Q1.When the solution of substance X is added to a solution of potassium iodide, then a yellow solid separates out from the solution.
(a) What do you think substance X is likely to be?
(b) Name the substance which the yellow solid consists of.
(c) Which characteristic of chemical reaction is illustrated by this example?
(d) Write a balanced chemical equation for the reaction which takes place. Mention the physical states of all the reactants and products involved in the chemical equation.
Ans ANSWER:
(a) Substance X is likely to be lead nitrate, because on reacting with potassium iodide it forms a yellow precipitate.
(b) The yellow solid or precipitate consists of lead iodide, which is one of the products in this reaction.
(c) This chemical reaction is characterised by the formation of precipitate.
(d) 2KI (s) + Pb(NO3)2(aq) → PbI2(s) + 2KNO3(aq)
Q2. When water is added gradually to a white solid X, a hissing sound is heard and a lot of heat is produced forming a product Y. A suspension of Y in water is applied to the walls of a house during white washing. A clear solution of Y is also used for testing carbon dioxide gas in the laboratory.
(a) What could be solid X? Write its chemical formula.
(b) What could be product Y? Write its chemical formula.
(c) What is the common name of the solution of Y which is used for testing carbon dioxide gas?
(d) Write chemical equation of the reaction which takes place on adding water to slid X.
(e) Which characteristic of chemical reactions is illustrated by this example?
ANSWER:
(a) Solid X is calcium oxide, commonly known as quicklime. Its chemical formula is CaO.
(b) Product Y is calcium hydroxide, commonly known as slaked lime. Its chemical formula is Ca(OH)2.
(c) Common name of the solution of Y is "lime water", which is used to test carbon dioxide gas.
(d) CaO (s) + H2O (l) → Ca(OH)2(aq) + HEAT
(e) This chemical reaction is characterised by change in temperature because a huge amount of heat is evolved in this reaction, causing rise in temperature of the mixture.
When water is added gradually to a white solid X, a hissing sound is heard and a lot of heat is produced forming a product Y. A suspension of Y in water is applied to the walls of a house during white washing. A clear solution of Y is also used for testing carbon dioxide gas in the laboratory.
(a) What could be solid X? Write its chemical formula.
(b) What could be product Y? Write its chemical formula.
(c) What is the common name of the solution of Y which is used for testing carbon dioxide gas?
(d) Write chemical equation of the reaction which takes place on adding water to slid X.
(e) Which characteristic of chemical reactions is illustrated by this example?
ANSWER:
(a) Solid X is calcium oxide, commonly known as quicklime. Its chemical formula is CaO.
(b) Product Y is calcium hydroxide, commonly known as slaked lime. Its chemical formula is Ca(OH)2.
(c) Common name of the solution of Y is "lime water", which is used to test carbon dioxide gas.
(d) CaO (s) + H2O (l)→ Ca(OH)2(aq) + HEAT
(e) This chemical reaction is characterised by change in temperature because a huge amount of heat is evolved in this reaction, causing rise in temperature of the mixture.
A metal X forms a salt XSO4. The salt XSO4 forms a clear solution in water which reacts with sodium hydroxide solution to form a blue precipitate Y. Metal X is used in making electric wire and alloys like brass.
(a) What do you think metal X could be?
(b) Write the name, formula and colour of salt XSO4.
(c) What is the blue precipitate Y?
(d) Write a chemical equation of the reaction which takes place when salt XSO4reacts with sodium hydroxide solution. Give the state symbols of all the reactants and products which occur in the above equation.
ANSWER:
(a) Metal X could be copper (Cu).
(b) The salt XSO4 is copper sulphate; its formula is CuSO4 and it is blue in colour.
(c) Copper hydroxide [Cu(OH)2] is the blue precipitate.
(d) CuSO4 (aq) + 2NaOH (aq)
→
→ Cu(OH)2(s) + Na2SO4(aq)
A compound ‘X’ is used for drinking, has pH =7.Its acidified solution undergoes decomposition in presence of electrictiy 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.
Ans.
reddish brown vessel developed a green colored solid X When left open in air for a long time. When reacted with dil , it forms a blue colored solution along with brisk efficient 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.
Ans.
A strip of metal X is dipped in a blue coloured salt solution YSO4. After some time, a layer of metal Y from the salt solution is formed on the surface of metal strip X. Metal X is used in galvanisation whereas metal Y is used in making electric wires. Metal X and metal Y together form an alloy Z.
(a) What could metal X be?
(b) What could metal Y be?
(c) Name the metal salt YSO4.
(d) What type of chemical reaction takes place when metal X reacts with salt solution YSO4? Write the equation of the chemical reaction involved.
(e) Name the alloy Z.
ANSWER:
(a) Metal X is zinc.
(b) Metal Y is copper.
(c) Metal salt YSO4 is copper sulphate.
(d) Displacement reaction takes place. The chemical equation is given as follows:
Zn (s) + CuSO4 (aq) → ZnSO4 (s) + Cu (s)
(e) The alloy is brass.
Two metals X and Y form the salts XSO4 and Y2SO4, respectively. The solution of salt XSO4 is blue in colour whereas that of Y2SO4 is colourless. When barium chloride solution is added to XSO4 solution, then a white precipitate Z is formed alongwith a salt which turns the solution green. And when barium chloride solution is added to Y2SO4 solution, then the same white precipitate Z is formed alongwith colourless common salt solution.
(a) What could the metals X and Y be?
(b) Write the name and formula of salt XSO4.
(c) Write the name and formula of salt Y2SO4.
