Ask a junior high school chemistry question, I can do it but I am not sure.

Select D to add a small amount of dilute hydrochloric acid to the filtered solid, no bubbles are generated, and the zinc is completely dissolved, then there must be no zinc, and there must be zinc nitrate.

If the amount of zinc is not sufficient, then the silver and copper cannot be completely replaced, and there may be silver nitrate and copper nitrate in the solution.

If zinc happens to completely displace silver and copper nitrate in silver nitrate and copper nitrate, then there must be no silver nitrate and copper nitrate in the solution.

Option D solves this problem according to the order of liveliness of the metal. Replace it with zinc, there must be zinc nitrate.

If zinc is sufficient, zinc is added to react with silver first, and then react with copper to form silver elemental and copper elemental respectively.

If the amount of zinc is insufficient, it may disappear before the reaction with silver is complete. So there may still be silver nitrate and copper nitrate. And after adding dilute hydrochloric acid, there are no bubbles, and there is definitely no zinc. Hope it helps.

Select D, add zinc powder will inevitably undergo a displacement reaction, and the oxidation of silver ions is stronger than that of copper ions, that is, it reacts before zinc, and the results will be different depending on the amount of zinc, that is, silver ions may be reduced due to the completion of the reaction, or copper ions may not react at all due to the completion of the reaction.

Pick D. Because Zn can replace H2, while Ag and Cu cannot, all Zn reacts, but it is not said that Zn is sufficient, so it is possible that it is exactly a complete reaction, or there may be an excess of silver nitrate and copper nitrate.

d。There are several possibilities:1:

Zinc is insufficient, because there are no bubbles when nitric acid is added dropwise, and copper and silver do not react with acid. So there is absolutely no zinc in the solids. But there may be salts of copper and silver in the solution2ZnZ just reacting.

The solids are copper and silver, and the solution is the salt of zinc. 3 The salt of zinc and copper happened to be reactive, but not with the salt of silver, because copper had to react before silver. So the solid is copper, and the solution is a salt of zinc and silver.

Adding a small amount of dilute hydrochloric acid without bubbles means that there is no Zn, so ab is wrong, Zn may be insufficient, so C is wrong, and D is selected

It should be selected, it must be zinc-free, but it may also be copper-free, and when there is enough zinc, it can only replace silver. (Silver ions are more oxidizing than copper ions and react with zinc first). b must not contain zinc, otherwise hydrochloric acid will be added to produce gas.

C is the same as A and may contain Agno3 and Cuno3 solutions.

The answer is not necessarily copper, B is definitely zinc-free, and C is too absolute.

Select D, add hydrochloric acid, no bubbles are generated, it means that there is no zinc, zinc is replaced with silver first, and copper is replaced by a mistake, a is wrong in a certain amount of copper, it should be possible to contain copper, B is wrong in may contain zinc, it should be there must be no zinc, c is wrong in there must be no silver nitrate and copper nitrate, if the replacement is not complete, then it also contains silver nitrate and copper nitrate.

Obviously, this question is that the hydrogen emitted by the beaker A [with iron] must be more than the hydrogen emitted by the beaker B [with zinc] [in other words, the mass added by the beaker A must be smaller than the mass increased by the beaker B].

And if all the "dilute sulfuric acid containing grams of sulfuric acid" participates in the reaction, then as much hydrogen is released, so there must be a surplus of sulfuric acid in the beaker. In this way, let's consider the first possibility: too much iron, not enough zinc.

Let they all be a grams, then a beaker increases the mass =

g, b beaker increases mass = 63a65

g, the difference between the mass increase of the two beakers = 63a 65

g-(g)=, substitute a=, get.

Lower limit value = grams. [This is the minimum value of the answer, which should be greater than it, not including it.] 】。

Consider the second possibility: both iron and zinc are insufficient, and if they are all A grams [A, then A beaker increases mass = 54A 56 grams, and B beaker increases mass = 63A 65

g, the difference between the mass increase of the two beakers = 63a 65

g - (54a 56 g) =

9a 1820, substitute a=, get.

