Chemistry solution for junior high school, a chemistry problem for junior high school solution

147 g of 10% sodium chloride solution. Sodium chloride is. Water is.

Na2CO3+2HCl=2NaCl+CO2+H2OA=g), B=g), C=g), D=

1) Mass fraction of sodium carbonate in a solid mixture.

2) The mass of carbon dioxide generated.

3) The solute mass fraction of the hydrochloric acid.

Your numbers are too annoying, and the rest is up to you. Teacher 147 should be 117

Solution: Let the mass of sodium carbonate be x and sodium chloride is.

na2co3+2hcl=2nacl+h2o+co2↑x73x/106

117x/106

44x/106

The mass of sodium chloride after the reaction is 10% 147g=

117x/106+

The solution is x=the mass of carbon dioxide generated is 44 106, and the mass of hydrochloric acid consumed is 73 106 1) The mass fraction of sodium carbonate in the solid mixture.

2) The mass of carbon dioxide generated.

3) The mass of this hydrochloric acid solution is 147g+

The solute mass fraction of this hydrochloric acid.

Na2CO3 + 2HCl = 2NaCl + H2O + CO2 (gas) can be found to be 106g sodium carbonate can be reacted to make 117g of sodium chloride. The mass difference is 11g in the solution obtained, m(NaCl)=, and the quality difference between the obtained sodium chloride and the quality of the original mixture is so that the mass of sodium carbonate in the original mixture is known to be 2g.

1.The mass fraction of sodium carbonate is:

2.From the relationship of the equation, it can be known that the sodium carbonate reaction can release carbon dioxide3It is also known from the equation that the HCl mass is, and the mass of the original hydrochloric acid solution can be calculated by the conservation of mass: 147+, so the hydrochloric acid solute mass fraction is:

Good evening! Let the mixture contain Na2CO3

xg,naclyg

x+y=na2co3+2hcl→2nacl+co2↑+h2ox———a

a=117x/106

117x/106+y=10%x147……Obtained from , x=, y=3g

m(na2co3)=

x100%=

m(co2)=

m(hcl)=

m (hydrochloric acid) =

w%=x100%=

Answer: The mass fraction of sodium carbonate is.

The mass of carbon dioxide is.

The solute mass fraction of this hydrochloric acid is:

It is known that the greater the concentration of sulfuric acid, the greater the density. After mixing the two sulfuric acid solutions with a mass fraction of 10% and 90% respectively in equal volumes, the solute mass fraction of the solution is ( ).

A cannot be determined: B is greater than 50%, C is equal to 50%, D is less than 50%.

Solution: Because the same volume of solution is taken, the greater the concentration of the sulfuric acid solution, the greater the density.

Therefore, the mass of the solution of concentrated sulfuric acid is large, and the mass of the solute contained is large, so the mass fraction is greater than 50%, if it is difficult to understand, give an example to calculate.

It is assumed that the density of concentrated sulfuric acid is and the density of dilute sulfuric acid is .

Then [(v* v*.]

c, if the mass of the two solutions is m, then the total mass of the solute is, and the total mass after mixing is 2m, then the mass fraction after mixing is m 2m = 50%.If it is an equal volume mixture, you should choose B, for the following reasons: let the masses of the two solutions be m1, m2, and the densities are a1, a2 respectively, and the mass fraction of the mixed solution = (, because it is an equal volume mix, then there is m1 a1 = m2 a2, because a1>a2, then m1>m2, subtract the mass fraction expression, and the result is obvious.

It is correct to choose the mass reduction of sodium chloride.

The seawater introduced into the salt pan here is the salt solution in the title, and the salt crystals precipitate out after the water evaporates, and it should be noted that the precipitated salt crystals have been separated from the solution system, that is, the precipitated salt is no longer part of the solution, so the salt quality in the seawater in the salt pan is reduced.

The quality of sodium chloride in B is unchanged, but it is wrong to think that the precipitated salt is still in the solution system.

He is the ...... of calcium chloride in seawaterOf course, the quality has decreased ......If it is based on the principle of quality, the law of constancy does not change.

It should be B, the answer is wrong, if it is not B, the mass of sodium chloride should also increase, the same space, the same substance, the more substance, the greater the mass, the same water is decreasing, the mass of sodium chloride should increase.

There is a play on words in this question, because there is wind blowing, and sodium chloride will definitely be reduced somewhat.

Of course, it has decreased, and some of the salt in the seawater has been precipitated and transported away.

The answer is wrong, you should choose B, your idea is correct.

You should choose C, no matter what, the quality of the solute will not.

Experiment: A white cloth strip soaked in iodine was placed in a test tube filled with anhydrous alcohol, and the white cloth strip was found to be slightly colored.

Place a white cloth strip soaked in iodine in a test tube filled with 20% alcohol and observe the results.

A white cloth soaked in iodine is placed in a test tube filled with 40% alcohol and the results are observed.

Place a strip of white cloth soaked in iodine in a test tube filled with 80% alcohol and observe the results.

If the results are different, it is related to the alcohol concentration, and if the results are all the same, it is not related to the alcohol concentration.

Do blank comparison tests Do some comparison tests with large differences in alcohol concentration.

Let's say the medicine is 600 grams.

600 grams of medicinal soup are made with 3000 grams of water at a time, and the active ingredients are distributed in 600 grams of medicine and 600 grams of medicinal soup, and the proportion of non-extracted is 50.

Decoction with 1000 grams 3 times, each time the active ingredient is distributed in 600 grams of medicine and 400 grams of medicinal decoction, and the proportion that is not extracted in the end is 6 out of 10 to the 3rd power).

It is not necessarily the same, according to the title this is a problem of solubility, decoction is solvent medicine is certain, and it is thought that there is solubility, boiled with water.

For example, when 3000 becomes 600, 600 is unsaturated, but when it reaches 400, then 1000 becomes 200 saturated for the first time, 1000 becomes 200 saturated for the second time, and 1000 becomes 200 for the third time.

If 3000 to 600 is saturated, then 1000 to 200 is saturated three times.

The decoction is to put a certain amount of water first, and then evaporate to the remaining amount to meet the requirements.

A decoction is a method in which the medicine is put in water and the useful ingredients in the medicine are boiled out. And the useful ingredients in the medicine are a certain amount, and boiling in three times is equivalent to the evaporation of the medicine and water every time it is cooked, and only one boil needs to evaporate once, so the concentration of one boil is high.