Junior high school chemistry questions Please give the prawns advice

1.If the upward reading is smaller than the actual number, and the downward reading is larger than the actual number, then it is known that it is actually more than 18ml before it is poured, and it is less than 10ml after it is poured, then it is obvious that the volume of liquid poured out is greater than 8ml, and the answer is c

2.Option B, incorrect, is that when there is no description, the liquid should be taken one-third of the volume of the test tube. This is common knowledge in chemistry.

3.The hardness of paraffin wax is less than that of knife material and greater than the hardness of water. Because the hardness of the substance is used to cut the substance of the lesser hardness.

4.(Method 1) Use a dropper to pipette a few drops of the beverage to be tested, drop into a saturated and clear calcium hydroxide (i.e., hydrated lime) solution, if there is white gray turbidity, it means that it is a carbonated drink: Ca(OH)2 + H2CO3 = CaCO3 (white precipitate) + 2H2O; If there is no white gray cloudiness, it means that it is not a carbonated drink.

It is important to remember that this method cannot be reversed, because if saturated and clarified lime water is dropped into the drink, dissolvable Ca(HCO3)2 will be generated due to excessive H2CO3, so it is impossible to judge that there is no precipitation.

Method 2) Take a little of the drink, add a few drops of vinegar to it, if there are bubbles released, it means that it is a carbonated drink, otherwise it is not. This method is relatively simple, and vinegar is easy to obtain at home.

1 The first time I looked up at the lowest part of the concave liquid level, the reading was 18ml

I guess it's 8 ml.

Remember that "pitch big and pitch small" is fine, so it should be greater than 8 ml and less than 10 ml.

2 is incorrect, B, take too much.

3. The hardness of paraffin wax is very soft.

4. Take a little test solution, add sodium carbonate, and there are bubbles to produce carbonated drinks.

1 is greater than 8ml, and the upward view result is small, indicating that the liquid inside is greater than 18ml, and the overhead result is large, and the remaining inside is less than 10ml, so the output is greater than 8ml

There is no clear standard for 2 b liquids, either the solids that cover the inside of the test tube, or 1-2ml3 paraffin is a solid that is less dense than water and is insoluble in water.

4 Take a little drink, add some vinegar to it, and if there are bubbles, it will be a carbonated drink.

Question 1 Option C If you don't know this question, you can draw a sketch and it will be solved very smoothly.

Question 2 Option B This is a common sense question, when taking liquid, the liquid generally does not exceed 2 3 of the container, and if it needs to be heated, it cannot exceed 1 3

Question 3 Paraffin wax hardness is small, density is less than water (less than 1g cm 3), paraffin wax is not allowed to water.

Question 4 The beverage is heated and the gas is released into the clarified lime water, if there is no turbidity, it proves that it is not a carbonated beverage.

Question 1 D The value of looking down and looking up can change with the angle It is impossible to determine !

Question 2 A If the dosage is not stated, put the drug into the test tube about 3 1!

Question 3 Paraffin: white solid, odorous, usually cylindrical, less dense than water, not tolerant of water, small in texture, easy to melt, soft.

Question 4 Add sodium carbonate, and bubbles are carbonated drinks!

1.Choose C greater than 8mlBecause when looking up at the concave reading, the result will be low, so the actual reading should be greater than 18ml; However, when looking down at the concave surface, the reading is high, and the actual reading of the first page is less than 10ml. Then the volume of the liquid that the student arrives at is greater than 8ml.

2.Pick B. Because there are also different sizes of measuring cylinders, such as 5ml graduated cylinders. The capacity of the graduated cylinder should be indicated.

3.The conclusion should be the density of paraffin wax rather than the hardness of paraffin, right? If the density of paraffin wax is less than that of water. The hardness is very small.

4.Take an appropriate amount of the beverage in a test tube or other container, add hydrochloric acid dropwise, see if there is gas generated (or directly heated), and pass the gas into the clear lime aqueous solution, if the solution becomes turbid, it proves that the drink is carbonated beverage.

Strictly carbon monoxide, sulfur dioxide, nitrogen dioxide.

In general, it should be nitrogen oxides, hydrocarbons, and sulfur dioxide, and the reason why nitric dioxide is said is because it is too easy to become nitrogen dioxide (famous poisonous gas) and cannot exist in nature, so it is considered harmful by default, nitric oxide is actually harmless, and it can also be used for cancer!

The decay of the corpse is a slow oxidation, even if some poisonous gas is released, it is only a small amount, and nature itself also has the ability to purify these gases.

Otherwise, how many creatures have died since ancient times, isn't the earth still fine, until now it is caused by human interference).

Sulfur dioxide, nitric oxide, carbon monoxide.

