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The mass fraction is the mass ratio of the solute solution, and the mass of the solvent increases after adding water, so it is feasible; Evaporation at constant temperature, the temperature is unchanged, because the solution is saturated, so the solvent will precipitate, but it is still in a saturated state, so the solute mass fraction remains unchanged, so B is wrong. The temperature is increased but the solute and solvent quality remain unchanged (it is regarded as no evaporation), so C is wrong. D added solute, but the solution was saturated, so the newly added KNO3 did not dissolve, so D was wrong.

It is also a saturated solution, so the addition of sugar or stirring will not change the solute mass fraction when the temperature is unchanged. Because the sucrose solubility curve is positively correlated with temperature, the temperature is still unchanged (C in the same question), and the solubility decreases after cooling, and crystals precipitate, so the mass fraction decreases. Therefore B is right.

Applicable to middle and high school chemistry).

Let me explain it to you:

Question 1: First of all, you need to know that the mass fraction is the mass of the solute and the mass of the solution*100%. In other words, it is necessary to analyze how the solute and solvent in the question change.

The first step is to exclude C. After the temperature rises, the solubility becomes larger, the potassium nitrate is the same as before, and the water is also so much, and there is no change.

The second step is to exclude D. At this time, the solution is saturated, and it is useless how much kno3 you add, it sinks directly to the bottom, there is no dissolution, and the solute and solvent still do not change.

Step 3: Exclusion B. This main main word is "constant temperature". The temperature is constant, the solubility is constant, and with the decrease of moisture, the precipitation of KNO3 is also decreasing, and the proportion is the same. So the quality score also remains the same.

Only a. The solute has not changed, the water has become more, and the mass fraction has become smaller.

Stirring goes without saying. Everyone knows it doesn't change anything.

The only option is cooling. When the temperature is cooled, the solubility becomes smaller, and the sucrose precipitates and becomes less, but there is still so much water. Therefore, the concentration of finishing should be reduced

I hope you can understand it, and if you don't understand it, you can ask questions.

Question 1. A correct is easy to understand. b evaporate part of the water, there will be crystal precipitation, and the temperature remains unchanged, but it is still a saturated solution, so the solute mass fraction remains unchanged.

cThe solubility increases at the temperature and changes from saturated to unsaturated, but the amount of solute and solvent does not change, so it remains unchanged. The addition of kno3 to the saturated solution is also insoluble, so it does not change.

Question 2. aThe solubility increases at the temperature and changes from saturated to unsaturated, but the amount of solute and solvent does not change, so it does not change. B cooling solubility decreases, crystals precipitate, and the amount of solvent does not change, so the decline of cd is easy to understand is unchanged.

I don't know why B is added, but ACD can be excluded.

It is worth noting that the biggest difference between the constant temperature evaporation part of the water and the temperature rise is whether the amount of solvent has changed. Judging from the meaning of the title, heating and cooling should not change the amount of solvent.

The first question is potassium nitrate saturated solution, the solute is water, a: add water, obviously the soluble mass increases, and the solute mass fraction also increases.

b: Evaporate part of the water at a constant temperature, because it is a constant temperature evaporation water, so the solubility of the solvent does not change. Then there will be a precipitation of the substance, and the remaining solution is also saturated, so the mass fraction of the solute remains unchanged.

c: When the temperature is raised to 60 degrees, although the solubility is changed, the boiling point of water is not reached, so it will not be vaporized, the solvent and solute will not be reduced, so the mass fraction of the solute will not change.

D: Add a certain amount of KNO3, the solution itself is potassium nitrate saturated solution, and the solution will not be affected by the addition, so the mass fraction of the solute remains unchanged.

Therefore, the second question of choice A is the saturated solution of sucrose, and the solute mass fraction needs to be increased, so the mass of water is increased or the mass of sucrose decreased.

b Heating up, if the boiling point of water is not reached, obviously does not change the amount of water. If the boiling point of water is reached, the water will vaporize and then the mass will decrease.

B: Cooling, the solution degree of sucrose will decrease after cooling, that is, sucrose will be precipitated, and the quality of sucrose in the solution will decrease, so the mass fraction of water will rise.

c: Added sugar, added sugar will not dissolve, has no effect on the solution.

D: Stirring, it is already a saturated solution, and it has no effect on the solution.

