What are the topics related to the first semester of junior high school chemistry?

Weigh the weight of the front and rear B device. On the small side.

a：fe

b：fe3o4

c：fe2o3

d：feso4

The e:co breakthrough is found in c and 'it is known that a, b, c, and d all contain the same element', from which it can be concluded that they are conversions in iron.

a fe

b fe3o4

c fe2o3

d feso4

e co, you check it and see if it's right.

From the question, if A is an iron element, B is ferric tetroxide, C is iron oxide, and D is ferrous sulfate, then E must be a reducing gas and carbon monoxide.

No picture, no truth, brother!

However, according to the meaning of the title, these assumptions should be included: 1. The combustible part of the plastic bag is completely combusted; 2. These plastic bags do not contain other substances that react with oxygen to form volatile gases.

Your question shows that you are very careful, so there are various components of plastic bags, such as polyvinyl chloride, polyethylene. In the case of polyethylene, because its molecules contain only CH, then only carbon dioxide gas is generated, and other substances do not necessarily react with oxygen by means of combustion. The title does have ambiguity because there is no guarantee that the gas does not contain other volatile substances.

However, a chemistry question in the third year of junior high school, you don't have to be serious, you can understand it.

(1) In order to ensure the accuracy of the measurement, the air tightness of the device should be checked after the experimental device is connected.

Then add the drug for experiments

2) Add a sufficient amount of H2O2 and catalyst to the small beaker of the device to continuously produce O2 for full combustion in plastic bags, and the chemical equation for producing O2 is.

2h2o2 mno2 . 2h2o+o2↑2h2o2 mno2 . 2h2o+o2↑

3) When the plastic bag burns out and the device gradually cools, the liquid in the device is not easy to suck into the device because.

Oxygen is generated in the device, and the internal pressure is increased, and the internal pressure is increased.

The quality of the plastic bag before the ACACA experiment.

b. The quality of the pre- and post-experimental device.

c. The quality of the pre- and post-experimental device

In this question, in order to measure the mass of CO2 produced after the combustion of a certain mass of plastic bags, and do not need to consider whether it is harmful to the environment, the combustion of plastic bags in this question is almost complete, so the mass reduced by plastic bags is the quality of CO2 generated, please think according to the topic!!

According to the law of conservation of mass, when a plastic bag is burned, only CO2 gas should be generated.

The main tissue is CO2, and the content of other substances in the whole is very small, so only the amount of CO2 is counted [maybe so].

Carbon dioxide is a gas, ash.

There is no picture. There's really no picture.

1. The mass ratio of iodine, potassium and oxygen in potassium iodate is 127:39:482, and the mass fraction of iodine in potassium iodate is 127 (39+127+48)*100%=

3. From the inscription, it can be seen that the iodine content per kilogram of salt is reduced from 40mg to 25mg, and the mass of less iodized per 500 grams of salt (40mg-25mg) 2 = The quality of potassium iodate per 500 grams of salt is less.

Mass of the element iodine Mass fraction of the element iodine in potassium iodate =

:39:48

(39 + 127 + 48) * 100% = 3, the mass of less iodized per 500 grams of salt (40mg-25mg) 2 = the quality of potassium iodate per 500 grams of salt.

(1) 127:39: (16x3) i.e. 127:39:48

2) Mass fraction of iodine element in potassium iodate = 127 214x100% =

This can be proven in three steps:

1.Operation: Add purple litmus test solution dropwise to distilled water, phenomenon: the test solution does not turn red.

Conclusion: The reddening of the purple litmus solution is not the cause of the water molecules.

2.Operation: Add purple litmus test solution dropwise to sodium sulfate solution, phenomenon: the test solution does not turn red.

Conclusion: The reddening of the purple litmus solution is not the cause of sulfate ions.

3.Operation: Add purple litmus solution dropwise to hydrochloric acid (or sulfuric acid), phenomenon: the test solution turns red.

Conclusion: The reddening of the purple litmus solution is the cause of hydrogen ions.

Experiment Observe which of water, sodium sulfate, and dilute hydrochloric acid can turn the purple litmus solution red. It was found that neither water nor sodium sulfate can make purple litmus red, while dilute hydrochloric acid can be litmus red. Therefore, it is the hydrogen ions in the dilute sulfuric acid solution that make the purple litmus reagent red.

1. Purple litmus test solution dropwise added to sodium sulfate solution does not change color, which proves that it has nothing to do with sulfate ions and water molecules.

2. Add purple litmus test solution dropwise to dilute hydrochloric acid to turn red, which proves that it is hydrogen ions that make the purple litmus reagent red.

Take three tubes.

Distilled water was added to the first tube, Na2SO4 solution was added to the second tube, and dilute hydrochloric acid was added to the third tube. Then add purple litmus test solution dropwise.

If the solution in the first tube turns red, it means that the water molecules are making the purple litmus reagent red;

If the solution in the first and third tubes does not turn red, and the solution in the second tube turns red, it means that the sulfate makes the purple litmus reagent red;

If the solution in the first and second tubes does not turn red, and the solution in the third tube turns red, it means that H+ makes the purple litmus reagent red.

It's easy! Do a comparative experiment! Take the same concentration and the same amount of dilute sulfuric acid and sodium sulfate solution, put them in two test tubes, and then drop a few drops of purple litmus solution each, the result must be: the purple litmus solution dropped into dilute sulfuric acid turns red, and the other does not change.

The basic idea is to exclude them one by one.

Start with distilled water to remove the water.

Then do it with sodium sulfate to exclude sulfate.

Then make it with dilute sulfuric acid.

Take three test tubes, add the same amount of distilled water, sodium sulfate solution, dilute hydrochloric acid, and then add purple litmus test solution dropwise respectively, only the test tube containing dilute hydrochloric acid turns red, indicating that it is hydrogen ions that make the purple litmus reagent red.

Find distilled water, potassium sulfate, and sulfuric acid for experiments.

（1）：1 2 3

2): Vitamins.

3）：a d e f

4): Heavy metals.

The question is simple.

Vitamins: potatoes, steamed buns, rice, bread.

Heavy metal salts.

（1）1 2 3

2) Lack of vitamins.

3) a, e4) heavy metal salts.