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# What is an equivalent?

Figure out how to calculate an equivalent and how it relates to a mole. Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.

## Want to join the conversation?

• Hi,
a bit confused, was just wondering why an equivalent is important in medicine?
Thanks
• Dealing with ions are relevant in medicine because osmotic gradients of ions are crucial to many functions necessary for life(e.g. neural conduction). Many pathologies are a result and/or cause of electrolyte imbalance due to a multitude of reasons. To understand, diagnose, and correct these imbalances of electrolytes(ions) they need to be measured both in the body, and in solutions administered as treatments. For many of these purposes the Equivalent is the most useful unit of measurement.
• Hi;
can someone tell me what normality is?i know the definition and the formula but i dont understand it. the formula:
normality= given mass of solute /gram equivalent mass in liters. this is the formula we were taught. can someone please explain this to me?or is there a video on this?
• Why does potassium have a + on top of it? I thought it was just represented with a K.
• Potassium has one electron in it's outer shell. In order to become stable, it loses this electron very easily. Losing an electron causing it to have one positive charge, which is represented with the little plus at the top right.
• Why does the balance have to be a monovalent? Why couldn't it still work with Ca+2 and S-2 or Fe+3 and O-2??
• I understand that you can easily find the charge for individual ions, Ca = 2+, Cl = 1- but how do you figure it out for molecules like CaCl2? The next step for using equivalents would be to use the equivalent in a normality equation, but for those you need to divide by the valence. Can you do a video on that?
• I want to point out that the above comment is incorrect, although the author was on the right track. In contrast to the video, we observe that water can be separated into ions, hydroxide and protons. We also observe the number of water ions relative to the number of electrolytes to solve for normality.

For calcium chloride, we have 1 calcium ion with 2 chloride ions.

You require two hydroxide ions to saturate a calcium ion, because the charge is 2+. You require one proton to saturate one chloride ion. You count how many water ions you needed to generate to dissolve the salt.

We have 2 water ions for calcium and 1 water ion for chloride, but I have two chloride ions. Therefore, we have a total of 4 water ions needed to saturate calcium chloride. If you have a mole of calcium chloride in a liter of water, then we say we have 4 Eq/L of calcium chloride in solution.
• At the end of the video, the "equivalency" of N3- is calculated. This would never exist in solution as an electrolyte so does it make any sense to calculate this or refer to a nitrogen atom having an equivalency of 3? Isn't equivalency usually restricted to ions such as Na+ or Ca2+? Do medical lab values come back with a N equivalency?
• I think he was just using these as examples, though potassium chloride (KCl) and calcium chloride (CaCl2) are more salient in medicine (to replete potassium, we administer potassium chloride in solution, and - for a variety of indications, if we administer calcium, we administer it as calcium chloride) than ammonia (though we can measure ammonia levels as part of a blood test).

Although we see Potassium Chloride (KCl) and Calcium Chloride (CaCl2)
(1 vote)
• hi
can someone calculate the equivalent weight of NaOH in this reaction :
3Br2+6NaOH=5NaBr+NaBrO3
• First of all, the equivalent mass of a compound will stay the same in any equation.
Lets take a simple equation of NaOH splitting into an Na+ ion and a hydroxide ion.
NaOH -----> Na+ + OH-

As NaOH is a base, we have to focus on the OH- ion.

Now in a base, the n factor is the number of OH- ions per mole of the substance.
As there is a single OH- ion per each mole of NaOH (see the equation), n=1.

Therefore, equivalent mass = Molar mass/n
=40/1
=40 !
• Despite knowing the medical use for the unit measurements of Eq or mEq, your lesson was a little hard to follow. I've always avoided getting into it but recently I have had no other choice but to do so. You gave the insight that I need. I just have to go over the video a few more times. The balancing act drives me crazy!
• Can anyone explain to me what a molar equivalent is? Is it the same as an equivalent?
• A molar equivalent is simply the number of moles needed to balance the particular molecule or compound.
(1 vote)
• i challenge to give the proof for
gram equivalent=molar mass / [n factor,acidity,basicity]
(1 vote)
• A gram equivalent of H2SO4 is 49g.

proof-

H2SO4-->2H+ +(SO4)2-

In acids, the n factor is equal to the number of H+ ions. Here there are 2.
therefore n=2

Molar mass of H2SO4 - 2 + 32 + 64 = 98.

Now, gram equivalent= molar mass / n
= 98/2
= 49
Hence proved.