Chemistry class 9thClass Matric Part 1 Notes

Class 9th Chemistry Unit 7 Question And Answer

Class 9th Chemistry Unit 7 Question And Answer On Newsongoogle By Bilal Articles

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Unit 7

Q1: What is meant by electrochemistry?

Ans: The branch of chemistry that deals with the relationship between electricity and chemical reactions is called electrochemistry.

Q2: Define oxidation.

Ans: Oxidation is defined as the addition of Oxygen or Removal of Hydrogen or loss of Electron or increase in oxidation number during a chemical reaction. C+O2→ CO₂

Q3: Define reduction.

Ans: Reduction is defined as the removal of oxygen 1 or addition of hydrogen or gain of electrons decrease in oxidation number during a chemical reaction. CuO+H₂Cu+H₂O

Q4: What is meant by Redox?

Ans: Chemical reactions in which the oxidation state of one or more substances changes are called oxidation-reduction or Redox reactions, H₂S+Cl2→ 2HC1+S

Q5: What is meant by oxidizing agent? Give examples. Ans: An oxidizing agent is a species that oxidizes a substance by taking electrons from it. The substance (atom or ion) which is reduced itself by gaining electrons is called oxidizing agent. For example a) Concentrated Sulphuric acid H2SO4 b) Potassium permanganate. KMnQ4

Q6: What is meant by reducing agent? Give examples.

Ans: Reducing agent is the species that reduces a substance by donating electron to it. The substance (atom or ion) which is oxidized by losing electrons is called reducing agent. For example a) Hydrogen (H) b) Hydrogen sulphide (H2S)

Q7: What are spontaneous reactions?

Ans: Spontaneous reactions are those which take place on their own without any external agent.

Q8: What are non-Spontaneous reactions?

Ans: Non-spontaneous reactions are those which take place in the presence of external agent.

Q9: What is meant by Oxidation State?

Ans: Oxidation state or oxidation number is the apparent charge assigned to an atom of an element in a molecule or in an ion. For example in HCl, the oxidation number of hydrogen is +1 and

Q10: Define valency.

Ans: The apparent charge on an atom, ion or molecule is called valency. It is written as their sign. followed by the number i.e., 2+ OR The combining power of an atom to another atom is called its valency

Q11: What is meant by electrochemical cell?

Ans: Electrochemical cell is a system in which two electrodes are dipped in the solution Of an electrolyte which is connected to the Battery. OR Electrochemical cell is an energy storage device in which either a chemical reaction takes place by using electric current or chemical reaction produces electric current.

Q12: What are electrolytes?

Ans: The substances, which can conduct electricity ity in the in their solutions or molten states, are called electrolytes. For example, solutions of salts, acids or bases are good electrolytes.

Q13: What are strong electrolytes?

Ans: The electrolytes which ionize completely i in aqueous solution and produces more ions, are called strong electrolytes. For example, NaCl, NaOH, H_{2}*S*O_{4} are strong electrolytes.

Q14: What are weak electrolytes?

Ans: The electrolytes which ionize to a small extent when dissolved in water and could not produce more ions are called weak electrolytes. For example, C*H_{3}*COOH Ca (OH) 2 etc.

Q15: What are non-Electrolytes?

Ans: The substances, which do not ionize in solution and do not allow the current to pass through their solutions, are called non-electrolytes. For example, sugar solution, benzene etc.

Q16: What is meant by electrolytic cell?

Ans: The type of electrochemical cell in which a non-spontaneous chemical reaction takes place when electric current is passed through the solution, is called an electrolytic cell c.g. Down’s cell.

Q17: Define Cation.

Ans: Chemical specie which carries a positive charge. e.g., N a^ + . K ^ + etc.

Q18: Define Anion.

Ans: Chemical specie which carries a negative charge. e.g. mathcal ,O ^ 2 ^ – ,C Gamma^ – etc

Q19: What is meant by galvanic cell?

Ans: The electrochemical cell in which a spontaneous chemical reaction takes place and generates electric current is called galvanic or voltaic cell. For example, Daniel cell

Q20: What is half cell?

Ans: A galvanic cell consists of two cells one having cathode while the other having anode end and which are connected with a salt bridge. Each of these known as shalf cell

Q21: What is meant by salt bridge?

Ans: Salt bridge is a U-shaped glass tube which consists of a saturated solution of strong electrolyte supported in a jelly type material. The ends of the U-shaped glass tube are sealed with a porous material like glass wool. The function of the salt bridge is to keep the solutions of two half cells neutral by providing a pathway for migration of ions.

