What is Acid: Definition and 698 Discussions

An acid is a molecule or ion capable of either donating a proton (i.e., hydrogen ion, H+), known as a Brønsted–Lowry acid, or, capable of forming a covalent bond with an electron pair, known as a Lewis acid.The first category of acids are the proton donors, or Brønsted–Lowry acids. In the special case of aqueous solutions, proton donors form the hydronium ion H3O+ and are known as Arrhenius acids. Brønsted and Lowry generalized the Arrhenius theory to include non-aqueous solvents. A Brønsted or Arrhenius acid usually contains a hydrogen atom bonded to a chemical structure that is still energetically favorable after loss of H+.
Aqueous Arrhenius acids have characteristic properties which provide a practical description of an acid. Acids form aqueous solutions with a sour taste, can turn blue litmus red, and react with bases and certain metals (like calcium) to form salts. The word acid is derived from the Latin acidus/acēre, meaning 'sour'. An aqueous solution of an acid has a pH less than 7 and is colloquially also referred to as "acid" (as in "dissolved in acid"), while the strict definition refers only to the solute. A lower pH means a higher acidity, and thus a higher concentration of positive hydrogen ions in the solution. Chemicals or substances having the property of an acid are said to be acidic.
Common aqueous acids include hydrochloric acid (a solution of hydrogen chloride which is found in gastric acid in the stomach and activates digestive enzymes), acetic acid (vinegar is a dilute aqueous solution of this liquid), sulfuric acid (used in car batteries), and citric acid (found in citrus fruits). As these examples show, acids (in the colloquial sense) can be solutions or pure substances, and can be derived from acids (in the strict sense) that are solids, liquids, or gases. Strong acids and some concentrated weak acids are corrosive, but there are exceptions such as carboranes and boric acid.
The second category of acids are Lewis acids, which form a covalent bond with an electron pair. An example is boron trifluoride (BF3), whose boron atom has a vacant orbital which can form a covalent bond by sharing a lone pair of electrons on an atom in a base, for example the nitrogen atom in ammonia (NH3). Lewis considered this as a generalization of the Brønsted definition, so that an acid is a chemical species that accepts electron pairs either directly or by releasing protons (H+) into the solution, which then accept electron pairs. However, hydrogen chloride, acetic acid, and most other Brønsted–Lowry acids cannot form a covalent bond with an electron pair and are therefore not Lewis acids. Conversely, many Lewis acids are not Arrhenius or Brønsted–Lowry acids. In modern terminology, an acid is implicitly a Brønsted acid and not a Lewis acid, since chemists almost always refer to a Lewis acid explicitly as a Lewis acid.

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  1. G

    Chemistry Why is the third hydrogen attached to P instead of O in phosphorus acid?

    Stumbled upon this when I was looking at lewis dot electron structures. The phosphorus acid is dibasic. What prevents the third hydrogen from attaching to the third oxygen instead of the central phosphorus? Is there a theoretical explanation or we can only memorize this for a fact? Thanks,
  2. I

    Magnesium bisglycinate + citric acid = ?

    Hello, I have a question or two that I need help with: What happens when you put magnesium bisglycinate and citric acid into water solution? Does magnesium change form here? Kind regards, IN
  3. BriggsMason

    Is there an acid that could dissolve Aluminium & leave Copper alone?

    [Mentor Note: Two thread starts merged into one] I need to remove the Aluminium heat fins from a CPU heat extange lined around some copper water heat pipes. I could use a saw, cnc or grinder to remove them, but it seems that this way could be cleaner, and less probable to ruin the heat pipes...
  4. A

    Chemistry Reactions With Dilute Hydrochloric Acid

    One of the alternatives was NaBr My resolution was as follows: NaBr + HCl forms NaCl and HBr I researched and saw that HBr would be a gas and would be denser than air because its molar mass is greater. However, the answer was not that. My error is in which step? In the reaction? What would...
  5. P

    Chemistry Mechanism for Solid-Phase Nucleic Acid Deprotection and Cleavage

    Hi everyone! I can‘t solve this following task. Can you explain me how I have to draw the mechanism? Task: Solid-phase nucleic acid synthesis: deprotection and cleavage of carrier with 2'-O-TOM protected suitable phosphoramidite building block synt. dinucleotide of 5'-UG. I started with...
  6. P

    Question about nucleotides and phosphoric acid

    Hi everyone! Is this sentence correct? "Phosphoric acid is linked to the hydroxyl groups of the sugars via ether bonds" I would say yes, but in the solutions this phrase is wrong and I'm a little bit confused. I think that's correct, isn't it?
  7. hexanimal

    How can I determine the shape of an oldie acid molecule?

