For chemistry calculation questions in the third year of junior high school, please write down the c

cacl2 + na2co3====caco3 + 2naclx= y= z=

Table salt is mixed with the mass of calcium chloride:

Mass fraction of solute in sodium carbonate solution:

Mass fraction of solute: (

Solution: (1) The precipitate mass must contain calcium carbonate.

Calcium ion = calcium chloride.

Mass of calcium chloride =

2) The number of moles of calcium ions = the number of moles of carbonate = the number of moles of sodium carbonate = the mass of sodium carbonate =

Mass fraction: There is original sodium chloride in the solution New sodium chloride added to water Original water:

So. Mass score ( + (173+ Do your own thing.)

1: Let calcium chloride be x 2: Let sodium carbonate be y

cacl2+na2co3=caco3↓+2nacl cacl2+na2co3=caco3↓+2nacl

x 1g y 1g

x 1g y 1g

x= y=w%= ——

53g w%=2%

3: Let the generation of sodium chloride be Z

cacl2+na2co3=caco3↓+2nacl1g z

1g zz=

mnacl=

m = 25 + 173 + 53-1

w%=——

The solution of chemical calculation problems is generally inseparable from chemical equations, first write the chemical equation of the reaction:

mno2+4hcl=mncl2+cl2+2h2omno2---cl2

m Secondly, the relation is listed according to the known conditions and the quantity to be sought (as above).

Finally, write the proportional formula: 87 71 = m m = mass fraction of manganese dioxide in the sample = (

Can't see clearly, are you making people see?

Find out the equation used.

Find out what is known and what is not known.

It is solved using the mass ratio of each substance in the chemical equation.

The requirements of the chemistry high school entrance examination, in fact, the score of this question can definitely be obtained. Usually the calculation problem can be handled like this:

Understand the meaning of the question and write the chemical equation that involves the reaction in the question;

List chemical equations, be sure to trim, and write correctly;

Set up the unknowns. Usually unknowns are reactants or products involved in chemical equations;

Find out the amount of reactants or products that can be brought into the calculation;

The mass fraction of the participating reaction corresponding to the chemical equation;

Another line writes the mass of the actual substance involved in the reaction, unknown;

List proportional relations;

solve for unknowns;

If the question of mass fraction is involved, it is calculated according to the formula;

Answer. If it involves images or ** questions, the sample contains impurities, and a simple conversion must be carried out to find the quality of the pure substance.

1co2

The relative molecular mass is.

2fe2(so4)3

The relative molecular mass is.

The mass of 3 h = 2 18 * 27 = 3g

Mass of hydrogen peroxide = 3 (2 34) = 51 g

m(fe2o3)=100t*80%=80tfe2o3---2fe

80 x160 80 = 112 x x = 56t to refine pig iron with 4% impurities: 56 (1-4%) = Fe3O4---3Fe

232 168x 56t232/x=168/56 x=

With magnetite containing 80% ferric tetroxide, it is required.

(1) 100t hematite 80%.

Then MFE2O3 = 100 80% = 80g

fe2o3--2fe

80g x solution gives x=56

Altogether then FE is 56

The mass fraction of Fe in pig iron is 96%.

Then m pig iron = 56

In the same way, (2) m magnetite = m pig iron divided by ((56 3) (56 3 + 16 4)) 80% = do the math yourself.

Analysis: Because the chemical formula in the chemical equation represents a pure substance, the mass of raw iron can be calculated from the mass of hematite and the mass fraction of iron oxide and the mass fraction of impurities in pig iron

Solution: Let the mass of smeltable pig iron be x

fe2o3+3co

High temperatures2fe+3co2

100t×80% x×（1-4%）

160/80t=112/96％x

x A: Pig iron containing 4% impurities can be smelted.

(3) As long as you calculate which fertilizer has the highest nitrogen quality to buy, first calculate the mass fraction of nitrogen element of the three chemical fertilizers. nh4no3 has already been calculated in the second question, now let's count the other two.

Nitrogen fraction of CO(NH2)2=(14 2) 60 100%=;

Nitrogen fraction of NH4HCO3 = (14 2) (14 + 4 + 1 + 12 + 48) 100% =.

If you buy CO(NH2)2, the mass of nitrogen is 10000 1080*;

If you buy NH4NO3, the mass of nitrogen is 10000 810*35%=;

If you buy NH4HCO3, the mass of nitrogen is 10000 330*;

So NH4HCO3 should be bought

(2) 14 + 4 + 14 + 16 * 3 = 80, which is the NH4NO3 mass fraction. The mass fraction of the nitrogen removal element (28) is equal to 35%.

Let the mass of the reacted sodium carbonate x, the mass of the sodium chloride generated, YN2CO3+2HCl=2NaCl+H2O+CO2106 117 44

x y106:x=117:y= x= y=10g sample contains sodium chloride:

The mass fraction of solute in the unsaturated solution obtained after the reaction = (A: .

2hcl + na2co3 == 2nacl + h2o + co2↑

m1 m2106 m1 = 117 m2 = 44 m1 = , m2 =

So in 10g of soda ash containing sodium chloride, the sodium carbonate mass = , the sodium chloride mass = = plus the sodium chloride generated by the reaction, the sodium chloride mass in the solution after the reaction = + = solution mass = 10 + =

So the mass fraction of solute in the unsaturated solution obtained after the reaction = = 10%.

The mass of CO2 is grams.

na2co3+2hcl=2nacl+h2o+co2↑106 73 117 44

x g y g z g column ratio, solution.

x= y= z=

The mass fraction of the final solution is: NaCl = (