BushyFromOz Posted August 6, 2012 Posted August 6, 2012 crazy crazy crazy topic, i know (well not really) because it all comes back to my complete incompetence when it comes to hasselbachs acid/base equation, so feel free to correct my stupidity. Also, i was transporting a patient a few days ago who had a troponin measurement done in nanograms per decilitre for some reason so i am really bloody confused 1 mol of an elements is equal to the elements atomic weight 1 mol of a compound is equal to the sum of the atomic weight of the elements in the compound 1 mmol is 1 mol/ 1000 (or 10-3 if your into it) or 1 thousandth 1 umol is 1mol / 1000000 (or 10-6) or 1 millionth 1 nmol is 1mol / 1000000000 (or 10-9) or 1 billionth In solution it is expressed as a concentration of 1 mol of the compound per litre pf solution? so .9% saline is .9% of 1 gram (mol) of NaCl?? Hydrogen because of atomic weight of 1 (close enough) can be expressed in milligram, micrograms or nanograms I gave up on the mEq to mmol conversion because i get lost on why the mEq doubles when its missing electrons form the valence shell and makes no sense to me becuase it looks like you double to molecular weight to overcome the lack of 2 electrons which makes no sense to me. Phew... im tired.....
BushyFromOz Posted August 6, 2012 Author Posted August 6, 2012 whethar the conversions are right... i cant ask the next bit without this being right
chbare Posted August 6, 2012 Posted August 6, 2012 (edited) You are on to the right track; however, when we start talking about mEq and Eq, the concept of charge becomes critically important. Remember, nearly all of chemistry is due to electronic configuration with the exception of certain types of nuclear decay (weak interactions) versus electricity & magnetism. Particularly, valence electron structure is the most important concept as that is what determines chemical reactivity for the most part. When dealing with ions, we can expect a very differently type of chemical reactivity. A quick, rule of thumb when dealing with simple ions is to multiply moles * charge to get mEq. Remember, it's the magnitude of charge that counts not the sign. (ie Ca++ is simply 2 as CL- is simply 1) I do not have reliable internet access now, but can do a more detailed explanation tonight or possibly even a video. How about you present your problem and your solution with an explanation and we can discuss this situation in it's specific context? Edit: Also, when talking about moles of an element, the technical standard is 6.02*10E23 atoms of "ideal" Carbon 12 would weigh 12 grams. Since, we are using fairly accurate approximations with the other elements, this is typically not a big deal. Edited August 6, 2012 by chbare
Just Plain Ruff Posted August 6, 2012 Posted August 6, 2012 Thats it, you had to take ch away from his target practice. Now he has to start all over again. Sent from my SPH-D710 using Tapatalk 2
chbare Posted August 6, 2012 Posted August 6, 2012 (edited) I am back and hopefully can clear some of this up: First, a mmol is commonly called a millimole. A millimole is 1/1000 of a mole just like a milligram is 1/1000 of a gram. In other words 1000 mmol equals one mole. If I have one mole of Carbon 12, I would have 12 grams. However, if I had one mmol of Carbon 12, I would have 12 milligrams. With that, we commonly use mmol as a concentration. The common dimensions will be mmol/litre of mmol/l. In other words, how many mmol do I have in a liter of solutions, typically water when talking about biology. Next, mEq is cammonly called milliequivalent. As you may have guessed a mEq is simply 1/1000 of an Eq. However, what exactly is an Eq? Well, if you remember mmol is simply a measure of mass. However, mEq takes something else into consideration. Specifically, Eq is a way of measuring something about the chemical reactivity of the substance you are measuring. The formal definition of an Eq is either the amount of a substance that will supply one mole of Hydrogen ions in an acid-base reaction or the amount of substance that will supply one mole of electrons in a REDOX (reduction-oxidation) reaction. Historically, different definitions have been used; however, let us simply stick with this line of thinking. Now that we have at least some sort of understanding of what these terms are looking at, let me give you a couple of conversions formulae: To convert mmol to mEq you take the amount of mmol * by the "valence" and then divide by a litre since we are typically measuring in mEq/litre. What is the deal with "valence?" Valence is simply the charge on the ion we are discussing. However, we do not care about the sign of the charge, only it's magnitude. For example Na+ and Cl- have exactly the same "valence." In this case, the valence would be one. If you had Ca++, the valence would be two and so on for all the different ions. Let us say you have 1 mmol/litre of Na+ and you wish to convert to mEq/litre. Simply plug and chug: 1 mmol of Na+ * Valence of 1 over a litre or 1 mEq/litre. That's easy, just remember when dealing with ions that have a higher valence, you will have a different conversion. For example, take 1 mmol/l of Ca++. This would convert to be 2 mEq/l because Ca++ has a valence of two. The basic answer to why we need to consider valence revolves around the fact that Eq and mEq are looking at the ability for one substance to chemically interact with another substance. An easy way to see where this becomes relevant is to take the simple case of Na+Cl-. In a perfect world, one mmol of Na+ will perfectly react with one mmol of Cl- to form one mmol of Na+Cl-. In other words, these substances ionically react on a 1:1 basis. Therefore 1 mmol/l of these substances equate to 1 Eq/l because of the 1:1 reaction. However, if you have Ca++ and Cl-, you would need two Cl- for every one Ca++. Therefore the valence of Ca++ becomes quite relevant. Does that make sense? Edited August 6, 2012 by chbare 2
