CBSE Chemistry Experiment Preparing Pure Copper Sulphate (CuSO4.5H2O) Crystals from a Given Impure Sample of the Blue Vitriol

By applying the recrystallisation method, it is possible to create pure copper sulphate from an impure sample. From its saturated solution, pure copper sulphate is produced as crystals through evaporation. Because soluble solids are separated from liquids using the evaporation process. For instance, the crystal of copper sulphate dissolves in water to create a copper sulphate solution. CuSO4 crystals are left behind after the water evaporates during evaporation.

Table of Content

• Aim

• Blue Vitriol Formula

• Blue Vitriol Chemical Name

• Preparation of Copper Sulphate Solution

• Filtration and Concentration Process

• Cooling Down the Hot, Saturated Solution

• Drying and Crystal Separation

• Result 

Aim

To prepare crystals of Pure Copper Sulphate (CuSO4.5H2O) from a given impure sample of the blue vitriol.

Materials Required

1. A porcelain Bowl

2. A Funnel

3. An Evaporating Dish

4. A 400 ml Beaker

5. Crude Copper Sulphate Sample

6. A Policeman (Glass Rod).

Theory

1. Blue vitriol- The term "vitriol" refers to a class of chemical compounds made up of the sulphates of particular metals, originally copper or iron. The popular name for hydrated copper sulphate is blue vitriol.

2. Blue vitriol formula and chemical name—Copper sulphate CuSO4.5H2O or blue vitriol, is a salt that occurs naturally as big, translucent, deep-blue triclinic crystals. It also appears as a white powder in its anhydrous state.

3. The provided sample is first shaken with water. It is mixed with a few drops of diluted sulphuric acid to stop copper sulphate from hydrolysing. The sample's copper sulphate dissolves, while the insoluble contaminants are left behind. The remedy has been filtered. The filtrate is heated to the point of crystallisation before cooling. Crystals of copper sulphate split out while cooling.

4. Copper sulphate can be stirred with a silver spoon, not an iron spoon. Silver is less reactive than copper because it follows copper in the reactivity series. Therefore, no reaction occurs when stirring the CuSO4 solution with a silver spoon.

Procedure

1. Preparation of Copper Sulphate Solution:

• Add minuscule quantities of the powdered crude copper sulphate to 25 to 30 ml of water.

• To dissolve it, vigorously stir. Add the powdered sample multiple times until just a small amount is left after stirring for a while.

• To make the solution transparent, add 2–3 ml of diluted sulphuric acid.

• This keeps the copper sulphate from hydrolysing. This way, the copper sulphate solution is prepared.

2. Filtration and Concentration Process:

The concentration of the filtrate is done after filtering the solution to the crystallisation point. Impurities remain on the filter paper after filtering the solution and collecting the filtrate in a china container.

3. Heating of the Solution:

The solution should be heated in the china dish on a sand bath until it is roughly one-third of its original volume. With a glass rod, the solution is thoroughly swirled while it warms up to prevent the development of a crust on the dish's edge. If a crust forms, it is removed with a glass rod and dissolves into the solution. The dish's solution shouldn't be allowed to boil.

A drop of the solution should be removed from the glass rod's end and cooled by blowing. The glass rod will develop a crust or little crystals after the crystallisation point has been reached. Now cease heating and extinguish the burner. Place the heated, saturated solution in a dish for crystallisation.

4. Cooling Down the Hot, Saturated Solution:

Place the crystallisation plate containing the hot saturated solution atop a beaker full of water, and let it cool for a while. Crystals of copper sulphate will emerge with a deep blue colour. The crystallisation is finished in around 30 minutes.

5. Drying and Crystal Separation:

Carefully decant the mother liquor. With a tiny amount of cold water and a little ethyl alcohol, clean the crystals. Removing the crystals requires soaking filter paper in solution. The crystals are then transferred to a different filter paper, gently pressed between the paper's folds or spread out on a permeable plate to dry. Place the crystals in a dry test tube and cork it.

Crystallization process

Observations

• On performing the crystallisation process, the water will evaporate, and you will receive pure crystals of CuSO4.

• These pure crystals of CuSO4 are deep blue-blooded transparent in nature.

Result

The crystals of pure Copper sulphate blue colour having formula CuSO4.5H2O are obtained and are transparent.

Precautions

1. When concentrating, the filtrate should be gently heated and allowed to slowly evaporate.

2. Only the amount of filtrate needed to cause crystallization should be evaporated. Never let it get too hot or dry.

3. Avoid heating the solution too much.

4. The solution should be gently chilled without being disturbed. Never let it cool down quickly.

5. Three to four times, using a very small amount of washing liquid each time, wash the crystals in the liquid.

6. If the resulting crystals are exceedingly tiny, the solution has been concentrated beyond what is necessary for the crystallization step.

