Advertisements
Advertisements
प्रश्न
Generally, when metals are treated with mineral acids, hydrogen gas is liberated but when metals (except Mn and Mg), treated with HNO3, hydrogen is not liberated, why?
Advertisements
उत्तर
Concentrated nitric acid is a very strong oxidising agent. When metals are treated with concentrated nitric acid the hydrogen gas that is produced during the reaction is further oxidised to water and thus hydrogen gas is not liberated.
`"Zn"("s") + 4"HNO"_3("conc".) -> "Zn"("NO"_3)_2 + 2"NO"_2("g") + 2"H"_2"O"("l")`
APPEARS IN
संबंधित प्रश्न
Which metals do not corrode easily?
What are alloys?
State two conditions for the rusting of iron.
Fill in the following blank with suitable word:
The corrosion of iron is called ................
Give the constituents and one use of brass.
What are the constituents of stainless steel?
What are the special properties of stainless steel?
A metal X which is resistant to corrosion is produced by the electrolysis of its molten oxide whereas another metal Y which is also resistant to corrosion is produced by the reduction of its oxide with carbon. Metal X can be used in powder form in thermite welding whereas metal Y is used in making cathodes of ordinary dry cells.
(a) Name the metals X and Y.
(b) Which of the two metals is more reactive : X or Y?
(c) Name one ore or metal X. Also write its chemical formula.
(d) Name one ore or metal Y. Also write its chemical formula.
(e) Name one alloy of metal X and one alloy of metal Y.
Mention two uses of the following metals and non-metals
Iron
Write scientific reasons.
Lemon or tamarind is used for cleaning copper vessels turned greenish.
Give a reason why rust turns moist red litmus blue.
Bronze : _______ : : Stainless steel : Fe + Cr + C
Write scientific reason.
On exposure to air, silver articles turn blackish after some time.
Complete flow chart given below.
Observe the following diagram and give answers.
- Name this method of prevention of corrosion.
- For prevention of which metal this method is used?
- What is used as anode in this method?
Give preventive methods by giving examples of corrosion?
Give the equation for the formation of rust.
Copper objects lose their shine and form green coating of ____________.
The table shown below gives information about four substances: A, B, C and D.
| SUBSTANCE | MELTING POINT (K) | ELECTRICAL CONDUCTIVITY | |
| SOLID | LIQUID/ AQUEOUS | ||
| A | 295 | Good | Good |
| B | 1210 | Poor | Good |
| C | 1890 | Poor | Good |
| D | 1160 | Poor | Poor |
Identify Ionic compounds from the above given substances.
| A process of forming a thick oxide of aluminium when aluminium is exposed to air. This coat makes it resistant to corrosion. Resistance can be improved by making a layer of oxide thinker. In this technique, the aluminium article is the anode, and the electrolyte is sulphuric acid. The anode reaction results in the formation of a black-coloured film of aluminium oxide on the anode. By putting appropriate dyes in the electrolytic solution, both coloured surface with the decorative finish is achieved. Kitchen articles like anodised such as pressure cookers, pans and frames of sliding windows are applications of this technique. |
- Name the anode and electrolyte used in this technique.
- How can we make aluminium articles made resistant to corrosion?
- Name the technique used to coat the aluminium articles.
