Question

1 A compound `X` is used for drinking, has pH =7.Its acidified solution undergoes decomposition in presence of electricity to produce gases `Y` and `Z` The volume of Y is double than Z. Y is highly combustible whereas Z is supporter of combustion .Identify X, Y & Z and write the chemical reactions involved.
2 An aqueous solution of metal nitrate P reacts with sodium bromide solution to form yellow ppt of compound Q which is used in photography. Q on exposure to sunlight undergoes decomposition reaction to form metal present in P along with reddish brown gas. Identify P&Q . Write the chemical reaction & type of chemical reaction.
3 Bhawana took a pale green substance A in a test tube. and heated it over the flame of a burner. A brown colored residue B was formed along with evolution of two gases with burning smell of sulphur.Idetify A & B. Write the chemical reaction involved.
4 A student took 2-3 g of a substance X in a glass beaker & poured water over it slowly. He observed bubbles along with hissing noise. The beaker becomes quite hot. Identify X.What type of reaction is it?
5 A reddish brown vessel developed a green colored solid X when left open in air for a long time. When reacted with dil H2SO4 , it forms a blue colored solution along with brisk effervescence due to colourless & odourless gas Z. X decomposes to form black colored oxide Y of a reddish brown metal along with gas Z, Identify X, Y, & Z.
6 A substance X used for coating iron articles is added to a blue solution of a reddish brown metal Y,the color of the solution gets discharged Identify X and Y & also the type of reaction.
7. A student has mixed the solutions of lead (II) nitrate and potassium iodide.
(i) What was the colour of the precipitate formed? Can you name the compound? precipitated ?
(ii) Write the balanced chemical equation for this reaction. (iii) What type of reaction is it?
8. Observe the following activity & answer the questions

a. Do you observe anything happening around the zinc granules?
b. Is there any change in its temperature?
c. Why is glass tube not dipped in dil H2SO4?
d. How is H2 gas collected by downward displacement or upward displacement of water?
e. Is H2 gas soluble or insoluble in water?
f. Is H2 gas heavier or lighter than air?
9. A reddish brown metal X when heated in presence of oxygen forms a black compound Y which is basic in nature when heated with hydrogen gas gives back X. Identify X & Y.Write the chemical reaction between Y & H 2 Identify the substance being oxidized & reduced.
10 Name the type of reaction seen in the diagram below. Write the reaction for the

11. A student burnt a metal A found in the form of ribbon. The ribbon burnt with a dazzling flame & a white powder B is formed which is basic in nature. Identify A & B.Write the balanced chemical equation.
12. A student dropped few pieces of marble in dilute HCl contained in a test tube. The gas evolved was passed through lime water. What change would be observed in lime water? Write chemical reactions for both the changes observed.
13. Astha has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings? Write the chemical name of black and green coatings
Answers

Answer 1

(1)
The compound 'X' is water.
'Y' has double volume indicating that it is hydrogen.
Hydrogen has double volume than 'Z' which is oxygen because water is made up of 2 parts of hydrogen and one part of oxygen.
The chemical reaction is as follows:
2H2O ------> 2H2 + O2.


(2)
The metal nitrate 'P' is silver nitrate , when it reacts with NaBr we get AgBr which is used in black and white photography.
Under sunlight AgBr decomposes to Ag and gas Br.
The reactions are as follows :

AgNO3 + NaBr ------> AgBr + NaNO3

2AgBr ----sunlight-----> 2Ag + Br2


(3)
The pale green substance 'A' is ferrous sulphate and the brown precipitate 'B' is ferric oxide.
The reaction is as follows:
2FeSO4 -------> Fe2O3 + SO2 + SO3

(4)
The substance 'X' is calcium oxide.
This is a combination reaction.
The reaction is as follows:
CaO + H2O ------> Ca(OH)2

(5)
'X' is basic copper carbonate.
CuCO3.Cu(OH)2.
It is generally referred to CuCO3 only.
When CuCO3 reacts with H2SO4
CuCO3 + H2SO4 -------> CuSO4 + H2O + CO2.
The odorless and odourless gas 'Z' is CO2.,
CuCO3 decomposes to form CuO (copper oxide).
The compound 'Y' Is CuO.

(6)
The substance 'X' is zinc and the metal solution 'Y' is copper sulphate.

Zn + CuSO4 ------> ZnSO4 + Cu.


(7)
(i) The colour of the precipitate is yellow.
The precipitate is lead nitrate.
(ii) Pb(NO3)2 + 2KI -------> 2KNO3 + PbI2. The reaction is a double displacement reaction.


(8)
(i) Bubbles are formed on the surface of zinc granules.
(ii) The test tube gets hot.
(iii) The test-tube may break due to intensive localised heating.
(iv) H2 is collected by the downward displacement of water.
(v) H2 gas is insoluble in water.
(vi) H2 gas is lighter than air.


(9)
The metal 'X' is copper.
The compound 'Y' is copper oxide.
Copper oxide is getting reduced in the reaction between CuO and H2.
In that reaction Copper oxide is getting reduced and H2 is oxidised.


(10)
The question is insufficient.


(11)
The metal 'A' is magnesium.
The white powder 'B' is Magnesium oxide.
The reaction is as follows:
2Mg + O2 ------> 2MgO


(12)
The lime water would turn milky because the gas is CO2.
Marble is CaCO3.
CaCO3 + 2HCl ------> CaCl2 + CO2 + H2O.
Ca(OH)2 + CO2 ------> CaCO3 + H2O


(13)
Corrosion is the phenomenon.
The black coating is silver sulphide.
The green coating is of basic copper carbonate.


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Answer 2

1. Compound Y is Water

hope this will help you

Answer 3

1. Compound Y is Water (H₂O)