A chemistry problem that has been bothering me for a long time

Composition of limestone: calcium carbonate. It contains 12% carbon, and now it contains 10% carbon, indicating that it contains other substances. Assuming that the limestone contains 100g, then adding other substances is 120g, that is, the mass fraction containing calcium carbonate is 100 120*100%=

Let the limestone mass be ag. Then the mass of carbon is: 10%*A The mass fraction of C element in GCACO3 is: 12%.

So the mass of CaCO3 is: 10%*a 12% g The mass fraction of calcium carbonate in limestone is: (10%*A 12%) a=10 12=

If the mass of carbon in the sample is 10 grams, the mass of the sample can be expressed as: 10g 10% = 100g

The mass fraction of carbon in calcium carbonate is: 12 (40+12+16*3)*100%=12%.

Therefore, the mass of pure calcium carbonate in the sample can be calculated from the mass of the carbon element:

10g/12%=

So the mass fraction of calcium carbonate in the limestone sample is:

Set limestone to 100g

10%*100=10g (for carbon mass).

10*100 12= (for the mass of calcium carbonate).

Divide by the total mass of 100g, and the answer is.

The answer is a

All other options are wrong.

Why. Because nitrogen and nitric oxide have the same molar mass.

The mass of both gases is also the same.

So the number of moles of the gas is the same.

And because there are two atoms in one molecule of both.

So the number of atoms of both gases is the same!!

Why is it bwrong?

Because the pressure may be different.

If the pressure is different.

The number of moles of the same volume of gas will be different!!

Why is c wrong?

Ethane and nitric oxide (i.e., equal mass) of the same volume and density have five atoms in the former, although the number of moles of the gas is the same.

The latter has only two atoms.

So the number of atoms is not equal!!

Why is d wrong?

The reason is similar to B.

The conditions for the temperature are not given in the options.

If the temperature is different, the number of moles of the two gases will be different!! Even if their molar masses are equal.

The number of atoms is also not equal!!

Do this kind of question. If it appears.

Temperature volume. Pressure.

The other two must be taken into account.

Indispensable!!

Guaranteed correct! Landlord please give points!

Pick the D answer.

Reason: Nitrous oxide and carbon dioxide have the same relative atomic mass, and because the external conditions are the same, the number of atoms contained in the two gases must be equal.

The reason for Fe2+ is that the addition of Fe can react with CuCl2 Fe+CuCl2===FeCl2+Cu, so the cation contained in the filtrate must be Fe2+

There must be Fe2+, if X is before H, then there is X2+ in the solution, if X is after H, there may be X2+, Cu2+ is also possible, depending on the amount of iron powder. And x is obviously before h, so fe2+, x2+ must be there, Cu2+ may be there.

The correct solution is obviously wrong, if there is no x2+, it means that it has been replaced, and the filtered solid with dilute hydrochloric acid will produce bubbles!!

You can't read English, this question is not difficult.

The precipitate should be lead iodide.

Question 1: Precipitation quality Relative mass of lead iodide * Avogadro's constant Question 2: Because the concentration of the solution is very large, and lead iodide is insoluble, there is no need to consider the solubility product. Directly calculate the excess of PD(II) and I ions, and find the yield.

The concentration of hydrogen ions consumed is, c(h+)=

Ice water mixture is a compound because it is both made up of water molecules.

Ice water mixture is an oxide because it has the chemical formula H2O and is composed of two elements, one of which is oxygen.

A primitive is a substance made up of only one element, and a compound is a substance made up of two or more elements.

An oxide is a compound composed of two elements, one of which is oxygen.

The highest valency of the main family element = the number of main families, and the lowest valency = the number of main families - 8.

In addition to the noble gas elements h, f, o

Select b for this question

Pick B. There is no negative price for metals, so the bottom price is zero price, and the most ** is the ordinal number of the main group of the element (the law of the secondary group is a little different, don't worry about high school, but remember a few common ones); The highest positive valence of nonmetals is also the ordinal number of the main group (except for oxygen and fluorine), and the sum of the absolute values of the lowest negative valence and the highest positive valence is 8 (8 minus the ordinal number of the main group). Only in B did not fully reach the minimum price of each substance.

I don't know how to ask again.

The known conditions are these:

brclx+so2+

By equation: n(brclx)=1

n(hbr)=

1;n(hcl)=

xm(brclx)=

Due to the fact that the ratio of the amount of the substances reacted with halogen and Ag+ is 1:1

And the mass of halogen mutuals is the same as that of HBR.

Columnable equations: x=3 by solving the equation; The second question came out.

The amount of agno3 substances participating in the reaction is:

I don't know if you can understand that.

1. Solution: The mass of the solute in the 530GN2CO3 solution is 530*25%=

na2co3+co2+h2o=2nahco310618

x=y=i.e., the solubility of NaHCO3 is (210-180) (

The answer is bBecause the elements in a are the lowest price, they can only be oxidized as reducing agents. B is the most important can be used as an oxidant. c. Magnesium is a metal that can only be used as a reducing agent. d. Aluminum is a metal that can only be used as a reducing agent. Hope to adopt. Thank you.

Because the metal element is only positive, it can only lose electrons in the chemical reaction, so it is only used as a reducing agent, so the particles in CD and A are at the lowest valence (F, I are in the VIIA group, S is in the VI group), so the valence can only be increased, as a reducing agent, and B is selected for the above answer

1.Reactions involved:

3CuSO4+2AL=AL2(SO4)3+3CU AL2(SO4)3+6NaOH=2AL(OH)3 precipitate+3Na2SO4

Al(OH)3+NaOH=Naalo2+2H2O The above two can be combined as:

Al2(SO4)3+8NaOH=2Naalo2+3Na2SO4 2Al+2NaOH=2H2O=2Naalo2+3H2 gas (1).The gas volume is , ie.

So by having to have with the superfluous al.

The amount of NaOH substance is: 200ml*2mol L = so the amount of HAOH substance that reacts with Al2(SO4)3 is:

The amount of Al2(SO4)3 of the substance is.

So the amount of al-matter in is .

So the mass of adding aluminum powder m = (

2).From the amount of cuso4 substance is obtained.

So the quantity concentration of the substance is: