Metals and Non-metals-Exercises

For a displacement reaction, a more reactive metal displaces a less reactive metal from its salt solution.

Reactivity series:
K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au

Now check each option:

(a) \(\ce{NaCl}\) solution + Cu metal
Cu is less reactive than Na → No reaction

(b) \(\ce{MgCl2}\) solution + Al metal
Al is less reactive than Mg → No reaction

(c) \(\ce{FeSO4}\) solution + Ag metal
Ag is less reactive than Fe → No reaction

(d) \(\ce{AgNO3}\) solution + Cu metal
Cu is more reactive than Ag → Displacement occurs

\[ \ce{Cu + 2AgNO3 -> Cu(NO3)2 + 2Ag} \]

Solution:

To protect an iron frying pan from rusting, we need to stop moisture and oxygen from coming in direct contact with the iron surface. Any method that creates a protective barrier can slow down or completely prevent rusting.

Now check each option:

(a) Applying grease
Grease forms a temporary layer that blocks air and moisture. It can prevent rusting, but only for short-term protection.

(b) Applying paint
Paint acts as a strong barrier and prevents iron from reacting with oxygen and water. This method is commonly used for long-lasting protection.

(c) Applying a coating of zinc
This process is known as galvanisation. Zinc protects iron not only by forming a physical layer but also by offering sacrificial protection, making it one of the best anti-rust methods.

(d) All of the above
Since grease, paint, and zinc coating all provide a protective layer against moisture and oxygen, each method helps prevent rusting.

Correct Answer: (d) All of the above.

Solution:

An element that forms an oxide with a very high melting point which is also soluble in water is most likely to be a reactive metal that gives an ionic basic oxide. Such oxides are generally ionic, have high lattice energies (so high melting points) and react with water to give soluble hydroxides.

Now examine each option:

(a) Calcium
Calcium burns in oxygen to give calcium oxide, an ionic compound with a high melting point. Calcium oxide reacts readily with water to form calcium hydroxide, which dissolves (to an appreciable extent) in water: \[ \ce{2Ca + O2 -> 2CaO}\] \[\ce{CaO + H2O -> Ca(OH)2} \] This behaviour (high-mp ionic oxide + water solubility → basic hydroxide) matches the description.

(b) Carbon
Carbon gives carbon dioxide (\(\ce{CO2}\)), a molecular acidic oxide (low melting/boiling relative to ionic solids) that dissolves in water to form weakly acidic solutions (carbonic acid). It does not form a high-melting ionic oxide.

(c) Silicon
Silicon forms silicon dioxide (\(\ce{SiO2}\)), which indeed has a very high melting point but is a covalent network solid and is essentially insoluble in water (it does not form a soluble hydroxide under normal conditions).

(d) Iron
Iron oxides have high melting points but are largely insoluble in water and do not produce a soluble hydroxide in the way reactive alkaline earth metals do.

Conclusion — Correct answer: (a) calcium.

Solution:

Food cans are designed to store edible items safely, so the metal used for coating must not react with the food. If the coating metal is too reactive, it can contaminate the food or corrode quickly. This is why choosing the right protective metal is essential.

Now analyse each option:

(a) Zinc is costlier than tin
This is incorrect. In fact, zinc is generally cheaper than tin, so cost is not the reason.

(b) Zinc has a higher melting point than tin
Although true, melting point has no relation to food safety or suitability for coating food cans. So this is not the correct explanation.

(c) Zinc is more reactive than tin
This is the key reason. Zinc reacts readily with acids present in many foods (like fruits, pickles, and acidic vegetables). If food cans were coated with zinc, the zinc could dissolve into the food, causing contamination and possible health risks.

(d) Zinc is less reactive than tin
This is incorrect. Zinc is actually more reactive, not less.

Correct Answer: (c) zinc is more reactive than tin.

Solution:

To differentiate metals from non-metals, we rely on two fundamental properties: malleability and electrical conductivity. Using simple tools like a hammer, battery, bulb, wires, and a switch, you can test both of these properties effectively.

(a) How to distinguish between samples of metals and non-metals?

• Test for malleability using the hammer:
Gently strike each sample with the hammer. Metals will flatten, bend or change shape without breaking because they are malleable. Non-metals, however, will break, powder, or shatter when hit since they are generally brittle.

• Test for electrical conductivity using the battery–bulb circuit:
Connect a simple circuit using the battery, wires, switch, and bulb. Place the sample in the gap between two wire ends. If the bulb glows, the sample conducts electricity → it is a metal. If the bulb does not glow, the sample does not conduct electricity → it is a non-metal.