Q22: Define corrosion.

Ans: It is a Redox reaction that takes place by the action of air and moisture with the metals. For example rusting of iron.

Q23: What is meant by rust?

Ans: It is a Redox reaction that takes place when iron is exposed to air and moisture. The chemical formula of rust is. F*e_{2}*O_{3} n*H_{2}*O

Q24: Define electroplating.

Ans: Electroplating is depositing of one metal over the other by means of electrolysis.

Q25: Define alloy.

Ans: Alloy is a homogenous mixture of one metal with one or more other metals or non-metals. For example stainless steel is an alloy of iron, chromium arid nickel.

Q26: Name different types of electrochemical cells.

Ans: The types of Electrochemical Cells are: i. Electrolytic cell. ii. Galvanic or voltaic cell.

Q27: How the oxidation number and valency are assigned?

Ans: Oxidation Number: While assigning oxidation number the sign precedes the number i.c. +2. For example, the oxidation number of Sodium is +1 Valency: While assigning valeney the sign followed by the number i.e. 2+, For example, the valency of sodium is 1+

Q28: Write construction of an electrolytic cell?

Ans: An electrolytic cell consists of a solution of an electrolyte, two electrodes (cathode and anode) that are dipped in the electrolytic solution and connected to the battery. The electrode connected to positive terminal is called anode and electrode connected to the negative terminal is called cathode.

Q29: Who was A. Volta?

Ans: Volta (1745-1827) was an Italian physicist known especially for the development of the first electric cell in 1800.

Q30: Write construction of Down’s cell?

Ans: This electrolytic cell is a circular furnace. In the center there is a large block of graphite, which acts as an anode while cathode around it is made of iron.

Q31: Differentiate between Spontaneous and non-spontaneous reactions.

Ans: Spontaneous reactions: Those reactions which takes place on their own without any external agent Example: Galvanic cell. Non-spontaneous reactions: Those reactions which takes place in the presence of an external agent. Example: Electrolytic cell

Q32: Give overall reaction for the preparation of sodium hydroxide.

Ans: 2NaCl + 2H2O→ H2 + Cl2 + 2NaOH

Q33: Why the process of rusting does only occur on iron and not on the surface of aluminum?

Ans: Aluminum corrodes but it does not rust. Rust refers only to iron and steel corrosion. A very hard material aluminum oxide protects the aluminum from further corrosion. In comparison to that when iron corrodes. Its color changes and produces large red flakes known as rust. Unlike aluminum oxide, the expanding and flaking of rust exposes new metal to further rusting.

Q34: Differentiate between Strong and Weak electrolytes.

Ans: Strong Electrolytes: The electrolyte which ionizes completely in solution is called Strong Electrolyte. It produces less ions in water Examples: NaOH, HCl etc. Weak Electrolytes: The electrolyte which do not ionize completely in solution is called Weak Electrolyte. It produces more ions in water. Examples: CH-COOH, Ca(OH)2

Q35: What is meant by stainless steel?

Ans: It is an alloy which is made up of iron, chromium and nickel. Which does not corrode.

Q36: What is meant by galvanizing?

Ans: The process of coating a thin layer of zinc on iron is called galvanizing.

Q37: How galvanizing process takes place?

Ans: This process is carried out t by dipping a clean iron sheet in a zine chloride bath and then heating it. After this iron sheet is removed, rolled into molten zine metal bath and finally air cooled.

Q38: Write advantages of galvanizing.

Ans: A major advantage of galvanizing is that zinc protects the iron against corrosion even after the coating surface is broken.

Q39: What is the principle of electroplating?

Ans: The principle of electroplating is to establish an electrolytic cell in which anode is made of the metal to be deposited and cathode of the object on which metal is to deposit. The electrolyte is an aqueous solution of a salt of the respective metal.

Q40: Differentiate between Electrolytes and non-electrolytes.

Ans: Electrolytes: The substances, which can conduct electricity in their solutions or molten states, are called electrolytes. Examples: NaOH, HCI etc. Non-Electrolytes: The substances, which cannot conduct, electricity in their solutions or molten states, are called non-electrolytes. Examples: Glucose solution, Benzene etc

Q41: Write a note on zinc electroplating.

Ans: A target metal is cleaned in alkaline detergent type solutions, and it is treated with acid, in order to remove any rust or surface scales. Next, the zinc is deposited on the metal by immersing it in a chemical bath containing electrolyte zinc sulphate. A current is applied which results in zine being deposited on the target metal i.e., cathode

Q42: Write a note on tin electroplating.

