(1) Weigh 65438±00g sample, dissolve it in water, and filter to remove insoluble impurities to obtain filtrate;
(2) A sulfuric acid solution with a mass fraction of 20% was added dropwise to the filtrate until the reaction was just completed, and the mass of the consumed sulfuric acid solution was measured to be 24.5 g;
(3) evaporating the reacted solution to dryness, and weighing the obtained white solid as11.2g. ..
Please calculate according to the experimental data of classmate A:
(1) The mass fraction of potassium carbonate in the sample.
(2) The mass fraction of potassium in the sample.
(3) Student B measures the pH value of the solution after the reaction in Step 2 of Student A with pH test paper, and the result shows that the pH value of the solution is greater than 7. You think that the mass fraction of potassium in the sample measured by classmate A is _ _ _ _ _ _ _ (fill in "big", "small" or "unchanged"), and the reason is _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.
1.( 1) Let the mass of K2CO3 in the sample be x.
k2co 3+h2so 4 = = = k2so 4+CO2 =+H2O( 1)
138 98
X 24.5 20%
138: 98 = x: 24.5g× 20% (1)
X = 6.9g (1 point)
(2) The mass fraction of potassium in the sample is
X100% = 50.2% (2 points)
(3) The white solid obtained after a small amount of evaporation contains potassium carbonate, and its mass is relatively small (1) (6 points for this question * * *).
2. When determining the composition of the mixture of sodium chloride and sodium sulfate, the extracurricular activity group of Qianjin Middle School conducted the following experiment: 20g of the mixture was dissolved in water, the obtained solution was divided into four parts, and then a certain amount of barium chloride solution with unknown mass fraction was added respectively. The experimental data are shown in the following table:
first
The second copy
The third copy
Fourth copy
Mass of solution added with barium chloride (g)
15
20
25
30
Mass (g) of the precipitate obtained by the reaction.
1.40
1.86
2.33
2.33
If the related chemical reaction is: Na2SO4+BaCl2=BaSO4↓+2NaCl, please calculate:
(1) According to the table, it can be inferred that in the first part of the table, BaCl2 is completely reacted, while Na2SO4 remains.
(2) The mass fraction of barium chloride solution is unknown.
(3) What is the mass fraction of sodium sulfate in the original mixture? (accurate to one decimal place)
3. Ammonium nitrate (NH4NO3), referred to as ammonium nitrate for short, is a white crystal with strong hygroscopicity and easy caking, so it should be stored in a cool and dry place. Ammonium nitrate can support combustion, and it is easy to explode at high temperature. It can't be put together with flammable materials to avoid explosion.
Please calculate:
(1) The relative molecular weight of ammonium nitrate is.
(2) The mass ratio of nitrogen, hydrogen and oxygen in ammonium nitrate.
(3) The mass fraction of nitrogen in ammonium nitrate is.
4.(8 points) One sample is a mixture of copper and copper oxide. In order to determine the content of copper oxide in this sample, 20g of this sample was taken and diluted hydrochloric acid was added in four times to make it fully react. The mass of hydrochloric acid used each time and the mass of residual solids after the reaction are shown in the following table:
frequency
Mass of dilute hydrochloric acid added/g
Mass of remaining solids
1
40
16
2
40
12
three
40
10
four
40
10
Q: (1)20g The mass of copper in this sample is.
(2) The mass fraction of copper oxide in the sample is.
③ Solute mass fraction of dilute hydrochloric acid. (Two decimal places are reserved for the calculation result)
6.(5 points) In order to explore the mass fraction of iron in ferroalloys, a classmate has conducted three experiments successively, and the experimental data are as follows:
Number of experiments
project
first time
second time
the third time
Alloy mass/gram
20
20
40
Mass of dilute sulfuric acid added/g
100
120
80
Mass of hydrogen produced/gram
0.4
0.4
0.4
According to the students' experiments, try to answer the following questions:
(1) In the three experiments in the above table, when the iron in the alloy has just completely reacted, the mass of dilute sulfuric acid solution consumed is _ _ _ _ _ _ g. ..
(2) What is the mass fraction of iron in Cu-Fe alloy?
