How to do 9 questions in chemistry? Choose B! Chemistry questions, what to do with option B

The amount of Fe3O4 substance is.

The amount of the substance of which is ferric is:

Becomes ferric iron and transfers electrons for.

Dichromate becomes Cr3+ and transfers 6 electrons.

Let the concentration be cc*c=

Reaction when there is a surplus of sulfuric acid.

fe3o4+4h2so4=feso4+fe2(so4)3+4h2onfeso4=

k2cr2o7+7h2so4+6feso4=3fe2(so4)3+cr2(so4)3+k2(so4)3+7h2oxx=

Solution: n(ferric tetroxide) =

So n (iron ions) = 3 * n (ferric oxide) = 36 725mol because Fe3+ -e = Fe2+

Therefore, the total loss of electrons in the reaction n(e) loss = n (iron ions) = 36 725molCr2O7 2- The valency of chromium element in the reaction is +6 valence.

So cr2o7 2-- 6e=cr 3+

Because the number of electrons gained in the redox reaction is equal to the number of electrons lost, that is, the amount of electrons obtained is 36 725mol

So N(K2Cr2O7)=N(CR2O7 2-)=1 6 *N(E) gives =1 6 *36 725mol=6 725mol

So C(K2Cr2O7)=N(K2Cr2O7) V(K2C2O7)AQ=6 725mol

b From the first part, it can be judged that there is NO2- CO32- and from the third step, it can be judged that there is NH4+, so the existence is easy to judge.

The white precipitate contains Agno2 Ag2CO3, and the mass is reduced by 1g after adding hydrochloric acid, and the change is that the precipitate changes from Agno2 Ag2CO3 to AgCl, so the mass of AgCl is the amount of Ag substance, and the amount of Ag can be obtained, and from the second part, it can be seen that the amount of carbonate substance is and the amount of Ag substance can be obtained, so the amount of Ag2- substance is.

The amount of NH4+ ion is well found from the third step.

So the ratio can be 5 2 1

The white precipitate is AGC3, and the mass is reduced is AGCl, and 1 g of white precipitate CaCO3,

At V(NaOH)=10ml, the weak acid hy concentration [hy]=[y-] is approximated. At this time, ka[hy]=[h+][y-] [hy]=[h+], so that at this time, ph=5, ka[hy]=10 -5

ksp=(2*10^-2)^2*5*10^-5=2*10^-5.After mixing, the concentration of silver ions is and the concentration of sulfate is, so q=10 -5 is less than k, so there is no precipitation, and I hope to adopt it.

HCO3- is ionizable and hydrolyzable, but both are relatively weak.

HCO3- =H+ +CO32- (reversible) ionization The sum of anion concentrations increases.

HCO3- +H2O = OH- +H2CO3 (reversible) hydrolysis with no change in anion concentration.

CO32- can only be hydrolyzed, which is also relatively weak, but the degree of hydrolysis is greater than that of HCO3-.

CO32- +H2O = HCO3- +OH- (reversible) The first step is hydrolyzed, the degree is greater than HCO3- The sum of anion concentrations is larger, and the degree of ionization is greater than that of HCO3-.

HCO3- +H2O = OH- +H2CO3 (reversible) is hydrolyzed in the second step with no change in anion concentration.

Therefore, the sum of the anion concentrations of Na2CO3 is greater than that of NaHCO3 solution.

Their ion concentration Na2CO3:

na+>co3^2->oh->hco3->h+nahco3:

Na+>HCO3->OH->H+>CO3 2-NaHCO3 is very weak in alkalinity, pH = about (because HCO3- hydrolysis is about greater than ionization, hydrolysis is HCO3-+H2O H2CO3+OH-; Ionization is HCO3-=H++CO32-). Therefore, HCO3- can neither exist in large quantities in acidic solution (H++HCO3-=H2O+CO2) nor in alkaline solution (oh-+HCO3-=H2O+CO32-). b

Because in B, the second solution has more carbonate, and the carbonate is bivalent, because the concentration of sodium ions in the two solutions is the same, the number of anions in the second solution is known from the conservation of charge, so B is wrong, and option C is also wrong.

That's right; The amount and concentration of anionic substances are equal, and it is simpler to consider cations;

1 cation concentration = c(na+) + c(h+) =. 1mol/l;

2 cation concentration = c(na+) + c(h+) =. 2mol/l;

If you have any questions, please ask

b pair, part of the hydrolysis of carbonate in 2 to form bicarbonate and hydroxide, so the amount of the substance will be slightly larger, and the hydrolysis of bicarbonate in 1 and the generation of anions, but bicarbonate is also lost, and the amount of anionic substances is still .

Strong acids and strong bases must have more neutralization heat than strong acids, weak alkalis or strong alkalis and weak acids, so it can be concluded that a is the smallest.

When the alkali is dissolved, it will also release a lot of heat, so the second B is greater than the third C, so B>C >A

Constant ionization in the reaction, whereas ionization of weak electrolytes is to absorb heat, while NaOH is solid. Solids are generally dissolved except for nitrate, so B is the largest and A is the smallest.

It should be B

c. Copper hydrochloric acid is added and does not react, and there is no obvious phenomenon.

Bubbles are created in the iron reaction, and the solution turns light green.

Oxidation pants copper reaction, black cover shouting slippery powder gradually decreased, solution wax colorless turned blue.

Solution: a, calcium oxide and water mixed will release a lot of heat, calcium carbonate is insoluble in water, potassium chloride is easily soluble in water, after adding water, the phenomenon is different, the use of water can be identified, so a does not meet the topic;

B, calcium chloride and barium hydroxide mixed will produce calcium hydroxide slightly soluble in water, there is precipitation phenomenon, sodium carbonate and barium hydroxide mixed will produce barium carbonate white precipitation, potassium sulfate mixed with barium hydroxide will produce barium sulfate white precipitation, the phenomenon is the same, the use of barium hydroxide solution without hall culture method identification, so b in line with the topic;

c. Copper and dilute hydrochloric acid are mixed without reaction, there is no phenomenon, iron and dilute hydrochloric acid are mixed with liquid to produce hydrogen, there are bubbles, copper oxide is mixed with dilute hydrochloric acid to produce copper chloride, the aqueous solution is blue, the phenomenon is different, the use of dilute hydrochloric acid can be identified, so C does not meet the topic;

d. The mixing of copper chloride and calcium hydroxide will produce copper hydroxide blue precipitation, sodium nitrate and calcium hydroxide do not react, and there is no phenomenon in mixing, and potassium carbonate and calcium hydroxide are mixed to produce calcium carbonate white precipitation, the phenomenon is different, and it can be identified, so d does not meet the topic;

Therefore, choose B