Haven't tested it and found contradicting information on the internet about it, but no answer why it would work.

One could hypothesize that salt dissolved in the molten wax would change how it flows, possibly making it travel up the wick slower.

I don't think that explanation works though - the wick would just burn shorter. My guess is it doesn't actually have an effect, that piece of folk wisdom is the result of poorly or not at all controlled experiments

I think that a candle might burn longer if you add salt, but for the sole reason that there is extra fuel for it to consume. The difference is pretty much negligible and I don't think there is any strange chemistry going on.

>that salt dissolved in the molten wax

Except wax is nonpolar, so the salt couldn't dissolve. And the temperature isn't high enough to melt it.

NaCl can't be used as flame fuel.

>NaCl can't be used as flame fuel.
Really? Because I seem to recall in high school chemistry Na creates an yellow flame when burned. And I just looked it up, NaCl burns with the same color when administering a flame test. It might not be efficient flame fuel but it can still be burned and therefore used as fuel.

I have another explanation however. I know that NaCl is used to melt ice, which means that NaCl is a good conductor of heat. This means that when added to a candle, it saps up some of the heat more quickly, causing a lower temperature flame and an overall slower burn.

>I know that NaCl is used to melt ice, which means that NaCl is a good conductor of heat.
Look up 'colligative properties', this is an instance of 'freezing point depression' and not the ability of solid NaCl to act as a heat conductor. In this case NaCl/ice it does depend on the fact that NaCl is soluble in water.

Na-ions send out orange/yellowish light when you supply enough energy to them.
Emission spectrum =|= actual fire

The ice melting is a result between the always existing balance between a thin film of water and the ice. The salt prevents water from turning into ice, tipping the balance towards water since ice is still melting. You can only refreeze salt water at a much lower temperature.

[cont.]
I'm not convinced that a qualitative test for sodium, by atomic emission spectroscopy, settles the issue.
Combustion is an example of oxidation using O2 as the oxidant.
The sodium in NaCl is already in the Na+ state.
There may be some processes that, when placing NaCl in a flame, produce some amount of atomic sodium, Na(0), such that it is detectable via emission spectroscopy.
I could go on, but beat me to it.

Thanks for the tips. I just did some reading and I found that NaCl is actually a poor conductor of heat, not good! However, I also read that in it's molten phase salt is a much better conductor of heat. I also noted that salt melts around 800 C, and google tells me that the hottest part of a candle burns at ~1000 C. So maybe my explanation is still correct, but for molten salt. I think you were wrong about the temperature not being high enough to melt it.
Emission spectrum =|= actual fire
But actual fire is just ions coming off the fuel source. If the fuel source is NaCl, why is that not "actual fire"? Does a fuel source need to be organic material?

>I also noted that salt melts around 800 C, and google tells me that the hottest part of a candle burns at ~1000 C.

Yeah, I noticed that too, and am unsure about the appropriate conclusion.
Suppose that some of the energy released by burning the wax goes into melting the salt (as opposed to being transferred to the air), then what?
It is not clear to me that this makes the candle burn slower.

Suppose that some of the energy released by burning the wax goes into melting the salt (as opposed to being transferred to the air), then what?
Well once the salt is molten, it becomes a better heat conductor. And like I said in my other post, this will sap up heat from the wax, air, flame, etc. Because there is now less total heat, the flame will burn at a lower temperature (this is an assumption. If you still aren't convinced of my argument I suggest you start by showing that this assumption isn't true). Okay, so the flame is burning at a lower temperature, this obviously means it will take longer to burn through the entire wick in the same amount of time.

>Except wax is nonpolar, so the salt couldn't dissolve.
Perhaps it's just dispersed like the fat in milk

>Because there is now less total heat
No, there is the same amount of heat, distributed differently.

>If you still aren't convinced of my argument I suggest you start by showing that this assumption isn't true
No, you need to show me that it is true.
I () did not stake out a position "it is not clear to me".

lets assume this is true.

one possibility is that the salt is drawn up the wick (it wont dissolve as mentions) and the grains coagulate along the surface, preventing diffusion of oxygen inwards, forcing the molten wax to burn instead and keeping the wick itself from burning as quickly. If the diffusion was limited well enough, you would limit wax consumption as well (need this to happen if you want the candle to last longer) and then you would have an observably smaller flame.

No matter how you cut it tho, if the treatment is effective, then you will have less light/heat from the candle per unit time. There is a strictly limited amount of fuel available, and the energy release is constant if you integrate over the oxidative rate.

>>Because there is now less total heat
>No, there is the same amount of heat, distributed differently.
No. There is the same amount of energy, distributed differently. The heat that use to be in the fire has transferred into internal kinetic energy of the wax (temperature). I guess you could say the total heat is the same but if we are considering the system as just the candle without the salt, the total heat of that system is in fact different.
>>If you still aren't convinced of my argument I suggest you start by showing that this assumption isn't true
>No, you need to show me that it is true.
I'm just trying to reason my way to an answer just like everyone else in this thread. No need to be a lazy dick about it. Is it really that retarded to think that less heat means a lower temperature flame? If the wax conducts heat away from the flame and increases in temperature, then the flame must decrease in temperature. The only reason I said this was an assumption was because I'm bored and want to continue this discussion in case there was an obvious flaw in my argument. But obviously you'd rather be spoonfed the answer than do any thinking for yourself.

