16. Copper when exposed to air for a long time acquires a green coat, Why?
III. Answer the following questions:
8 x 2 = 16
17. Draw circuit diagram showing the combination of Resistors R, and R, in
parallel, R and R, in Seires, including ammeter and voltmeter and mark the
direction of electric current
18. Draw the diagram of the apparatus used in electrolytic refining of copper
and label the electrode where impure copper is taken.
19. Draw the ray diagram showing the formation of image of an object in Convex
lens when it is placed at 2F.
20. What is the need for a system of control and coordination in an organism?
21. What are ionic compounds? Mention any two properties of Ionic compounds
OR
A student was given Manganese, Zinc, Iron and Copper metals. Identify
i) Will not displace hydrogen from dilute hydrochloric acid.
ii) Will react only with steam to give hydrogen gas.
Answers
Answer:
( 16. )
When copper is exposed to air for a long time, it gains a layer of copper carbonate along with copper hydroxide in presence of moist carbon dioxide. This layer is greenish in colour and ir responsible for the greenish appearance of the copper metal.
2Cu+H₂O+O₂+CO₂→Cu(OH)₂+CuCO₃
( 17. ) Refer the attachment (i'st)
( 18. ) Refer the attachment(ii'nd)
( 19. ) Refer the attachment(iii'rd)
( 21. )
The compounds that are formed between two or more metal and non metal by the transfer of electrons are called as Ionic compounds. There are formation of ions during the formation of these compounds and they exists till their bond sustains due to opposite attraction between them.
E.g. NaCl(Sodium Chloride),
Na₂O(Sodium Oxid)
The properties of ionic compounds are:
(i) They are hard solid and brittle(break easily when hit hard) in nature.
(ii) They have High melting and boiling points;
*Due to high force of attraction between the ions*
(iii) They are soluble in water.
(iv) They conduct electricity in their Aqueous and molten state.
*Because of formation of ions*
