Chemical effects of electric current - III

Chemical effects of electric current - III

Electroplating

APPLICATIONS OF THE CHEMICAL EFFECT OF ELECTRIC CURRENT

• Electroplating metals

• Purification Of metals

• Production Of certain metals from the ores

• Production Of chemical compounds

• Decomposing chemical compounds.

ELECTROPLATING

• The process Of depositing a thin layer Of a desired metal over a 'metal Object' with the help Of electric current is called electroplating. 

• The purpose of electroplating is

  (i)for protection against corrosion (Or rusting) (ii). for decorative purposes.

•  For example, bathroom taps made Of iron are electroplated with chromium metal to prevent their corrosion (or rusting).

  And at the same time, chromium plating gives a shining appearance to the bathroom taps due to which they look more attractive 

Various examples of electroplated objects

The following points should be remembered while electroplating :

• The 'metal Object on which electroplating is to be done' is made the negative electrode (cathode) i.e It is connected to the negative terminal Of the battery.

• The 'metal whose layer is to be deposited' is made the positive electrode (anode) i.e It is connected to the positive terminal Of the battery.

• 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 a soluble salt).

Multiple Select

Electroplating is a process whereby a metal surface is coated with a non-metal.

• True

• False

Multiple Choice

Electroplating is based on ___________of an electric current.

• Physical effect

• Chemical effect

• Heating effect

• Magnetic effect

Multiple Choice

Which is not a reason for metal plating?

• decorative purposes

• prevent rust and corrosion

• to make the metal stronger

Multiple Choice

The electrode that contains the plating metal

• Anode

• Cathode

Multiple Choice

The electrode that contains the item to be electroplated

• Anode

• Cathode

For electroplating an iron Object with copper metal :

(a) The iron Object is made negative electrode (cathode).

(b) A copper plate is made positive electrode (anode).

(c) Copper sulphate solution (CuSO₄ solution) is taken as electrolyte (It contains copper metal in dissolved form as copper ions, Cu²⁺).

Explanation for copper coating at Cathode

• The dissolved copper metal present in copper sulphate solution as positively charged copper ions(Cu2+) gets attracted to the negatively charged electrode 'iron key

• The positively charged copper ions (Cu²⁺) lose their positive charge on coming in contact with negatively charged iron key and form copper atoms (Cu)

• These copper atoms deposit on the iron key to form a thin layer Of copper metal all over the surface Of iron key.

• The copper metal at positively charged copper plate electrode dissolves by forming positively charged copper ions, (Cu²⁺) because copper atoms lose their negative charge to positively charged electrode. The copper ions thus formed go into the copper sulphate solution.

• Thus ,the loss Of copper ions from CuSO₄ solution (utilised in copper plating) is made up and the process continues.

• Since the copper ions are taken Out from the solution at the negative electrode (iron key) but put into solution at the positive electrode (copper plate), therefore, the concentration Of copper sulphate solution (or electrolyte) remains constant.

Uses of Electroplating

• Chromium metal has a shiny appearance and it does not corrode (it does not rust). Chromium plating is done on many Objects made Of iron metal (or steel) such as bicycle handlebars, bicycle bells, wheel rims, bathroom fittings (taps, etc.), LPG Stoves, motor cycle parts, and many, many Other Objects . Metallic car bumpers and car grills are also chromium plated 

• Tin metal has a shiny appearance, it does not corrode and it is non-poisonous. It is less reactive than iron. Tin 'cans' used for storing food are made by electroplating tin metal on to iron. Due to tin plating over the surface Of iron, the food does not come in contact with iron and is protected from getting spoilt. 

Uses of electroplating 

• Electroplating is used to give objects made Of a cheap metal a coating Of a more expensive metal to make them look more attractive. For example, less expensive metals are electroplated with more expensive metals like silver and gold to make jewellery . These ornaments have the appearance Of silver or gold but they are much less expensive than ornaments made Of pure silver Or gold. 

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Uses of Electroplating

 Electroplating is used to give objects made Of a cheap metal a coating Of a more expensive metal to make them look more attractive.

