Nitric acid is a type of powerful mineral acid that is used to create products such as fertilizers, dyes, and strong explosives. Caustic and colorless liquid is typically produced on an industrial scale using highly specialized chemical processes and equipment. However, you can also prepare nitric acid with different levels of purity using common laboratory materials, such as nitrate salts, sulfuric acid, and copper. Some of the substances needed for this experiment are corrosive, so you must wear the appropriate safety gear before holding them. You can also review laboratory safety procedures to be prepared in the event of an accident.
Steps
Method 1 of 2: Getting Nitric Acid from Copper
Step 1. Dissolve 3 oz (80 g) of nitrate salt in 2 oz (50 ml) of water
First add the nitrate salt to a small glass container. Then pour all the water in one go. Whisk the mixture in the bowl so it dissolves faster.
- It is important that you use distilled water instead of ordinary tap water. Tap water typically contains residues of other chemicals that can ruin the composition of the acid you produce.
- For this experiment, the easiest thing to do is use sodium, potassium, or ammonium nitrate. All of these chemicals are available at all online chemical supply stores.
- Some of these stores will only sell to institutions, not private individuals. This could make it difficult for you to get the ones you need, unless a teacher or supervisor buys them on your behalf.
Step 2. Add 100 ml (3.5 oz) of hydrochloric acid
Measure the acid into a graduated cylinder to ensure that you are using the correct amount. Transfer the acid to the nitrate salt solution carefully, avoiding spilling or splattering. Shake the contents of the container again to mix the chemicals.
- You can buy a container of concentrated hydrochloric acid for about $ 1 for every 1 oz (30 ml).
- It is a good idea to work under an exhaust hood or to place the equipment in a ventilated open area, as the test materials will emit strong gases when they come into contact with acid.
Warning:
always wear gloves and safety glasses when working with acids. Hydrochloric acid in particular is very corrosive. If you don't use proper protection, even a small drop on your skin could cause severe burns.
Step 3. Fill a second larger container with 2 oz (50 ml) of water
Pour in enough water to cover the bottom of the second container. You will be placing the mixing container inside it to prevent it from spilling or overflowing, so make sure it is large enough to comfortably hold the test materials.
- Ideally, the second container should also be slightly taller than the first.
- If you are using a 250 ml beaker to prepare the mixture, you could place it in a 1000 ml beaker to leave enough space.
Step 4. Place the mixing bowl in the bottom of the large bowl
Place the mixing bowl in the shallow water. Make sure that at least 1/4 inch (0.5 cm) of water is still exposed on all sides of the mixing container. Otherwise, get a bigger one.
Step 5. Add at least 32 g (1 oz) of copper to the acid mixture
If possible, use 99% pure laboratory copper granules. Weigh them on a precision scale in a lightweight container, making sure to weigh the container only first and subtract the weight from the final reading. When you have a minimum of 1 oz (32 g), put the copper in the mixing bowl.
- If you can't find copper granules, you can also use copper in small pieces, shavings, wire, or even coins. However, keep in mind that the acid mixture will mostly dissolve the copper, so you will lose it.
- Copper is necessary to start the oxidation reaction that will produce nitric acid.
Step 6. Cover the mixing bowl with another bowl and wait about an hour
The third container will retain the nitrogen dioxide generated as the copper dissolves in the acid mixture. The gas will come out of the mixing container and rise through the water, forming bubbles in the container that contains it, producing nitric acid.
- A beaker one or two sizes larger will fit perfectly over the one with the mixture. You could also use a jar or other beverage container, as long as it is made of glass.
- It may help to place a small heavy object (such as a book or a piece of wood) on the cover container to secure it and prevent it from moving when the escaping gas propels it upward.
- The nitric acid that you produce with this method will only be 40-60% pure. To make one of higher purity, you will have to distill it using nitrate salts and sulfuric acid.
Method 2 of 2: Distill Pure Nitric Acid
Step 1. Measure 3 oz (80 g) of pure potassium nitrate into a flask
The mixture of potassium nitrate and sulfuric acid usually produces nitric acid with the highest degree of purity. Use a precision balance to measure the exact amount of nitrate salt. Remember to take into account the weight of the measuring container.
- You have to use a round bottom flask for this experiment. The curved surface and reduced neck of the flask will prevent evaporated nitric acid from escaping during the distillation process.
- You can also use sodium or ammonium nitrate if you have it on hand, but the purity of the resulting acid could be much lower.
Step 2. Add 60 to 65 ml (2 to 2.2 oz) of concentrated sulfuric acid
Pour the acid into the flask using a plastic funnel. If you don't have one on hand, you can also use an instrument with a dropper, as long as it has precise increments marked for measuring liquids.
- Work under a range hood or in a ventilated outdoor space, and put on gloves and safety glasses before holding any of the necessary chemicals.
- The purer the acid, the better. Using sulfuric acid diluted with water will produce a weaker nitric acid.
Tip:
If you accidentally come into direct contact with acid, wash the affected area with cold water for a minimum of 15 to 20 minutes.
Step 3. Prepare an empty glass container and condenser for distillation
Insert a glass-stoppered distillation head into the mouth of the flask. Connect the slanted stem of the head with a condenser tube. Place the bottom end of the condenser into the opening of the empty container.
- You can get a basic distillation kit (with everything you need to do your own chemical distillations at home) at any chemical supply store.
- Recheck that the stoppers on the distillation apparatus are secure. Otherwise, harmful gases may leak!
Step 4. Heat the acid mixture for one hour
Light a lighter or hot plate, sit back and watch the magic happen. As the acid mixture heats up, the nitrate salt and sulfuric acid will react and produce bisulfate and liquid nitric acid. The nitric acid will evaporate and go to the condenser, where it will cool and form small droplets that will slowly drain into the empty container.
- If you have a thermometer, place it on top of the distillation head and keep an eye on it while the acid mixture is on the heat source. The temperature inside the flask will fluctuate a bit, but ideally it should stay around the boiling point of the acid (337 ° C or 639 ° F).
- You may notice that concentrated nitric acid develops a yellow hue as it builds up. This is a normal side effect of hydrogen dioxide contamination. The acid will remain pure enough to use for various purposes.
Step 5. Air the nitric acid to test its purity
Take a rubber tube or plastic straw, and place one end inside the mouth of the flask. Blow gently on the other end. As you blow, watch for the acid to give off thin, pale yellow gases. A considerable amount of gases will only arise if the nitric acid is more than 80% pure. Due to this unique effect, acid with a high purity is sometimes referred to as a "fuming".
- Be very careful not to inhale the gases. This could cause severe irritation to your airways.
- If you are wearing latex or nitrile gloves, remove them before testing for acid. This might seem counterproductive to you, but pure nitric acid can set latex and nitrile on fire!
Advice
- Always have a first aid kit on hand in the work area, in case of an unexpected mishap.
- Nitric acid is useful for starting chemical reactions and producing many other chemical compounds in a laboratory.
- Copper is not cheap, especially if you are going to melt it. Recycle it by adding small pieces of aluminum foil to the liquid copper residue, and straining it through a paper towel once it dissolves. The leftover solid pieces will have low purity, and you can use them for other experiments.
Warnings
- Some of the procedures outlined in this article can be dangerous if not performed responsibly. For this reason, they are best used only by experienced chemists and laboratory personnel. If this is your first time doing a chemistry experiment, consider doing a simpler project, like changing the pH of the water or neutralizing the citric acid.
- Seek immediate medical attention if you notice any burning, swelling, itching, or irritation as a result of exposure to the chemicals. If left untreated, chemical burns can lead to more serious symptoms, including shock.