Mix Examples - Chemical Reactions and Equations Questions in English

(N/A) $(i)$ Moist air leads to the corrosion of metals like iron (rusting),while acidic gases react with metals like copper and silver,causing them to tarnish or corrode.
$(ii)$ Nitrogen is an inert gas. By flushing the bags with nitrogen,manufacturers displace oxygen,which prevents the oxidation of fats and oils in the chips,thereby keeping them fresh and preventing rancidity.

(D) $1$. In this reaction, Aluminum $(Al)$ displaces Manganese $(Mn)$ from Manganese dioxide $(MnO_{2})$ because Aluminum is more reactive than Manganese. This is a displacement reaction.
$2$. The reaction releases a significant amount of heat, as indicated by the '+ Heat' term in the product side. Reactions that release heat are called exothermic reactions.
$3$. Therefore, the reaction is both a displacement reaction and an exothermic reaction.

(N/A) $(i)$ Before heating, the copper sulphate crystals are blue in colour because they contain water of crystallisation $(CuSO_4 \cdot 5H_2O)$.
$(ii)$ After heating, the crystals lose their water of crystallisation and turn white, forming anhydrous copper sulphate $(CuSO_4)$.

(N/A) Crystals of copper sulphate $(CuSO_{4} \cdot 5H_{2}O)$ contain water of crystallisation.
Upon heating,these crystals lose their water of crystallisation and turn white (anhydrous).
This released water evaporates and condenses as liquid droplets on the cooler inner upper side of the test tube.

(N/A) $(i)$ The substance '$X$' is lime water,which is a solution of calcium hydroxide,$Ca(OH)_{2}$.
$(ii)$ When carbon dioxide gas is passed through lime water,it reacts to form calcium carbonate,which is insoluble in water and makes the solution appear milky.
$(iii)$ The balanced chemical equation for the reaction is: $Ca(OH)_{2}(aq) + CO_{2}(g) \rightarrow CaCO_{3}(s) + H_{2}O(l)$.

(N/A) $(i)$ $Ca(OH)_2(aq) + CO_2(g) \to CaCO_3(s) + H_2O(l)$
(Lime water turns milky due to the formation of insoluble calcium carbonate.)
$(ii)$ $2NaOH(aq) + Zn(s) \xrightarrow{\text{Heat}} Na_2ZnO_2(aq) + H_2(g)$
(Sodium zincate is formed along with the evolution of hydrogen gas.)

(A) Compound $'A'$ is sodium carbonate $(Na_{2}CO_{3})$ and the gas evolved is carbon dioxide $(CO_{2})$.
The chemical reaction is as follows:
$Na_{2}CO_{3}(s) + H_{2}SO_{4}(aq) \to Na_{2}SO_{4}(aq) + CO_{2}(g) + H_{2}O(l)$
In this reaction,sodium carbonate reacts with dilute sulphuric acid to form sodium sulphate,water,and carbon dioxide gas. Carbon dioxide does not support combustion,which is why it extinguishes a burning candle.

(N/A) The two categories for this reaction are:
$(i)$ Displacement reaction (specifically,a thermite reaction).
$(ii)$ Redox reaction (reduction-oxidation reaction).
$(b)$ Oxidation is defined as the addition of oxygen to a substance or the removal of hydrogen from a substance.
In the given reaction:
- Aluminium $(Al)$ is oxidised because it gains oxygen to form $Al_{2}O_{3}$.
- Iron$(III)$ oxide $(Fe_{2}O_{3})$ is the oxidising agent because it provides oxygen to aluminium.

(A) $1$. In the given reaction,$4 NH_{3} + 5 O_{2} \longrightarrow 4 NO + 6 H_{2}O$,the oxidation state of Nitrogen $(N)$ changes from $-3$ in $NH_{3}$ to $+2$ in $NO$ (oxidation).
$2$. The oxidation state of Oxygen $(O)$ changes from $0$ in $O_{2}$ to $-2$ in $NO$ and $H_{2}O$ (reduction).
$3$. Since both oxidation and reduction occur simultaneously,it is a redox reaction $(iii)$.
$4$. This is also a displacement reaction $(i)$ because the oxygen atom displaces hydrogen from ammonia to form water.
$5$. Therefore,the reaction is both a displacement reaction and a redox reaction.

(C) An exothermic process is a reaction or process that releases energy in the form of heat.
$(i)$ The reaction of water with quicklime $(CaO + H_2O \rightarrow Ca(OH)_2 + \text{Heat})$ is highly exothermic, releasing a significant amount of heat.
$(ii)$ The dilution of an acid is a highly exothermic process, which is why it is recommended to add acid to water slowly with constant stirring.
$(iii)$ Evaporation of water is an endothermic process because it requires the absorption of heat from the surroundings to change the state from liquid to gas.
$(iv)$ Sublimation of camphor is an endothermic process as it requires the absorption of heat to change the state from solid to gas.
Therefore, $(i)$ and $(ii)$ are exothermic processes.

