Urgent! 5 junior high school chemistry questions must be answered before 24 00 today

1.Choose D because concentrated hydrochloric acid volatilizes and concentrated sulfuric acid absorbs water from the air.

2.Choose B, because this is the only one that embodies the meaning of the title.

3.Put brass in a sufficient amount of hydrochloric acid (or sulfuric acid) first, and zinc will react completely, while copper will not.

The mixture is filtered and dried, and the filter residue (copper) is heated to obtain copper oxide.

The resulting solid is put into sulfuric acid to obtain copper sulfate.

zn + h2so4 = znso4 + h22cu + o2 = 2cuo

cuo + h2so4 = cuso4 + h2o4.I didn't study it seems to be in high school, and it's even the third year of junior high school) but it's only a few.

The density of 200ml of a concentrated sulfuric acid solution is 98, and 10ml of the solution is diluted to 100ml with water. Calculation: 1the amount and concentration of concentrated sulfuric acid; 2.The amount of sulfuric acid after dilution, the concentration of the substance.

1.The concentration is independent of the volume of the solution, which is the best way to calculate the concentration.

2.Such a question is best calculated using a dilution formula.

c1v1=c2v2

c2=c1v1/v2=

To water 200 2 5 = 80 grams.

There is also 3mol l in the question, using these two data, you can calculate the volume of sulfuric acid that needs to be concentrated at 3mol l, do you remember the dilution formula? c1v1=c2v2

Suppose you want to prepare a concentration of 200 l, calculate the volume of sulfuric acid with a concentration of 3mol l, then.

v1=c2v2/c1=

Calculation of the volume of water is required.

The density of 3mol l sulfuric acid 3 98 (1000 25%) = the density of sulfuric acid.

The volume of water is required, and the density of water is calculated as 1 gram ml.

It should actually be more than 88 liters, because the volume of water and sulfuric acid must be less than the sum of the volumes of the two, so the data provided in the question is not accurate. Only the calculation method is provided here.

In the first question, concentrated hydrochloric acid will volatilize, the mass will decrease, and the mass fraction of the solution will decrease. Concentrated sulfuric acid is absorbent and absorbs moisture in the air, the mass increases, and the mass fraction of the solution decreases. Therefore, choose D.

The second question is to use hydrochloric acid washing before electroplating because the oxides on the surface of the metal react with carbonic acid to remove the oxides on the surface. Therefore, choose B.

Question 3: 1. Put the solid into dilute hydrochloric acid, filter, and collect the solid (elemental copper).

2. Heat the solid in air (copper oxide).

3. Put the solid into dilute sulfuric acid, filter, and filtrate.

Question 5: According to the conservation of dissolved mass, 40*98%=(40+x)*x+360g.

3.Your answer is right. Congratulations!

The analysis of the ethanol oxidation reaction was inadequate, so that carbon monoxide was formed but did not affect the formation of water and the total moles of CO and CO2 generation.

Write the equation for the full reaction: C2H5OH+3O2=2CO2+3H2O water.

Ethanol participating in the reaction, grams.

The generated CO+CO2 altogether, grams, the average molecular weight of the mixed gas is 42, then the molar ratio of CO to CO2 is 1:7

The mass ratio is 1:11

1. NaOH should be prepared with Shicong Town gray milk and sodium carbonate solution.

The reason for not using acres of Zhengyunqing lime water is that calcium hydroxide is slightly soluble in water, and there is only a very small amount of Ca(OH)2 in the clarified lime water, and the amount of NaOH obtained by its reaction with Na2CO3 is also less, so the preparation of NaOH is made with lime milk with a relatively large concentration of Ca(OH)2 instead of clarifying lime water.

2. Lime water is slightly soluble, and the solubility is calculated according to 1%, so the hydroxide concentration is only 1%, and the solute mass fraction of sodium hydroxide will not be higher than 1% no matter how high it is.

The concentration of caustic soda solution prepared in this way is relatively low, because calcium hydroxide is a slightly soluble substance, and there will be fewer calcium ions in the solution of a small number of cherry blossoms, and the calcium carbonate precipitate generated by the rental leakage plexus is also relatively small, and a large number of carbonate ions will remain in the solution. It is recommended to use a barium hydroxide solution or a calcium chloride solution.

You can understand it yourself.

