Class 8 Science Chapter 11 MCQ

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 liquids that conduct electricity are solutions of acids, bases and salts in water. Vinegar and lemon juice also conduct electricity because they are solution of acids. Similarly, a solution of sodium hydroxide, potassium hydroxide or any other soluble base in water conducts electricity. A solution of copper sulphate, common salt or sodium chloride or any other salt in water also conducts electricity.

In electroplating factory, the disposal of the used conducting solution is a major concern because it is a polluting waste, therefore it should be disposed-off according to the disposal guidelines of the local authority.

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.

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.

Sodium hydroxide (NaOH) is manufactured by using the chemical effect of electric current when a sodium salt is electrolysed. In other words, the chemical effect of electric current is used in the production of various chemical compounds. Such as sodium hydroxide or caustic soda is produced by the electrolysis of an aqueous solutions of sodium chloride.

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.

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

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.

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

The decomposition produced by passing current through a conducting liquid is called “Electrolysis”.

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.

The electroplating of chromium on metal object is called chrome. This procedure is used to reduce corrosion and for decorative purpose. Trivalent chromium plating is done on graphite to avoid oxidation reaction taking place in it. Here, chromium chloride or chromium sulphate is used for electroplating. This is majorly used to make the product thicker. Chromium is plated on steel for decorative purpose and make the metal corrosive resistant. It is used in car parts and utensils. Bakelite and teflon both are special type of plastic.

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.

The copper acts as cathode (+) and iron acts as anode (-). This setup is used for electroplating. The electrochemical reaction between copper and iron is: Fe (iron) + CuSO₄ (copper sulphate) = FeSO₄ (ferrous sulphate) + Cu (copper) When electricity is passed through electrode then the copper sulphate ionizes to form copper ions and sulphate ions. Copper (positive) ions move towards iron (negative) ions and this forms a layer of copper over iron which is called as electroplating.