(b) Usefulness of these tests

These tests are very effective because they check two reliable and easily observable properties:

• Malleability test: This is a quick and clear indicator since metals can be hammered into sheets while most non-metals cannot.

• Conductivity test: Metals are excellent conductors of electricity, whereas non-metals are generally poor conductors (with a few exceptions like graphite). Thus, the bulb test provides a straightforward confirmation.

Conclusion: Both tests are simple, practical, and accurate for distinguishing between metals and non-metals, making them highly useful for school-level identification and understanding material properties.

Solution:

Whether a metal can displace hydrogen from a dilute acid depends on its position in the reactivity series. Metals that are placed above hydrogen in the series are more reactive and can displace hydrogen gas from dilute acids. Metals that lie below hydrogen cannot do so because they are less reactive.

Metals that will displace hydrogen from dilute acids:

1. Zinc (Zn)
Zinc is above hydrogen in the reactivity series and reacts briskly with dilute acids like \(\ce{HCl}\) to release hydrogen gas:
\[ \ce{Zn + 2HCl -> ZnCl2 + H2} \]

2. Iron (Fe)
Iron also lies above hydrogen and reacts with dilute acids such as \(\ce{H2SO4}\):
\[ \ce{Fe + H2SO4 -> FeSO4 + H2} \]

Metals that will not displace hydrogen from dilute acids:

1. Copper (Cu)
Copper is placed below hydrogen in the reactivity series, so it does not react with dilute acids to produce hydrogen gas.

2. Silver (Ag)
Silver is even less reactive and, like copper, cannot displace hydrogen from dilute acids.

Conclusion: Metals such as zinc and iron will displace hydrogen from dilute acids, while metals like copper and silver will not.

Solution:

In electrolytic refining, the aim is to obtain pure metal from an impure sample using electricity. The setup uses two electrodes and a suitable electrolyte so that the pure metal slowly deposits on one electrode while the impurities either dissolve or settle down as sludge.

Understanding the role of each component:

Anode (positive electrode):
The anode is always the impure metal M. When current passes, metal atoms from the impure anode lose electrons and go into the electrolyte as metal ions.

Cathode (negative electrode):
The cathode is the pure, thin strip of metal M. Metal ions from the electrolyte gain electrons here and deposit as pure metal on the cathode.

Electrolyte:
The electrolyte is a solution containing ions of the same metal M — usually a salt solution of the metal, such as nitrate or sulfate of metal M. This allows continuous transfer of metal ions during the refining process.

Conclusion:
In electrolytic refining of metal M:

• Anode: Impure metal M
• Cathode: Pure metal M
• Electrolyte: A soluble salt solution of metal M (e.g., \(\ce{MNO3}\), \(\ce{MSO4}\), etc.)

This arrangement ensures that impurities either fall off as anode mud or remain in the solution, while pure metal continuously deposits on the cathode.

Solution:

When sulphur is heated in air, it burns to form a pungent, acidic gas. Pratyush collects this gas by heating sulphur powder on a spatula and holding an inverted test tube above it. The behaviour of this gas helps us understand its chemical nature.

(a) Action of the gas on litmus paper

(i) On dry litmus paper:
Dry litmus does not show any change because the gas needs moisture to exhibit its acidic behaviour. So, there will be no colour change in dry litmus paper.

(ii) On moist litmus paper:
In the presence of moisture, the gas dissolves in water to form an acid. Moist blue litmus will turn red, indicating that the gas is acidic in nature.

(b) Balanced chemical equation for the reaction

When sulphur is heated, it reacts with oxygen in the air to form sulphur dioxide gas: \[ \ce{S + O2 -> SO2} \] This sulphur dioxide dissolves in water present on moist litmus to form sulphurous acid, which turns the litmus red: \[ \ce{SO2 + H2O -> H2SO3} \]

Conclusion:
The gas formed is acidic, shows no effect on dry litmus, turns moist blue litmus red, and is produced by the burning of sulphur.

Solution:

Iron rusts when it comes in contact with moisture and oxygen. To stop this, we must create a barrier that prevents air and water from reacting with the iron surface. Several practical methods are used in everyday life to slow down or completely prevent rusting.

Two effective ways to prevent rusting:

1. Painting or applying oil/grease
A layer of paint, oil, or grease blocks moisture and oxygen from reaching the iron surface. Because the metal is no longer exposed to air and water, rusting cannot start. This method is commonly used on gates, tools, and machinery.

2. Galvanisation (coating with zinc)
In this method, iron is coated with a thin layer of zinc. Zinc not only acts as a protective barrier but also provides sacrificial protection because it is more reactive than iron. Even if the coating gets scratched, zinc reacts first and prevents the iron underneath from rusting.

