Nitric acid is a strong acid with the molecular formula HNO3. If you need to clean up a spill of this chemical, you should neutralise it with the acid neutraliser (typically sodium bicarbonate) in your lab and follow your lab's cleanup and safety guidelines. If you need to neutralise a solution of nitric acid, however, and bring it to neutral pH, you should titrate it with a burette. There are a variety of different bases you can use, although sodium hydroxide is probably the best for this purpose.
Put on your safety gear, including goggles, gloves and lab coat. Make sure your shoes are closed-toed. If the nitric acid is concentrated, this procedure should be performed under a fume hood for safety.
Add sodium hydroxide solution to your burette. Set the burette up on the ring stand and clamp so that its end is directly over the beaker.
Pour the nitric acid solution into the beaker and place it under the tip of the burette. Do not bash the bottom of the pH meter against the bottom of the beaker. Insert the calibrated pH meter into the solution.
Open the stopcock on the burette to allow a little sodium hydroxide to drip into the nitric acid. Keep the solution stirred using the stir bar and watch the pH on the pH meter.
Continue to add sodium hydroxide until the pH approaches 7. Remember that as you approach pH 7, the pH will begin to change much more rapidly -- the same amount of sodium hydroxide sufficient to increase pH by 0.1 point earlier on, for example, may now cause a 0.5-point increase. Adjust the amount of sodium hydroxide you add accordingly.
Stop once you reach pH 6.5 to 7.5. The solution is now neutral and can be poured down the drain.
Keeping the solution well-mixed will be much easier with a magnetic stir bar, but a glass stirring rod will work also. Either way, make sure you do not damage the pH meter while stirring your solution.
Nitric acid and sodium hydroxide are both highly corrosive, caustic and toxic. You will suffer serious harm if you bring either chemical in contact with your eyes or skin or if you swallow them. Make sure you are wearing safety gear and take all appropriate precautions. Remember, in a lab, safety is always the most important consideration.