Q.1. A water insoluble substance â—X on reacting with dilute H2SO4 released a colourless and odourless gas accompanied by brisk effervescence. When the gas was passed through water, the solution obtained turned blue litmus red. On bubbling the gas through lime water, it initially became milky and milkyness disappeared when the gas was passed in excess. Identify the substance X. Write its chemical equations of the reactions involved
. Q.2. Ahmad took a magnesium ribbon (cleaned) and burned it on a flame. The white powder formed was taken in a test tube and water was added to it. He then tested the solution formed with red and blue litmus paper. What change was seen? Why?
Q.3. Give one example of a combination reaction in which an element combines with a compound to give you a new compound.
Q.4. Marble statues often slowly get corroded when kept in open for a long time. Assign a suitable explanation.
Q.5. Mohan took pure water for the electrolytic decomposition of water but did not see any bubbles near the electrodes. Explain why? Q. 6 Rancidity is a process used for spoiling of cooked food materials like vegetables, etc. When kept for long time in open. How can you prevent such process to proceed? Give an example.
Q. 7 A substance â—Xdisplaces â—Y from its solution in water. It is called displacement reaction. What other chemical name can be given to such type of reactions? Explain, giving an example?
Q. 8 A grey coloured metal â—Z (Atomic weight=65) is used in making dry cell. It reacts with dil. HCl to liberate a gas. What is the gas evolved? Calculate the minimum amount of â—Z required to produce 100 litres of gas? Q. 9 Why is respiration considered an exothermic reaction? Explain. Q. 10 Why are decomposition reactions called opposite of combination reactions? Write equations for these reactions.
Q. 11 A shiny brown colored element â—X on heating in air becomes a black coloured compound. Name the element â—X black the coloured compound formed. Also write the equation
Q. 12 In one of the industrial process used for manufacture of sodium hydroxide, a gas â—X is formed as by product. The gas â—X reacts with lime water to give a compound â—Y which is used as a bleaching agent in chemical industry. Identify â—Xand â—Ygiving the chemical equation of the reaction.
Q 13 Dry hydrogen chloride gas does not turn blue litmus, whereas hydrochloric acid does. Why?
Q. 14. Acid when react with metals release hydrogen gas but there is one acid which when reacts with metals does not release hydrogen except for two metals. Prove this statement. Q. 15. Name the properties responsible for the following uses of baling powder. (i) Baking industry (ii) As an antacid (ii) As soda-acid fire extinguisher.
Q. 16 What is meant by water of crystallization of a substance? What is its importance?
Q. 17 What effect does an increase in concentration of â—H ions in a solution have on the pH of a solution
Q. 18 Fresh milk has a pH Of 6. When it changes to curd, will its pH value increase or decrease? Why?
Q. 19 How does the flow of acid rain water into a river make the survival of aquatic life in a river difficult?
20 Two solutions A and B have pH values of 5 and 8 respectively. Which solution will be basic in nature?
Q. 21 Why does an aqueous solution of acid conduct electricity?Q. 22 How is alkali different from a base?