So choose B

The first question is because it is a saturated solution, so B is still a saturated solution after evaporation at a constant temperature, the solubility of the saturated solution is a certain solubility, so the mass fraction is certain, although the solubility changes after the temperature is raised, the mass fraction remains the same, D adds kno3 will not continue to dissolve because the dead saturated solution is unchanged, a because the mass of the solvent changes after adding water, the mass fraction of the solution also changes, so the mass fraction is smaller. Question 2: Seriously, I feel that there is something wrong with the question. A: The solubility increases after heating, but neither the solute nor the solution changes, the mass fraction does not change, and B also does not change although there will be crystal precipitation, but the mass of the solute decreases, the solvent does not change, the mass fraction decreases, and the CD has no effect!

If you don't understand, you can ask!

The first one is saturated, and a certain amount of water can only dissolve a certain amount of solute. After the water is added, the solvent is increased and the solute is not increased, resulting in a decrease in concentration, after the water is evaporated, the solute of the evaporated part of the water will precipitate, so the concentration of the remaining solution remains unchanged, after the C answer is warmed, the solubility will only increase, but the concentration remains the same, and the D answer adds a certain amount of kno3, because it is saturated, so it will not be dissolved again. The concentration does not change.

2. The solubility of sucrose decreases with decreasing temperature, so cooling will lead to solute precipitation and the concentration will become smaller.

Because the 20% potassium nitrate saturated solution may be a saturated solution, the potassium nitrate dissolved in this part of the water will be precipitated by evaporating part of the water at a constant temperature, and the solubility will increase when the temperature rises to 60 degrees, the quality of water and potassium nitrate has not changed, the mass fraction has not changed, and adding a certain amount of KNO3 may also be a saturated solution that cannot be dissolved, resulting in the same mass fraction. aThe mass of the water with water increases, the solute mass remains the same, and all mass fractions decrease.

The second question is the same, the requirement is to increase the mass fraction of the solvent, that is, to reduce the mass fraction of the solute.

In the first question, the solvent was increased by adding water, the solute mass remained unchanged, and the solute mass fraction decreased.

In the second question, the solubility of sucrose is affected by temperature, and cooling will cause the saturated solution to precipitate crystals, resulting in a decrease in solute mass, while the solvent mass remains unchanged, so the solute mass fraction also decreases.

This is also true if there is an option in question 2 to add a certain amount of water.

1b is already saturated, so it's useless. cThe solubility of potassium nitrate decreases with increasing temperature. d, it's still saturated, so it's useless to add it.

The second question should be to reduce the mass fraction, choose B to precipitate the crystal, and the solute will be reduced.

First, the solubility of potassium nitrate does not change with temperature, and only the addition of water can reduce its mass fraction. In the second question, the solubility of sucrose increased when cooling.

Select A, itself is a saturated solution, and the temperature is still unchanged, so the mass fraction of the solute remains unchanged and the solubility remains unchanged.

Quicklime reacts with water to produce mature lime, the quality of water decreases, and a part of the original solute precipitates due to supersaturation, and the mass of the solution decreases.

It turned out to be a saturated solution, and when water was added, it became an unsaturated solution, the solute mass remained unchanged, the solvent mass increased, and the solute mass fraction decreased.

Cooling, crystals are precipitated, solutes are reduced, solvent is unchanged, and solute mass fraction is reduced.

D Because the solubility of hydrated lime is somewhat special, its solubility decreases with the increase of temperature, and when it returns to the original temperature, its solubility will increase Of course, even if the original temperature is higher than the recovered temperature, there is no answer, so choose D

A is always a saturated solution, but the reaction between quicklime and water is an exothermic reaction, and the mass of water in the solution decreases.

c is not true, the solute mass fraction remains unchanged and is always a saturated solution.

d No, the solubility of the solute is only related to the temperature, and the temperature does not change.

aQuicklime reacts violently with water, consuming a lot of water and releasing a lot of heat, and a lot of water is evaporated. The solvent is greatly reduced, and the solute is naturally reduced under the condition of saturated solution at the same temperature.

Same as aboveB, because the solution is saturated, quicklime is mainly calcium hydroxide, and the main component of lime water is calcium carbonate, which is more stable than calcium hydroxide, so the solvent remains unchanged.

1. Dipping is used to determine whether the solution you add is sufficient.

For example, add sodium hydroxide to remove magnesium ions, after adding a certain amount, to determine whether the magnesium ions are completely precipitated, use a glass rod to dip a small amount of supernatant drops in sodium hydroxide, if the magnesium ions have been removed, then the precipitation should not be visible at this time.

2, 1), Correct, water absorbs ammonia and air enables the person to breathe normally and expel ammonia.

