Purchasing the most diluted acid that suits your needs is highly recommended for safety and ease of use, but sometimes you may need to dilute it more at home. Do not reduce the budget for safety equipment, as concentrated acids can cause serious chemical burns. When calculating the amount of acid and water you should mix, you must know the molar concentration (M) of your acid and your desired molar concentration after dilution.
Step
Part 1 of 3: Calculating the Dilution Formula
Step 1. Check the things you already have
Look for the concentration of the acid solution on the label, or on the story problem you are working on. This number is often written in units of molarity, or molar concentration, abbreviated to M. For example, 6M acid contains six moles of acid molecules per liter. We call it concentration C1.
The formula below also uses the term V1. This is the volume of acid we will add to the water. That said, we probably won't be using a full bottle of acid, so we don't know the volume yet.
Step 2. Determine the final result
The desired concentration and volume of acid is usually determined by your schoolwork or by the requirements of the laboratory you work in. For example, we might want to dilute our acid to a concentration of 2M, and require 0.5 liters. We will refer to this desired concentration as C2 and the desired volume as V2.
- If you use unusual units, convert all units to molar concentration units (moles per liter) and liters, before you continue.
- If you are unsure of the amount or volume of acid required, consult your teacher, chemist, or specialist about assignments that will use acids.
Step 3. Write down the formula to calculate the dilution
Whenever you are ready to dilute a solution, you can use the formula C1V1 = C2V2. This means that the initial concentration of the solution x the initial volume = the concentration of the diluted solution x the volume of the dilution. We know this because concentration x volume = amount of acid, and the amount of acid stays the same as acid is added to water.
In our example, we can write this formula (6M)(V1)=(2M)(0, 5L).
Step 4. Solve the formula for V1.
This tribe, V1, will tell us how much of the initial acid solution we must add to the water to get the desired concentration and volume. Rearrange the formula to V1=(C2V2)/(C1), then enter the numbers you know.
In our example, we will get V1=((2M)(0, 5L))/(6M)=1/6 liter. It is about 0.167 liters or 167 milliliters.
Step 5. Calculate the amount of water you need
Now that you know V1, the amount of acid you will use, and V2, the amount of solution that will be produced, you can easily calculate the amount of water you need to reach the required volume. V2 - V1 = volume of water required.
In our case, we want to get 0.5 liters and will use 0.167 liters of acid. The amount of water we need = 0.5L – 0.167L = 0.333L or 333 milliliters
Part 2 of 3: Setting Up a Safe Workplace
Step 1. Read the online Chemical Safety Card
The International Chemical Safety Card provides concise and detailed safety information. Look up the exact name of the acid you're going to use, such as "hydrochloric acid," in online databases. Some acids may require additional safety precautions, in addition to those described above.
- Sometimes several cards are issued, depending on the concentration and addition of the acid. Choose the one that best fits your initial acid solution.
- If you want to read it in another language, select one here.
Step 2. Wear protective eyewear, gloves, and a lab coat
Protective goggles that cover all sides of the eye are required when working with acids. Protect your skin and clothing by wearing gloves and a lab coat or apron.
- Tie long hair before working with the acid.
- The acid can take several hours to perforate clothing. Even if you're not aware of a spill, a few drops of acid can damage your clothing if it's not protected by a lab coat.
Step 3. Work in fume hoods or areas with ventilation
Whenever possible, store the acid solution in a fume hood to use while you're working. This limits contact with the fumes of acid-generating gases, which can be corrosive or toxic. If you don't have a fume hood, open all windows and doors, and turn on the fan to air out the room.
Step 4. Know where the water is flowing
If the acid gets into your eyes or skin, you should wash it with cold running water for 15-20 minutes. Don't start diluting until you know a nearby eye wash or sink that can be used.
