Experiments were used to determine that a certain acid HA was a weak electrolyte. The plan of the tw

It is known that a certain acid HA is a weak electrolyte determined experimentally. The plan of the two students is: A:

Weigh a certain mass of HA to prepare 100 ml of mol L solution; Measuring the pH value of the solution with a pH test paper proves that HA is a weak electrolyte. B: Prepare 100 ml of each of the two acid solutions with pH L with the amount and concentration of HA solution and hydrochloric acid of known substances; take 10ml of each of these two solutions and dilute them with water to 100 ml; Two dilutions of the same volume were each loaded into two test tubes, and zinc grains of the same purity were added at the same time, and the phenomenon was observed, which proved that HA was a weak electrolyte.

1) In the first step of the two schemes, the quantitative instruments to be used are: (2) In scheme A, the reason for stating that HA is a weak electrolyte is to measure the pH 1 of the solution (optional, in scheme B, the phenomenon that HA is a weak electrolyte is (a) the rate of H2 is released from the test tube containing HCl solution is fast; (b) H2 is released quickly from the test tube containing the HA solution; (c) Gas is produced at the same rate in both tubes. Why the first question is a 100ml volumetric flask, not a graduated cylinder, and the second question why is the second option, help explain, thank you.

100ml volumetric flasks (2)> b (3) It is not easy to dispense acetic acid with pH=1. It is not easy to observe the bubble rate (4) pH test paper to measure the pH > 7 of sodium acetate solution

1) 100 mL volumetric flask (2) B (3) Prepare NaA solution and measure its pH 7 at room temperature, which proves that HA is a weak electrolyte.

Take 1mol ha acid, dissolve spring rot in 1 L water, and then measure the pH value, if it is 1, it is a slow strong acid, and if it is not 1, it is a weak acid.

Take the amount of the same substance of the aqueous solution of HA and NaOH solution and mix the same volume after the full reaction and then measure the pH value, if the pH value is greater than 7, it is a weak acid.

1.Take a small amount of HA solution in a test tube, measure its pH A, dilute it 10 times, and then measure the pH of B, if B is not equal to A plus 1, then HA is a weak electrolyte. 2.

Take its salt solution (such as Naa) to measure its pH, if the pH is greater than 7 at room temperature, it is a weak electrolyte.

Radical 1).Acid burettes are difficult to accurately configure (2) >b (3) HA with pH = 1 The concentration of acid is low and the reaction phenomenon is not obvious.

4) Prepare the same concentration of hydrochloric acid and HA with Sen, and measure their conductivity respectively

1) Volumetric flasks.

2) Greater than partial ionization.

A zinc grains of the same purity, but also spring fiber rent to ensure that the particles are the same, can not be done. The difference in the rate of hydrogen release is also closely related to the acid concentration.

Prepare two bottles of 100ml NaOH solution, add phenol erector phthalein plus the two acids mentioned above, and see the color change.

It is known that a certain acid HA is a weak electrolyte determined experimentally. The plan of the two students is: A: Weigh a certain quality of HA for preparation.

l of solution 100

ml；Measuring the pH value of the solution with a pH test paper proves that HA is a weak electrolyte. B: Prepare pH L of two acid solutions of 100 each with a known concentration of HA solution and hydrochloric acid

ml；take 10ml of each of these two solutions and dilute them with water to 100 ml; ③

Two dilutions of the same volume were each loaded into two test tubes, and zinc grains of the same purity were added at the same time, and the phenomenon was observed, which proved that HA was a weak electrolyte. (1) In the first step of both schemes, the quantitative instruments to be used are:

2) In scheme A, the reason for indicating that HA is a weak electrolyte is that the pH1 of the solution is measured (optional, and in scheme B, the phenomenon that HA is a weak electrolyte is explained is that (a) the rate of H2 is released from the test tube containing HCl solution is fast; (b) H2 is released quickly from the test tube containing the HA solution; (c) Gas is produced at the same rate in both tubes. Why the first question is a 100ml volumetric flask, not a graduated cylinder, and the second question why is the second option, help explain, thank you.

