Question

a student noted down the following precautions for the experiment "to varify the law of conservation of mass in a chemical reation"
1 mixing of two solutions should be done quickly
2. chemical reation should be exothermic
3.the reading of the balance should be noted when its pointer comes to rest .
4.the spring balance should be held vertical while in use.
5.before making use of the balance it must be ensured that its pointer is at zero mark
which precaution needs modification

Answer 1

The first precaution is wrong, because mixing two solutions quickly may lead to fire. The solutions must be mixed very slowly and steadily to prevent accident