"Amount and Concentration of Substances" Amount of Substances PPT Download

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"Amount and Concentration of Substances" Amount of Substances PPT Download

Part One: Literacy Goals

1. Learn to understand the meaning of the quantity concentration of a substance by analogy with the mass fraction of solute in a solution.

2. Through experimental operations, learn the methods and operations of preparing a solution with a certain concentration of a certain substance, and analyze experimental errors to improve experimental exploration capabilities and innovation awareness.

3. Know the characteristics, uses and precautions for use of volumetric flasks.

4. Master the relevant calculations of the quantity and concentration of substances, and gradually improve your evidence reasoning thinking ability.

PPT on the quantity and concentration of substances, part 2: independent preview before class

Knowledge foundation

1. The solution is composed of solvent and solute. The mass fraction of the solute is the ratio of the mass of the solute to the mass of the solution. The calculation formula is mass fraction of the solute = "mass of the solute" / "mass of the solution" × 100%.

2. The first step in using a pallet balance to weigh solid mass is to adjust the balance. When weighing, place the medicine on the left pan and the weight on the right pan.

3. The laboratory wants to prepare the following solution. Please fill in the blanks:

(1) To prepare 100 g of 40% NaOH solution, use a tray balance to weigh 40.0 g of NaOH, then add 60 g of water and stir evenly.

(2) To prepare a solution containing 1 mol NaOH in 1 L, use a tray balance to weigh 40.0 g NaOH, and then add water until the solution volume is 1 L.

Preview of new knowledge

1. The amount and concentration of a substance

[Micro Thought 1] Take out 20 mL solution from 100 mL 0.5 mol·L-1 NaCl solution. What is the concentration of NaCl in this 20 mL solution?

It is suggested that according to the uniformity of the solution, the concentration of NaCl in the 20 mL solution taken out is still 0.5 mol·L-1.

2. Preparation of solutions with a certain amount and concentration of a substance

1.Main instruments

(1) Balance: An analytical balance should be used. Depending on the actual situation, an ordinary electronic balance or pallet balance can be temporarily used instead.

(2) Volumetric flask

(3) Other instruments: measuring cylinder, beaker, glass rod, rubber dropper, etc.

[Micro Thought 2] What is the first operation to be performed before using a volumetric flask?

Tip: First check whether the volumetric flask is in good condition and whether there is water leakage at the mouth of the bottle. The leak detection process is: add water → stopper the bottle → stand upside down → check for leaks → stand upright, rotate the bottle stopper 180° → stand upside down → check for leaks.

2. Preparation process

Take preparing 100 mL of 1.00 mol·L-1 NaCl solution as an example.

3. Dilution of concentrated solutions

1. Calculation formula: c(rich)·V(rich)=c(thin)·V(thin).

2. Dilution rule: Before and after the solution is diluted, the amount of solute in the solution is equal.

Autonomous testing

1. Judge whether it is right or wrong (mark “√” if it is correct and “×” if it is wrong).

(1) The substance concentration of the solution formed by adding 58.5 g NaCl into 1 000 mL water is 1 mol·L-1. ()

(2) Take 50 mL of solution from 200 mL of 0.1 mol·L-1 hydrochloric acid, and its substance concentration is still 0.1 mol·L-1. ()

(3) Use a tray balance to weigh 5.85 g NaCl. ()

(4) When injecting the solution into the volumetric flask, use a glass rod for drainage. ()

(5) When the final volume of the solution is reached, use a rubber dropper to add distilled water dropwise. ()

Answer(1)×　(2)√　(3)×　(4)√　(5)√

2. Accurately prepare 250 mL of NaOH solution with a certain substance concentration. The following experimental operation is correct ()

A. When selecting an instrument, use a 500 mL volumetric flask

B. Put the weighed solid sodium hydroxide into a volumetric flask and add a small amount of water to dissolve it.

C. After dissolving sodium hydroxide in the beaker, immediately pour the resulting solution into the volumetric flask

D. Cool the sodium hydroxide solution in the beaker and pour it into a clean volumetric flask that has not been dried.

AnswerD

To analyze item A, a 250 mL volumetric flask should be used; item B, the volumetric flask cannot be used as a dissolving instrument and should be dissolved in a beaker; item C, the solution obtained by dissolving NaOH should be returned to room temperature before being transferred to the volumetric flask; Item D. If the volumetric flask is not dried, it will have no effect on the concentration of the prepared solution. This is correct.

