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प्रश्न
A chemical reaction is often accompanied by external indications or characteristics which include –
- Colour change
- Effervescence or gas evolved
- Evolution or absorption of heat
- Formation of a precipitate.
With reference to each of the above indications, state the external indication seen during – Addition of dilute acid to an active metal.
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उत्तर
Addition of dil. acid to an active metal: Gas is evolved, test tube or flask becomes hot (heat is produced).
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संबंधित प्रश्न
Complete and balance the following chemical equations:
Fe `"SO"_4` + NaOH `→`
(aq.) (aq.)
MULTIPLE CHOICE QUESTIONS
Tick the most appropriate answer
Which of the following is a reducing agent?
- oxygen
- chlorine
- hydrogen
- none of these
TRUE \ FALSE
A precipitation reaction takes place only in a solution.
TRUE \ FALSE
Ammonia is a good oxidizing agent.
What are biocatalysts ?
State what you would observe when the following substance is heated in a glass test tube Copper (II) carbonate Red lead .
Write the chemical reaction where the following changes are observed.
Gas is evolved
Explain,giving one example of the following chemical changes:
Reversible reaction
What is a chemical change? Give two examples of chemical change?
Give an example of the following chemical changes.
A reaction involving
(i) Change of state
(ii) formation of precipitate
Give a chemical test to distinguish between the following gases.
H2 and O2
What do you observe when dilute sulphuric acid is added to the following:
Sodium Sulphide
Explain the term ‘chemical reaction’ with special reference to – ‘reactants’ and ‘products’.
State the following reaction represent oxidation or reduction.
\[\ce{H->H+}\]
What happens when cane sugar is strongly heated? Mention any two changes in it.
Classify the following as physical or chemical properties
Most metal oxides form alkalis on interacting with water.
Which of the following is/are true when milk changes into curd?
- Its state is changed from liquid to semi solid.
- It changes colour.
- It changes taste.
- The change cannot be reversed.
Choose the correct option from below:
Classify the following processes into physical or chemical changes:
- Beating of aluminium metal to make aluminium foil.
- Digestion of food.
- Cutting of a log of wood into pieces.
- Burning of crackers.
The simplest method of preventing rusting of iron is to coat it with oil, grease, or paint. The reason being ______.
Match the following:
| Column I | Column II | ||
| 1. | Burning of coal | a. | Rusting |
| 2. | Painting of a surface | b. | Evaporation |
| 3. | Dipping iron in the water | c. | Chemical change |
| 4. | Salt from seawater | d. | Prevention of rusting |
