The efficient transportation of liquids by unmanned aerial vehicles (UAVs) is of utmost importance in various autonomous missions, including firefighting and field spraying. Nevertheless, liquid sloshing during transportation can lead to undesirable effects such as instability, unwanted forces, position error, and increased control effort resulting in inefficient power utilization and payload constraints. To mitigate the effects of Chlorpyrifos (pesticide) sloshing, a Lagrangian-based dynamic model of UAV and resulting slosh was developed. Using SMD analogy, sloshing and the dynamic equation of the quadcopter was modeled based on the geometry of the liquid container. An effective classical control algorithm for a liquid carrier quadcopter is presented which has been extensively investigated, validated, and compared. Simulations based on Coppelia V-rep are also presented to investigate the real-time implementation of the proposed system. The results demonstrate a decrease in chlorpyrifos slosh amplitude and intuitively, a reduction in the control effort. These findings have significant implications for improving the quality of quadcopter control in various real-world applications.