When testing the pH of a solution, which method should be used with pH or litmus paper?

The most appropriate method when testing the pH of a solution with litmus or pH paper is to dip a stirring rod into the solution and then touch the rod to the pH paper. This technique ensures that the paper only comes into contact with a small amount of the liquid. It is important because adding pH paper directly into the solution (as suggested in another choice) can lead to contamination or improper readings if the paper absorbs too much of the solution.

Moreover, using a stirring rod allows for better control and avoids the risk of losing the integrity of the pH paper through excessive wetting or interaction with the solution. The rod can be removed and then gently used with the pH paper for a clear readout. This method is particularly useful when dealing with limited volumes of solution or when ensuring that the pH paper remains intact for accurate measurement.

While a digital pH meter is another reliable option to measure pH, it represents a different approach that may require calibration and training. Temperature measurement, while relevant for some applications in pH measurement, is not a method for assessing the pH itself and does not contribute directly to the process of using litmus or pH paper.