Take 1mol

HA acid is soluble in 1

l Water pH value again.

If it is 1, it is a strong acid.

If it is not 1, it is a weak acid.

Take the amount of the same substance.

Aqueous solution of HA.

and NaOH solution.

Mix by volume.

Measure the pH value after sufficient reaction, if the pH value is greater than that.

is a weak acid.

100ml volumetric flask (2 points).

1 point) take a small piece of pH test paper and put it on the hail rubber glass plate, dip the liquid to be measured in the pH test paper with a glass rod**, compare the color card, and read the pH of the solution (2 points).

H2 is released from the tube containing the HA solution

The rate is fast (2 points).

Prepare a small amount of NaA solution with distilled water, and then measure its pH, if the pH next to the source is 7, it means that HA is a weak electrolyte (2 points, other reasonable answers can be scored).

Test question analysis: (1) The volume of the prepared solution is 100ml, so use a 100ml volumetric flask.

2) If HA is a weak electroelectric substance, incomplete ionization occurs, mol?l?1

HA ionized out of H+

The concentration is less than? l?1

ph>1；The key points of using pH test strips should be comprehensive.

3) The pH of the two acids prepared is the same, the ionization equilibrium of the weak electrolyte diluted with water is shifted to the right, and the H+ of the weak electrolyte is removed

The concentration is larger, and H2 is released from the tube containing the HA solution

The rate is fast, which can prove that HA is a weak electrolyte.

4) Using the hydrolysis of salts, measuring the acidity and alkalinity of the NaA solution can prove that HA is a weak electrolyte.

C, A is not right, because the conductivity is also related to the concentration of pants deficiency, and B is also not right, because it can be done regardless of weak electrolytes or strong electrolytes. It is exactly the stoichiometric ratio, d indicates a strong electrolyte, and as for cph 7, it indicates that a- hydrolysis, then ha must be a weak electrolyte.

C Because the pH of Naa is >7, it is said that it consumes H+ in the process of hydrolysis and repentance, forming a weak electrolyte, so that the concentration of Oh- in the solution is more than that of H+.

Answer] (1) 100ml dissolving volume bottle (Note: 1 point will be deducted if the specifications are not indicated).

2) >b (multi-choice deduction).

3) It is difficult to prepare a HA solution with pH = 1, and the inappropriate part is that the surface area of the zinc particles added is difficult to be the same.

4) Prepare NaA solution and measure its pH value"7 proves that HA is a weak electrolyte.

Answer analysis] Test question analysis: (1) The quantitative instrument required to prepare a 100ml solution of a certain substance is a 100ml volumetric flask.

2) Weak electrolytes have ionization equilibrium and cannot be completely ionized. So if HA is a weak electrolyte, the pH of the solution must be greater than 1; Weak acid will continue to ionize anions and cations during the dilution process, so after diluting the same multiple, the concentration of hydrogen ions in the HA solution is greater than the concentration of hydrogen ions in the hydrochloric acid, so the rate of H2 released in the test tube containing the HA solution is fast, and the answer is B.

3) The weak acid will continue to ionize hydrogen ions during the dilution process, so it is difficult to prepare a HA solution with pH=1; And because the surface area of the solid also affects the reaction rate, it is not appropriate to add the same surface area of zinc grains.

4) If HA is a weak acid, the corresponding NAA will be hydrolyzed, and the solution will be alkaline. Therefore, the preparation of NaA solution and the measurement of its pH value"7 proves that HA is a weak electrolyte.

Test center: Examine the judgment of weak electrolytes.

Comments: This question is a common question type in the college entrance examination, and the test question is more difficult. This question is conducive to cultivating students' rigorous logical thinking ability, as well as phonetic organization and expression ability, improving students' learning efficiency and stimulating students' interest in learning.

Take 1mol ha acid and dissolve it in 1 L of water and then measure the pH value If it is 1, it is a strong acid, and if it is not 1, it is a spring rot and weak acid.

Take the amount of the same substance of the aqueous solution of HA and NaOH solution and mix the same volume after the full reaction and then measure the pH value, if the pH value is greater than 7, it is a weak acid.