If all water in 4 L of a 0.5 M NaCl solution evapoprates what mass of NaCl will remain ? The mass is _ grams

Alidded glass container is filled with a colored gas. after a period of time, it is observed that the gas is uniformly spread throughout the box and that the movement has slowed considerably. next, a warm iron plate is carefully placed under the box. why is there resumed movement of the gas in the container?