Tag: chemistry

Questions Related to chemistry

Hydrogen gas will not be produced by :

aluminium patterns and properties of metals chemistry

  1. heated cupric oxide

  2. heated Ferric oxide

  3. heated stannic oxide

  4. heated aluminium oxide

Show answer
Correct Option: D
Explanation:

When alluminium oxide is heted it liberates oxygen gas
$2Al _2O _3\rightarrow 4Al+3O _2$
So alluminium oxide on heating do not produce hydrogen gas
Hence option D is correct.

$AlCl _3$ is an electron deficient compound but $AlF _3$ is not. This is because:

aluminium patterns and properties of metals chemistry

  1. atomic size of F is smaller than Cl which makes $AlF _3$ more covalent

  2. $AlCl _3$ is a covalent compound while $AlF _3$ is an ionic compound

  3. $AlCl _3$ exists as a dimer but $AlF _3$ does not

  4. $Al$ in $AlCl _3$ is in $sp^3$ hybrid state but Al in $AlF _3$ is in $sp^2$ state

Show answer
Correct Option: B
Explanation:

There is this rule called as Fajan's rule which states that with increasing size of the anion and with decreasing size of the cation ionic character of the compound decreases while the covalent character increases.

Here, since the cation is same in both the compounds, the size of the anion decides the nature of the compound. Size of chlorine being greater than fluorine, $AlCl _3$ is covalent while $AlF _3$ is ionic.

All of the following are true for aluminum except that:

aluminium patterns and properties of metals chemistry

  1. it is a good conductor of electricity

  2. it is a metal of high density

  3. it forms a protective coating in air that resists further corrosion

  4. it is an excellent reducing agent

  5. it forms a hydroxide that that is soluble in both strong base and acid

Show answer
Correct Option: B
Explanation:

The properties of aluminium include low density and therefore low weight, high strength, superior malleability, easy machining, excellent corrosion resistance and good thermal and electrical conductivity.
The surface of aluminum metal is covered with a thin layer of oxide that helps protect the metal from attack by air. So, normally, aluminum metal does not react with air. Aluminium hydroxide is amphoteric in nature. Hence, it dissolves in both acidic and basic solution.

$Al$ is more reactive than iron but it is less easily corroded than iron because :

aluminium patterns and properties of metals chemistry

  1. it is a noble metal

  2. oxygen forms a protective oxide layer

  3. iron undergoes easily reaction with water

  4. iron formsmono and divalent ion

Show answer
Correct Option: B
Explanation:

Aluminum unlike iron ,does not corrode in moist conditions. Its surface is protected by layer of aluminium oxide. This prevents thealluminium to come in contact with air and oxygen. The layer of aluminium oxide do not vanish, unlike rust which can flake off the surface of iron and steel objects. So $Al$ is covered with a layer by the oxygen

Hence option B is correct.

A metal X reacts with aqueous NaOH solution to form Y and a highly inflammable gas. Solution Y is heated and $CO _2$ IS poured through it. Z precipitates out and $Na _2CO _3$ is formed. Z on heating gives $Al _2O _3$. Identify X, Y and Z.

aluminium patterns and properties of metals chemistry

  1. $Al-X$, $NaAlO _2 -Y$, $Al(OH) _3-Z$

  2. $Al _2O _3-X$, $NaAlO _2-Y$, $Al _2CO _3-Z$

  3. $Al _2O _3-X$, $[Na _2AlO _2]^+Oh^--Y$, $Al(OH) _3-Z$

  4. Al-X, $Al(OH) _3-Y$, $Al _2O _3-Z$

Show answer
Correct Option: A
Explanation:

Solution:-

$X + NaOH(aq) \; \longrightarrow \; Y + \text{highly inflammable gas}$
$Y + CO _2 + H _2O \; \longrightarrow \; Z + {Na} _2CO _3$
$Z \; \xrightarrow [On \; heating] \; {Al} _2O _3$
${Al} _2O _3$ is formed when $Al{(OH)} _3$ is heated. 
$2Al{(OH)} _3 \; \xrightarrow [On \; heating] \; {Al} _2O _3 + 3H _2O$
Thus Z is $Al{(OH)} _3.$
When $NaAlO _2$ is heated and $ CO _2$ is poured through it, $Al{(OH)} _3$ precipitates out and $Na _2CO _3$ is formed.
$2NaAlO _2 + CO _2 + 3H _2O \; \longrightarrow \; 2Al{(OH)} _3 + {Na} _2CO _3$
Thus Y is $NaAlO _2$
When $Al$ reacts with aqueous $NaOH$ solution, it forms $NaAlO _2 \; and \; H _2 \; \text{(Highly inflammable gas)}$
$Al + NaOH(aq) \; \longrightarrow \; NaAlO _2 + H _2 \; \text{(highly inflammable gas)}$
Thus X is $Al$.
Hence, (A) is correct answer.

Thermite is a mixture of iron oxide and ___________.

aluminium patterns and properties of metals chemistry

  1. aluminium powder

  2. zinc powder

  3. iron turnings

  4. copper turnings

Show answer
Correct Option: A
Explanation:

Answer:- (A) Aluminium Powder
Thermite is the mixture of iron oxide $Fe _2O _3$ (rust) and aluminum powder. When it is ignited the aluminum powder reacts with the $O _3$ part of the rust in a highly exothermic reaction, the resulting product is molten iron. Thermite is commonly used in welding because the molten iron has the ability to seep into cracks in metal.

In the following reaction sequence,
$(A)+N _2 \xrightarrow { \triangle } (B) \xrightarrow {+H _2O} (C)+(D)$
white ppt. (C) is formed and gas (D) is evolved. White ppt. (C) dissolves in NaOH solution, while gas (D) gives white fumes in HCl. Thus, (A) is :

aluminium patterns and properties of metals chemistry

  1. B

  2. Al

  3. Ga

  4. C

Show answer
Correct Option: B
Explanation:
$\underset{(A)}{2Al}+N _2 \rightarrow \underset{(B)}{2AlN}$
$\underset{(B)}{AlN}+3H _2O \rightarrow \underset{(C)}{Al(OH) _3}+\underset{(D)}{NH _3}$

Aluminium metal gets corroded or 'rusted' in places that are near to the sea, because the oxide film that protects it:

aluminium patterns and properties of metals chemistry

  1. is attacked by salt from sea water

  2. reacts with water

  3. is removed by sea water

  4. reacts with sand particles

Show answer
Correct Option: A
Explanation:
The presence of salt (or any electrolyte) in the water accelerates the reaction because it increases the conductivity of water, effectively increasing the concentration of ions in the water and so increasing the rate of oxidation (corrosion) of the metal.
Thusm aluminium metal is corroded in places that are near to the sea.

Serving trays for tea or food, made of aluminium, often have coloured finish. These finishes are formed when an electric current in passes, which creates an oxide of aluminium layer than absorbs dyes. This is called:

aluminium patterns and properties of metals chemistry

  1. Galvanizing

  2. Anodizing

  3. Sherardizing

  4. Annealing

Show answer
Correct Option: B
Explanation:

Anodizing is an electrochemical process that converts the metal surface into a decorative, durable, corrosion-resistant, anodic oxide finish. Aluminum is ideally suited to anodizing, although other nonferrous metals, such as magnesium and titanium, also can be anodized.

Hence option B is correct answer.

Metals rust when they come in contact with oxygen of the air that forms oxides and thereby destroys the metal. Which metal forms an oxide with oxygen, that protects it from further rusting:

aluminium patterns and properties of metals chemistry

  1. aluminium

  2. zinc

  3. iron

  4. copper

Show answer
Correct Option: A
Explanation:
Aluminium does not rust (corrode) because its surface is protected by a natural layer of aluminium oxide $\left( {Al} _{2}{O} _{3} \right)$. This prevents the metal below from coming into contact with air.