# Three students heated a mixture of zinc and sulfur powder weighing 12 g. At the same time

Three students heated a mixture of zinc and sulfur powder weighing 12 g. At the same time, one of them completely reacted zinc and sulfur, another had sulfur in excess after the reaction, and a third had zinc. For how many students did the test tube weight change at the end of the reaction?

1) All three students had a chemical reaction:
Zn + S => ZnS;
2) For the first student, zinc and sulfur reacted completely, so the mass of the test tube did not change;
3) The mass of the test tube after the end of the reaction changed in the other two students;
4) In the second student, who had an excess of sulfur after the reaction, the mass of the test tube decreased due to the fact that gas was formed and evaporated:
S + O2 => SO2 ↑;
5) In the third student, who had zinc in excess after the reaction, the mass of the test tube increased due to the formed zinc oxide:
2Zn + O2 => 2ZnO.

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