For example, less expensive metals are electroplated with more expensive metals like silver and gold to make jewellery

These ornaments have the appearance Of silver or gold but they are much less expensive than ornaments made Of pure silver Or gold. 

Disposal of electrolytes in Factories

The electrolytes used in electroplating contain various type Of salts which may be poisonous. The conducting solutions are also usually acidic in nature. so, in electroplating factories, the disposal Of electrolytes is a major problem.

There are specific guidelines issued by the Government for the safe disposal Of electrolyte wastes produced by the electroplating factories.

Multiple Choice

Chromium corrodes easily.

• True

• False

Multiple Choice

Out of the following, which metal is used to electroplate iron to make it shining and rust resistant?

• Gold

• Chromium

• Zinc

• Tin

Multiple Choice

Which of these is plated on the iron to prevent it from chemically reacting with food?

• Gold

• Chromium

• Tin

• Zinc

Multiple Choice

Boojho’s uncle has set up an electroplating factory near his village. He should dispose off the waste of the factory

• in the nearby river.

• in the nearby pond.

• in the nearby cornfield.

• according to the disposal guidelines of the local authority.

Multiple Choice

The method of coating metals by immersing the metals in a liquid and then passing an electric current through the liquid is called ________

• Electrolysis

• Electroplating

• Electropalting

• Electroplation

Multiple Choice

Why do we add little dilute sulphuric acid to copper sulphate solution during electroplating?

• to increase acidity

• to increase conductivity

• So that the colour becomes more prominent

• to burn copper sulphate

Multiple Choice

Which of the following is not used for electroplating metal articles?

• Nickel

• Silver

• Chromium

• Sodium

Multiple Choice

If the fork is to be electroplated with silver metal, what electrolyte should be used?

• Molten calcium chloride

• Aqueous silver nitrate

• Sodium chloride solution

• Copper(II) sulphate solution

Purification of Metals

• A thick rod Of impure metal is made positive electrode (or anode)

  
  

• A thin strip Of pure metal is made negative electrode (or cathode)

   

• A water soluble salt Of the metal to be purified is taken as electrolyte.

  
  

• On passing electric Current, the metal dissolves from the impure anode and goes into electrolyte solution. The metal present in dissolved form in electrolyte gets deposited on the cathode in the pure form. The impurities are left behind in the electrolyte solution.

• The metals like copper, zinc and aluminium, etc., are purified by the process Of electrolysis by using the chemical effect Of electric current.

Copper plating

Copper is purified by electrolysis . Electricity is passed through solutions containing copper compounds, such as copper(II) sulfate.

The anode (positive electrode ) is made from impure copper and the cathode (negative electrode) is made from pure copper.

Production of Metals

• The chemical effect Of electric current is used in the production (or extraction) Of certain metals from their naturally occurring compounds called ores.

   For example, 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 .

  
  

• Aluminium metal is produced by the electrolysis Of molten aluminium oxide.

  
  

• In all the cases, metal is produced at the negatively charged electrode (Or cathode). This is because the positively charged ions Of metals present in their molten compounds are attracted by the negatively charged electrode.

Production of Compounds

·     The chemical effect Of electric current is used in the production Of various chemical compounds.

·     For example, sodium hydroxide (Or caustic soda) is produced by the electrolysis Of an aqueous solution Of sodium chloride.

Decomposition of Compounds

·     The chemical effect Of electric current (or electrolysis) is used to decompose various chemical compounds into their elements.

·     For example, water can be decomposed by passing electric current (or electrolysis) into two elements : hydrogen and oxygen.

 

 

Multiple Select

The conductors among the following are

• Hydrochloric acid

• Sugar solution

• Vinegar

• Salt water

Multiple Choice

When current is passed through a mixture of water and lemon juice, bubbles rise from one of the electrodes. The bubbles are rising from the solution because

• of the heating effect of current
• of the chemical effect of current
• current produces magnetic field around the electrodes
• current always produces air bubbles when passed through a liquid

Multiple Choice

Copper will form at which electrode

• Positive

• Negative

• Neutral

• Neither