"Physical Quantities Commonly Used in Chemistry—Amount of Substances" Understanding Chemical Science PPT (Amount and Concentration of Substances in Lesson 2)

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"Physical Quantities Commonly Used in Chemistry—Amount of Substances" Understanding Chemical Science PPT (Amount and Concentration of Substances in Lesson 2)

Part One: What are the new curriculum standards?

1. Understand the meaning and application of quantity and concentration of substances, and appreciate the important role of quantitative research in chemical science.

2. Ability to perform simple calculations using the relationship between the amount of a substance and its amount and concentration.

Quantity of physical quantities commonly used in chemistry PPT, part 2 content: exploration of new knowledge

quantity concentration of substance

[New textbook for self-study]

Read the textbook and answer the following questions:

As shown in the figure, Figure 1 is the label on the laboratory analytical pure hydrochloric acid reagent bottle, and Figure 2 is a part of the blood test sheet of a patient in the hospital.

(1) "Content (HCl) - 35.38%" in the hydrochloric acid label in Figure 1 means ____________________.

(2) The physical quantity indicating the content of K and Na in the laboratory test sheet in Figure 2 is ____________. This physical quantity represents _______________________________, symbol: _____, and the common unit is ____________________________.

(3) In a solution with a certain substance concentration, the relationship between the amount nB of solute B, the volume V of the solution, and the amount concentration cB of solute B is ____________.

①The amount of CaCl2 contained in 100 mL of CaCl2 solution with a concentration of 2 mol·L-1 is ________, the amount of Ca2+ is ________, and the amount of Cl- is ________.

② If 0.1 mol CaCl2 is required during the experiment, the volume of 2 mol·L-1 CaCl2 solution needs to be measured as ________.

③ Dissolve 0.3 mol CaCl2 in water to prepare a 100 mL solution. The concentration of CaCl2 in the solution is ________, the concentration of Ca2+ is ________, and the concentration of Cl- is ________. If 10 mL is taken out, the amount and concentration of CaCl2, Ca2+, and Cl- in the 10 mL solution taken out and the remaining 90 mL solution will change _____ (fill in "yes" or "no").

(4) Dissolve 0.5 mol CaCl2 in 1 L of water. The concentration of CaCl2 in the resulting solution is ________ (fill in “yes” or “no”) 0.5 mol·L-1. Because________________________.

[Implement new knowledge]

1. The amount concentration of a substance: the amount of solute B contained in a unit volume of solution. Symbol: cB, unit: mol·L-1, mol·m-3, mmol·L-1.

2. Relationship: The relationship between the amount of the substance of solute B (nB), the volume of the solution (V), and the amount and concentration of the substance of solute B (cB): cB=nBV.

3. Precautions

(1) When calculating the amount and concentration of relevant substances, it should be noted that V represents the volume of the solution, not the volume of the solvent. Its common unit is L, which often needs to be converted into mL during calculation.

(2) Take any volume of solution from a solution with a certain substance concentration. Its concentration remains unchanged, but the amount of solute contained varies with the volume.

(3) When crystal hydrate is dissolved in water, crystal water serves as the solvent. For example, when CuSO4·5H2O is dissolved in water, CuSO4 serves as the solute, and crystal water and other distilled water serve as solvents.

(4) The solution is electrically neutral, that is, there is charge conservation between anions and cations. For example, there are Na+ and SO2-4 in the Na2SO4 solution, and c(Na+)=2c(SO2-4).

