Why does copper sulphate (CuSO4) in water increase surface tension?
From Sayok#6589 on Discord:


  
  When dissolving CuSO4 in H2O, it does not remain as CuSO4. It's a soluble salt, so you make [Cu(H2O)6]2+ and [SO4]2-. The first coordination shell of either ions is filled with water, forming electrostatic/polar bonds between the water molecules and the ions. 
  Because the water molecule are forming bonds with charged ions, their polarity is slightly increased compared to a regular water molecule. 
  Surface tension of H2O is formed because of the polarity of the water molecules. They like each other and want to stick with each other. In general, the more polar a solution is, the more surface tension it can have.
  Increasing the polarity of the water molecules because of the presence of the charged ions in solution thus results in a small increase in the surface tension.