Two chemistry questions for junior high school, please, ask a few chemistry questions for junior hig

D. Quicklime cao

The equation is as follows.

cao+h2o=ca（oh）2

Ca(OH)2+Cu2+=Cu(OH)2+Ca2+Cu(OH)2 is the precipitation.

A limestone b sulfuric acid c sodium hydroxide is too acidic or alkaline and will pollute the environment.

Coexistence conditions: no precipitation, no volatile gases, no unstable substances, simply put, no reaction that reduces the total number of ions.

Select ccu2+2oh- cu(oh)2

Coexistence conditions: no precipitation, gases, water, weak electrolytes are generated

c naoh

Ca2+ in quicklime Ca2+ is a heavy metal that is harmful.

NaOH neutralizes acid and generates Cu(OH)2 precipitate.

No precipitation, no weak electrolytes (e.g. HF, etc.) No water is generated, no gas is generated.

I choose DQuicklime is put into water to form calcium hydroxide, and the neutralization reaction continues, and the acidity and copper ions are removed at the same time, so the final product is water and copper hydroxide, and a small amount of calcium hydroxide has no effect on crops.

The conditions for the coexistence of ions in aqueous solutions are: the isolated ions must exist at pH>7, the acidic ions must exist at the pH<7, and the strong ions are not limited by this (sodium, nitrate ion types), and there should be no ions that can be precipitated in combination with them.

The second floor is wrong, CA is not a heavy metal.

I guess it's for cost reasons.

Quicklime is much cheaper.

cao+ho2====ca(oh)2

2oh-+cu2+====cu(oh)2 This is the precipitation.

Quicklime is not alkaline, but Cao is dissolved in water to generate Ca(OH)2CaO+Ho2====Ca(OH)2, an alkaline substance, which can neutralize acidity.

Ca(OH)2 can react with copper ions to form Cu(OH)2 precipitates, thereby removing copper ions. In addition, quicklime is cheaper, and if sodium hydroxide is used, although it can neutralize the acidity, the cost is higher. Therefore, choose D

Coexistence conditions: no precipitation, no volatile gases, no unstable substances.

Ca(OH)2+CuSO4---Cu(OH)2+CaSO4 (precipitate), Ca(OH)2+Na2CO3---2NaOH+CaCO3 (precipitate), CaCO3+2HC---CaCl2+H2O+CO2 (gas), 2AL+6HC---2ALC3+3H2 (gas).

1 ca(oh)2 + cuso4 = cu(oh)2 down arrow + caso4

2 Na2CO3 + Ca(OH)2 = CaCO3 down arrow +2NaOH

3 CaCO3+2HCl=CaCl2+H2O+CO2 up arrow.

1) Ethanol C2H5OH Ethane C2H6 Observing their chemical formula, ethanol is only one more oxygen atom than ethane, and the ratio of C and H is 2:6, and the ratio of their relative atomic mass is 12:1, you can know that whether it is ethanol or ethane, in one of their molecules, the mass ratio of C and H is 4:

1 (i.e. 5 copies in total, 4 copies for C).

Carbon element mass fraction = (1-oxygen %) 4 5 = (1-c%)4 52) In the remaining mixture, since manganese dioxide is the catalyst, the mass of the catalyst is unchanged, and the remaining hydrogen peroxide = then oxygen is produced Original hydrogen peroxide - remaining hydrogen peroxide = according to the chemical equation 2H2O2 = 2H2O+O2 amount of substance 2: 2: 1

Mass 68 : 36 :32 now set h2o2xg x :

68：x=32： x=

So the hydrogen peroxide solute is.

Alcohol is C2H6O, ethane C2H6 is easy to obtain the mass ratio of carbon and hydrogen, and carbon and hydrogen account for 1-C% to obtain the mass fraction ratio.

1.Extra-nuclear electrons move around the nucleus at high speed on different electron large tars, a phenomenon called hierarchical arrangement of extra-nuclear electrons

2.The schematic diagram of the atomic structure can be used to represent the internal structure of the atom The schematic diagram of the imitation bending structure of the atomic junction and failure is composed of two parts, one is the nucleus part, which is represented by a circle, and the number of charges carried by the nucleus is marked with a "+" sign and a number;

The second is the extra-nuclear electron part, where the electron layer is represented by an arc and the number of electrons on each layer is indicated by numbers

1.Orbital hierarchical arrangement of extranuclear plexus

2 Composition of atoms. The number of the sails of the original seepage - the number of electrons.

1) The mass of hydrogen divided by the mass fraction of hydrogen is the mass of urea, but the answer is that there is a problem with no wild resistance?

It should be: 5 (4 (12+16+28+4))=

2) You assume that the milk has a total of 100 grams, then the protein content in the milk is 100*, and the nitrogen mass fraction in the protein is 16%, so the nitrogen element of the protein in the milk is 100*, so the protein in the milk has a nitrogen mass fraction of (100*100

The teacher will talk about it in class

The first hand asked.

Personally, I think you wrote it wrong, please check it again, if there is any problem, if not, I will give it to you.

Second question. It is simplified.

Let the mass of milk m, then the content of protein in milk is m*, then the content of nitrogen in protein in milk is m*, therefore, the mass fraction of nitrogen in protein in milk is m*

This is the calculation process that is really suspicious, and the method you write is the calculation process of celery peel after simplification.

1) D2) first calculate the mass of sulfate, which is 70g 7% (SO4 H2SO4=, according to the law of conservation of mass, so the mass of sulfate is generated, so the mass of the metal is 6g 20%=.

1) I can't do it, I can't help you.

2) Set the metal to x grams.

x/70+x=20%

x=1400/80