Middle School Chemistry Questions? Junior high school learning questions?

Regarding the second question, there is really no answer to be precise. Everything in the kitchen is pure, it's a mixture. However, if you take the high school entrance examination, you can only choose D.

The main component of soda ash is NACO3, and of course there are other magazines in daily necessities, which is a process problem. Sodium carbonate can also be hydrolyzed, which can also cause impurity.

Forehead. You say, how can you children do this? How much fun is studying chemistry?

You still don't study well?! Still looking for answers on the Internet? Do it yourself!

Are you still a student? Tell you about Ang! Don't tell him the answer!

Let him do it himself! Sadly, how can China's next generation be like this?!!

It's sad that you can't do such a simple question! If you send over next year's high school exam questions, I will help you do it in advance! What else are you reading?。。。

The classmate who went upstairs You are sadder than him What is the second question without an answer Aren't you misleading Obviously you choose b will not be able to learn from others.

b No answer a c b b c a a c a

Do the calculations yourself.

1. CaSO4 solid can be used for drying, which is a neutral desiccant. CaSO4 reacts with water to become calcium sulfate dihydrate (gypsum), which absorbs water. The specific equation for nuclear hail is as follows:

CaSO4+2H2O=CaSO4·2H2O2, hydrometallurgical transformation to sail copper requires malachite (a copper-containing ore), sulfuric acid and iron powder. The equation is as follows:

cu2(oh)2co3=(△2cuo+h2o+co2↑cuo+h2so4=cuso4+h2o

fe+cuso4=cu+feso4

3. Yes.

Step 1 concludes the manuscript, and there is a book of Jingchang precipitation and barium sulfate precipitation. So there is sodium sulfate, barium chloride.

pH>7 is alkaline, so there is sodium hydroxide, and the precipitation is insoluble or barium sulfate.

Colorless transparent solution, no iron state pickle ions.

To sum up.

<> "Therefore, which search hail chooses the forest to leak code b."

Right. The less dense solution is poured into the larger solution, and the inside of the solution is divided into upper and lower layers, the upper layer is a lighter solution, and the lower layer is a thicker layer. There will be an interface in between.

The solution on both sides will mix slowly over time (speed and temperature dependent). But generally we use glass rods to stir directly to speed up the mixing process.

So what you said is right.

Pure matter cannot be composed of different molecules, different molecules represent different substances, only one molecule must be pure, the mixture can contain only one atom (such as O2, O3), understand and try, turn the book to see the concept. In addition, all solutions are mixtures (solution definition: both.

1. Stable mixture), the alcohol solution is a mixture of alcohol (alcohol alone is pure) and water.

The first question is b 1, zn + 2h2so4 == znso4 + so2 (gas) + 2h2o

2. Zn + H2SO4 == ZNSO4 + H2 (gas) This is the chemical equation for the reaction of Zn and H2SO4, 6H2SO4 + 2FE=Fe2(SO4)3+3SO2 +6H2O This is the chemical equation for the reaction of FE and H2SO4 (both equations have gas production) The mass before and after the chemical reaction is conserved, and the added zinc is of the same mass as iron. So if the balance is balanced, the amount of hydrogen emitted is the same. Because the stoichiometric ratio of zinc reacts with iron and dilute sulfuric acid is certain (that is, the amount of zinc reacts with iron in the same amount of substance and the amount of dilute sulfuric acid reacts with iron), and the relative atomic mass of zinc and iron is different.

So there must be something unanswered.

The second question is zinc The relative atomic mass of zinc is larger than that of iron, and if the same mass of zinc and iron is added, if it is not balanced, the amount of iron reacted should be more, and more hydrogen should be released. The iron end is light, so the tray containing zinc sinks.

A must have no remaining sulfuric acid, and B must have a remaining substance, iron.

c The substance that may be left is Zn

2) zn upstairs explained very well, the second question.

Aluminum doesn't rust like iron.

Because aluminum is very reactive, it reacts with oxygen in the air to form a dense oxide film that prevents aluminum from continuing to corrode.

Aluminum products are not easy to rust. It is because aluminum reacts with oxygen at room temperature to form a dense alumina film. The alumina film adheres to the aluminum surface.

Prevents oxygen from the outside from continuing to react with the aluminum inside. So aluminum products. It is not easy, and the rust resistance is very good.

Even in contact with water, there will be no oxidation reaction and rust.

For reference, it should not be said to prevent rust, and the purpose of washing and drying should be to prevent aluminum from being reacted. The "rusting" of aluminium products actually refers to the reaction of aluminium with oxygen in the air to form a dense alumina film on its surface (this substance actually helps to prevent aluminium from being re-oxidized, i.e. it helps to prevent the aluminium inside from continuing to rust); It is difficult for aluminum to react with cold water, but if the water contains salts or acidic substances, some of the aluminum will react with it and disappear, and the surface of aluminum products will be uneven. (Covering his mouth and laughing).

2NaOH + H2SO4 = = Na2SO4 + 2H2O, it can be seen from the equation that 80GNOH and 98GH2SO4 are completely reacted, and the existing waste sulfuric acid, if the mass of the treated NaOH containing wastewater is xt, then 80 98 = (x*, the solution is x=1t.

It should be "grams of existing waste sulfate."

The steps to solve the problem can be:

Let the quality of the wastewater that can be treated be x

2naoh+h2so4=na2so4+2h2o2×40 98

x solution x = 100 grams.

Let the quality of wastewater that can be treated be m

The solution is m=245

The unit of mass is the same as the unit of your sulfuric acid mass.