The decay of animal carcasses is chronic, the oxidation is relatively thorough, and these reducing gases are not produced. Why is nitrogen dioxide excluded? Because nitric oxide easily combines with oxygen to become nitrogen dioxide, nitrogen dioxide combines with water and releases nitric oxide.

It should be sulphur dioxide, carbon monoxide and nitrogen dioxide. Carbon dioxide is not considered pollution. Nitric oxide is also not right because it is not stable in the air and will be oxidized to nitrogen dioxide! Upstairs wrong @@

To be precise, there are two types of pollutants that cause air pollution: dust pollution and gas pollution. Among the gas pollutants are carbon monoxide, sulfur dioxide, nitrogen dioxide.

Carbon dioxide gas is non-toxic, it is not a polluting gas, although it will bring harm to human beings in large quantities, but there must be a certain amount of carbon dioxide in the air. Because the oxygen that people breathe needs it to photosynthesize with green plants.

68000*

First find the relative molecular mass of iron in hemoglobin, and then divide it by the atomic weight of iron, which is the number of iron atoms.

Mass of iron in hemoglobin: 68000

Then count the number of iron-containing amounts:

You haven't studied molar mass, have you? That's all there is to it)

68000* to obtain the atomic mass of all iron atoms.

An iron atom has an atomic mass of 56

So... 68000*。。So d 4 pcs.

Solution: Ad

Take 10g of the sample and add 100g of dilute hydrochloric acid, just completely react to get only a colorless solution, indicating that there must be no copper sulfate and carbon powder in the sample, because if there is copper sulfate in the sample, the solution is blue; If there is charcoal powder, there will be insoluble matter.

A total of 4 g of carbon dioxide gas was collected, and if 10 g of calcium carbonate can be completely reacted to produce carbon dioxide, it means that there must be potassium carbonate with a carbon content lower than calcium carbonate, and there may be magnesium carbonate with a carbon content higher than calcium carbonate.

D: The composition may have 1Calcium carbonate + potassium carbonate, 2Calcium carbonate + magnesium carbonate + potassium carbonate.

Choose A, D

A is correct: the copper sulfate solution is blue, and the question requires colorless, and the toner is insoluble in water, so there must be no copper sulfate and carbon powder.

B Error: There must be potassium carbonate in the sample, but not necessarily magnesium carbonate.

Let the average molecular weight of carbonate be x.

xco3+2hcl====xcl2+h2o+co2

x 4410g 4g

x=110

caco3---100

k2co3---138

mgco3---84

If the molecular weight of CaCO3 is 100 and the average molecular weight of carbonate is 110, there must be K2CO3 with a molecular weight greater than 110 in the powder sample, but not necessarily MgCO3 less than 110.

C error: There are at least 3 cations, Ca2+, K+, H+, and possibly Mg2+.

Water itself is ionized, and there must be h+ and oh-.

d correct: there is 1Calcium carbonate + potassium carbonate, 2Calcium carbonate + magnesium carbonate + potassium carbonate in two cases.

It happens that the complete reaction only gives a colorless solution, which means that it must be free of copper sulfate and carbon powder.

Suppose the sample is all calcium carbonate.

caco3+2hcl=cacl2+h2o+co2↑

10g assumes that the sample is all magnesium carbonate.

mgco3+2hcl=mgcl2+h2o+co2↑

10 g assumes that the sample is all potassium carbonate.

k2co3+2hcl=2kcl+h2o+co2↑

10g collects 4g of carbon dioxide gas, so it must contain potassium carbonate and possibly magnesium carbonate!

So choose ACD

Doesn't it seem like the title is wrong? It should read - according to this analysis, the following judgment is incorrect.

Solution: aBecause it happens to be a complete reaction only to get a colorless solution. If there are copper ions in the solution, it will appear blue; If there is toner, there will be a black precipitate at the end (the toner does not react with dilute hydrochloric acid).

100 44 10gcaco3 produces gas.

mgco3+2hcl=mgcl2+co2↑+h2o

84 44 10 gmgCO3 produces gas.

k2co3+2hcl=2kcl+co2↑+h2o

138 44 10gk2CO3 produces "Gas.

Question conditions: A total of 4g of carbon dioxide gas was collected If the impurity is only mgCO3, then the amount of gas produced must be greater than 4g, so it must contain K2CO3. When K2CO3 is mixed with CACo3 in a certain ratio, 4g of gas can be produced.

Therefore, it is not certain whether it contains a mistake or not.

C: If you are sure that there must be CaCO3 and K2CO3, then the solution must contain Ca2+, K+, and H+, so it contains at least three cations.

D: There may be two compositions: may contain only CaCO3 and K2CO3: may contain CaCO3, K2CO3 and Mg2CO3.