[Practice the new exam]

1. Physiological saline refers to a NaCl solution with a mass fraction of 0.9%. Which of the following statements about this solution is correct ()

A. 100 g solution contains 0.9 g NaCl

B． 100 g of water contains 0.9 g NaCl

C． 100 g of solution contains 0.9 mol NaCl

D． 100 g of water contains 0.9 mol NaCl

2. Which of the following statements about 1 mol·L-1 K2SO4 solution is correct ()

A. The solution contains 1 mol K2SO4

B． 1 mol K2SO4 dissolved in 1 L water

C． c(K+)=2 mol·L-1 in solution

D． 1 L solution contains 2 mol K+, 2 mol SO2-4

3. Dissolve 4 g NaOH in water to prepare a 200 mL solution. Take out 10 mL. The concentration of the substance in this 10 mL solution is ()

A. 2 mol·L－1　B． 1 mol·L－1

C． 0.1 mol·L－1 D． 0.5 mol·L－1

4. The laboratory plans to prepare 500 mL of 1 mol·L-1 NaOH solution. The mass of solid NaOH needs to be weighed as ________.

Prepare a solution with a certain concentration of a substance

[New textbook for self-study]

Read the textbook and answer the following questions:

1. Prepare 50 g of NaCl solution with a mass fraction of 6%. The process is as follows:

(1) Calculation: The required mass of NaCl is ________g, and the required mass of water is ________g.

(2) Weighing: Use a tray balance to weigh the required NaCl and put it into a beaker. (When weighing, add NaCl to the ________ pan of the balance and add weights to the ________ pan of the balance)

(3) Measure: Use a ________ (fill in "10 mL", "50 mL" or "100 mL") measuring cylinder to measure the required volume of water. When measuring, keep your sight level with the __________________ in the measuring cylinder, and Pour it into the beaker containing NaCl along the inner wall of the beaker.

(4) Dissolution: Stir gently and continuously with a glass rod to completely dissolve NaCl.

(5) Transfer: Transfer the prepared solution to a labeled container.

2. The laboratory plans to prepare 100 mL of 2.00 mol·L-1 NaCl solution.

(1)Main instruments

Pallet balance, medicine spoon, beaker, measuring cylinder, __________, __________, _____________, reagent bottles.

(2)Experimental steps

① Calculation: The mass of NaCl solid required: ________.

②Weighing and dissolving: Use a tray balance to weigh the required NaCl, put it into a beaker, add water to dissolve it, the role of the glass rod during the dissolution process is ______________.

③ Pipetting and washing: After ___________ the solution, transfer it into a 100 mL volumetric flask, _______________, and shake well. The role of the glass rod during pipetting is _______.

④Constant volume: Continue to add water to the volumetric flask. When the liquid level is below the scale line of the volume bottle neck, use ____________________ to add distilled water dropwise to ____________________.

⑤ Shake well and bottle: Cap the bottle stopper, shake it upside down repeatedly, and transfer the prepared solution to a labeled reagent bottle.

[Implement new knowledge]

1. Volumetric flask structure and usage precautions

(1) Structure of volumetric flask

(2) Precautions when using volumetric flasks

① Check for leaks before use; ② Do not dissolve solids; ③ Do not dilute concentrated solutions; ④ Do not heat; ⑤ Do not use as reaction vessels; ⑥ Do not store solutions for long periods of time.

(3) Principles for selecting volumetric flasks

When selecting a volumetric flask, the principle of "big and close" should be followed. The specifications of the volumetric flask are fixed, and the commonly used specifications are 50 mL, 100 mL, 250 mL, 500 mL, 1000 mL, etc., so solutions of any volume cannot be prepared. When selecting, the size of the volumetric flask should be equal to or slightly larger than the volume of the solution to be prepared. For example, to prepare a 400 mL solution, a 500 mL volumetric flask should be selected.

2. Specific steps and instruments used in the preparation process

(1) Preparation steps

(2) Pay attention to the problem

① Transfer the solution to a volumetric flask only after it returns to room temperature.

② Wash the beaker and glass rod 2 to 3 times, and pour the washing liquid into the volumetric flask.