    I have done all of the questions apart from c and d. For a I got the answer 2.58*10^_5 cm^3 B) 3.72*10^-7 cm But for c I don’t really know how to start. I first thought of using the formula for volume of cuboid but don’t know how that’d give the answer for the dimension. For D, I turned the...
  8. A

    Is MySQL or PostgreSQL more ACID compliant for database projects?

    Hello All, I am working on a database project and I am good at SQL commands. I want to know which one supports ACID compliant between MySQL and PostgreSQL. I have asked this question on Quora and according to this post, MySQL is not completely ACID compliant. It supports ACID only when used in...
  9. M

    Optimizing Sugar Paste Consistency with Vacuum-Assisted Heating

    Hello, I'm in the process of developing a sugar paste for hair removal and trying to find a good ratio between sugar, water and acid in order to get a gewy consistency. I currently use 8 tbs sugar, 4 tbs water and 2 citric acid and let it reach a temperature around 128 degrees Celsius (262.4...
  10. PainterGuy

    Medical Drinking water and the release of gastric acid

    Hi, I think of a human body as an intelligent biological machine. Could you please help me with the query below? Question: The stomach produces gastric acid and pepsinogen among other enzymes etc. When a glass of water is taken without any food, wow would the stomach react to water? Assume...
  11. Rub3y

    Do oxides react react with a weak acid like phosphoric acid?

    I have an ash which is a mix of oxides (Cr2O3, CuO, ZnO, PbO, CdO, NiO, SiO2, MgO, CaO). I am adding phosphoric acid. But as a weak acid, will it react with oxides? If so, are these conversions 100% or more of a equillibrium (partial conversion). I you need more information, be sure to ask.
  12. Rub3y

    How do I find conversions for a reaction with phosphoric acid?

    I have a solid ash mix containing oxides(ZnO, NiO, MgO, Cr2O3, etc.) and salts (Na2SO4, K2SO4, apatite, etc.). I am supposed to write all of the reactions with phosphoric acid (should be between 1 and 2 mol/l) and put it in a simulation for mass and energy balances. But since phosphoric acid is...
  13. Y

    Milk + citric acid or pineapple juice formula? (chemistry)

    I have a chemistry project involving milk coagulation under certain circumstances. One of the circumstances is milk combined with citric acid or pineapple juice. I need to find the chemical formula of this reaction.
  14. samy4408

    Something that doesn't make sense to me about calculating the pH

    Hello , the problem that i refer to is present when we try to calculate the pH of a solution without any assumption. in a lecture entitled "calculating the pH of a strong acid/base solution " after adding a certain amount of HCl in water we are asked to calculate the pH (the amount of HCl and...
  15. B

    Extracting carbohydrates from food dissolved in hydrochloric acid

    I know that food is dissolved in hydrochloric acid in the stomach, and carbohydrates are eventually extracted for use in cellular respiration which if I understand correctly is essentially a complex combustion reaction, using oxygen and releasing CO2. Outside the stomach, I can partially...
  16. A

    Mono-esterify a mono-phosphate salt group to a carboxylic acid

    I am interested to see if anyone knows the easiest way to mono-esterify a mono-phosphate salt group to a carboxylic acid. How to facilitate the resultant -> product ? CH3COOH + NaH2PO4 ‐> C2H4NaO5P + H20
  17. SilverSoldier

    Approximations in Chemical Equilibrium (add a weak acid HA into pure water)

    Suppose we add a weak acid HA into pure water, so that upon addition its initial concentration is c. The following equilibria should establish in the system. $$\text{HA}+\text{H}_2\text{O}\rightleftharpoons\text{H}_3\text{O}^++\text{A}^-$$...
  18. C

    Anti-oxidants, uric acid, and evolution

    This might be a 'that's just how it is' sort of question, but are there any theories of how humans and higher apes have evolved so that they don't break down uric acid? All other animals break this down into allantoin, and fish go one further and break that down into ammonia. Did 'us apes' end...
  19. I

    Chemistry Vapor pressure of ethanoic acid vs. ethanol

    I think the answer is D because both molecules can hydrogen bond with their OH groups, but the C=O bond in ethanoic acid is polar and contributes to dipole-dipole interactions. The solution says B is the correct answer, because ethanoic acid molecules strongly hydrogen bond so that most...
  20. I

    Chemistry Citric acid polyprotic acid equilibria

    Using the first equilibrium, H3A <-> H2A- + H+, the [H+] is solved to be 0.01165 M ~ 1.1 * 10^-2 M. Using the second equilibrium, H2A- <-> HA2- + H+, the additional change in H+ is found to be 1.8 * 10^-5 M. The solution says that this second equilibrium is negligible, because 1.1 * 10^-2 M +...
  21. T

    What is the dissociation constant of acetic acid in water?