Ans: Tin usually electroplated on steel by placing the steel into a container containing a solution of tin salt. The steel is connected to an electrical circuit acting as cathode. While the 4 other electrode made of tin metal acts as anode. When an electrical current passes through the circuit, tin metal ions present in the solution deposit on steel.

Q43: Which material is used to make cathode in electroplating?

Ans: The cathode is made up of the object that is to be electroplated like some sheet made up of iron.

Q44: Why is the anode made up of a metal to be deposited during electrolysis?

Ans: When current is passed, the metal from anode dissolves in the solution and metallic ions migrate to the cathode and discharge or deposit on the cathode. ution a

Q45: What is the difference between corrosion and rusting?

Ans: Corrosion is slow and continuous eating away of a metal by the surrounding medium. It is a Redox chemical reaction that takes place by the action of air and moisture with metals. While, rusting is an example of corrosion. The condition for rusting is the moist air (air having water vapors in it).

Q46: What happen to iron in the rusting process?

Ans: The rusting process continues until all the pieces of iron is eaten up.

Q47: Explain the role of O₂ in rusting?

Ans: The free electrons move through iron sheet, until they reach to a region of relatively high oxygen concentration, near the surface surrounded by water layer. This region acts as cathode and electrons reduce the oxygen molecule in the presence of H ions. O2+4H++4e-2H₂O

Q48: State the best method for protection of metal from corrosion.

Ans: The best method for protection against the corrosion of metals exposed to acidic conditions is coating the metal. Corrosion resistant metals like Zn, Sn and Cr are used for this method.,

Q49: Why tin-plated iron is rusted rapidly when tin layer is broken?

Ans: When tin layer is broken and iron is exposed to the air and water, iron rusts. rapidly. a galvanic cell is established and

Q50: Name the metal which is used for galvanizing iron?

Ans: Zinc metal is used for galvanizing iron.

Q51: Anode of Down’s cell is made of a non-metal, wha sits name? What is the function of this anode?

Ans: In Down’s cell anode is made up of carbon (graphite). The CI- ions are oxidized to give Cl the anode. gas at

Q52: Where does the sodium metal His collected in Down’s cell?

Ans: In Down’s cell Nations are reduced at cathode and molten sodium metal floats on the denser medium salt mixture from where it is collected in a side tube.

Q53: What is the name of the by-product produced in the Down’s cell?

Ans: Chlorine gas is produced as a by-product in the Down’s cell.

Q54: Are anodes of Down’s cell and Nelson’s cell made of same element? If yes, what is its name?

Ans: Yes, anodes of both Down’s cell and Nelson’s cell are made up of same element known as graphite.

Q55: What is the shape of cathode in Nelson’s cell? Why is it perforated?

Ans: In Nelson’s cell, cathode is internally lined with asbestos diaphragm. Cathode is a U-shaped perforated iron from where sodium hydroxide solution slowly percolates in a catch basin.

Q56: Which ions are discharged at cathode in Nelson’s cell and what is produced, at cathode? Ans: Cl- are discharged at cathode in Nelson’s cell and chlorine gas is evolved from that electrode.

Q57: Why are the strong electrolytes termed as good conductors?

Ans: Strong electrolytes are termed as good, conductors because they ionize completely in their

Q58: Does Non-electrolyte form ions in solution?

Ans: No, non-electrolytes do not ionize in Solution and do not allow the current to pass, through their solutions.

Q59: Identify a strong or weak electrolyte among the following compounds.

Ans. CuSO4 (Strong electrolyte) b. H_{2}*C*O_{3} (Weak electrolyte) c. Ca (OH) 2 (Weak electrolyte) d. HCI (Strong electrolyte) e. AgNO3 (Strong electrolyte)

Q60: Which force drives the non-spontaneous reaction to take place?

Ans: Non-spontaneous reactions are those which take place in the presence of external agent. This external agent is known as electrical energy.

Q61: Which type of chemical reaction takes place in electrolytic cell?

Ans: Non-spontaneous chemical reaction takes place with the help of electricity in electrolytic cell.

Q62: What type of reaction takes place at anode in electrolytic cell?

Ans: The process of oxidation takes place at anode in electrolytic cell.

Q63: Why the positively charged electrode is called anode in electrolytic cell?

Ans: The electrode connected to positive terminal of the battery is called anode.

Q64: In the electrolysis of water, towards which terminal H ^ + ions move?

