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How do I recognize a strong acid?

October 8, 2016

 

You are doing acids/bases problems. You see a formula and wonder: How do I know if this is an acid and if it's strong or weak?

 

Fear no more, Transformation Tutoring is to the rescue with great chemistry tips and tricks!

Let's begin by figuring out what is an acid. Then we will see the difference between strong and weak acids.

 

There are 2 basic definitions of acids. According to Arrhenius theory, acid gives off Hydrogen ions (H+, also called protons) when dissolved in water. Bronsted-Lowry defined acid to be a proton donor ( pretty much same thing but without the need for water).

So what do acids do? Willingly give off their H's in the form of H+ ions (hydrogen ions also called protons).

 

A strong acid dissociates completely. If we take 5 moles of HCl and put it into water, it will break down completely to give 5moles of H+ ions and 5 moles of Cl- ions. A weak acid holds on to its proton more and is not as willing to give it up. So only a small part of it will dissociate.

 

Finally how do i know if my acid is strong? All you need to do is memorize all the strong acids. There are only 7 of them! Here is the list: HI, HCl, HBr, HNO3, HClO4, HClO3, H2SO4.

If you have an acid, and it's not one of these, it's not strong!

 

How do you know if you have an acid to begin with? Look out for H in front of the formula such as HF, or anything that has COOH in the formula (this is a weak organic acid).

 

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