Salt ‘disappears’ in water. But a taste of the liquid tells you that the salt is still there. So what has happened to the salt? When salt is mixed with water, the sodium and chlorine atoms break away from each other and move freely in the water. Gradually, the sodium and chlorine atoms and the water molecules are mixed up evenly. The liquid is called a salt ‘solution’. The salt has ‘dissolved’.
Many substances dissolve in water. Water is a good ‘solvent’. Carbon dioxide gas dissolves in water and makes it fizzy. Some substances dissolve in different solvents — paint dissolves in white spirit. Detergents ‘help’ water to dissolve oil.
Drops of oil floating on water will rush away from a drop of detergent added to the water. This is because detergent causes the surface of the water to change and the oil starts to dissolve.
Diffusion
If orange juice is poured down a straw into a glass of water, an orange patch forms in the middle of the water. The molecules of the water and the orange juice are moving all the time. Eventually, the orange molecules spread evenly throughout the water and the solution looks pale orange all over. This spreading of molecules is called ‘diffusion’.
Sea water is a massive solution of salt and water.
Oil-based paint does not dissolve in water, but it will dissolve in a solvent called white spirit.
Picture Credit : Google