7.NaOH solid contains Na2CO3. The teacher arranged the first group to do the experiment of removing Na2CO3 from NaOH solution. The students in the second and third groups did experiments to determine the mass fraction of Na2CO3 in the solid mixture.
I. The students in the first group take a certain amount of solids and dissolve them in water to get a mixed solution. In order to remove Na2CO3 impurities from the solution, students A, B, C and III respectively chose the following reagents for experiments. Among them, the unreasonable reason is.
A: Appropriate amount of dilute hydrochloric acid. B: A proper amount of barium hydroxide solution. C: appropriate CaCl2 _ 2 solution.
Ⅱ. In the second group, the mass fraction of Na2CO3 in the mixture of NaOH and Na2CO3 was measured by the device shown in the left figure, and the data was weighed by an electronic scale in the following table:
Weighing item
Mass (gram)
A mixture of sodium hydroxide and sodium carbonate
9.30
Conical bottle quality
4 1.20
Conical flask+dilute hydrochloric acid mass (excess)
14 1.20
After the conical flask+a certain mass of dilute hydrochloric acid+a mixture of all NaOH and Na2CO3, the mass is weighed for the first time.
148.50
After conical flask+a certain amount of dilute hydrochloric acid+a mixture of all NaOH and Na2CO3, the mass of the second weighing.
148.30
After the conical flask+a lot of dilute hydrochloric acid+all the mixture of NaOH and Na2CO3, weigh the mass for the third time.
148.30
(1) Write the chemical equation of the chemical reaction between solid mixture and hydrochloric acid:
(2) What is the mass fraction of Na2CO3 in the mixture?
29. At room temperature, add 17. 1% barium hydroxide solution to the mixed solution of 2. Og is added with hydrochloric acid and sulfuric acid drop by drop. When the alkali solution was added to 20g, the barium sulfate precipitation reached the maximum. When the alkali liquor is added to 60g, the PH=7 of the solution is equal to 7, and the following equation is obtained:
(1) The mass fraction of sulfuric acid in the original mixed solution.
(2) The mass of solute in solution at 2)pH = 7.
29.(5 points) Solution: (1) Let the mass of sulfuric acid in the original mixture be X.
h2so 4+Ba(OH)2 = bas 04↓+2h2o
98 17 1
x 2Ogx 17 1%
98: 17 1 = x:2 ogxl 7. 1%
. x= 196g
The mass fraction of sulfuric acid in the original mixed solution is1-1.9662ogx100% = 9.8j% < 2 points >.
(2) When pH=7, the mass of solute BaCl2 in the solution is y..
2 HCl+Ba(OH)2 = bacl 2+2h2o
17 1 208
(60g-20g)× 17. 1% y
17 1:208 =(60g-20g)× 17. 1%:y
Y = 8.32g (3 points)
28.(6 points) Xiao Liang and Xiao Huan studied the reaction products of copper and oxygen.
Explore:
(1) Xiao Huan took 16g copper wire and put it on an alcohol lamp to heat it, and the surface of the copper wire became
Black, the black substance is _ _ _ _ _ _ _ (fill in the chemical formula);
2 Xiao Huan reacted the heated copper wire A with excessive dilute sulfuric acid and found that
Black substance B is completely dissolved to obtain red substance C.C. After washing and drying, the mass is 9.6g Then the mass ratio of B to C is _ _ _ _ _ _ _ _ _;
(3) Xiao Liang thinks that the mass fraction of dilute sulfuric acid can also be measured. The following is his determination method:
Take 16g copper wire each time, and the mass after heating is m 1, and add dilute sulfuric acid to react with it, so that black solid remains. Take out the remaining solid, wash and dry it, which is called m2, and calculate the mass m3 of dilute sulfuric acid participating in the reaction from the change of solution quality before and after the reaction.
After three experiments, Xiao Liang recorded the experimental data in the following table and calculated the mass fraction of dilute sulfuric acid as 49%.
quality
quantity
solid
cheque
m 1(g)
Square meter (gram)
Cubic meter (gram)
1 time
17
13
10
second
19
1 1
20
the third time
22
six
40
Xiao Huan found that the data of the _ _ _ _ _ time in the above three experiments was wrong. Please explain the reason of the error through simple calculation.