A: There must be no copper sulfate right (copper sulfate solution has color), and there must be no toner (no reaction) if it can completely react. b：

The amount of carbon dioxide collected does not mean that there is magnesium carbonate or potassium carbonate or both, or it may not be both. However, 10 g of sample produces 4 g of gas, indicating that there is at least one magnesium carbonate or sodium carbonate. c：

With the same meaning as b, h ions are also considered cations, so there are at least 3 kinds of cations and at least 2 kinds of metal cations. D: The composition may have 1

Calcium carbonate + magnesium carbonate, 2Calcium carbonate + potassium carbonate, 3Calcium carbonate + magnesium carbonate + potassium carbonate.

So, alas

First, first of all, according to the chemical equation calculation, it is clear that the carbon dioxide generated by the reaction of 10g of pure calcium carbonate and sufficient hydrochloric acid is. The carbon dioxide produced by the reaction of 10g of magnesium carbonate and 10g of potassium carbonate with sufficient hydrochloric acid is more than less.

Second, the question says that a total of 4g of carbon dioxide gas was collected, which is less than the theoretical calculation. It shows that in the sample calcium carbonate, 1 contains impurities that do not participate in the reaction (only the mass, not CO2); 2. Contains impurities that participate in the reaction (but does not generate CO2; or substances that produce CO2 but less CO2 than the same mass of calcium carbonate); 3. The sample is excessive, the hydrochloric acid is insufficient, and the 4GCO2 generated is obtained according to the quality of HCl. (Other circumstances are not considered for the time being.)

In summary, 3 is excluded according to the condition "just complete response" in the question; "Only a colorless solution is obtained" excludes copper sulfate (blue) and carbon powder (black insoluble), and case 1 is also excluded in this question, [which also leads to the correct answer A]; It can only be case 2.

Specific analysis situation 2: According to the above one, it can be seen that the sample must contain potassium carbonate. If it is pure calcium carbonate, or only magnesium carbonate is mixed with, the CO2 produced is equal to or greater than that.

As for magnesium carbonate, it is impossible to determine whether it contains it, and the key depends on the quality of the substance.

Final possible composition scenarios:1Contains 2 substances: calcium carbonate and potassium carbonate; 2.Contains 3 substances: calcium carbonate, potassium carbonate, magnesium carbonate.

So only b is incorrect, and the other 3 are all correct.

I think it's a d copper sulfate is a blue solution and the toner is insoluble.

Copper sulfate crystals are decomposed by heat: CuSO4·5H2O=CuSO4+5H2O

Copper sulfate powder reacts with water: CuSO4+5H2O=CuSO4·5H2O

Zinc reacts with dilute sulfuric acid: Zn+H2SO4=ZnSO4+H2

Zinc reacts with hydrochloric acid: Zn+2HCl=ZnCl2+H2

Iron reacts with hydrochloric acid: Fe + 2HCl = FeCl2 + H2

Magnesium reaction with hydrochloric acid: stool Mg+2HCl=mgCl2+H2

Magnesium reacts with dilute sulfuric acid: Mg+H2SO4=MGso4+H2

Reaction of aluminum with dilute sulfuric acid: 2AL+3H2SO4=AL2(SO4)3+3H2

Reaction of aluminum with hydrochloric acid: 2al+6HCl=2alcl3+3H2

Copper oxide reacts with sulfuric acid: CuO+H2SO4=CuSO4+H2O

Copper oxide reacts with hydrochloric acid: CuO+2HCl=CuCl2+H2O

Iron oxide reacts with dilute sulfuric acid: Fe2O3 + 3H2SO4 = Fe2 (SO4) 3 + 3H2O

Iron oxide reacts with hydrochloric acid: Fe2O3 + 6HCl = 2FeCl3 + 3H2O

Copper hydroxide reacts with dilute sulfuric acid: Cu(OH)2+H2SO4=CuSO4+2H2O

Copper hydroxide reaction with hydrochloric acid: Cu(OH)2+2HCl=CuCl2+2H2O

Iron hydroxide reacts with dilute hydrochloric acid: Fe(OH)3+3HCl=FeCl3+3H2O

The sodium hydroxide solution reacts with dilute sulfuric acid: 2NaOH + H2SO4 = Na2SO4 + 2H2O

The sodium hydroxide solution reacts with hydrochloric acid: NaOH + HCl = NaCl + H2O

The sodium hydroxide solution reacts with dilute nitric acid: NaOH + HNO3 = NaNO3 + H2O

Aluminum hydroxide reacts with hydrochloric acid: Al(OH)3+3HCl=AlCl3+3H2O

Carbon monoxide reduces iron oxide: 3CO+Fe2O3= 2Fe+3CO2