PPT on the amount and concentration of substances, part three: classroom inquiry learning

Calculations related to the amount and concentration of substances

Question exploration

Please explore the following questions:

(1) Take out 100 mL solution from 500 mL 2 mol·L-1 NaCl solution. What is the concentration of the substance in this 100 mL solution? What is the amount of NaCl substance contained?

Tip: 2 mol·L-1;n(NaCl)=2 mol·L-1×0.1 L=0.2 mol.

(2) Under standard conditions, 448 L NH3 is dissolved in water to form a 1.5 L solution. What is the concentration of the substance in the solution? Write down the calculation steps.

(3) To prepare 500 mL of 1 mol·L-1 CuSO4 solution, what is the mass of CuSO4 required? What is the mass of bile vitriol (CuSO4·5H2O)? Write down the calculation steps.

Tip n(CuSO4)=0.5 L×1 mol·L-1=0.5 mol,

m(CuSO4)=0.5 mol×160 g·mol-1=80.0 g,

m(CuSO4·5H2O)=0.5 mol×250 g·mol-1=125.0 g.

(4) What is the substance concentration of 98% H2SO4 solution (ρ=1.84 g·cm-3)?

(5) To prepare 250 mL of 1 mol·L-1 concentrated hydrochloric acid, how many milliliters of 5 mol·L-1 hydrochloric acid are needed?

Tip: 250 mL×1 mol·L-1=V×5 mol·L-1, V=50 mL.

(6) What are c(Al3+) and c(S) in 0.5 mol·L-1 Al2(SO4)3 solution?

Prompt c(Al3+)=2c[Al2(SO4)3]=1.0 mol·L-1,c(S )

=3c[Al2(SO4)3]=1.5 mol·L-1.

Deepen and expand

1. “Four types” of substance concentration calculations

(1) Simple calculation of substance concentration:

(2) Calculation related to solution dilution: The amount and mass of the solute remain unchanged before and after dilution.

c(rich)·V(rich)=c(thin)·V(thin)

m(rich)·w(rich)=m(thin)·w(thin)

(3) Calculations related to the mixing of solutions (with solutes): the total amount and mass of solutes remain unchanged before and after mixing.

c1·V1+c2·V2=c(mixed)·V(mixed)

m1·w1+m2·w2=m(mixed)·w(mixed)

(4) The relationship between the quantity concentration of a substance and the mass fraction of the solute:

PPT on the amount and concentration of substances, part 4: in-class testing

1.1 mol·L-1 NaCl solution represents ()

A.1 mol NaCl dissolved in 1 L water

B.58.5 g NaCl is dissolved in 941.5 g water

C. The solution contains 1 mol NaCl

D.1 L solution contains 58.5 g of NaCl

AnswerD

In the analytical formula cB=n_B/V, V refers to the volume of the solution, the volume of the non-solvent, A is wrong; only the amount and concentration of the solute substance is known, the volume of the solution is uncertain, and the amount of the solute substance cannot be calculated, C is wrong; item B , the volume of the solution is uncertain, so the amount concentration of the solute cannot be calculated through the condition of item B, error.

2. Take 100 mL from 2 L 1 mol·L-1 NaOH solution and dilute it with water to 1 L. The following statement about this 100 mL solution is incorrect ()

A. The concentration of the 100 mL solution taken out is 0.1 mol·L-1

B. The concentration of the diluted solution is 0.1 mol·L-1

C. The 100 mL solution taken out contains 4 g NaOH

D. The diluted solution contains 0.1 mol NaOH

Answer A

The amount and concentration of the substance extracted from the solution remains unchanged, still 1 mol·L-1.

3. In the experiment, 950 mL of 0.1 mol·L-1 Na2CO3 solution is required. When preparing it with a volumetric flask, the mass of Na2CO3 powder should be weighed ()

A.10.6 g B.10.1 g C.10.07 g D.12.0 g

Answer A

The analytical laboratory does not have a 950 mL volumetric flask, so a 1 000 mL volumetric flask must be used to prepare it. 0.1 mol of Na2CO3 is required, and the mass is 0.1 mol×106 g·mol-1=10.6 g.

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Update Time: 2024-10-03

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