Grade 7 Examination Portion coverage 3rd Term exam 21-22 and Answer Key

Grade 7 Chapter 7 Electrolysis 

Class Assessment

1.     Loss of electron by an atom is called ………….?
Oxidation                    b.  Reduction         c. Redox  reaction
2. In ………… state of electrolytes, ions are not free to move?
Liquid                            b. Solid                 c. Gas
3. Compounds that do not conduct electricity even in molten or solution form are called ……………….. ?
a. Electrolytes   b. Metal Electrode    c. non-Electrolytes
    4.  Lead, Pb2+, gains -------- electrons forming lead atoms.
    a)  2              b) 4                       c)  6
5. Metals donate electrons forming positive ions 
For example:      
       a)            Na+,    K+,      Ca2+,     Al3+
       b)           Cl-,    Br-,     I-,     O2-
       c)            Both a & b

1.  Lead as a metal will be collected on cathode. T
2.  Bromine being a non-metal will be collected on anode. T
    3.  Aluminum is highly reactive metal. T
   4.  Oxygen reacts with hot carbon anodes making carbon dioxide gas & burns away. T
   5.  Aluminum is extracted mainly from its ore called Bauxite (Al2O3). T
  6.  Aluminum oxide is dissolved in a chemical Cryolite (Na3AlF4). T
7.  Ions are free to move in solution of the compounds. T
8.  Hydrogen being a non – metal, is deposited on cathode. T
    9.  Hydrogen is a monoatomic molecule. F 
10.  Calcium is more reactive & stable than hydrogen. T 
11.  Active electrode is a metal that is used in electrochemical cells. T
12.  Mostly we use Iron electrodes. F
    13.  Copper is a best conductor of electricity. T
    14.  During the electrolysis, impurities fall down in cell. T 
15.  Smelting copper ores is the main source to provide  copper. T
16.  Rock-eating bacteria are Bio-leaching. T 
17.  About 10% copper is extracted by leaching method. F
    18.  Addition of acid costs money. T
19.  Iron oxide is reduced to iron by loss of iron. F
20.  Carbon monoxide  is oxidised to carbon dioxide by gain of oxygen. T 
21.  Oxidation is loss of electrons. T 
22.  Reduction is gain of electrons. T  
23.  Copper as a metal will be collected on cathode. T 
24.  Chlorine being a non-metal will be collected on anode. T 
25.  Half – equation shows the external chemistry of a chemical reaction. F 
26.  Cl is a diatomic molecule. T 
27.  Electrodes are rods (plates) made up of graphite or metals. T 
28.  The negative electrode is called Anode. F 
29.  The positive electrode is called Cathode. F 
30.  Negative ions are called Anions. T  
31.  Positive ions are called Cations. T   
32.   Decomposition of a compound by passing electricity through is called Electrolysis. T 
33.   A compound that does not conduct electricity in solid form but it only conducts in molten or solution form is called Electrolyte. T 
34.   Electrolytic cell is a device that uses electrical energy to start a chemical reaction. T


 

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