When washing your eyes, open your eyelids wide. Rotate your eyes looking up, right, down, and left to make sure all sides of your eyeball are rinsed
Step 5. Have a plan for handling the spill, which is specific to your acid
You can purchase an acid spill treatment kit, which contains all the ingredients needed, or purchase a neutralizer and absorber separately. The process described here can be used for hydrochloric, sulfide, nitric, or phosphoric acids, but other acids may require further research to be cleaned properly:
- Exchange indoor air by opening windows and doors, and activating fume hood ventilation and turning on fans.
- Use a weak base such as sodium carbonate (soda ash), sodium bicarbonate, or calcium carbonate on the outside of the spill, avoiding splashing.
- Continue to use the base slowly, working from the outside in, until the spill is covered.
- Mix thoroughly with plastic utensils. Check the pH of the spill with litmus paper. Add more base if needed to get a pH between 6 and 8, then flush the spill with plenty of water.
Part 3 of 3: Diluting the Acid
Step 1. Cool the water in an ice bath while using concentrated acid
This step is only necessary if you will be working with a highly concentrated acid solution, such as 18M sulfuric acid, or 12M hydrochloric acid. Cool the water you will be using by placing it in a container surrounded by water for at least 20 minutes before starting the dilution.
For most dilutions, water can be kept at room temperature
Step 2. Add distilled water to the large pumpkin
For projects that involve precise measurements, such as titrations, use a volumetric flask. For most practical purposes, an Erlenmeyer flask can be used. In either case, choose a container that can easily hold the volume you want, with plenty of space left, to minimize spills at the edges.
You don't need to measure this water precisely, as long as it comes from a container that is properly measured to hold the total required water
Step 3. Add a little acid
If using a small amount of acid, use a measuring pipette (Mohr) with a rubber head on top. For a larger volume, place the funnel against the neck of the flask, and slowly pour in a little acid using a measuring cylinder.
Never use a mouth dropper in a chemistry laboratory
Step 4. Allow the solution to cool
Strong acids can accumulate a lot of heat when added to water. If the acid is very concentrated, the solution may splash or produce corrosive fumes. If this is the case, you will need to do the entire dilution in very small doses, or cool the water in an ice bath before you proceed.
Step 5. Add the remaining acid in small doses
Allow time for the solution to cool for each dose, especially if you notice heat, smoke, or splashes. Continue until the required amount of acid has been added.
This number is calculated as V1, like above.
Step 6. Stir the solution
For best results, you can stir the solution with a glass stir bar after each addition of acid. If the size of the flask makes mixing impractical, stir the solution after dilution is complete and the funnel is removed.
Step 7. Save the acid and rinse the equipment
Pour your acid solution into a clearly labeled container, preferably in a PVC coated glass bottle, and store it in a safe place. Rinse the flask, funnel, stirring rod, pipette, and/or measuring cylinder in water to remove any residual acid.
Tips
- Always add acid to water, not the other way around. When the two substances meet, they will produce quite a lot of heat. The more water used, the more heat must be absorbed, to prevent boiling and splashing.
- As a reminder aid to remember the correct sequence: 'do what must be done, add acid to the water'. Alternatively, you can also remember STAS: "Always Add Acid."
- When mixing two acids, always add the stronger acid to the weaker acid, for the reasons described above.
- You can add half the water as needed, dilute completely, then slowly mix in the rest of the water. This method is not recommended for concentrated solutions.
- Purchase the most dilute acid that suits your needs, for maximum safety and ease of storage.
Warning
- Even if the effects of the acid are not very strong, the acid may still be toxic. An example is the acid hydrogen cyanide (not very strong, very toxic).
- Never handle the effects of an acid spill with a strong alkaline solution, such as KOH or NaOH. Use water or a weak base such as dilute sodium hydrogen carbonate (NaHCO3).
- Don't dissolve ingredients for fun or any other reason, unless you know exactly what you're doing. In this way, you may manufacture highly hazardous products such as toxic or explosive gases or explosives that explode immediately.
- So-called 'weak' acids can also generate a lot of heat and are very dangerous. The difference between weak and strong acids is only in chemical terms.
