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].

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.

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].

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.

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.

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].

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].

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].

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.

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.