Can anyone explain acids and bases to me like I'm an idiot?

[MrsWhattery]

Hi all, posting in Education in the hope of finding some chemistry teachers/experts.

For reasons too dull/potentially outing to go into here I need to understand, and be able to explain, acids and bases, and I have tried using books and google to no avail. I'm scientifically minded and understand most things but I cannot get it. If anyone can answer my questions I would be eternally grateful!

What is confusing me is it seems to have something to do with water. So an acid for example is in water and can be more or less strong, and/or more or less dilute.

So what is an acid, is it a chemical compound (like a salt) or it is some kind of mixture with water (like a salt solution)? If I buy citric acid powder in solid form, is that an acid - and/or how is it different if I add water?

If anyone can simply explain the hydrogen ion aspect too, and why acids and bases are "opposites", but are also somehow on a spectrum, please do!

TIA. It's driving me mad.

That's because I edited and added a bigger chunk.

I then cross-posted a link.

From my brief glance at your other posts, I think you are making it more complicated than it is.

Water is pH neutral. (pH7)
'Table salt' is neutral, but Sodium is a base (alkaline, pH>7), and Chlorine an acid. (pH<7)
Salt in water is a solution (again pH 7).

'Citric acid' is acid. Adding it to water, you get a weak citric acid.
Don't try it but Citric acid has a sour taste. It's naturally in lemons.

Citric acid is made of Carbon, Oxygen and Hydrogen atoms.

For the purpose of what you asked, ignore the Citric acid - that's 'Organic Chemistry' - put simply 'Chemistry based on atoms with Carbon (and Oxygen and Hydrogen) in them'

@FrogTaker , I might well not be right, but OP wanted a simplified version.

I think what I want is simple language, but to understand the reality of what happens. Some of "Frogtaker's* post was too technical for me but it also helped me grasp the atomic processes.

Water is pH neutral. (pH7)
'Table salt' is neutral, but Sodium is a base (alkaline, pH>7), and Chlorine an acid. (pH<7)
Salt in water is a solution (again pH 7).

So an element can be an acid or a base? Is that right?

Some are inert. Only those that have acidic or basic properties are acids or bases.

• Elemental Form vs. Compound Form: Elements like sodium (Na) and chlorine (Cl) are neither acidic nor basic in their elemental form. It’s only when they form compounds (like NaOH or HCl) and interact with water that they exhibit acidic or basic properties.
• pH of Solutions: The pH of a solution is determined by the presence of acidic or basic compounds in water, not by the elements themselves in isolation.

In summary, while elements can form compounds that are acidic or basic, the elements themselves are not classified as acids or bases. Sodium and chlorine in their elemental forms are reactive substances that, when combined with other elements (especially with water), can produce acidic or basic compounds, which in turn influence the pH of solutions.

Thanks. It's actually oddly reassuring that some of the answers don't fully agree! But the thread is really helping and I'm getting there.

Yes. That describes it more clearly.

Sodium itself isn't alkaline. Sodium Hydroxide (NaOH) is.
Chlorine itself isn't acidic. Hydrochloric Acid (HCl) is.

I think you need a proper primer.

---

I'd stick to concentrating on why atoms form acids and bases.

The way water atoms bond is slightly different.
Organic Chemistry is fascinating, but Carbon atoms have special properties.
Chemistry is amazing.
I'm just someone with an interest.

Shall I investigate the properties of C2H6O this evening?

I think you need a proper primer.

There are countless primers, chemistry for dummies, study guides and chemistry for kids explainers online, plus lots of books, and I've read loads of them - but they all seem to leave out the nitty gritty of what's actually happening and what the role of water is.

I know you’ve had a lot of replies already but I’m having a go too…

pH is a measure of the concentration of hydrogen ions.

It’s on a logarithmic scale which makes it complicated but basically acids are substances that release hydrogen ions in aqueous solution. So the water is necessary for it to exhibit its qualities, but not for it to actually be an acid (so you can have e.g. citric acid crystals).

If almost all the H ions dissociate in water (eg in HCl) it’s a strong acid with a pH around 1. fewer H ions dissociate in water it’s a weaker acid (e.g. vinegar). If you put a base in water it reacts with H ions and reduces the concentration and therefore increases the pH.

If you use more water it becomes more dilute but doesn’t change the strong or weak characteristics of the acid.

Did you hear about the atom who went into a police station and said "I've lost an electron"

The desk sergeant said "are you sure?"

The atom said "yes, I'm positive".

(Off the point of the thread)

@HappiestSleeping , was he charged?

YoureTheTop

No the police officer just said "You want to keep an ion that"

fairlygoodmother

Thanks v much that's really useful too.

No, but a flat battery was taken into custody and charged.

Simple definition is that an acid is a substance that readily donates an H+ ion and a base is a substance that readily donates an OH- ion.

In the case of your citric acid, in powder form it is not an acid (by this definition) however as soon as you dissolve it in water, the weak H-O bonds split and it donates three H+ ions.

The weaker the bond, the stronger the acid - so HCl is a very strong acid as it so easily donates its H+.