Lab Manual Questions

1. What method is utilized to isolate blue vitriol crystals from their impure samples?

Ans: Solids can be purified through crystallization, such as when alum crystals are separated from impure samples.

2. Which techniques are used to clean an impure sample of table salt?

Ans: Evaporation is the mechanism employed to separate impure salt from pure salt.

3. Which solvent is employed in the purification of benzoic acid and copper sulphate?

Ans: Water is the purifying agent used for copper sulphate and benzoic acid.

4. What happens if you put copper sulphate crystals in water?

Ans: A tiny quantity of heat energy is released during the dissolution process of pure copper sulphate when it is maintained in water.

Viva Questions

1. What happens when the crystals of blue vitriol are heated independently?

Ans: It turns into a white powder when it crystallizes because water is lost throughout the process.

2. Mother liquor: what is it?

Ans: The mother liquor is the liquid that remains after crystals are separated from a saturated solution.

3. What are the chemical formulas for crystals of green vitriol and potash alum?

Ans: The chemical formulas for crystals of green vitriol and potash alum are FeSO4.7H2O and (K2SO4.Al2(SO4)3.24H2O) respectively.

4. Why doesn't the hot, saturated solution cool down immediately?

Ans. Crystals enlarge as the saturated solution slowly cools. Instead of providing a massy substance with improper geometry, it aids in their better separation into units.

5. What does the word “seeding” mean?

Ans: Seeding occurs when a crystal of the same chemical is dissolved in a saturated solution. It facilitates fast crystal separation from a saturated solution.

6. What traits do crystals have?

Ans: The shape and geometry of crystals are clearly defined.

7. What does “saturated solution” mean?

Ans: A saturated solution is one in which, at a certain temperature, no more solute can dissolve.

8. What does the phrase "water of crystallization" refer to?

Ans: The water of crystallization is the specific quantity of water molecules that are present in proximity to one unit of the compound's formula.

9. How are crystals of pure substances obtained?

Ans: Crystals can develop straight from gas phase breakdown or from a pure melt.

10. What is solubility?

Ans: This is the amount of the solute needed to create a saturated solution in 100 g of solvent.

Practical Questions

1. From an impure sample, pure copper sulphate can be obtained using the process of

1. Fractional distillation

2. Centrifugation

3. Evaporation

4. Crystallization

Ans: From an impure sample, pure copper sulphate can be obtained using the process of crystallization.

2. Copper carbonate + ________________→ Copper sulphate + Water.

1. Copper sulphate

2. Sulphuric acid

3. Carbonic acid

4. Nitric acid

Ans: Copper carbonate + Sulphuric acid, → Copper sulphate + Water.

3. The most widely used solvent for crystallization is _______________.

1. Water

2. Alcohol

3. Saline water

4. Sulphuric water

Ans: The most widely used solvent for crystallization is water.

4. The solvent should dissolve a large amount of solute at ____________.

1. Cold temperature

2. Room temperature

3. Melting point

4. Boiling point

Ans: The solvent should dissolve a large amount of solute at room temperature.

5. The insoluble impurities from the solution during crystallization are removed by

1. Drying 

2. Filtration 

3. Heating 

4. Cooling 

Ans: The insoluble impurities from the solution during crystallization are removed by filtration.

6. When is supersaturation achieved?

1. When the solvent contains more solute.

2. When the solute contains more solvent.

3. When the solvent contains less solute.

4. When the solute contains more solvent.

Ans: Supersaturation is achieved when the solvent contains more solute.

7. Which of the processes is crystallization?

1. Solid-liquid separation

2. Solid-solid separation

3. Solid-gas separation

4. Liquid-gas separation

Ans: Solid-liquid separation is the process of crystallization.

8. Recrystallization process is used to_________

1. Purify chemicals

2. Dissolve crystals

3. Clean crystallizer

4. Continue the process of crystallization

Ans: The recycling process is used to purify chemicals.

9. Effect of concentration on crystallization is__________

1. An increase in concentration leads to large crystals.

2. An increase in concentration leads to small crystals.

3. A decrease in concentration leads to large crystals.

4. A decrease in concentration leads to small crystals.

Ans: The effect of concentration on crystallization leads to an increase in concentration leads to large crystals.

10. Supersaturated solution is unstable because__________

1. The concentration is higher than the equilibrium concentration.

2. Concentration is lower than the equilibrium concentration.

3. Concentration is equal to equilibrium concentration.

4. Contains impurities

Ans: A supersaturated solution is unstable because the concentration is higher than the equilibrium concentration.

Conclusion

From the above experiment, we can conclude that blue crystalline granules or powders are the typical forms of copper sulphate pentahydrate. The pentahydrate of copper(2+) sulphate is copper(II) sulphate, a crystallized bright blue substance. This tutorial helped us to learn all the different prospects of blue vitriol and pure copper sulphate.