Class 8 Science Chapter 11 MCQ

Here, all the statements are correct. Hence, your answer will be option [D].

Bulb in the set-up B glows more brightly because higher current is flowing through the circuit in set up B, as solution B is better conductor of electricity than that of A.

Here, all the statements are correct. Hence, your answer will be option [D].

Bulb in the set-up A glows more brightly because higher current is flowing through the circuit in set up A, as solution A is better conductor of electricity than that of B.

Here, all the statements are correct. Hence, your answer will be option [D].

The chemically reactive metals are produced by the chemical effect of electric current. The reactive metals such as sodium, aluminium and magnesium etc., are produced by passing electric current through their compounds in molten state. Sodium metal is produced by the electrolysis of molten sodium chloride whereas aluminium metal is produced by the electrolysis of molten aluminium oxide. In these cases, metal is produced at the negatively charged electrode or cathode because the positively charged ions of metals present in the molten compounds are attracted by the negatively charged or opposite charged electrode. This method is used in the production or extraction of certain metals from their naturally occurring compounds called as “ores”.

Here, all the statements are correct. Hence, your answer will be option [D].

Water is a chemical compound and hydrogen and oxygen are elements. When electric current is passed through water. A chemical compound “water” has been decomposed into two elements, hydrogen and oxygen, by the action of electric current. So, this reaction is an example of chemical effect of electric current. The breaking up of water into hydrogen and oxygen is actually a “chemical decomposition reaction” caused by passing an electric current through acidified water which is a conducting liquid. Oxygen gas is formed at the positive electrode which is connected to the positive terminal of the battery and hydrogen gas is formed at the negative electrode which is connected to the negative terminal of the battery.

Here, all the statements are correct. Hence, your answer will be option [D].

The passage of an electric current through a conducting solution causes chemical reactions. As a result, change of colour of solution occurs. This indicates the chemical effect of current.

Here, all the statements are correct. Hence, your answer will be option [D].

Vegetable oil will not conduct electricity because it does not make irons easily.

Distilled water is a poor conductor or non-conductor of electricity because it does not contain any dissolved salts in it which can provide it ions to conduct electricity. Thus, distilled water is pure water and it does not conduct electricity.

Chromium is used for electroplating to make objects appear shining because chromium has a shiny appearance and it resists scratches.

Here, all the statements are correct. Hence, your answer will be option [D].

When electrodes are placed in an electrolyte and a voltage is applied, the electrolyte will conduct electricity. Alone electrons normally cannot pass through the electrolyte; instead, a chemical reaction occurs at the cathode, providing electrons to the electrolyte. The dissolved electrolyte separates into cations and anions, which disperse uniformly through the solvent. Electrically, such a solution is neutral. If an electric potential is applied to such a solution, the cations of the solution are drawn to the electrode that has an abundance of electrons, while the anions are drawn to the electrode that has a deficit of electrons. The movement of anions and cations in opposite directions within the solution amounts to a current.

In electrolysis process, electrode is one of component is complete the reaction. The chemical reaction takes place between electrodes. Carbon is just like other substance used for electrode but it is widely used in production of silicon and phosphorus. Carbon electrodes have good electrical and thermal conductivity, mechanical strength, chemical purity, easy mounting and accurate machining. It also withstands high temperature, carries large amount of electric current and cost effective. And it is resistant to corrosion also.

Sugar solution in dilute water does not make ions and is a poor conductor of electricity. Therefore, it will not make the current to flow through it and the bulb will not glow.

We should follow all the three methods, except one which is option [D]. A distilled water salt of the metal to be purified is taken as electrolyte is not required for electrolyte. Hence, your answer should be option [D].

Decomposition of elements is not an application of the chemical effect of electric current. Electroplating, purification and decomposition of compounds can be done with the help of chemical effect of electric current.

When electric current flows through a conducting solution, it causes a chemical reaction or chemical change. The chemical reaction is brought about by an electric current may produce one or more of the following effects. Such as: i)bubbles of a gas may be formed on the electrodes ii)deposits of metals may form on electrodes iii)change in colour of solution may occur These are some of the chemical effects of the electric current. But formation of a precipitate is not produced by the chemical reactions by an electric current.

Here, all the statements are correct. Hence, your answer will be option [D].

Impure and pure metal are taken as electrode and water-soluble salt of the metal is taken as electrolyte. Here, impure copper metal should take as cathode and pure copper metal taken as anode. Copper sulphate solution is taken as electrolyte. When electricity is passed through electrode, the atoms of the impure metal react with electrolyte and the metal in electrolyte is deposited into cathode. After sometimes, the impure metal electrode becomes thinner and pure metal electrode becomes thicker.

The device which can be used to detect very small current flowing in an electric circuit is light emitting diode or LED.

We should not follow the method is option [C]. For electroplating an iron object with copper metal or copper plating, we should follow the method is: The iron object is made negative electrode. The copper plate is made positive electrode. Copper sulphate solution is taken as electrolyte. Because the metal object on which electroplating is to be done is made the negative electrode or cathode. The metal whose layer is to be deposited is made the positive electrode and a water-soluble salt of the “metal to be deposited” is taken as the electrolyte (the electrolyte contains the metal to be deposited in the form of soluble salt.