Weak, you can't defend your own assumptions, and when called out insist that others are lazy because of it.

>If the wax conducts heat away from the flame and increases in temperature, then the flame must decrease in temperature.

Really? The flame is supplied with more fuel and oxidant, thereby maintaining temp until one or the other is exhausted.

>But obviously you'd rather be spoonfed the answer than do any thinking for yourself.
LMAO.
OP begins a thread asking for information/understanding and accuses others of seeking to be 'spoonfed'.

You are not very good at this.

>Weak, you can't defend your own assumptions, and when called out insist that others are lazy because of it.
You're the one that originally assumed candles aren't hot enough to melt salt. That was a worse assumption than I made, because I at least have some education in thermodynamics. But you had no idea whether candles could melt salt, unless you're some kind of candle expert.
>Really? The flame is supplied with more fuel and oxidant, thereby maintaining temp until one or the other is exhausted.
Where are you getting that the flame is supplied with more fuel and oxidant? The salt is conducting heat away from the system. That means less wax will melt, less will make its way up the wick and into the flame, and therefore less fuel. The cooler air also moves at a slower velocity, which means the flame will consume less per unit time, and therefore there's less oxidant as well. Have you ever tried starting a fire? The more force you blow with the faster it burns. That's because the air is moving faster and there is more of it.
>OP begins a thread asking for information/understanding and accuses others of seeking to be 'spoonfed'.
I'm not even OP.

>You're the one that originally assumed candles aren't hot enough to melt salt.
false

>Where are you getting that the flame is supplied with more fuel and oxidant?
literally the un-burnt wax and atmospheric oxygen

>That means less wax will melt, less will make its way up the wick and into the flame, and therefore less fuel.
So long as there is sufficient liquid hydrocarbons, the wick can be saturated. There maybe sufficient fuel even if some energy is diverted to melting the salt. You have not demonstrated that the wick fails to deliver sufficient fuel to the flame to maintain temp.

>I'm not even OP.
ok

>The more force you blow with the faster it burns.
>bellows
Lel, I didn't realize that throwing salt on a candle and opening up a pressurized tank of air were the same thing.

try harder

>false
Alright, you're a different user. It's hard to keep track of who I'm arguing with, especially when you jump in late.
>literally the un-burnt wax and atmospheric oxygen
But that's there without the salt too. My point is that when salt is added there is MORE un-burnt wax then there would be if the salt isn't there. More unused fuel means a longer burn.
>So long as there is sufficient liquid hydrocarbons, the wick can be saturated.
The whole point of my last post was to show that there is less liquid hydrocarbons. Less liquid=less saturation and less saturation=less fuel and less fuel=slower burn.
>There maybe sufficient fuel even if some energy is diverted to melting the salt.
The energy goes into melting the salt, then once the salt is molten it saps up much more energy. This is the part you seem to be forgetting/ignoring. Molten salt is a much better conductor of heat than solid salt, so once it's melted it will divert energy even faster.
>You have not demonstrated that the wick fails to deliver sufficient fuel to the flame to maintain temp.
Yes I have. We already discussed this, less fuel=lower temp. Even if the difference in fuel is minuscule, it's still there. Even if the temperature difference is .0001 C, it's still going to slow down the burn.

>My point is that when salt is added there is MORE un-burnt wax then there would be if the salt isn't there.

Salt or no salt, there is wax, and that is the fuel. Adding salt does not magically make wax disappear.

>Less liquid=less saturation
No.
Saturation is not a proposition of more or less so. Rather it is a condition that is or is not met, saturated or unsaturated.
>inb4 supersat

Suppose the following:
Your shirt is organic fiber like a wick.
You dunk your shirt in 10L of EtOH, it takes up as much alcohol as it possibly can, but the EtOH is in vast XS compared to what the shirt can absorb.

Take the same shirt, dry, some other day, and dunk it in 100L EtOH.
It takes up the same amount of alcohol as before.
It doesn't take up 10X more alcohol simply b/c there is 10X available.

>then once the salt is molten it saps up much more energy. This is the part you seem to be forgetting/ignoring.
The molten salt transfers energy to the wax it is in contact with...

>You have not demonstrated that the wick fails to deliver sufficient fuel to the flame to maintain temp.
>Yes I have. We already discussed this, less fuel=lower temp.
No, again we disagree about the notion of saturation, or threshold.

>No, again we disagree about the notion of saturation, or threshold.
That's an interesting point. But one counterargument would be that although the wick is saturated, some of the material in the wick is actually molten salt not liquid wax. And since we already agreed that salt cannot be a fuel source, it means that there will be less fuel in the wick even though it remains saturated.

Let's use the example you gave: You dip a shirt in 10 L of alcohol, much more than what it can absorb. Now you add some salt to the EtOH (let's pretend it dissolves). The volume has increased as before, but the same number of moles of alcohol are present. When you dip the shirt this time, it can't absorb as much alcohol because some salt will be taking its place.

Now if you can show me that molten salt won't saturate a wick, be my guest. You are the candle expert after all.