Rusting can be prevented by coating iron with paint, oil, or grease, and by applying a protective zinc layer through galvanisation—both methods effectively stop moisture and oxygen from reaching the metal.

When non-metals react with oxygen, they form oxides that show acidic behaviour. These oxides dissolve in water to produce acids, and they also turn blue litmus paper red. Their acidic nature is one of the key properties that distinguishes them from metal oxides, which are usually basic.

Understanding their behaviour:
Non-metal oxides generally form acidic solutions when mixed with water. For example, carbon dioxide and sulphur dioxide both dissolve in water to form weak acids.

Examples:

• Carbon dioxide forms carbonic acid:
\[ \ce{CO2 + H2O -> H2CO3} \]

• Sulphur dioxide forms sulphurous acid:
\[ \ce{SO2 + H2O -> H2SO3} \]

When non-metals combine with oxygen, they form acidic oxides, which produce acids on dissolving in water and show typical acidic properties.

Each metal or ore behaves differently based on its physical and chemical properties. Understanding these properties helps explain why certain materials are chosen for jewellery, why some metals are stored safely under oil, and why specific steps are necessary during metal extraction.

(a) Platinum, gold and silver are used to make jewellery.

These metals are chosen for jewellery because they are lustrous (shiny), highly malleable (can be shaped easily), and do not corrode or react with air, moisture, or most chemicals. Their resistance to tarnishing ensures that jewellery made from them lasts long and retains its shine.

(b) Sodium, potassium and lithium are stored under oil.

These metals are extremely reactive, especially with oxygen and moisture present in air. If left exposed, they can catch fire or even explode due to vigorous reactions. Storing them under oil prevents contact with air and moisture, keeping them safe and stable.

(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.

Although aluminium is reactive, it quickly forms a thin, hard layer of aluminium oxide (\(\ce{Al2O3}\)) on its surface. This oxide layer is protective, stable and prevents further corrosion. As a result, aluminium becomes safe, durable, and excellent for making cooking utensils due to its light weight and good thermal conductivity.

(d) Carbonate and sulphide ores are usually converted into oxides during extraction.

It is easier to extract metals from their oxide forms than from carbonates or sulphides. Carbonates are first heated strongly to undergo calcination and form oxides:
\[ \ce{MCO3 -> MO + CO2} \] Sulphides are often heated in air for roasting, which converts them into oxides:
\[ \ce{MS + O2 -> MO + SO2} \] Once converted to oxides, the metal can be extracted more efficiently through reduction.

These reasons are based on the chemical reactivity, stability, and behaviour of metals and ores, which determine how they are used and processed.

Solution:

When copper vessels remain exposed to air and moisture for some time, their surface reacts with oxygen, carbon dioxide and water to form a greenish layer of basic copper carbonate (\(\ce{CuCO3.Cu(OH)2}\)). This layer makes the vessel look dull and tarnished.

Why lemon or tamarind juice works:
Lemon and tamarind juice contain natural acids such as citric acid and tartaric acid. These acids react with the basic copper carbonate layer and dissolve it, exposing the shiny copper surface underneath.

The reaction can be represented as:

Because the acidic juice breaks down and removes the green coating, the copper vessel becomes clean and bright again.

Sour substances like lemon or tamarind are effective cleaners because their acids dissolve the basic green coating on copper vessels, restoring their shine.

Solution:

Solution:

In this scenario, the man likely used a strong acid solution to clean the gold bangles. The fact that the bangles became shiny again, but their weight reduced drastically, suggests that a reaction took place where the outer layer of the gold was dissolved, removing any tarnish or dirt. However, gold itself is not easily reactive with acids, so the solution he used might have contained a strong oxidizing agent that dissolved impurities like copper or silver, often alloyed with gold in gold jewelry.

What could have happened?
Gold is relatively non-reactive, but many gold alloys contain metals like copper or silver, which are more reactive. When the gold ornaments were dipped into the solution, an acid like aqua regia (a mixture of concentrated hydrochloric acid and nitric acid) could have been used. Aqua regia is capable of dissolving metals such as copper and silver, but not gold itself, as the acid oxidizes these less noble metals, removing them from the surface. This results in the gold looking shiny again, but the mass of the ornament decreases due to the removal of the alloyed metal.

Conclusion:
The man likely used a mixture of aqua regia or a similar acid solution that dissolved the impurities in the gold, causing the weight of the bangles to decrease. This would have led to the bangles sparkling but at the expense of their original weight.

Solution: