A physical change happens when the substance’s composition and chemical nature remain the same, while a change in state can occur between solid, liquid, and gas.
On the other hand, a chemical change is when a substance undergoes a transformation that alters its chemical properties, forming a new substance. For instance, burning oil or fuel causes heat to be produced or absorbed, and bubbles, gas, and fumes may appear. Additionally, a change in the reactants’ color can occur as they transform into products through a chemical reaction, represented by A + B → C.
|Experiment to classify changes observed to be physical or chemical change||Procedure||Reactions involve and observation|
|Reaction between Copper sulphate solution and water||1 . Use sandpaper to clean an iron nail until it appears greyish|
2 . Label two test tubes as A and B, then pour 10 mL of newly made copper sulfate solution into each tube. Finally, secure the test tubes separately on two clamp stands.
3 . Hang the iron nail in test tube B using a thread, making sure the nail is entirely submerged in the CuSO4 solution. Then, tie the other end of the thread to the stand.
4 . Place the other iron nail on a sheet of white paper.
5 . Allow the setup to sit undisturbed for some time.
6 . Remove the nail from the solution, then position it next to the second iron nail on the paper.
7 . Note your observations.
|The iron nail’s brown coating suggests that copper has been transferred onto it through iron displacement.|
Reaction: Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
The blue color of the copper sulfate solution changes to green.
Reaction: CuSO4(aq) + H2O(l) → CuSO4·5H2O(s)
The greenish color of the solution in the test tube indicates the presence of Fe2+ ions.
Reaction: Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
This reaction is an instance of single displacement where iron displaces copper from copper sulfate solution, resulting in the creation of a new compound, ferrous sulfate.
The reaction that occurs is a chemical change.
|Burning of magnesium ribbon in air||1 . Rub a piece of magnesium ribbon with sandpaper to eliminate impurities.|
2 . Hold the magnesium ribbon above the watch glass or china dish using a pair of tongs.
3 . Ignite the magnesium ribbon using the Bunsen burner and collect the ash in a watch glass or china dish.
4 . Test the ash with red litmus paper that has been dampened.
|Magnesium is a metallic element that has a silver-white color. When magnesium is burned in air, it emits a bright white flash, and then reacts with oxygen to form a new compound called magnesium oxide (MgO). This reaction can be represented by the following equation:|
2Mg + O2 → 2MgO
The product, magnesium oxide, is a basic element, which means it has a pH greater than 7.
The experiment in which magnesium ribbon is burned in air demonstrates a direct combination reaction, which is a type of chemical reaction where two or more elements combine to form a single compound. In this case, magnesium and oxygen combine to form magnesium oxide.
The formation of magnesium oxide is a chemical change because the composition of the reactants (magnesium and oxygen) changes to form a new substance with different properties (magnesium oxide). This chemical change is accompanied by the emission of light and heat, which are characteristic of exothermic reactions.
|reaction of Zinc with dilute sulphuric acid||1 . Pour 5mL of diluted sulfuric acid into a test tube.|
2 . Add zinc granules to the test tube, making sure they are fully submerged in the sulfuric acid solution.
3 . Secure a cork with a delivery tube and fine jet to the opening of the test tube immediately.
4 . Hold a burning matchstick near the fine jet of the delivery tube.
|When zinc granules are added to dilute sulfuric acid, they react to produce hydrogen gas and zinc sulfate. The chemical equation for this reaction is:|
Zn + H2SO4 → ZnSO4 + H2
In this reaction, zinc displaces hydrogen from sulfuric acid to produce zinc sulfate and hydrogen gas. The hydrogen gas produced can be tested by bringing a burning matchstick near the gas, and it will burn with a pop sound. This reaction is an example of a displacement reaction of a non-metal by a metal.
Overall, this is a chemical change as a new substance (zinc sulfate) is formed and hydrogen gas is produced.
|reaction of Heating of copper sulphate crystals||1 .Place copper sulfate crystals in a dry test tube and heat them.|
2 .Observe any changes in the color of the copper sulfate crystals after heating.
3 .Observe water droplets forming along the sides of the test tube as the copper sulfate is heated.
4 .Remove the test tube from the flame and let it cool down for some time.
5 .Add 2-3 drops of water to the sample of heated copper sulfate to test for any changes.
|Copper sulfate crystals are commonly found as hydrated copper sulfate, which means that water molecules are part of the crystal structure. When hydrated copper sulfate crystals are heated, the water molecules are driven off, leaving behind anhydrous copper sulfate. This process is called dehydration.|
The reaction can be represented as:
CuSO4 . 5H2O → CuSO4 + 5H2O
When anhydrous copper sulfate is exposed to water, it can absorb the water molecules and revert to its hydrated form. This process is called hydration. The reaction can be represented as:
CuSO4 + 5H2O → CuSO4 . 5H2O
The fact that this process is reversible makes it a chemical change. The hydrated and anhydrous forms of copper sulfate have different physical and chemical properties, such as color, crystal structure, and reactivity, which can be used to distinguish between them.
|reaction of Sodium sulphate with barium chloride in the form of their solutions in water||1 .Prepare a solution of sodium sulphate in a test tube.|
2 .Introduce a small quantity of barium chloride solution into the same test tube.
3 .Stir the solution gently with a glass rod and let it stand undisturbed for a while.
4 .Finally, add a small amount of dilute hydrochloric acid to the mixture.
|When Na2SO4 (sodium sulphate) and BaCl2 (barium chloride) are mixed, they undergo a double displacement reaction, which produces BaSO4 (barium sulphate), an insoluble white precipitate. The chemical equation for this reaction is:|
Na2SO4 (aq) + BaCl2 (aq) → BaSO4 (s) + 2NaCl (aq)
The formation of the white precipitate indicates a chemical change because the products formed (BaSO4 and NaCl) have different chemical properties and composition from the reactants (Na2SO4 and BaCl2). The addition of dilute hydrochloric acid to the flask can be used to confirm the presence of BaSO4, as it will result in the formation of a white precipitate of BaSO4 again. This reaction is also a double displacement reaction, as it forms HCl and BaSO4.