What can I do with leftover muriatic acid?

Muriatic acid, also known as hydrochloric acid, is a common household chemical with a variety of uses, from cleaning concrete to adjusting pH levels in pools. Leftover muriatic acid should never be poured down the drain, as it can damage pipes and sewer systems. Instead, there are several safe and effective ways to use up extra muriatic acid. This article will provide tips on storing, neutralizing, and repurposing surplus muriatic acid. With some creativity and care, that leftover bottle doesn’t have to go to waste!

How to Properly Store Muriatic Acid

Before discussing how to use leftover muriatic acid, it’s important to know how to store it properly. Here are some tips:

  • Keep it in the original container. Don’t transfer it to containers not intended for corrosive chemicals.
  • Tightly seal the cap. Evaporation can concentrate the acid over time.
  • Store in a cool, dry place away from direct sunlight and heat sources.
  • Keep it up high and out of reach of children and pets.
  • Never store near bases or oxidizing agents that could have a dangerous reaction.

Proper storage keeps muriatic acid from degrading and contains fumes. Always check the bottle for wear before using old acid, as containers can degrade over time. Dispose of the acid if the bottle is compromised.

How to Neutralize Muriatic Acid

One option for dealing with excess muriatic acid is to neutralize it. When carefully diluted and mixed with a base, the acid and base cancel each other out, creating a neutral saltwater solution. Here’s how to do it:

  1. Work outdoors in a well-ventilated area. Wear gloves, eye protection, and closed toe shoes.
  2. Dilute the acid by slowly adding small amounts to water. Use 5 parts water to 1 part acid.
  3. Add baking soda to the diluted acid. The baking soda is a base that will react with the acidic muriatic acid.
  4. Slowly stir until fizzing stops. The solution is neutralized when it measures between 6-8 pH.
  5. Pour the neutralized saltwater waste down an exterior drain. Rinse area thoroughly with water.

Go slowly to avoid splashes or boiling over. Neutralization creates salt, water, and carbon dioxide gas. Done correctly, this makes muriatic acid safe for disposal.

How to Use Muriatic Acid for Cleaning

Cleaning is one of the most common uses for muriatic acid. With proper safety precautions, leftover acid can be applied to:

  • Clean mineral deposits from drains or toilet bowls. Pour about 1/2 cup down the drain, let sit 15 minutes, then flush with hot water.
  • Remove soap scum and hard water stains from tubs, sinks or showers. Apply diluted acid to stains, let sit 5-10 minutes, then rinse.
  • Clean concrete driveways and sidewalks. Wet the concrete and apply diluted acid, scrubbing with a broom. Rinse thoroughly.
  • Clean bricks and etch concrete before painting. Wear gloves and eye protection when applying.
  • Clean rust stains from tools or equipment. Soak the rusted item in a diluted acid bath.
  • Clean coffee and tea stains from cups. Fill cup with diluted acid and let sit for 5 minutes before rinsing.

Always dilute the acid, work in a ventilated area, and rinse surfaces completely after application. Be cautious using around metal, as the acid can damage some materials.

How to Adjust pH with Muriatic Acid

Another popular use for muriatic acid is lowering pH in swimming pools and spas. Here are some tips for getting the chemistry right:

  • Test water frequently. Use test strips or a testing kit to determine existing pH and alkalinity levels.
  • Determine how much you need to lower pH. Consult your pool chemical supplier for guidance specific to your volume of water.
  • Dilute acid in a bucket before adding to pool water. Never add acid directly from the bottle.
  • Pour diluted acid into areas of high water flow for proper mixing and dispersion.
  • Retest pH after 4-6 hours. Additional acid may be needed to reach desired levels between 7.2 and 7.6 pH.

Muriatic acid quickly brings down pH levels in pools. But use proper safety precautions, start with small amounts, and retest frequently.

How to Make Hydrogen Chloride Gas

With some basic chemistry supplies, leftover muriatic acid can be used to make hydrogen chloride gas. Here’s a home science project to try:

  1. Gather supplies – muriatic acid, crushing spoon, glass jar, food coloring, balloon.
  2. Pour 1 tablespoon muriatic acid into the glass jar.
  3. Add 3-5 drops of food coloring to visually see gas formation.
  4. Use the spoon to crush and add 1 antacid tablet to the jar. Stand back!
  5. Hydrogen chloride gas immediately forms, blowing up the balloon.
  6. Tie off balloon when full and discard the spent reaction mixture in the jar.

The chemical reaction between the acid and base produces hydrogen chloride gas. This project demonstrates the reactive nature of muriatic acid and should only be done with adult supervision.

How to Dispose of Muriatic Acid

While the above projects repurpose extra acid, you may eventually need to dispose of it. Here are some proper disposal methods:

  • Allow microorganisms to break acid down over time. This takes 6 months to a year in optimal conditions.
  • Dilute acid 10:1 with water and use up as described for cleaning.
  • Neutralize acid with baking soda as outlined previously.
  • Check for hazardous waste collection days in your community. These are supervised locations to dispose of chemicals.
  • Contact local waste management authorities regarding business disposal services.

Never pour concentrated muriatic acid down drains or on the ground. Always use up, dilute, neutralize, or seek proper disposal help when dealing with hazardous leftover chemicals.

Safety Tips When Working with Muriatic Acid

When handling muriatic acid for any purpose, follow these important safety guidelines:

  • Wear protective equipment – gloves, eye protection, closed toe shoes, and face shield.
  • Work in well-ventilated outdoor areas when possible.
  • Pour acids by rolling the bottle to avoid splashing.
  • Add acid to water when diluting, not the reverse.
  • Never use hot water, as it can cause acid to splash.
  • Store acid safely away from other chemicals and child access.
  • Have a supply of baking soda on hand to immediately neutralize any spills.
  • If skin contacts acid, flush area with running water for 15 minutes.

Muriatic acid can cause severe burns and injury if improperly handled. Always put safety first and proceed cautiously when working with this caustic chemical.


Leftover muriatic acid has many applications if handled carefully. From cleaning to adjusting swimming pool pH, surplus acid can be put to good use instead of being disposed of improperly. Always take steps to neutralize and dilute excess acid before disposal. And adhere to basic safety protocols like wearing gloves and eye protection when working with muriatic acid. With some informed planning, that leftover bottle can be efficiently repurposed instead of wasted.

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