(d) What is the name and formula of white precipitate Z?
(e) Write the name and formula of the salt which turns the solution green in the first case.
ANSWER:
(a) Metal X is copper and metal Y is sodium.
(b) The salt is copper sulphate; its formula is CuSO4.
(c) The salt is sodium sulphate; its formula is Na2SO4.
(d) Compound Z is barium sulphate; its formula is BaSO4.
(e) The salt that turns the solution green is copper chloride; its formula is CuCl2.
Two solutions X and Y are tested with universal indicator. Solution X turns orange whereas solution Y turns red. Which of the solutions is a stronger acid?
Solution Y is stronger because the red colour indicates a pH value of 1, whereas the orange colour indicates a pH value higher than 1 (around 4)
a) The pH values of six solutions A to F are given below:
A = 0, B = 11, C = 6, D = 3, E = 13, F = 8
A = 0, B = 11, C = 6, D = 3, E = 13, F = 8
Which of the above solutions are (i) acids (ii) alkalis?
(b) Name the acids or alkalis used to make (i) car batteries (ii) explosives (iii) soaps (iv) fertilisers.
ANSWER:
(a) (i) Acidic solutions: A with pH = 0, D with pH = 3, C with pH = 6
(ii) Basic solutions: F with pH = 8, B with pH = 11, E with pH = 13
(b) The acids or alkalis used to make the following products are given against them.
(i) Car batteries – Sulphuric acid
(ii) Explosives – Nitric acid (in explosives such as TNT, or trinitrotoluene)
(iii) Soaps – Sodium hydroxide
(iv) Fertilisers – Nitric acid, sulphuric acids
Hydrochloric acid reacts with a metal X to form a gas Y which burns with a 'pop' sound. Sodium hydroxide solution also reacts with the same metal X (on heating) to form the same gas Y.
(a) Name X and Y
(b) Write the chemical equation of the reaction of metal X with (i) hydrochloric acid, and (ii) sodium hydroxide solution.
ANSWER:
(a) X is the metal zinc (Zn) and Y is hydrogen gas.
Zinc reacts with hydrochloric acid and forms zinc chloride salt with the liberation of hydrogen gas (Y), which burns with a 'pop' sound. Zinc displaces hydrogen from hydrochloric acid.
Hence, X is zinc and Y is hydrogen.
(b) The chemical equation is as follows.
(i) Zn + 2HCl →ZnCl2 + H2 ↑
(ii) 2NaOH + Zn →Na2ZnO2 + H2
13.A compound ‘X’ is used for drinking, has pH =7.Its acidified solution
undergoes decomposition in presence of electrictiy 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.
Ans: Compound X is Water ( H₂O) It's Neutral Hence pH 7 . Hydrogen released is double the amount of Oxygen.So, Y will be Hydrogen which burns and Z will be Oxygen which is Reduced during combustion.
14.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.
Ans : This is double displacement reaction. The yellow precipitate is AgBr. AgBr is the compound Q. AgBr in sunlight decomposes to form silver {the metal present in compound P (silver nitrate.).}
15.A reddish brown vessel developed a green colored solid X When left open
in air for a long time. When reacted with dil , it forms a blue colored
solution along with brisk efficient 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.
.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. Identify A & B. Write the chemical reaction involved.
Ans : Substance A is ferrous sulphate (FeSO4).
Two gases, sulphur dioxide and sulphur trioxide are evolved.
Substance Sis ferric oxide (FeSO3).
The reaction involved is
You have four solutions A, B, C and D. The pH of solution A is 6, B is 9, C is 12 and D is 7
a) Identify the most acidic and most basic solutions.(b) Arrange the above four solutions in the increasing order of H+ ion concentration.(c) State the change in colour of pH paper on dipping in solution C and D.
a) Most acidic - A, Most basic - C
(b)C,B,D,A/C
(c) In C- blue, In D- green
A metal carbonate (X) on reacting with an acid gives a gas which when passed through a solution (Y) gives the carbonate back. On the other hand, a gas (G) that is obtained at anode during electrolysis of brine is passed on dry substance (Y). It gives a compound (Z), used for disinfecting drinking water. Identity X, Y, G and Z.
Answer:
The gas (G) obtained at anode during the electrolysis of brine is chlorine. The compound (Z) used for disinfecting drinking water is bleaching powder. It is formed on reacting chlorine with dry slaked lime i.e., Ca(OH)2. It is denoted as ‘Y’ This means that the metal carbonate ‘X’ is calcium carbonate. Upon heating, it evolves CO2 gas which gives back ‘X’ on reacting with calcium hydroxide. The chemical reactions involved are listed :
Case Study based questions
Oxidation is the process of gaining of oxygen, or losing of hydrogen. Reduction is the process of losing of oxygen or gaining of hydrogen. The substance which undergoes oxidation is the reducing agent while the substance which undergoes reduction is known as the oxidising agent. Oxidation and reduction always take place together and these type of reactions are known as redox reactions. Some of the examples of redox reactions are given below:
(i) Give two examples of oxidation reaction from your everyday life.
Answer
Answer: Corrosion and Rancidity
(ii) Write the oxidising agent in the reaction III and VI.
Answer
Answer: CuSO4 in (III) and CuO in (VI)
(iii) Which of the following is an oxidising agent?
(a) LiAlH4
(b) Alkaline KMnO4
(c) Acidified K2Cr2O7
(d) Both (b) and (c)
Answer
Answer: d
(iv) Out of oxidation and reduction, which reaction takes place at anode?
Answer
Answer: Oxidation takes place at anode.
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