Question

please ans this as fast as possible

Answer 1

HEY SIVA!!
Rajdeep here.....

9. 
(a) When dilute sulphuric acid is poured on a copper plate, there is no observation. WHY?
Let me tell you about the metallic reactivity series:
K
Na
Ca
Mg
Al
Zn
Fe
Ni
Sn
Pb
H
Cu
Hg
Ag
Au
Pt

The metals above Hydrogen in the series can only produce hydrogen gas when they react with dilute acids like sulphuric acid. However, metals below H cannot. Copper is a metal which is present below hydrogen in the reactivity series, so it cannot produce hydrogen gas when dilute H₂SO₄ is added to it. Hence,
Cu + H₂SO₄ (dil) --------> NO REACTION



(b) In the series, iron is located far above copper, hence, iron can displace copper from the salt solution of copper. Thus, when iron nails are placed in the copper sulphate solution, iron sulphate is formed. The blue coloured solution (of copper sulphate) turns green (due to formation of iron sulphate).
Reaction:
Iron + Copper Sulphate -----> Iron sulphate + Copper



10. Saloni obtained a gas by burning charcoal. When charcoal is burnt, Carbon dioxide gas is formed.
To test this gas,

1. Pass it through lime water; Lime water turns milky.
2. Pass it through alkaline Potassium permanganate solution, there is no effect.

Reactions:
2C + O₂ -----> 2CO
2CO + O₂ ------> 2CO₂

Word equation:
Charcoal (Carbon) + Oxygen (of air) ------> Carbon monoxide
Carbon monoxide + Oxygen --------> Carbon dioxide.



11. The jewellery was old, so many impurities may be mixed in it, which might have increased its weight. On polishing, the impurities are removed, which reduces the weight of gold.



HOPE MY ANSWER IS SATISFACTORY.....

Answer 2

hiii student of class 8th CBSE board!!

here's ur answer...

9. (a) when dilute sulphuric acid is poured on a copper plate, the copper plate (metal) will react with sulphuric acid and their will be evolution of hydrogen gas with crystals of copper sulphate.

CHEMICAL EQUATION :-

H2so4 + Cu ==> CuSo4 + H2

sulphuric acid + copper ==> copper sulphate + hydrogen gas

(b) first lemme tell about displacement reaction.

DISPLACEMENT REACTION - in this reaction a more reactive metal replace a less reactive metal. but a less reactive metal can't replace more reactive metal.

eg :- CuSo4 + Zn ==> ZnSo4 + Cu

now,

examples of some metals which are less reactive and more reactive than others :-

copper is a reactive metal, iron is more reactive than copper and zinc is more reactive than iron.

among these three the least reactive metal is copper, then iron and zinc is the most reactive.

in this question, here's asked that what will happen if iron nails are placed in copper sulphate solutions??

as I told u before more reactive metals replace less reactive metal.

iron is more reactive, as compared to copper so it will replace copper from copper sulphate solution.

CHEMICAL EQUATION:-

CuSo4 + Fe ==> FeSo4 + Cu

copper sulphate + iron ==> iron sulphate + copper

10. (a) she will add lime water in the test tube and it's colour will turn milky, which shows that the gas is carbon-dioxide.

(b) C + O2 ==> Co2

carbon + oxygen ==> carbon dioxide

11. in the process of polishing, jewellers dip jewelleries in an acid solution. so jeweller must have dipped Rita's mother's gold jewellery in acid and also rubbed it. thus the gold reacts will acid and the outer layer of gold is dissolved in the solution. therefore, there was a slight loss in weight.

hope this helps u..!!