(1)③ The temperature reaches the ignition point; According to stem data (covering with dry phosphate powder, dry yellow sand and cement, and isolating fire fighting), the purpose of this is to isolate the contact between combustible substances and the outside world, so the answer is: the principle is to isolate the contact between combustible substances and oxygen (and water).
(2) According to the common sense of life, guess A: Calcium oxide is impossible, because calcium oxide and water can react quickly to generate calcium hydroxide; According to the topic information, we can guess that C: calcium carbonate is also wrong, and the phenomenon of reaction between calcium carbonate and hydrochloric acid is gas production; Calcium hydroxide is alkaline and turns red with phenolphthalein. Therefore, the answer is: Method Phenomena Conclusion It is incorrect to add dilute hydrochloric acid to the sample, and add phenolphthalein solution to the sample to turn red. Guess b is correct. (3) If a is selected, the mixed gas passes through sodium hydroxide, and the weight obtained by sodium hydroxide is carbon dioxide. But it will also bring some water into concentrated sulfuric acid, so the weight gain of concentrated sulfuric acid is no longer all the product water of combustion. So the answer is: b?
Water quality:127.1-125.3 ═1.8; ∴ Hydrogen mass: 1.8×2 18═0.2
Mass of carbon dioxide: 87-78.2-8.8; Mass of carbon element: 8.8× 1244═2.4.
The mass fraction of hydrogen is 0.20.2+2.4×100% ═113×100%.
Let the number of hydrogen atoms in the chemical formula be x, then the number of carbon atoms is 4-x;
So the mass fraction of hydrogen: XX+48? 12x× 100% = 1 13× 100%； Solution: X=2
So the answer is: the chemical formula of acetylene? C2H2？
Ii. According to the topic information, the chemical equation of the reaction between calcium carbide and water is CaC2+2H2O═Ca(OH)2+C2H2↑.