most important question, class 10, science, ch – 1

  1. What is the colour of K2CrO4 (Potassium chromate)?
  2. What happens when a chemical reaction occurs?
  3. What happens when Hydrogen combines with Oxygen in the presence of an electric current?
  4. Why do gold and platinum not corrode in moist air?
  5. Give an example of a double displacement reaction.
  6. What happens when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride? State the physical conditions of reactants in which the reaction between them will not take place. Write the balanced chemical equation for the reaction and name the type of reaction. (Delhi 2010)
  7. When the powder of a common metal is heated in an open china dish, its colour turns black. However,when hydrogenis passed over the hot black substance so formed, it regains its original colour. Based on the above information answer the following questions;(i) what type of chemical reaction takes place in each of the two given steps? (ii) Name the metal initially taken in the powder form. Write balanced chemical equations for both reactions.   (AI 2010)
  8. A housewife wanted her house to be whitewashed. She bought 10 kg of quick lime from the market and added it to 30 litres of water. On adding quick lime to water she noticed that the water appeared to be boiling even when it was not being heated. Give reason for her observation. Write the corresponding chemical equation and name the product formed.   (CBSE Sample Paper 2009)
  9. When magnesium ribbon burns in air or oxygen a product is formed. State the type of chemical reaction and name the product formed in the reaction. Write balanced chemical equation of this reaction. ( AI 2009C)
  10. What is a redox reaction? When a magnesium ribbon burns in air with a dazzling flame and forms a white ash, is magnesium oxidised or reduced? Why? (Foreign 2009)

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