Journal 1/12/16

What do you think would happen if we were to put just a few drops of very strong acid into a swimming pool?

Objective Tonight’s HomeworkTo learn how to dilute and concentrate acids

Be prepared for the lab tomorrow

Acid Base ConcentrationLast time, we talked about how we measure the strength of an acid or base – the amount of H+ we have floating around.

While that’s useful to know, it’s not very practical. If I take sulfuric acid and put a few drops into the ocean, it’s hardly going to turn the whole ocean acidic.

We need to be able to talk about the concentration of an acid. Whether it’s dilute or concentrated.

Acid Base ConcentrationWe generally measure acid strength with something called “molarity”.

You’ll learn a lot more about this concept in chemistry, but for now, all you need to know is that molarity is a way of measuring how many H+’s we have for every liter of liquid.

Every acid and base has a natural molarity, which gives the pH’s we talked about yesterday, but we can add more water to any of these to dilute them.

Acid Base ConcentrationFor example, standard concentrated sulfuric acid is often listed as “10 M”. (means 10 molar). This is a way for scientists to know that it’s pure.

If we were to pour 1 liter of this acid into a container with 9 liters of water, we would be diluting our acid down to 1 M. With this label, scientists would know we’ve diluted our acid by a factor of 10, and made the pH higher by 1.

Acid Base ConcentrationIn summary, we can dilute or concentrate an acid or base by adding or removing more of the water.

Diluting an acid or base brings its pH closer to 7.

To go back to our warm up, adding a few drops of strong acid to a swimming pool would do pretty much nothing since we’re trying to spread a very small amount of acid over a very large amount of water.

Acid Base ConcentrationThere’s another way that we can make an acid or base harmless, though.

We can do this through something called neutralization. In neutralization, we combine an acid and a base of the same strength to try and get them to cancel each other out.

Acid Base ConcentrationExample:

We can take hydrochloric acid and add it to sodium hydroxide to make salt water.

HCl + NaOH Na+ + Cl- + H2O

In theory, you could drink this water and it would be salt water. However, this reaction doesn’t always work perfectly. There’s always a little HCl and NaOH floating around that didn’t cancel each other out.

Acid Base ConcentrationIn every neutralization reaction, we’re left with some pieces that could combine ionically. We call all of these pieces “salts”, even if they’re not made of NaCl, because they share similar properties to actual salt.

If we want to get that salt so we can use it, we need to evaporate the water after our reaction is done.

Exit Question

A bottle of acid has “8 M” written on the side. What does this tell us?

The concentration of the acidHow much the acid can burn skinWho manufactured the acidWhat kind of acid it isAll of the aboveNone of the above