Upper limit = grams. [This is the maximum value of the answer, which should be smaller than it, not including it.] 】。So, I think the answer should be that the AB beaker mass difference before the reaction is greater than 0 and less than grams, and the mass of metal added should be greater than 0 and less than grams.

1.When heating the solids in the test tube, why should the mouth of the test tube be slightly inclined downward?

Prevent the condensation of water vapor from being released, and the formation of liquid droplets flowing back to the bottom of the test tube and bursting.

2.Why does the amount of liquid not exceed one-third of the volume and is about the table top at a 45-degree angle when heating the liquid for the management of the matter? (Prevents liquid from splashing out).

3.Why do you need asbestos mesh when using a beaker flask to heat liquids?

The above-mentioned glassware is easy to burst when exposed to open flames).

4.Why can't the leftover drugs in the lab be put back in the original reagent bottles?

It can contaminate the reagents in the bottle.

Introduction of impurities) 5Why can't solutions be prepared directly in graduated cylinders or used as chemical reaction vessels?

The graduated cylinder will be corroded by reactants.

The scale is broken).

6Why can some glass instruments be heated directly, and some need to pad asbestos nets?

Some glass is thin.

It is heated evenly and there is no temperature difference between inside and outside.

Not easy to burst. The thick one will burst)

Because the question asks at least how many grams of iodized salt should be supplemented.

The maximum amount of iodine intake has been set! So take the high content. This way the gram will be smaller.

So it is to ensure the minimum number of grams of this intake.

You should be clear about this: too much iodine supplementation is not a good thing, iodine supplementation is to prevent endemic goiter, not to overdose, excessive iodine can cause iodine hyperthyroidism and other thyroid diseases, and even cancer.

There was a little boy in Lanjing City who received a malignant thyroid tumor due to excessive iodine supplementation.

So, you can't count at the lower limit of iodine, but at the upper limit of iodized salt.

Yes, the teacher used the wrong data, saying that it was at least, then using the minimum straight to infer that every 30 days of intake of milligrams, then the daily intake of milligrams is necessary, then the amount of salt ingested per day is: divided by 20 is equal to kilograms equal to one gram, and the answer is one gram.

You're right, and for good reason. Let's ** with your classmates and teachers.

It is unreasonable to d, because copper sheet and copper powder are the same reactant, and the cause of influence is the contact area with oxygen. Copper powder is larger than copper sheet.

b is reasonable. Because carbon is low in energy at room temperature, it cannot cross the barrier when it comes into contact with oxygen, and carbon monoxide or carbon dioxide is formed. After ignition, it reacts with oxygen, because the temperature rises, so that carbon atoms and oxygen molecules can cross the barrier and react.

So the influencing factor is the reaction temperature.

However, this expression is a bit problematic, because the ignition of carbon means that it has reacted with oxygen. It should be in high temperatures. But let's do the question, the multiple-choice question uses the elimination method or the direct method, D is obviously wrong, of course, D is not B

B is correct! Carbon does not react with oxygen at room temperature, but can react with oxygen when ignited, which is the effect of temperature! The higher the temperature, the higher the percentage of activated molecules, the greater the chance of an effective collision, and the easier it is to react!

The factor affecting the D term is not the type of reactant, but the shape of the reactant, that is, the state of the reactant! The contact area between copper powder and oxygen is large, and the reaction is violent! So d is wrong.

Because the temperature of the reaction has an impact on whether the reaction occurs, it does not react at room temperature, and the temperature is higher when it is ignited, so it is related to the reaction temperature. Option D: The composition of copper sheet and copper powder is Cu, so it is the same substance, but the contact area between the latter and oxygen is larger during the reaction, so the reaction is more violent.

So it should be related to the contact area of the reactants.

Answer: B carbon does not react with oxygen at room temperature, but it can react with oxygen when ignited. This is not the "reaction temperature", but the "reaction condition".

= =d

This is not a kind. It should be the contact area of the reactants. =

B is obviously okay. Isn't it just that the temperature is high?

Pick D. B, yes, the temperature hasn't arrived, and they all say "normal temperature", and then they say ignition, and it's obviously too hot.

d The change in temperature during the reaction will affect the chemical reaction.