(C) An endothermic process is one that absorbs heat from the surroundings.
$(i)$ Dilution of sulphuric acid is an exothermic process because it releases a large amount of heat.
$(ii)$ Sublimation of dry ice ($CO_2$ solid to gas) requires the absorption of heat,making it an endothermic process.
$(iii)$ Condensation of water vapours (gas to liquid) releases heat,making it an exothermic process.
$(iv)$ Evaporation of water (liquid to gas) requires the absorption of heat from the surroundings,making it an endothermic process.
Therefore,both $(ii)$ and $(iv)$ are endothermic processes.

(FALSE) The statement is False.
In black and white photography,the decomposition reaction of silver chloride $(AgCl)$ or silver bromide $(AgBr)$ is used,not calcium sulphate.
The reaction is: $2AgCl(s) \xrightarrow{sunlight} 2Ag(s) + Cl_2(g)$.

(A) When we exhale,the air we breathe out contains a significant amount of $CO_2$ (carbon dioxide).
When this $CO_2$ is passed through lime water $(Ca(OH)_2)$,it reacts to form calcium carbonate $(CaCO_3)$,which is an insoluble white precipitate.
The chemical reaction is: $Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O$.
This formation of calcium carbonate makes the lime water appear milky.

(B) The electron was discovered by $J.J. Thomson$ in $1897$ during his experiments with cathode ray tubes. He identified these particles as fundamental constituents of atoms.

(B) The number of moles of a substance is calculated by dividing the given mass (weight) of the substance by its molar mass (molecular mass).
Formula: $\text{Mole} = \frac{\text{Given mass (Weight)}}{\text{Molar mass (Molecular mass)}}$.
Therefore,option $B$ is the correct formula.

(B) When sulfur trioxide $(SO_3)$ reacts with water $(H_2O)$,it undergoes a hydration reaction to form sulfuric acid $(H_2SO_4)$.
The chemical equation for this reaction is:
$SO_3(g) + H_2O(l) \rightarrow H_2SO_4(aq)$
Sulfur trioxide is an acidic oxide,and when it dissolves in water,it forms a strong mineral acid known as sulfuric acid.

(C) Molar mass is defined as the mass of one mole of a substance.
It is expressed as the mass in grams per mole of the substance.
Therefore, the $SI$ unit for molar mass is grams per mole, which is written as $g \ mol^{-1}$.

(C) The molar mass of $H_{2}SO_{4}$ is calculated as follows:
$M = (2 \times 1) + 32 + (4 \times 16) = 2 + 32 + 64 = 98 \ g/mol$.
Given mass of $H_{2}SO_{4} = 4.9 \ g$.
The number of moles $(n)$ is calculated using the formula: $n = \frac{\text{Given mass}}{\text{Molar mass}}$.
$n = \frac{4.9}{98} = 0.05 \ mol$.
Therefore,the correct option is $C$.

(C) When sodium metal $(Na)$ reacts with water $(H_2O)$,it forms sodium hydroxide $(NaOH)$ and releases hydrogen gas $(H_2)$.
This is a highly exothermic reaction.
The balanced chemical equation is:
$2Na_{(s)} + 2H_2O_{(l)} \longrightarrow 2NaOH_{(aq)} + H_{2(g)}$
Therefore,the correct option is $C$.

(B) $SO_{2}$ (Sulfur dioxide) is widely used as a food preservative in fruit juices,jams,and squashes.
It acts as an antimicrobial agent,inhibiting the growth of bacteria,yeasts,and molds,thereby extending the shelf life of these products.
It also helps in preventing the browning of fruits due to oxidation.

(B) Combustible gases are those that can burn in the presence of oxygen to release energy.
$H_{2}$ (Hydrogen gas) is highly combustible and reacts with oxygen to form water,releasing a significant amount of heat.
$CO_{2}$ (Carbon dioxide) is a product of combustion and does not support burning.
$SO_{2}$ (Sulfur dioxide) is not combustible.
$NH_{3}$ (Ammonia) is generally considered non-combustible under normal conditions,although it can burn under specific high-temperature conditions,$H_{2}$ is the most standard example of a highly combustible gas in this context.

(D) The Haber process is used for the industrial production of ammonia $(NH_{3})$ from nitrogen $(N_{2})$ and hydrogen $(H_{2})$ gases.
The chemical equation for the reaction is: $N_{2}(g) + 3H_{2}(g) \rightleftharpoons 2NH_{3}(g)$.
In this process,finely divided iron $(Fe)$ is used as a catalyst to increase the rate of the reaction.
Additionally,molybdenum $(Mo)$ is often used as a promoter to enhance the efficiency of the iron catalyst.

