"Configuration of Sodium Chloride Solution with Certain Solute Mass Fraction" Solution PPT Courseware 2

"Configuration of Sodium Chloride Solution with Certain Solute Mass Fraction" Solution PPT Courseware 2

【Pre-class test】

1. Mass fraction of solute =---------×100%

2. When preparing 50g of 6% NaCl solution:

(1) After calculation, weigh ____g NaCl on ____ and pour it into a dry and clean beaker. Then use ____ to measure ____ml distilled water and pour it into the beaker containing NaCl, and stir continuously with ____. NaCl is completely dissolved to obtain the desired solution.

(The density of water is about 1g/ml)

(2) When weighing a certain mass of NaCl, ___ should be placed first, then ___, the weight should be placed on ___, NaCl should be placed on ___, and a ___ should be placed on both sides of the tray. When the balance is close to equilibrium, the technique for adding medicine in order not to overdose is ___. (Use game code below 5g)

(3) When using the measuring cylinder, the measuring cylinder must be placed ___, and the line of sight must be kept level with the ___ inside the measuring cylinder. When it is close to the scale line, use ___ to add liquid.

3. When a concentrated solution is diluted with water:

(1) Mass of solute in concentrated solution Mass of solute in dilute solution (fill in >, <, =)

(2)Quality of water used=______________.

learning target

1. Understand the steps and required instruments for preparing a solution with a certain solute mass fraction;

2. Preliminarily learn to prepare solutions with a certain solute mass fraction.

3. Practice weighing, measuring, dissolving and other operations.

4. Cultivate students’ thinking abilities of analysis, comparison, abstraction and generalization through independent exploration, observation and comparison.

Preparing a solution with a certain solute mass fraction is a required content in the instructions for the junior high school chemistry entrance examination. It is not only an important experiment in the junior high school chemistry experimental operation assessment, but also a hot topic in the high school entrance examination in recent years.

1. Experimental principle

1. Solute mass fraction = mass of solute / (mass of solute + mass of solvent) × 100%

2. Dilution of solution: m (concentrated solution) × a% = m (dilute solution) × b% (a>b)

2. Experimental instruments

Pallet balance, measuring cylinder, beaker, glass rod, medicine spoon, dropper

3. Experimental operation

1. Calculation: Calculate the required amount of solute and solvent according to the preparation requirements (calculate the mass for solids and the volume for liquids).

2. Weighing or measuring: Weighing refers to weighing the mass of a solid substance; measuring refers to measuring the volume of a liquid substance.

3. Dissolve: Mix the solute and solvent and stir until fully dissolved.

4. Bottle: Put the prepared solution into a reagent bottle and label it.

4. Error analysis

1. Changes in the mass of the actual dissolved solute and the solute

The relationship between changes in quality scores

(1) The amount of solute dissolved is reduced: the solute itself

Impure; less solute is weighed (weigh the left object and the right object)

(After weighing, the pointer moves to the right) (When the balance is unloaded, the pointer moves to the left); the solute is spilled; the solute is bottled and stored before it is completely dissolved.

(2) The amount of solute dissolved increases: more solute is weighed, (the pointer moves to the left) (when the balance is unloaded, the pointer moves to the right)

2. The relationship between the change in the mass of the actual solvent used and the change in the mass fraction of the solute (1) causes the amount of solvent to decrease: measuring from above; the solvent is not completely transferred to the beaker; liquid splashes out during dissolution. (2) The amount of solvent increases: look up to measure; there is water on the inner wall of the beaker; there is water on the inner wall of the reagent bottle

Did you discover it

1. Do I need to use weights when weighing sodium chloride?

2. When pouring the sodium chloride solid into the beaker, there is still some sodium chloride solid left on the paper, then the mass fraction of the obtained sodium chloride solution is ___6%;

3. When a student was nervous and poured the water from the measuring cylinder into the beaker, it accidentally splashed outside the beaker. The resulting sodium chloride solution had a mass fraction of ___6%;

4. When the prepared sodium chloride solution is transferred into the reagent bottle, part of it is still left in the beaker, then the mass fraction of the prepared sodium chloride solution is ___6%;

4. Classroom training

1. Some operating steps for preparing a sodium chloride solution with a certain mass fraction of solute are shown in the figure below. The correct operating sequence is ( )

A． ①②③④⑤ B. ②①④③⑤

C. ③④①②⑤ D. ④⑤①②③

2. To prepare 100g of sodium chloride solution with a solute mass fraction of 10%, the following operations are correct ( )

A. Place 10g of sodium chloride solid directly on the tray of the balance and weigh it

B. When measuring 90ml of water, read from above

C. To speed up the dissolution of the solid, stir the solution with a thermometer

D. Pour the prepared solution into a narrow-mouth bottle, cap the bottle tightly, and label it

3. When preparing a certain mass fraction of sodium chloride solution, the following operational errors will cause the solute mass fraction of the prepared solution to decrease ( )

A. When weighing sodium chloride with a pallet balance, place the weight on the left pan but do not use the balance.

B. When measuring distilled water with a graduated cylinder, look up at the lowest point of the concave liquid surface.

C. When pouring the water from the measuring cylinder into the beaker, water spilled out

D. When transferring the prepared sodium chloride solution to a narrow-mouth bottle, part of the solution was accidentally spilled

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