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प्रश्न
Give reason for the following:
Colourless concentrated sulphuric acid in a test tube changes to blue on adding a small piece of copper to it.
उत्तर
Copper displaces hydrogen from sulphuric acid and forms blue-coloured copper sulphate and hydrogen gas is evolved.
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संबंधित प्रश्न
How do the following help in bringing about a chemical change?
light.
Fill in the blank
A catalyst either ................or ............... the rate of a chemical change but itself remains ............... at the end of the reaction.
MULTIPLE CHOICE QUESTIONS
Tick the most appropriate answer.
Compounds, which in their molten state allow an electric current to pass through them are called
- electrolytes
- non-electrolytes
- non-conductors
- none of these
TRUE \ FALSE
Positively charged electrode is called the anode. True or false ?
Name three reducing agents ?
State four conditions necessary for chemical reactions to take place.
Write true or false .
A black residue is formed when sugar is heated .
Copper carbonate when heated, it turns :
State the type of reactions for the following represent and balance the ones that are not balanced.
Cl2 + 2KBr → 2KCl + Br2
State the main characteristics of chemical reactions. Give at least one example in each case.
Give a word equation for the following reaction.
Two gases which combine to give a solid.
Explain the term chemical reaction with special reference to reactants and products.
Name the solid residual product formed reaction and state its colour during – thermal decomposition of the following substance.
Copper nitrate.
Mention the various conditions required for a chemical reaction to occur.
Burning of paper is the best example of ______ change.
Match the following:
| 1. | Sodium Chloride | a. | CaSO41/2H2O |
| 2. | Calcium sulphate dihydrate | b. | C2H5Oh |
| 3. | Magnesium sulphate hydrate | c. | CaSO4.2H2O |
| 4. | Calcium sulphate hemihydrate | d. | NaCl |
| 5. | Phenol | e. | MgSO4.H2O |
Give an example of a chemical reaction for each of the following situations:
A change in colour is observed.
Beating an egg to make a cake is a ______.
Heat may evolve or be absorbed during a ______ change.
Assertion (A): Cutting paper into very small pieces is an irreversible change.
Reason (R): Physical changes are always reversible.
