How to Clean a Copper Radiator With Muriatic Acid

When I was designing and preparing my PC for my first loop, I discovered that cleaning a new radiator before you put it into your loop is a step which must be done.

I cleaned them by using the old staple method of using hot boiling water and shaking it around in my radiator. It did work as it got out a few chunks, but I was not satisfied with the results at all. I poked around a bit more and read about another method which uses a half vinegar/DI mixture. When I tested the vinegar rinse method I was not satisfied with the results at all as well.

That got me thinking. Seeing as I know (and hope you guys agree with me) that chemistry is amazing, I decided to nerd out and create a procedure to etch/clean all of the flux and other contaminates out of a newly purchased radiator. This method works MUCH better than a vinegar rinse.

Now lets begin....

Before we get into it lets break out our activity series. (If you remember this...then yes...you're actually going to use some of the "crap" you learned in CHEM101!)

As copper is lower than Hydrogen (H, the "eating" part of acid) on the activity series it will displace H2 when it is in presence of an acid. When you displace H2, active reactions tend to occur. This is why you are not supposed to wash aluminum radiators with an acid, as if you refer to the activity series it will displace H2 and create a non desirable active reaction.

So what's a good alternative to acetic acid which does a better job? We want something which falls under the following criteria:

Is fairly easy to find. Not everyone has access to lab grade reagents/chemicals.
The end product of this acid + copper reaction is soluble. (I'll get to this later)
Isn't super dangerous. Example: The badboy acid Sulfuric Acid which oxidizes and turns organic things black.

An acid which fits all 3 of those criteria quite well is Hydrochloric Acid or it's historical/consumer product name Muriatic Acid. Chemical formula: HCl

As HCl is used in many purposes, typically in home improvement/pool maintenance, it can be found quite easily at those stores. You may have to buy a gallon jug of it, but sometimes they sell in smaller amounts. Either way it's fairly cheap.
When copper is put in a HCl solution it reacts with the Cl ion in the solution. This creates CuCl or Copper Chloride. As most chlorides (including Copper Chloride of course) are very water soluble you're good to go!
Some people could say consumer grade (~10%) Muriatic Acid is dangerous...it can be. Just wear gloves and goggles when handling it and do not smell the vapors. Other than that just don't take a shower with it and you'll be fine.

Now...to decide what solution we are going to make for our wash. We do not want something super strong or something which is weak. So, I chose to have the wash at a pH of 2, which should get the job done just fine in a reasonable amount of time.

To calculate the pH of an acid, you first need to know if the acid is a strong or weak acid. As HCl on that list, it is a strong acid. To figure out the concentration of acid we need in moles/L or Molarity (M) is very easy:

C = 10^(-X)
Where X is the desired pH and C is the concentration calculated.

So, we need to make a 0.01M HCl solution (For you chemistry nuts .01N as HCl is monoprotic).

To make said solution, you can follow the calculations I used to make mine:

The concentrated HCl I had was listed at 38% HCl and has a density of 1.19g/mL as per this chart.

I need to get the molarity of the concentrated HCl:

38% of HCl means there is 380g of HCl by weight per 1000g (1000ml) of water.
If the water is 1.19g per mL and I have 1000mL, the total weight is 1190g.
1190g * .38 = 452.2g of HCl.
Whip out your periodic table! HCl has a molar mass of 36.5g (Hydrogen H is 1 and Chlorine Cl is 35.5)
Finally divide 452.2g/36.5g to get the molarity of HCl in your solution. The answer is 12.38M

Now we have the molarity of our HCl solution! Now we calculate how much we need in the end product, right? Nope. Who wants to measure out less an a mL of concentrated HCl? When making something with such a low concentration it is a good idea to make intermediate solutions, or stock solutions. So I decided on a 0.5M stock solution of HCl as my intermediate solution.

Now onto the stock solution creation. Remember this formula kids??

M1V1 = M2V2
(Molarity of the first solution * Volume needed = Desired molarity * volume of second container)

12.38M * X = 0.5M * 1000mL

When you solve X you get 40.38mL or ~40mL. So I put 40mL of that concentrated 38% HCl and filled it up with 960mL of DI water.

Now we are finally going to make our wash solution. To make our .01M solution we do the same thing as before with the M1V1 = M2V2 formula.

0.5M * X = 0.01M * 1000mL

When you solve for X you get 20mL. So put 20mL of that stock you made and fill the rest of it up with 980mL of DI water.

Anddddd you're done! If you read or went through all of that you get this sticker:

You only get that sticker if you did everything.

Phew...SCIENCE OVER

But where's the shortcut?! Fine fine...I'll give you one!

Now...you could just put in ~.8 mL or ~15-18 drops (from a small syringe or similar) of concentrated 12.38M HCl in a litre (1000mL) of water. Remember...readjust the number of drops to the concentrated HCl you have. There are about ~20 drops in a 1mL aqueous solution. Where's the fun in that though?!

Now it's time to put that solution into a rig which can flush the radiator...like below:

CAUTION: Do not run an acid solution in a radiator for more than ~2 hours (changes depending on the pH) Acid works fast! If you see the water turning a blueish-green color, then the acid is working. If you see copper participating out (which will happen) then you should stop immediately (If copper is collecting in your pump's reservoir then it's also collecting in your radiator). Once you are done remember to rinse +3 times with DI water to get the acid out.

Washing my radiators with the 0.01N HCl (pH of 2) solution I made