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Help with lab work

MermaidWonders

Active member
Feb 20, 2018
113
Which of the following will burn your skin if you get it on you?
a. concentrated sulfuric acid
b. concentrated nitric acid
c. concentrated potassium hydroxide
d. concentrated hydrochloric acid


My first instinct was that all of them would since they are either concentrated acids or bases. I then tried to answer this question by consulting the MSDS for all of the above, but then all of them had "Causes severe skin burns and eye damage". So now, I am confused. Should we be considering the strength of the acids and base?
 

Klaas van Aarsen

MHB Seeker
Staff member
Mar 5, 2012
8,780
Hi MermaidWonders,

Isn't it the same thing?
That is, yes, in their concentrated forms they all cause chemical burns.
In a weak form they only irritate the skin.
 

MermaidWonders

Active member
Feb 20, 2018
113
Hi MermaidWonders,

Isn't it the same thing?
That is, yes, in their concentrated forms they all cause chemical burns.
In a weak form they only irritate the skin.
Sorry, I didn't clarify. "Strength" as in whether the acid/base is strong or weak. So should I consult the table of relative strengths of acids and bases, or is it already obvious to say that all of them would burn the skin?
 

Klaas van Aarsen

MHB Seeker
Staff member
Mar 5, 2012
8,780
Sorry, I didn't clarify. "Strength" as in whether the acid/base is strong or weak. So should I consult the table of relative strengths of acids and bases, or is it already obvious to say that all of them would burn the skin?
An acid or base must both be strong and concentrated to burn the skin.
This is the case for all 4 of them.
I think we can assume that if we call it an acid or a base that it will burn the skin in a sufficiently concentrated form though.
Even vinegar will burn the skin if sufficiently concentrated.
Still, if it's hardly an acid at all (even water is considered to be both acidic and basic), it will obviously not burn the skin.
 

MermaidWonders

Active member
Feb 20, 2018
113
An acid or base must both be strong and concentrated to burn the skin.
This is the case for all 4 of them.
I think we can assume that if we call it an acid or a base that it will burn the skin in a sufficiently concentrated form though.
Even vinegar will burn the skin if sufficiently concentrated.
Still, if it's hardly an acid at all (even water is considered to be both acidic and basic), it will obviously not burn the skin.
Ah, makes sense now. Thank you so much! :)
 

MermaidWonders

Active member
Feb 20, 2018
113
Hi, sorry if this is a really dumb question, but since soaps have both a polar and a non-polar component to them, does it mean that they can actually dissolve all substances (polar and non-polar)?
 

DavidCampen

Member
Apr 4, 2014
64
I would not use the word dissolve; solubilize is a better term. The soap will help create an oil in water emulsion wherein the oil is dispersed into small particles. This property of soap is why it is a member of the more general class of materials called surfactants. The basic feature of a surfactant is that one end of the molecule is hydrophobic such as a long hydrocarbon chain while the other end is hydrophilic such as a sulfonate group; depending on the balance of strength between the 2 ends of the molecule you get surfactants that can form oil in water emulsions and others that can form water in oil emulsions.
 

MermaidWonders

Active member
Feb 20, 2018
113
I would not use the word dissolve; solubilize is a better term. The soap will help create an oil in water emulsion wherein the oil is dispersed into small particles. This property of soap is why it is a member of the more general class of materials called surfactants. The basic feature of a surfactant is that one end of the molecule is hydrophobic such as a long hydrocarbon chain while the other end is hydrophilic such as a sulfonate group; depending on the balance of strength between the 2 ends of the molecule you get surfactants that can form oil in water emulsions and others that can form water in oil emulsions.
So they essentially solubilize everything?
 

DavidCampen

Member
Apr 4, 2014
64
You can manage to emulsify most any hydrocarbon liquid in water or water in a hydrocarbon and solubilize is an extreme case of emulsification where the emusified particles are so small that they don't scatter light. It can be hard to make a stable emulsion and even harder to make one where the particles are so small that they don't scatter light. Making stable emulsions is an art.
 

MermaidWonders

Active member
Feb 20, 2018
113
Hey, just another question pertaining to the same lab from last week... since soap can make oil/grease soluble in water, why is hexane immiscible in soap solution?
 

DavidCampen

Member
Apr 4, 2014
64
I went from you saying solution to me saying emulsion. A surfactant is not going to make a true solution, it will make an emulsion and if you work really hard you might be able to make the emulsion particles so small that the liquid will appear clear.

I would expect that you could make a hexane in water emulsion by selecting the proper surfactants. There are thousands of different surfactants you can purchase, selecting the correct combination for a particular emulsion is the art. A place where I worked, they made a paraffin in water emulsion; perhaps hexane would be more difficult.

You can also use a co-solvent to bring immiscible substances into solution. Colognes contain water and essential oils etc. that would not normally be miscible; you get a clear solution because 70% or more is ethanol. If you start diluting the cologne with more water it will become cloudy as the organics drop out of solution. Another example is the alcoholic drink called absinthe, it is a clear green colored liquid containing essential oils along with the alcohol but as you add it to water it becomes cloudy as the essential oils drop out of solution (forming an emulsion).
 

MermaidWonders

Active member
Feb 20, 2018
113
I went from you saying solution to me saying emulsion. A surfactant is not going to make a true solution, it will make an emulsion and if you work really hard you might be able to make the emulsion particles so small that the liquid will appear clear.

I would expect that you could make a hexane in water emulsion by selecting the proper surfactants. There are thousands of different surfactants you can purchase, selecting the correct combination for a particular emulsion is the art. A place where I worked, they made a paraffin in water emulsion; perhaps hexane would be more difficult.

You can also use a co-solvent to bring immiscible substances into solution. Colognes contain water and essential oils etc. that would not normally be miscible; you get a clear solution because 70% or more is ethanol. If you start diluting the cologne with more water it will become cloudy as the organics drop out of solution. Another example is the alcoholic drink called absinthe, it is a clear green colored liquid containing essential oils along with the alcohol but as you add it to water it becomes cloudy as the essential oils drop out of solution (forming an emulsion).
So is soap just not the appropriate surfactant to make a hexane in water emulsion? Also, is it true that we can essentially make almost any emulsion by choosing the right surfactants?
 
Last edited:

DavidCampen

Member
Apr 4, 2014
64
To the first question: yes, that would be my guess.

To the second question: that is saying more than should be inferred. Making emulsions is an art, I don't know of any way to compute a result.
 

MermaidWonders

Active member
Feb 20, 2018
113
To the first question: yes, that would be my guess.

To the second question: that is saying more than should be inferred. Making emulsions is an art, I don't know of any way to compute a result.
Alrighty, thank you so much!