This paper presents an experiment in which students determine the mass sensitivity of three crystal quartz resonators, designed to be carried out in "Physics Laboratory II" at the Institute of Experimental Physics, University of Wroclaw. The authors discuss the process of setting up the experiment and the results of the measurements. They clearly show that the set-up is simple, easy to assemble and allows obtaining satisfactory results. The advantages and the disadvantages of the apparatus are discussed along with the implementation into the teaching process. The results support the gathering of knowledge and skills necessary for experimental physicists. (Contains 4 figures and 2 tables.)