    The solubility product for water is 10 to the minus fourteenth power.(water forming hydronium ion and its complement). What is the solubility product of pure acetic acid forming HHOAC(+) and OAC(-) ?
  22. I

    Chemistry PKb of weak base titrated with strong acid

    What is true about the pK of the analyte? a) pKa = 9.2 b) pKb = 9.2 c) pKb = 4.8 d) pKa = 11.7 The halfway point is at point 4, at approximately pH=9.2. Therefore, the pOH = pKb = 4.8, and I think the answer is c). The solution says b) is the correct answer. Could anyone explain why, or whether...
  23. G

    Questions about muriatic acid and hypochlorite sodium

    is muriatic acid the same as hydrochloric acid? here in Brazil in markets it sells muriatic acid and disinfectant sodium hypochlorite active chlorine 2.5% if someone uses these two products if they are stopped for cleaning the bathroom when the bottles are open they evaporate it travels all...
  24. G

    Chemistry What is the correct way to do Acid Starch Hydrolysis?

    I have tried corn mill, now I am trying corn from a grocery store can. I tried 5% vinegar, now I am trying 40% hydrochloric acid. Heat to 150° F for 2 hours. Starch should turn to sugar but it is not working? I don't know how much acid to use to make this work? 1 lb corn + 2 lbs water +...
  25. Maruska

    Question: How to remove capric acid (caprate) from estrenes?

    Hello everyone, happy to have found this forum! My name is Maruska. I was wondering if anyone could give me ideas/suggestions on how, in general, to remove capric acid (caprate) from estrenes? Thanks for any help/suggestions.
  26. C

    Solubility of weak acid salts of aluminum and silver

    I'm curious what weak acids will form soluble salts with aluminum, but not silver. From a solubility chart (https://www.flinnsci.com/globalassets/flinn-scientific/all-product-images-rgb-jpegs/ap6901etc.jpg?v=cc7f986a028e4adf833ea6341200add2), HCl, HBr, and HI will form soluble aluminum salts...
  27. Nick tringali

    How to turn a weak acid into a strong acid

    so my question is how do I turn .1M HCL into a super strong acid like 10M or higher HCL. What is the highest M ever recorded for HCL? At what Molarity do I have to wear gloves and avoid skin contact?
  28. I

    Calculate Equilibrium Constant for Polyprotic Acid Reaction

    The principal equilibrium in a solution of NaHCO3 is HCO3-(aq) + HCO3-(aq) <-> H2CO3(aq) + CO32-(aq) Calculate the value of the equilibrium constant for this reaction. My solution: This overall reaction is the same as the sum of the following reactions: HCO3-(aq) <-> H2CO3(aq) + OH-(aq)...
  29. Justinboln

    Chemistry Calculating Concentration of Acid using a pH Titration Curve

    Use the equivalence volume from the pH curve to calculate the concentration of the acid, HA. I'm not sure which equation to use or how to approach this question (Attached). Please elaborate on the steps on how to answer the question. Thank you!
  30. L

    How to clean polymaliec acid deposits off the inside of a barrel

    Found a blue water barrel at a thrift store. It is empty, no order but it held belcline 200 aka polymaliec acid. The barrell will be used to hold food scraps, dirt to make compost. How do i clean the barrel? Water? Or should i try and find another barrel Thanks
  31. Physics lover

    Chemistry Conversion of Orthophosphoric acid to Pyro and Meta Phosphoric acid

    I know that both Pyro and Meta phosphoric acid exists in solid form.But the temperature mentioned here are more than melting points of both. So the acids will be obtained in liquid state.But the answer was given as b). I can't make out the reason.Please explain.
  32. H

    Can I combine an Acid dissociation with autoionization of H2O?

    The problem states that I'm adding a certain volume of a known [KOH] to a certain volume of a known [HCH3COO]. The goal is to calculate the final pH. Since I don't know the K value of the rxn of HA w/ OH-, I set up 2 equations and combined their K values to derive the K value. Since the new...
  33. P

    Chemistry Acidity of H2O vs H2S: Formal Charge vs Electronegativity

    I'm aware that the structure on the left is correct, but given that the formal charges are the same for each structure, I can't figure out why hydrogen is more likely to bond to the sulphur atom than it is to the nitrogen atom. Thank you for your help here!
  34. JorgeM

    What is the medium size of a Hydrochloric acid molecule?