For example, in copper sulfate solution, copper ions have 2 units of positive charge, and sulfate particles have 2 units of negative charge, that is, the number of positive charges and the number of negative charges are equal and invisible. Whereas, sulfate ions are made up of clusters of particles.

For example, in copper chloride solution, the ratio of the number of copper ions to the number of chloride ions is 1:2, and the copper chloride solution is not electrically charged, also because the number of positive and negative charges in the copper chloride solution is equal.

Therefore, this sentence should be changed to be true: because the electrolyte solution is not electrical, the number of positive and negative charges in the solution must be equal.

Are CaCl2 anions and anions equal?

It should be said that the charge is equal.

At this time, the anion in the electrolyte solution will run over to neutralize the cation, and the positive end will gain electrons and become anions, and then the cations in the electrolyte solution will run over and neutralize him, so the remaining anions and cations in the electrolyte will not be equal.

The number of charges is not equal.

It is equal in charge, not in the number of ions.

1:b, by definition, o is 16 times the mass of 1/12 of carbon 12, and the same is 32 times that of s.

2:D, Fe and HCl, Cuo and HCl, calcium hydroxide and HCl, MgCl2 and calcium hydroxide (solution).

3:a, the other term has neither gas nor precipitation, and there is no refractory ionization of the substance 4: Fe + H2SO4 = = FeSO4 + H2

1. The solubility of the saturated solution is unchanged at the same temperature, that is to say, the mass of the solute is unchanged when the solvent is unchanged, but the mass of the solvent decreases (because it has to react with quicklime), the solute in the relative solution should also be relatively reduced, and the mass fraction is unchanged, because the precipitation of calcium hydroxide is precipitated proportionally (the front and back are saturated solutions, you have to think about it yourself!). The acidity and alkalinity of the solution is judged by the concentration of hydrogen ions or hydroxides, and the concentration is constant.

2. The previous algorithms are correct, you can set the mass fraction of the original solution to m, then the first wash (equivalent to dilution of the solution, the solute is the solute in the milliliter at this time, the mass fraction of the solution is:, the same reason, the second wash is equivalent to dilution on the basis of the first time, the mass fraction of the solution at this time is [(1m 41), and the mass fraction m of the original solution is 1 1681

Answer: a, the temperature does not change, and the solubility of the solution does not change. Quicklime is added to the solution, that is, calcium oxide, which reacts with water to form calcium hydroxide, and water is lost, because the solution is still a saturated solution, so the solute must be reduced.

b, the temperature is unchanged, the solubility is unchanged, and the solute mass fraction of the saturated solution will not change.

c, the solution is still saturated, the concentration of solute in it will not change, the concentration of hydroxide does not change, so the alkalinity does not change.

d, the temperature does not change, the solubility does not change.

2. There is going to be a power outage, and the second question is temporarily unsolved.

1.The reaction of quicklime with water is exothermic, which also reduces the solvent in lime water, which reduces the solute mass, even if the temperature is restored, the solvent will be reduced without solute, and because it is a saturated solution, the crystals are still saturated at this temperature after precipitation. Choose A

2.It is equivalent to preparing the solute into a 20ml solution, and the resulting solution is diluted to 20ml, let's do the math!

1) CAO reacts with water and the water decreases, a because it is a saturated solution, there will be solute precipitation, the solute mass decreases, b is the largest when saturated, it will not become larger, c because of the precipitation of solutes, oh- in the water - decreases, the alkalinity weakens, the temperature and pressure remain unchanged, and the solubility does not change.

1. Because quicklime will react with the water in lime water, the solvent will be reduced, so the solute will precipitate and the quality will be reduced. Since the temperature is the same as before, the solubility remains the same, and the quicklime is saturated before and after the addition of quicklime, so the statements in b, c, and d are all unchanged.

2. The density of water is 1 gram per milliliter, and the solute mass remains unchanged when diluted, so it is equivalent to adding water to the gram solution, and the concentration becomes 1 41 times, and washing again is to shrink 41 times, so the concentration is about 1681 times of the original.

Quicklime Cao will hydrate mature lime: CaO+H2O Ca(OH)2

Hence the solute water will decrease while the solution will remain saturated and hence, the mass of the solute will decrease.

The mass fraction of the solute in the solution does not change, and the alkalinity of the solution does not change. The solubility of calcium hydroxide does not change (solubility and temperature dependent).