2), no, should be used glass stopper, concentrated nitric acid to corrode a variety of rubber.

3) Yes, this is also a toxic gas.

4) Yes, they catalyze ozone decomposition.

3. The water gas method is to let the water vapor react with carbon at high temperature to produce carbon monoxide and hydrogen, and then use these two gases to reduce metals.

Thermite chromium smelting, that is, 2Al+Cr2O3==Al2O3+2Cr, can heat the mixture of aluminum powder and chromium trioxide.

Magnesium is smelted in carnallite, that is, carnallite heated to a liquid state is dissolved to produce chlorine and magnesium. (One of the main components of carnallite is MGCL2).

The coke method is to directly reduce metals with solid carbon.

It seems to be difficult, so try it.

1. Isoprene is 2-methyl-1,3-butadiene, so its carbon chain structure is. ci

c=c—c=c

The arrangement of c atoms can be divided into several carbon chain structures of isoprene molecules, with a molecular weight of 152", indicating that it can only be two isoprenees (one 5c molecular weight is only 60, which is obviously insufficient; 3 x 5C molecular weight 180, exceeded), 10C.

The products are CO2 and water, and the CO2 generated is 2mol. more than H2O"Explain that it contains only c, h, o, let c be x+2mol, we can know that h is 2xmol, then there is, and the remaining 16 is exactly the atomic weight of 1 o.

This is an aldehyde and should have an aldehyde group. Considering the ratio of h to c, there should be only two double bonds, otherwise the number of h is not enough.

In summary, the molecular formula is C10H16O, and the simple formula of the structure is: CH3CHC=CH3(CH2)2CH=CCH3CHo, that is, 2,6-2-methyl-2,6 octadienal.

2. Unsaturated carbon-carbon bonds: fade bromine water or potassium permanganate solution.

3. Let me think about ...... again

(1) c10h16o

Isoprene is C5H10, and the molecular weight is 152, so there should be two isoprene units, that is, the molecular formula must contain C10; CO2 is 2mol more than H2O, so the molecule contains 16 hydrogen, and then subtract the known molecular weight from 152 and divide by 16 to get the number of oxygen.

2) First, identify the aldehyde group and react with a silver mirror. The specific phenomenon is troublesome for the landlord to check the book; The double bond is then identified with bromine water, and the fading of the bromine water indicates that there is also a double bond.

3) Draw a three-ring carbon skeleton, and then just find a carbon atom with an alcohol hydroxyl group, for example, the structure in this ** can be drawn with one oh less.

Answer C Reason: You can look at 200g of solution as two parts of AB, evaporate 11g of A, and the rest is still saturated, and then pour it back to B, without any effect. So a=b. This is relatively easy to understand in chemistry in this separator.

Because there is no blue, there are no copper ions, there is no copper sulfate, because the precipitate is insoluble in nitric acid, so the precipitate is either barium sulfate, or silver chloride, because there is no silver, so it is barium sulfate, so there are sulfate ions, barium ions, so there must be barium chloride and sodium sulfate. Because calcium carbonate is a precipitate, it dissolves in dilute nitric acid, so it is not.

Answer: There is barium chloride, sodium sulfate, no copper sulfate, calcium carbonate.

It is known by 1 that there are no copper ions because both copper ions and copper hydroxide are blue; It is known by 2 that the precipitate is non-carbonate because it is insoluble in acids. So it must be barium sulfate. Therefore, there must be barium chloride and sodium sulfate, and there must be no copper sulfate.

The supernatant is colorless: CuSO4 is not present

This white precipitate is insoluble in dilute nitric acid: if the precipitate is not CaCO3, it must contain NaSO4 and BaCl2

There seems to be a problem with the title, and there is no such thing as "not necessarily containing".

The white precipitate may be that A and B dissolve dilute nitric acid, C cannot dissolve dilute nitric acid, the supernatant is colorless, and CuSO4 must be absent if Cu ions are blue.

Na2SO4, BaCl2 must be there.

As for caco3, it doesn't necessarily contain it.

I feel that this question is unscientific.

1》Take a small amount of solution and put it in a test tube, add a sufficient amount of hydrochloric acid dropwise, and there is no precipitation; A few drops of barium chloride solution were added dropwise, and a white precipitate appeared.

so4 2- +ba 2+ =baso4|2》Take a small amount of solution in the test tube, add a sufficient amount of sodium hydroxide solution, heat, put a moist red litmus test paper at the mouth of the test tube, and the test paper turns blue.

nh4+ +oh- =nh3 + h2o