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].

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.

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

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].

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].

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.

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.

As we know that electrolytes are of two types; strong electrolytes and weak electrolytes. A strong electrolyte is a liquid which conducts electricity very well but a weak electrolyte is a liquid which conducts electricity to a lesser amount because it contains a lesser number of ions. As example of weak electrolytes are; vinegar or acetic acid solution, lemon juice, carbonic acid solution, ammonium chloride solution, rain water, tap water etc.

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.

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

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

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.

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.

The silver metal is taken as anode whereas copper metal is taken as cathode. This process is used in electroplating of silver over copper metal. When electricity is passed through electrodes, then silver nitrate ionizes into silver ions and nitrate ions. Copper ions react with nitrate ions to form salt on electrolyte. The silver ions of the electrolytes are deposited on cathode (negative). The silver undergoes reduction reaction and copper undergoes oxidation reaction.

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

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.

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.