Give reasons: Aluminium utensils should not be kept in water overnight.
The oxygen present in water reacts with aluminium to form a thin layer of aluminium oxide. This layer prevents aluminium from further reaction. However, when water is kept in an aluminium vessel for long periods of time, some amount of aluminium oxide may dissolve in water. As aluminium ions are harmful, water should not be stored in aluminium vessels overnight.
Generally, aluminium metal does not react with water quickly but, when it is kept overnight, it reacts slowly with water in presence of air.
2Al(s) + O2(g) + H2O(l) ——–> Al2O3(S) + H2(g)
a very small amount of (in ppm) Al3+ produced in the solution is injurious to health if the water is used for drinking purposes