Determine the content of copper sulfate crystal water, why is it ground first

Because grinding can make copper sulfate with crystalline water.

More evenly and faster.

Decomposes into anhydrous copper sulphate and water vapor.

When heating, because the crystal particles are too large, the crystal water inside the particles cannot be lost, resulting in the value of M1-M2 is small, and W or X is small.

Reference: When it becomes anhydrous copper sulfate (completely white), the heating should be stopped quickly and cooled in a dryer.

Because anhydrous copper sulfate continues to be heated to decompose SO2 and copper oxides, the experiment is inaccurate.

Therefore, the copper sulfate crystal cannot be heated continuously, and then the outer layer becomes anhydrous copper sulfate powder, and the inner layer continues to heat after the powder falls, and after the outer layer becomes anhydrous copper sulfate, it may decompose before the inner layer continues to dehydrate.

After grinding, the copper sulfate temperature can be measured with a suitable thermometer to determine what step of decomposition and whether all the crystal water has been decomposed, because the temperature required when each crystal water is removed is different, and there will be a large temperature increase between the last crystal water and the decomposition of the copper sulfate itself.

Copper sulfate crystals sometimes form large crystals, and they need to be ground to reduce the size of the crystals to reduce the crystals from cracking and flying out when the crystal water is lost by heating (for example, the crystals will jump when the sodium chloride is evaporated). Since the crystal water is located inside the crystal, the vibration of the water molecules when heated will cause the crystal to crack. Small crystals crack less.

The specific steps for determining the crystal water content of copper sulfate crystals are as follows.

1.First, use crucible pliers (not the test tube clamp you said, this experiment does not need to use the test tube clamp) to clamp the crucible and put it on the tripod, light the alcohol lamp to burn the crucible, remove the volatile substances in it, and then put the crucible into the dryer to cool, and weigh the empty crucible mass m1 with a tray balance

2.The copper sulfate crystals are ground into powder with a mortar, carefully transferred to the crucible, and placed on the tray balance together with the crucible to weigh the total mass m2, and the mass of the copper sulfate crystals is obtained from m2-m1.

3.For the first time, place the above-mentioned crucible filled with copper sulfate crystal powder on an alcohol lamp and heat it for a period of time, and constantly stir the crystal powder in the crucible with a glass rod to prevent splashing. After sufficient heating, the crucible is cooled in a dryer and then the mass of the crucible (containing copper sulfate) is weighed m3 with a tray balance

4.Repeat the operation of step 3 until the difference between the mass of the crucible (containing copper sulfate) after heating and the mass weighed after the previous heating is less than that, then the mass of this time can be taken as the sum of the mass of the crucible and the copper sulfate after losing the crystalline water m4

m2-m4 to obtain crystal water content.

I think this will help you understand the purpose of mortars, crucible pliers, and glass rods. Hope it helps.

Solution: (1) Select the weighing instrument according to the accuracy;

3) When cooling after heating, in order to prevent copper sulfate from absorbing water, copper sulfate should be placed in a dryer for cooling, so as to obtain pure and dry anhydrous copper sulfate;

4) Take the average value of two times and calculate the relative error;

5) In order to confirm that the copper sulfate crystal completely loses the crystal water, it is necessary to heat and cool the weighing and then heat and cool the weighing until the difference between the two consecutive weighings does not exceed the point that this is to determine whether the crystal water in the sample has been completely removed;

6) The quality of two consecutive weighing is unchanged, indicating that the crystal has lost all the crystal water;

7) Average value of multiple operations can reduce accidental errors;

8) In the measurement, if the measured sample contains heated volatile impurities or the surface of the tested sample is wet before the experiment, the measurement result will be high

1) The accuracy of the pallet balance is, the accuracy of the electronic balance, according to the data, the electronic balance should be selected, so the answer is: electronic balance;

3) Because anhydrous copper sulfate is easy to combine with water, it should be placed in a dryer for sealing and cooling, so the answer is: dryer;

4) The experimental measurement of the crystal water is: [, the relative error of the experiment = [, so the answer is: ;

5) In order to confirm that the copper sulfate crystal completely loses the crystal water, it is necessary to heat and cool the weighing and then heat and cool the weighing until the difference between the two consecutive weighings does not exceed the point that this is to determine whether the crystal water in the sample has been completely removed; Therefore, it needs to be heated at least 2 times and weighed 4 times;

So the answer is: 2; 4；

6) The quality of two consecutive weighing is unchanged, indicating that the crystal has lost all the crystal water, so the answer is: to ensure that the crystal water is all lost;