Ans: In the electrolysis of water, H ^ + ions move towards cathode and reduced to hydrogen gas and liberates.

Q65: In the electrolysis of water, where is the oxygen produced?

Ans: In the electrolysis of water, oxygen is produced at anode electrode.

Q66: Towards which electrode of the electrolytic cell moves the cations and what do they do there?

Ans: In electrolytic cell, cations move towards cathode electrode and they are reduced there.

Q68: How the half cells of a galvanic cell are connected? What is function of salt bridge?

Ans:The half cells of a galvanic cell are connected electrically by a salt bridge. It is used to keep the solutions of two half cells neutral by providing a pathway for migration of ions.

Q69: In the following reaction, how can you justify that H_{2}*S is oxidized and S*O_{2} is reduced? S*O_{2} + 2H_{2}*S -> 2H_{2}*O + 3S

Ans: As hydrogen is removed from H_{2}*S therefore H_{2}*S is oxidized, while removal of oxygen takes place in S*O_{2} therefore S*O_{2} reduced.

Q70: The reaction between MnO2 and HCl is a Redox reaction written as balance chemical equation as: MnO2 + 4HC1→ MnCl2 + 2H2O + Cl2 Then find out. a) The substance oxidized b) The substance reduced c) The substance which acts as oxidizing agent d) The substance which acts as reducing agent

Ans: In the given balanced Chemical Equation: a) Cl is oxidized b) Mn is reduced c) MnO2 is oxidizing agent d) HCl is reducing agent

Q71: The following reactions are Redox reaction. Find out the element which has been reduced and the element which has been oxidized. a) Zn + CuSO4→ ZnSO4 + Cu b) Cu+2AgNO3 → Cu(NO3)2 + 2Ag c) H_{2}*S + C*l_{2} -> 2HCl + S

Ans: The Reduced and Oxidized elements are as: a) Zn. is oxidized and Cu is reduced b) Cu is oxidized and Ag is reduced c) Sulphur (s) is oxidized and Cl is reduced

Q72: Why the following reaction is not a redox reaction, Explain with reasons? NaOH+HCI NaCl+H₂O

Ans: Because, acid & base reactions are considered to be neutralization reactions. Whenever, acid reacts with bases, they form salt and water.

Q73: Why the oxidation number of Oxygen in O*F_{2} is 2′

Ans: The oxidation number of Oxygen on O*F_{2} is +2, because fluorine has. a high electronegative value as compared to oxygen. Therefore, fluorine will carry negative (-1) charge while oxygen will carry (+2) charge on it.

Q74: An element X, has oxidation state 0. What will be its oxidation state when it gains three electrons?

Ans: When X will gain three electrons in its valence shell its oxidation state will become X-3

Q75: An element in oxidation state +7 gains electrons to be reduced many electrons did it accept? ed to to oxidation state +2, How

Ans: When an element in oxidation state +7 gains electrons and reduced to that it has accepted +5 electrons in its valence shell. duced to to oxidation state +2, it shows

Q76: If the oxidation state of an element changes from 5to – 3 Has it been reduced or oxidized? How many electrons are involved in this process?

Ans: When the oxidation state of an n element changes from +5 to -3, it is considered to be reduced, there are eight electrons involved in this process.

Q77: How can you justify that a reaction between magnesium and oxygen i bety while the reaction shows only addition of oxygen (oxidation)? is a Redox reaction, 2Mg + O_{2} -> 2MgO

Ans: The above reaction is a Redox one, because oxygen tends to gain electron which is known as reduction, while magnesium tends to remove electrons which is known as oxidation. The simultaneous oxidation-reduction process is known as Redox.

Q78: An element M reacts with another element X to form M*X_{2} in terms of loss or gain of electrons, identify the element which is oxidized and which is reduced.

Ans: When an element M loses its electron, oxidation process takes place. When this electron is gained by element X, reduction process takes place. Therefore, element M is oxidized while element X is reduced.

Q79: How can you justify that the following reaction is not only an oxidation reaction but also a complete Redox reaction? FeO + CO→ Fe + CO2

Ans: When FeO reacts with CO, oxygen is removed from FeO which shows reduction process. On the other hand when oxygen is added to CO it shows oxidation process. Therefore, it is a complete redox reaction.

Q80: Write applications of galvanic cell?

Ans: As a result of Redox reaction, electric current is electric cur produced. The. batteries which are used for starting automobiles, running calculators and toys and to lit the bulbs work on the same principle.

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