③When setting the volume, when the liquid level is 1 to 2 cm below the scale line of the volume bottleneck, use a rubber dropper to drip distilled water until the lowest point of the concave liquid level of the solution is tangent to the scale line, and the line of sight should be level with the scale line. .

a. When adding distilled water to a constant volume, it accidentally exceeds the scale line. Do not use a rubber-tipped dropper to suck out the liquid that exceeds the scale line. Because the liquid that exceeds the scale line is not added distilled water, but a solution containing solute, use a rubber dropper to suck it out, the solute will be reduced, and there is no other way to make up for it, so you can only prepare it again.

b. When transferring the solution to the volumetric flask, if a drop of liquid accidentally falls outside the volumetric flask, the solute cannot be added. Because the amount of solute spilled outside the volumetric flask cannot be determined, the solute cannot be added and can only be prepared again.

④The role of the glass rod during the preparation process: the role of the glass rod during the dissolution process is stirring and accelerating dissolution; the role of the glass rod during the pipetting process is drainage.

[Practice the new exam]

1. The volumetric flask must be marked with () among the following six items:

①Temperature②Concentration③Capacity

④Pressure ⑤Scale mark ⑥Acid type or alkaline type

A. ①③⑤ B． ③⑤⑥

C． ①②④ D． ②④⑥

2. An experiment requires 480 mL of 0.1 mol·L-1NaCl solution. The most appropriate capacity of the volumetric flask required to prepare the solution is ()

A. 50 mL B. 100mL

C． 250 mL D. 500mL

3. (2018•Shandong Qualification Examination) The laboratory uses bile alum to prepare 500 mL of 0.1 mol·L-1 CuSO4 solution. The following statement is correct ()

A. Use a pallet balance to weigh 8.0 g of bile alum.

B． Place the bile alum in a 500 mL volumetric flask and add water to dissolve

C． If the water added exceeds the mark when setting the volume, immediately use a dropper to suck out the excess liquid.

D． If you look down at the scale line of the volumetric flask when setting the volume, the concentration of the solution will be too high.

Calculations related to the amount and concentration of substances

[More difficult]

[Typical example] The mass fraction of hydrochloric acid commonly used in laboratories is 36.5%, and the density is 1.20 g·cm-3.

(1) The concentration of this concentrated hydrochloric acid is ________mol·L-1.

(2) To prepare 100 mL of concentrated hydrochloric acid, the volume of HCl required under standard conditions is ________.

(3) To prepare 100 mL of 3 mol·L-1 hydrochloric acid, the volume of the above concentrated hydrochloric acid required is ________.

(4) Mix 10 mL of 3 mol·L-1 hydrochloric acid and 10 mL of 1 mol·L-1 MgCl2 solution. The concentration of Cl- in the mixed solution is ____________. (Assume that the volume of the solution remains unchanged after mixing)

[Know more deeply]

Calculations related to the amount and concentration of substances

1. Conversion of substance concentration cB and solute mass fraction (w)

2. Calculation method for the concentration of solute in a solution formed when a certain volume of gas (standard conditions) is dissolved in water

(1) If the volume of the solution is known

(2) If the density of the solution is known

Assume that the molar mass of the gas is M g·mol-1, V L (standard conditions) and the density of the solution obtained by dissolving the gas in 1 L of water is ρ g·mL-1. The calculation process is as follows:

① First calculate the amount of solute material: n=V22.4 mol;

3. A method of finding the mass concentration of other particles if the mass concentration of a certain particle in a solution is known

(1) Single solute solution

A single solute solution can be calculated according to the law of composition, that is: in the solution, the ratio of the concentration of anions to cations is equal to the ratio of the number of ions in the chemical composition. Based on this, the concentration of another ion in a solution with a known concentration of one ion can be calculated. concentration.

For example, in K2SO4 solution: c(K+)=2c(SO2-4)=2c(K2SO4).

(2) Mixed solution

For example, in Na2SO4, NaCl mixed solution:

① If the concentration of each solute is known, it can be calculated based on the composition rules.

For example, if c(Na2SO4)=2 mol·L-1, c(NaCl)=3 mol·L-1, then in the mixed solution c(Na+)=c(Na+, in Na2SO4) + c(Na+, in NaCl )=2 mol·L-1×2+3 mol·L-1×1=7 mol·L-1.

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