(C) Henry Cavendish is credited with the discovery of hydrogen gas in $1766$. He identified it as a distinct substance by reacting metals with strong acids and called it 'inflammable air'.

(A) The weight of a gas is determined by its molar mass.
$1$. The molar mass of $H_2$ (Dihydrogen) is approximately $2.016 \ g/mol$.
$2$. The molar mass of $NH_3$ (Ammonia) is approximately $17.03 \ g/mol$.
$3$. The molar mass of $SO_2$ (Sulfur dioxide) is approximately $64.06 \ g/mol$.
$4$. The molar mass of $O_2$ (Dioxygen) is approximately $32.00 \ g/mol$.
Since $H_2$ has the lowest molar mass among the given options,it is the lightest gas.

(B) $H_2$ gas is insoluble in water and is lighter than air. Therefore,it is collected by the downward displacement of water. In this method,the gas jar is filled with water and inverted over the delivery tube in a water trough. As the $H_2$ gas enters the jar,it displaces the water downwards,filling the jar with the gas.

(A) In the industrial production of hydrogen gas, specifically through the Bosch process (reaction of water gas with steam), $Iron$ $(Fe)$ is used as a catalyst. The reaction is: $CO(g) + H_2O(g) \xrightarrow{Fe} CO_2(g) + H_2(g)$. This is known as the water-gas shift reaction, where $Iron$ oxide (promoted with chromium oxide) acts as the catalyst to increase the yield of hydrogen.

(B) The apparatus used for the electrolysis of water is called a $Voltameter$ (specifically a Hofmann Voltameter).
It consists of three joined upright cylinders,usually made of glass.
The central cylinder is open at the top to allow for the addition of water and an electrolyte (to increase conductivity,as pure water is a poor conductor).
Electrodes are placed at the bottom of the two side cylinders to collect the hydrogen and oxygen gases produced during the process.
Note: $A$ $Voltmeter$ is an instrument used to measure electrical potential difference,whereas a $Voltameter$ is an electrochemical cell used to perform electrolysis.

(D) $1$. $H_2$ gas acts as a strong reducing agent because it can remove oxygen from metal oxides.
$2$. $H_2$ gas is highly combustible and burns with a pale blue flame.
$3$. $H_2$ gas is neutral in nature,meaning it does not change the color of blue or red litmus paper.
$4$. $H_2$ gas is $NOT$ a supporter of combustion; it is combustible itself. Oxygen $(O_2)$ is the gas that supports combustion. Therefore,statement $D$ is incorrect.

(B) When $H_2$ and $Cl_2$ gases react,they form hydrogen chloride gas $(HCl)$.
In the presence of moisture or when the gas is released into the atmosphere,$HCl$ gas reacts with water vapor to form dense white fumes of hydrochloric acid droplets.
Therefore,the white fumes observed are of hydrogen chloride $(HCl)$.

(B) The industrial production of ammonia $(NH_3)$ is achieved through the Haber process. This process was developed by the German chemist Fritz Haber in the early $20^{th}$ century. In this process,nitrogen gas $(N_2)$ and hydrogen gas $(H_2)$ are reacted under high pressure and temperature in the presence of an iron catalyst to produce ammonia.

(C) Ammonia $(NH_3)$ is manufactured on an industrial scale using the Haber's process.
In this process, nitrogen gas $(N_2)$ and hydrogen gas $(H_2)$ are reacted in a $1:3$ ratio at high temperature and high pressure in the presence of an iron catalyst.
The chemical reaction is: $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$.

(D) The chemical equation for the Haber's process is: $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$.
According to the stoichiometry of the reaction, $1$ mole of dinitrogen $(N_2)$ reacts with $3$ moles of dihydrogen $(H_2)$.
Therefore, the ratio of dihydrogen gas to dinitrogen gas is $3:1$.

(A) Substances that are added to a catalyst to increase its activity or efficiency are known as $Promoters$ (or $Activators$).
For example,in the $Haber$ process for the manufacture of $NH_3$,$Fe$ acts as a catalyst,while $Mo$ acts as a promoter to increase the efficiency of $Fe$.

(B) The gas $NO_2$ (Nitrogen dioxide) is a reddish-brown gas.
$NO$ (Nitric oxide) is a colorless gas.
$N_2O$ (Nitrous oxide) is a colorless gas.
$SO_2$ (Sulfur dioxide) is a colorless gas.
Therefore,the correct option is $B$.

(C) The industrial production of nitric acid $(HNO_{3})$ is primarily carried out using the $Ostwald's$ process.
In this process,ammonia $(NH_{3})$ is catalytically oxidized to nitric oxide $(NO)$ in the presence of platinum-rhodium gauze as a catalyst.
The nitric oxide is then oxidized to nitrogen dioxide $(NO_{2})$,which is subsequently absorbed in water to produce nitric acid $(HNO_{3})$.
Therefore,the correct option is $C$.

