Class 8 Science Chapter 11 MCQ

When an electric current is passed through a conducting solution, it causes chemical reactions. The resulting effect is called “chemical effect of current”. When an electric current is passed through a bulb, its filament gets heated to a high temperature and bulb starts glowing. The resulting effect is heating effect of current. Whenever an electric current is passed through a circuit, a magnetic effect is produced around it. The resulting effect is magnetic effect of current. Thus, an electric current can produce chemical, heating and magnetic effects.

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].

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].

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].

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.

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].

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

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.

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

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].

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].

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.

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.