BushyFromOz Posted August 7, 2012 Author Posted August 7, 2012 Brilliant, i wonder how many people read that awesomeness. For some reason i knew chbare would be the guy who chimed in Sorry for al the questions, i can learn this stuff provided i re-write it in bush-a-nese... but if i ask this stuff at work people look at me like i have 2 heads, and seeley, stephens and tate is leaving me with more questions than answers. I get it though, mostly I understand the mEq/L relation to moles of electrons or hydrogen in redox and acid base What i dont get is which ion are involved in acid / base or redox reactions. I know what an acid, base, oxidisation and reduction reaction is but i dont understand if the mEq of a substance is related to hydriogen or redox So with the Ca++ example you gave, 1mmol of Ca++ is equal to 2mEq of Ca, but is this for 2mmol of hydrogen for 1mmol of Ca++ or 1 mmol of electrons? Is weather a it is a redox reaction dependent on the compound being broken / formed? H20 + C02would be a redox reaction?
chbare Posted August 7, 2012 Posted August 7, 2012 I am not sure what you are asking? H2O + CO2 is not a proper reaction. For a proper reaction, you need to identify the environment (often aqueous in biochemistry), the reactants, the products and ideally, a balanced equation with proper stoichiometry would be the proper way to write said reaction. Fundamentally, you have to change the oxidation state of an atom for an reaction to be considered a REDOX reaction. An acid-base reaction involves acids and bases, but the confusion only confounds as there are several acid-base theories. The Bronsted-Lowry, Arrhenius and Lewis are the top contenders with significant amounts of overlap and subtle differences. Additionally, some use what is called the strong acid definition. Unfortunately, it will probably not be possible for me to explain all of your questions on this thread. If you are struggling in chemistry, I would absolutely suggest you get with a tutor and your chemistry professor. I made my chemistry professor work for her money. Basically, I would not leave the class room until I had a deep understanding of the material. I find many people simply leave after lecture or lab and do not take time to have their questions explained. Not me. You will earn every cent of your pay if you are my instructor.
BushyFromOz Posted August 7, 2012 Author Posted August 7, 2012 I am not sure what you are asking? H2O + CO2 is not a proper reaction. For a proper reaction, you need to identify the environment (often aqueous in biochemistry), the reactants, the products and ideally, a balanced equation with proper stoichiometry would be the proper way to write said reaction. Fundamentally, you have to change the oxidation state of an atom for an reaction to be considered a REDOX reaction. An acid-base reaction involves acids and bases, but the confusion only confounds as there are several acid-base theories. The Bronsted-Lowry, Arrhenius and Lewis are the top contenders with significant amounts of overlap and subtle differences. Additionally, some use what is called the strong acid definition. Believe it or not im just doing this for the hell of it. 2 things lead me down this confusing path, one was getting a patients troponin level a few days ago in ng/dL, the other was doing some work on action potentials and all principle cations and anions being given in mmol except calcium which was in mEq's - and i didn't have a clue what that was. The C02 + H20 thing was a reference to the hasselbach equation. The solution would be blood plasma and ive always know it to be a decomposition, the bicarb to carbonic and hydrogen i know is catalyzed by an carbonic anhydrase enzyme. I was just wondering if the bicarb to water / c02 was also a redox? Youve answered my main question in you first post anyway bro, much appreicated
chbare Posted August 7, 2012 Posted August 7, 2012 No worries mate. It wouldn't matter if you were doing it for the hell of it. Unfortunately, all of the systems of measurement are rather arbitrary and we often run into the problem of different systems and dimensions being used. Imagine my horror when somebody stated a patient's blood sugar was 6 for the first time in front of me only to follow it after my reaction with "what, 4-8 feeling great." However "ionically" active substances are probably better off being measured in mEq/l simply because common formulae such as the anion gap take this method of measurement into consideration. Large, complex molecules that are not particularly ionically relevant such as troponin are easier to report in a weight based dimension. However, it will ultimately come down to recognising what system a particular lab uses and their normal reference ranges.
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