(B) When an aqueous solution of ammonia $(NH_{4}OH)$ is added to a solution of cupric sulfate $(CuSO_{4})$,a pale blue precipitate of copper$(II)$ hydroxide $(Cu(OH)_{2})$ is formed initially.
The chemical reaction is: $CuSO_{4}(aq) + 2NH_{4}OH(aq) \rightarrow Cu(OH)_{2}(s) + (NH_{4})_{2}SO_{4}(aq)$.
Upon adding excess ammonia,this precipitate dissolves to form a deep blue complex,tetraamminecopper$(II)$ sulfate.

(B) Acid rain is primarily caused by the emission of sulfur dioxide $(SO_2)$ and nitrogen oxides $(NO_x)$.
When these gases are released into the atmosphere,they react with water vapor,oxygen,and other chemicals to form sulfuric acid $(H_2SO_4)$ and nitric acid $(HNO_3)$.
These acids then fall to the ground with rain,causing environmental damage.
Among the given options,sulfur dioxide $(SO_2)$ is the primary gas responsible for acid rain.

(C) Sulfur dioxide $(SO_2)$ is a colorless gas with a pungent,irritating smell that resembles the scent of a burnt match. When inhaled,it reacts with the moisture in the respiratory tract to form sulfurous acid,which causes severe irritation,choking,and coughing. Among the given options,sulfur is the element that forms this gas upon combustion.

(D) The reaction for the formation of sulphur trioxide $(SO_3)$ from sulphur dioxide $(SO_2)$ is a key step in the Contact Process for the manufacture of sulphuric acid.
The chemical equation is: $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$.
This reaction is carried out at high temperatures (approximately $450^{\circ}C$) in the presence of $V_2O_5$ (Vanadium pentoxide) as a catalyst to increase the rate of reaction and yield.
Therefore,the correct catalyst is Vanadium pentoxide.

(C) Potassium dichromate $(K_2Cr_2O_7)$ is a strong oxidizing agent. In an aqueous solution,the dichromate ion $(Cr_2O_7^{2-})$ exists in equilibrium with the chromate ion $(CrO_4^{2-})$. The potassium dichromate solution is characteristically orange in color due to the presence of the dichromate ion.

(C) Potassium dichromate is an inorganic chemical reagent with the formula $K_{2}Cr_{2}O_{7}$.
It is a common oxidizing agent used in various laboratory and industrial applications.
In this compound,the dichromate ion is $Cr_{2}O_{7}^{2-}$,which balances with two potassium ions $(K^{+})$ to form a neutral compound.

(A) When boiling sulfur reacts with dihydrogen gas $(H_{2})$,it forms hydrogen sulfide gas $(H_{2}S)$.
The chemical equation for this reaction is:
$S(l) + H_{2}(g) \xrightarrow{\Delta} H_{2}S(g)$
Here,sulfur is in the liquid state (boiling) and reacts with hydrogen gas to produce hydrogen sulfide.

(C) Sulfur dioxide $(SO_{2})$ is a gas that is widely used as a food preservative and antimicrobial agent.
It inhibits the growth of bacteria,molds,and yeasts by interfering with their metabolic processes and enzyme activity.
Therefore,$SO_{2}$ is effective in preventing bacterial growth in various food products.

(D) In the contact process for the industrial production of sulfuric acid $(H_{2}SO_{4})$, sulfur dioxide $(SO_{2})$ is oxidized to sulfur trioxide $(SO_{3})$ in the presence of a catalyst.
The catalyst used for this reaction is vanadium pentoxide $(V_{2}O_{5})$.
The chemical equation for this step is: $2SO_{2}(g) + O_{2}(g) \xrightarrow{V_{2}O_{5}} 2SO_{3}(g)$.

(D) When sulfur trioxide $(SO_3)$ gas is absorbed in concentrated sulfuric acid $(H_2SO_4)$,it reacts to form pyrosulfuric acid,which is commonly known as oleum $(H_2S_2O_7)$.
The chemical reaction is as follows:
$SO_3 + H_2SO_4 \rightarrow H_2S_2O_7$ (Oleum).
This process is a key step in the contact process for the industrial production of sulfuric acid.

(A) The Contact Process is the industrial method used to produce sulfuric acid $(H_2SO_4)$.
In this process,the primary raw material used is elemental sulfur $(S)$.
First,sulfur is burned in air to produce sulfur dioxide $(SO_2)$: $S(s) + O_2(g) \rightarrow SO_2(g)$.
Then,$SO_2$ is oxidized to sulfur trioxide $(SO_3)$ in the presence of a catalyst $(V_2O_5)$,which is subsequently absorbed in concentrated sulfuric acid to form oleum $(H_2S_2O_7)$,and finally diluted to obtain sulfuric acid.