    I was just thinking on the fact that there are some comercial gas masks . These ones have a filter, that doesn´´´'t let the Hydrochloric acid gas molecules to go into the mask. This is the way it basicly works, isn't it? So this filther has some little holes that are smaller than these...
  35. Kaushik

    Chemistry Finding the pH of this acid and its sodium salt solution

    For finding the pH of the acid, I made use of the equilibrium law (or the law of mass action) to arrive at the degree of dissociation which I later used to get the [H+] concentration. I am stuck in finding the pH of the salt solution. ##CH2ClOO^- + H2O <---> CHClOOH + OH^-## Could you please...
  36. H

    Zinc Chloride: The Lewis Acid with Electrophilic Properties

    Zinc chloride is Electrophilic and so acts as a Lewis acid.This characteristic is due to it's ability to accept electrons to it's 4 d orbital.My question is why it receives electrons to it's 4 d orbital when 4 p remain empty( according to Aufbau diagram)?Are there any other d block element...
  37. kelvin490

    Easy way to make carbonic acid from other chemicals

    Hi, everyone. I would like to test for the reaction between carbonic acid and copper (to simulate the effect of acid rain on copper). However, I find that many supplies failed to provide carbonic acid (either in powder or liquid form). Some says that carbonic acid is unstable and thus cannot...
  38. H

    Comparing a hydronium with a hydroxide in a weak acid solution (0.1M)

    This question says: An HA weak acid solution with a molarity of 0.1M is dissolved in water. In the new solution, is the molarity of OH- greater than the H3O+ molarity, or the opposite? Or are they equal? I came up with two possible answers: 1. [H3O+]>[OH-] because there are no hydroxides...
  39. Mr-Thirty

    Concentrations at equilibrium (strong base weak acid)

    So my professor covered acids and bases recently, and this is how he presented the method (please see attached word document). I believe its the same as the I.C.E method, though I am not sure. Anyways my problem is perhaps conceptual, but I don't understand why the concentrations at equilibrium...
  40. asca

    Ancient production of sulfuric acid

    Hi everydoby, the closest thread I found was this one, https://www.physicsforums.com/threads/production-of-sulfuric-acid.77077/, but I am not puzzled by and "missing oxygen". I'm trying to find a detailed description, or even better a video, where someone tries to replicate the process that we...
  41. J

    What is the molar heat of self-decomposition of nitric acid?

    I am curious as to what is the value of the molar heat of self-decomposition of nitric acid. I've searched online and cannot seem to find the above value. Essentially, I am looking for the value for anhydrous nitric acid although I am aware that the acid is generally not provided in pure...
  42. X

    B Exploring the Nature of H+ Ions: Acid or Plasma?

    If we heat up hydrogen gas in a sealed container to tens of thousands of degrees Celsius (via microwave or other radiation) , until the nucleus and electrons start to separate from each other, which becomes plasma. Then use a polarised magnetic field to separate the protons and electrons. Where...
  43. L

    How Volatile Are Hydrohalic Acids Like HCl and HF?

    HCl and HF are amongs Hydrohalic Acid group
  44. L

    Automotive Are some car glasses more resistant to acid rain?

    I have two cars, one an early 2000 Honda CRV and second one a 2016 Subaru Forester. The Subaru Forester is prone to acid rain marks in the windshield and side windows and rear. But the CRV didn't seem to have obvious acid rain after more than 14 years parked in open air. Are some glass more...
  45. K

    What is the equation for calculating [H3O+] in a salt of weak acid and base?

    Because of character limit I have exposed my question in the attached pdf
  46. TytoAlba95

    How many amino acid residues are there for the transmembrane domain?

    Total no. of amino acid in each transmembrane domain = 4 nm/ 0.15 nm +1 =27.66 Total no. of amino acids in 7 transmembrane domains = 27.66 x 7 = 193.62 ≈ 190 Hence option d. Is my approach correct?
  47. Tesla1963

    I How does high level radiation affect lead acid batteries?

    During episode 2 of the HBO miniseries “Chernobyl”, the search lights held by the three technicians entering the area beneath the reactor eventually go out from exposure to radiation. If the search lights were powered by lead acid batteries, how does radiation interfere with and/or hasten the...
  48. E

    What is the product of the reaction between ammonia and benzoic acid?

    Summary: I came across a question in my chemistry homework where i am supposed to write the balanced equation between ammonia and benzoic acid. I am not really good with chemistry but it's my last exam of chemistry ever in my high school experience, so i need to (and want to) get a good grade...