7) Occasional error can be reduced by averaging multiple operations, so the answer is: reduce accidental error;

8) a. A small amount of crystals splash out during the heating process, resulting in a large water quality measurement result, so a is correct;

b. The impurities contained in the tested sample will cause the quality of the measured water to be small, so B is wrong;

c. Before the experiment, the surface of the crystal was moist, and the water volatilized after heating, resulting in a large water quality measurement result, so C was correct;

d. After heating, the container is not cooled in the dryer, which will lead to the large quality of the measured copper sulfate and the small quality of the water held by the measuring car, so D is wrong

So the answer is: ac

Comments: Test point of this question: Determination of crystal water content in copper sulfate crystals

Test Center Comments: This question is a quantitative experimental question, which not only requires students to analyze the key and details of the experiment, but also requires the analysis of the reasons for the errors in the experimental results It not only examines the students' understanding and use of the basic operation of chemical experiments and common instruments, but also examines the students' ability to analyze and solve problems From the question itself, the students' experimental ability is required to be higher, but this question is actually a student experiment based on the course Xiangfan, as long as the students have carefully operated, experienced, and thought, they will feel very familiarIt's simple

The determination of the crystal water content of copper sulfate is described as follows:

The experimental procedure is: grinding; Weigh the mass of the empty crucible; Weigh the mass of the crucible containing the sample; Heating; Cooling; Weigh the mass of the crucible and sample after heating and cooling; Repeat until the mass difference between two consecutive weighings does not exceed; Recording data, calculating results; Experimental evaluation.

Copper sulphate CuSO4 (copper thiometaate crystals: CuSO4·5H2O) molecular weight wheel 249 68. Dark blue large granular crystals or blue granular crystalline powder, slightly transparent.

Toxic, odorless, with a metallic astringency. Density 2 2844g cm3. Weathering is slow in dry air.

Soluble in water, the aqueous solution is weakly acidic.

Insoluble in ethanol, slowly soluble in glycerol. Above 150, it will lose all its water crystallization into white powdered anhydrous copper sulfate. Copper sulfate pentahydrate has strong water absorption, and it is restored to blue crystals by putting it into 95% ethanol into aqueous organic matter (i.e. absorbing water).

Copper sulfate crystal pentahydrate loses water in three steps. In the figure above, the two water molecules bound to copper ions only with coordination bonds are the first to lose, with a approximate temperature of 102 degrees Celsius. Two water molecules bound to copper ions with coordination bonds, and one of the outer water molecules bound to hydrogen bonds, are lost with the increase of the temperature of the Tung year, which is roughly 113 degrees Celsius.

The outermost water molecule is the most difficult to lose, because it forms hydrogen bonds between its hydrogen atoms and the oxygen atoms in the surrounding sulfate ions, and its oxygen atoms form hydrogen bonds with the hydrogen atoms of the water molecules coordinated with copper ions. The temperature required to lose the outermost molecule is roughly 258 degrees Celsius.

1.Generate 9g of water

2.The percentage is 36%.

Copper sulphate crystals =

m anhydrous copper sulphate =

That is, the mass of H2O is: 25g-16g=9g

cuso4 + xh2o = cuso4·xh2o160 18x

16g 9g

160/16g=18x/9g

x= 5 looks!

According to the first data, it can be known that the crystal mass is 2g, and then from the later results, it can be seen that the mass of copper sulfate after the water is completely evaporated, then the water is, so the mass fraction of water in the original crystal is 45%.

(I guess the number of times you have 12345 should be the meaning of the step???

What is the meaning of the final formula for the measurement of copper sulfate crystal crystal water?

The denominator is the number of moles of cuso4.

The molecule is the number of moles of H2O.

The resulting n is the amount of substance of one mole of cuso4 with crystal water.

W3-W1 is the mass of white powder Cuso4. 160 is its molecular weight. Divide the amount of cuso4 substance.

w2-w1 is the result of (w2-w1)-(w3-w1), that is, the quality of the crystal water that is the difference before and after heating.

Divide by the molecular weight of the crystal water by 18 to get the number of moles of the crystal water.

over。

The mass of the copper sulfate crystal buried in the nuclear defense body =

Mass of crystalline water =

Mass of copper sulphate 16

CuSO4+2NaOH=Cu(OH)2 precipitate+Na2SO416 x y x= y=

The final solute is Na2SO4, which is lacking in mass bending.

The final solution mass is 100+

Mass fraction is known as =

Finally, the quality of Rongling Kai is Na2SO4, which is good for quality.

Finally, the quality of the socks is 100+

Mass Score =