Understanding pH Levels
Introduction to pH:

• pH stands for "potential of Hydrogen" and is a scale used to measure the acidity or alkalinity of a solution.
• The pH scale ranges from 0 to 14, with 7 being neutral. A pH below 7 indicates acidity, while a pH above 7 indicates alkalinity.
• The scale is logarithmic, meaning each whole number on the scale represents a tenfold difference in hydrogen ion concentration. For example, a pH of 6 is ten times more acidic than a pH of 7.

The Role of Water in pH:

• Water (H₂O) is a critical factor in the pH of a solution. It dissociates into hydrogen ions (H⁺) and hydroxide ions (OH⁻).
• In pure water, the concentration of H⁺ and OH⁻ is equal, which results in a neutral pH of 7.
• The pH of a solution is determined by the relative concentrations of H⁺ and OH⁻ ions. If a substance is added to water that increases the concentration of H⁺ ions, the pH decreases, making the solution more acidic. Conversely, if a substance increases the OH⁻ concentration, the pH increases, making the solution more alkaline.

The basics of pH
Water's Dissociation Constant (Kw):

• Water constantly undergoes self-ionization, where a small fraction of water molecules dissociate into H⁺ and OH⁻ ions. This is represented by the dissociation constant of water, Kw, which is 1.0 x 10⁻¹⁴ at 25°C.
• Kw = [H⁺][OH⁻]
• Since pure water has equal concentrations of H⁺ and OH⁻, [H⁺] = [OH⁻] = 1.0 x 10⁻⁷ M, resulting in a pH of 7.

Buffer Solutions and Water's Role:

• Buffer solutions resist changes in pH when small amounts of acid or base are added. This is crucial in biological systems where enzymes require a specific pH to function.
• Water acts as the solvent in buffer solutions, facilitating the equilibrium between weak acids and their conjugate bases (or weak bases and their conjugate acids).

Water as a Medium for Acid-Base Reactions:

• In any solution, water serves as a medium where acids and bases dissociate, leading to changes in pH. For instance, when hydrochloric acid (HCl) is added to water, it dissociates completely into H⁺ and Cl⁻ ions, significantly lowering the pH.
• Similarly, when a base like sodium hydroxide (NaOH) is added, it dissociates into Na⁺ and OH⁻ ions, increasing the pH.

Water plays a fundamental role in determining the pH of a solution due to its ability to dissociate into H⁺ and OH⁻ ions. The balance of these ions in water influences whether a solution is acidic, neutral, or alkaline. Understanding the dissociation constant of water and its role as a solvent provides deeper insight into how pH is regulated and why water is essential in acid-base chemistry.

I think when you're asking about the role of water you're asking about why things only have pH in water?

Though the oxygens and hydrogens in water are covalently bonded, the electrons in that bond are more attracted to the oxygen than the hydrogen, meaning that the oxygen is 'slightly negative' and the hydrogens are 'slightly positive'.

This means that ionic compounds like acids, alkalis, and salts, dissolve easily. What's happening is that the negative ions are attracted to the slightly positive hydrogen 'end' of the water molecule, while the positive ions are attracted to the slightly negative oxygen 'end', so they split up. For an acid, this releases H+ ions, which decreases pH (more H+ means lower pH). For an alkali, it releases OH-, which acts to remove some of the H+ already present from the dissociation of water, increasing the pH (and making more water)

Water is neutral because it dissociates just enough to have the right amount of H+ to be pH 7, anything that changes that changes the pH.

Strong acids like HCl 'fully dissociate' meaning all the H+ and all the Cl- split up, weak acids like citric acid 'partially dissociate' so not all the possible H+ is released, so they will have a lower pH at the same concentration when compared to a strong acid.

A base is anything that reacts with an acid to neutralise it, an alkali is a base that dissolves in water to give a pH greater than 7.

I skim read so apologies is I'm repeating pps.
I've pitched at GCSE level, happy to go deeper if required, some of this is not technically 'correct' once you do.

Well if you put sodium chloride (common salt or table salt) into water then the sodium cations and chloride anions will separate off as the thing dissolves into water. Well at least some of them.

But the addition of these ions to the water does not change the concentration of H+ or OH-.

It is interesting to note that in strong salt solutions the sodium cations and chloride anions attract each other and start to associate with each other. One of my academic interests is the chemistry of very strong salt solutions.

Sorry but water while common is not unique in terms of acid / base chemistry. You can have acid base chemistry in liquid ammonia.

I used to years ago work in 5 L flasks with about 3 L of liquid ammonia in each one. I used to make a base KNH2 which is formed by deprotonation of ammonia. I would at the end of the chemistry stop all the base chemistry by adding ammonium chloride (NH4+ Cl-) to the reaction mixture.

In liquid ammonia you have

2NH3 going to NH2- and NH4+

Equally if you mix nitric and sulfuric acids, the sulfuric acid transfers protons to the nitric acid.

H2SO4 plus HNO3 makes HSO4- and H2NO3+

The Fairlygoodmother looks like she has got things correct