## OH and H3O

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kanikubari
Posts: 30
Joined: Fri Dec 07, 2018 12:18 am

### OH and H3O

So is the general rule of thumb is that OH- and H3O+ determines whether it's an acid or base? Is there any other way of telling? Also how do you know if it's a strong acid or weak and same goes for base?

jessicahe4Elavelle
Posts: 61
Joined: Fri Sep 28, 2018 12:27 am
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### Re: OH and H3O

To distinguish weak acids from strong acids you should just essentially memorize the list of strong acids (they are 7 in total HCl - hydrochloric acid, HNO3 - nitric acid, H2SO4 - sulfuric acid, HBr - hydrobromic acid, HI - hydroiodic acid, HClO4 - perchloric acid and HClO3 - chloric acid). The strong bases instead always have an -OH

404975170
Posts: 68
Joined: Thu Jul 27, 2017 3:00 am

### Re: OH and H3O

When looking at a recation, if the number of hydrogens has decreased when going from reactants to products then the substance is an acid (donates hydrogen ions). If the number of hydrogens increases from reactants to products then that substance is the base (accepts hydrogen ions).

Posts: 64
Joined: Fri Sep 28, 2018 12:27 am

### Re: OH and H3O

When you have an acid reacting with water, you'll result in H3O+ because the atom donates an H to water. With bases, you'll get OH- because that atom will take an H from water.

Neil Hsu 2A
Posts: 61
Joined: Fri Sep 28, 2018 12:16 am

### Re: OH and H3O

There are many ways to determine if something is acidic or basic. One way is definitely to write out its reaction with water and see if it creates H3O+ or OH-. Another way can be to look at its Ka or Kb. The larger the Ka, the stronger the acid; the larger the Kb, the stronger the base. On the flip side, the smaller the pKa, the stronger the acid; the smaller the pKb, the stronger the base. For strong acids and bases, I suggest just memorizing them. Strong Acids: HCl, HI, HBr, HNO3, H2SO4, HClO4, HClO3. Strong Bases: Group 1 and 2 oxides and hydroxides.

Tony Chung 2I
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Joined: Fri Sep 28, 2018 12:19 am

### Re: OH and H3O

You should also memorize the strong acids and bases that we had to use in 14A

Sarah Fatkin 4I
Posts: 71
Joined: Fri Sep 28, 2018 12:27 am

### Re: OH and H3O

Yes, OH- and H3O+ do indicate whether something is an acid or a base. This is because OH- is formed when bases are combined with water and H3O+ is formed when acids are combined with water. It might be helpful to draw out the lewis structures of these reactions so that you can visualize the proton donors / acceptors.

Vana Mirzakhani 3I
Posts: 62
Joined: Fri Sep 28, 2018 12:24 am

### Re: OH and H3O

Simply put, anything with OH- is a base and anything with H30+ or H+ is an acid.

yuetao4k
Posts: 60
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### Re: OH and H3O

You can calculate pH and pOH from [H30+] and [OH-] respectively by taking the negative log of the concentrations. This will indicate if the chemical compound is an acid or base.

David Effio 1H
Posts: 38
Joined: Wed Feb 14, 2018 3:01 am

### Re: OH and H3O

Calculating the pH and pOH from their concentrations is the easiest way to tell if an acid or base is strong or weak. pH of around 1 or lower is usually a strong acid, while 13 or higher is a strong base. Memorizing the list of the most common strong acids is a great plan too.
It's also worth noting that some acids are polyprotic, and this brings forth different pKa and pkB values. It's also a good idea to memorize the general properties of strong acids or bases, as well as weak acids or bases.

jocelyntzeng
Posts: 59
Joined: Fri Sep 28, 2018 12:18 am

### Re: OH and H3O

from OH and H3O concentrations you can determine which one is in excess and that determines if it is a acid or base

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