Junior high school chemistry problem (+100 mark)

1. To find the content of copper, I understand that it is to find the mass fraction of copper in copper oxide, that is to say, after reducing copper oxide with hydrogen, the mass of copper is weighed. If there is a lot of copper oxide and enough hydrogen, the quality of copper will increase indefinitely, but the content of copper is certain ~ ~

2.MnO2 plays a catalytic role, so the reaction should be started from the beginning. However, in some experiments, the catalyst is not added at first, and then the reaction is carried out in order to verify the catalytic effect of the catalyst. Maybe the reaction you said later is like this.

3. When the current year is a multiple of 4, it becomes a leap year, with 366 days in a year. However, it should be noted that the time for the earth to go around the sun is still 365.2422 days, and in a normal year, according to the calculation of 365 days, four years is 0.9688 days shorter, so one day is added every four years, and this year there are 366 days, which is a leap year.

This is your junior high school chemistry knowledge ... the 24 solar terms are determined according to the position of the earth in the revolution.

What about the picture of 5.6?