Mix Examples - Chemical Reactions and Equations Questions in English

(A) The balanced chemical equation is:
$Na_{2}SO_{3}(aq) + BaCl_{2}(aq) \rightarrow BaSO_{3}(s) + 2NaCl(aq)$
$(b)$ This reaction is also known as a double displacement reaction.
$(c)$ $BaSO_{3}$ is a salt of a weak acid,sulphurous acid $(H_{2}SO_{3})$. When dilute hydrochloric acid $(HCl)$ is added,it reacts with the insoluble barium sulphite to form soluble barium chloride,water,and sulphur dioxide gas. The reaction is:
$BaSO_{3}(s) + 2HCl(aq) \rightarrow BaCl_{2}(aq) + H_{2}O(l) + SO_{2}(g)$
Since $BaCl_{2}$ is soluble in water,the white precipitate disappears.

(A-D) When solutions are kept in a copper container:
$(a)$ Dilute $HCl$: Copper does not react with dilute $HCl$,so it can be kept.
$(b)$ Dilute $HNO_{3}$: Nitric acid is a strong oxidizing agent and reacts with copper,so it cannot be kept.
$(c)$ $ZnCl_{2}$: Zinc is more reactive than copper,so no displacement reaction occurs; it can be kept.
$(d)$ $H_{2}O$: Copper does not react with water,so it can be kept.
$(B)$ When solutions are kept in an aluminium container:
$(a)$ Dilute $HCl$: Aluminium reacts with dilute $HCl$ to form $AlCl_{3}$ and $H_{2}$ gas,so it cannot be kept. Reaction: $2Al + 6HCl \rightarrow 2AlCl_{3} + 3H_{2}$.
$(b)$ Dilute $HNO_{3}$: Aluminium forms a protective oxide layer $(Al_{2}O_{3})$ with dilute $HNO_{3}$,which prevents further reaction,so it can be kept.
$(c)$ $ZnCl_{2}$: Aluminium is more reactive than zinc and will displace zinc from the solution,so it cannot be kept. Reaction: $2Al + 3ZnCl_{2} \rightarrow 2AlCl_{3} + 3Zn$.
$(d)$ $H_{2}O$: Aluminium does not react with cold or hot water,so it can be kept.

(B) When a strip of copper metal is placed in a silver nitrate solution,a displacement reaction occurs because copper is more reactive than silver.
Metallic silver is precipitated as a solid,and the solution turns blue due to the formation of copper$(II)$ nitrate.
The chemical equation is: $Cu(s) + 2AgNO_3(aq) \to 2Ag(s) + Cu(NO_3)_2(aq)$.

(N/A) The reduction process is widely used in metallurgy for the extraction of metals from their ores. For example,metal oxides are reduced to their respective pure metals by using reducing agents like carbon or hydrogen.

(A) The correct answer is $A$. Burning of wax.
Reason: Burning of wax is a chemical change because candle wax is a hydrocarbon that reacts with oxygen to produce new substances like carbon dioxide $(CO_{2})$ and water vapor $(H_{2}O)$. This process is irreversible,as the original wax cannot be recovered from the combustion products.
In contrast,the melting of wax is a physical change because it only involves a change in the state of matter from solid to liquid,and the wax can be solidified again by cooling.

(A) chemical change involves the formation of new substances with different chemical properties.
Fermentation of fruit juice is a chemical change because microorganisms (like yeast) convert sugars into alcohol and carbon dioxide,resulting in a new substance.
Diluting fruit juice is a physical change because it only involves adding water to the juice,which does not change the chemical composition of the juice components.

(A) Rusting of iron is a chemical change because it involves a chemical reaction between iron,oxygen,and moisture to form a new substance called iron oxide $(Fe_2O_3 \cdot xH_2O)$.
Melting of iron is a physical change because it only involves a change in the state of matter from solid to liquid,and no new substance is formed.

(B) In a physical change,the chemical composition of the substance remains the same and no new substance is formed.
In a chemical change,the chemical composition of the substance changes,resulting in the formation of one or more new substances with different properties.

(N/A) During the electrolysis of water,the water molecule $(H_{2}O)$ decomposes into hydrogen gas $(H_{2})$ and oxygen gas $(O_{2})$ in a specific molar ratio.
The chemical equation for this process is:
$2H_{2}O(l) \xrightarrow{\text{Electrolysis}} 2H_{2}(g) + O_{2}(g)$
According to the balanced chemical equation,for every $2$ moles of water decomposed,$2$ moles of hydrogen gas are produced at the cathode and $1$ mole of oxygen gas is produced at the anode.
Therefore,the volume of hydrogen gas collected is double the volume of oxygen gas collected,resulting in a ratio of $2:1$.

(N/A) In the given reaction: $CuO + H_{2} \longrightarrow Cu + H_{2}O$
$1$. The oxidising agent is $CuO$ because it provides oxygen to $H_{2}$ and gets reduced to $Cu$.
$2$. The reducing agent is $H_{2}$ because it removes oxygen from $CuO$ and gets oxidised to $H_{2}O$.

(B) When copper oxide $(CuO)$ reacts with dilute hydrochloric acid $(HCl)$,a neutralization reaction occurs.
The chemical equation is: $CuO(s) + 2HCl(aq) \rightarrow CuCl_2(aq) + H_2O(l)$.
The new compound formed is copper $(II)$ chloride $(CuCl_2)$,which imparts a blue-green colour to the solution.

(B) When silver articles are exposed to air,they react with sulfur compounds present in the atmosphere,such as hydrogen sulfide $(H_2S)$.
This chemical reaction leads to the formation of a black layer of silver sulfide $(Ag_2S)$ on the surface of the silver.
This process is a form of corrosion known as tarnishing.

(C) When copper articles are exposed to moist air for a long time,they react with atmospheric carbon dioxide,oxygen,and moisture.
This process leads to the formation of a green-colored layer on the surface of the copper.
This green coating is chemically known as basic copper carbonate,which has the formula $[CuCO_{3} \cdot Cu(OH)_{2}]$.
Therefore,the correct answer is a green coating of basic copper carbonate.

(A) To balance the equation $Fe(s) + H_2O(g) \rightarrow Fe_3O_4(s) + H_2(g)$:
$1$. Balance $Fe$: There are $3$ atoms of $Fe$ on the right side,so place a coefficient of $3$ before $Fe$ on the left side: $3Fe + H_2O \rightarrow Fe_3O_4 + H_2$.
$2$. Balance $O$: There are $4$ atoms of $O$ on the right side,so place a coefficient of $4$ before $H_2O$ on the left side: $3Fe + 4H_2O \rightarrow Fe_3O_4 + H_2$.
$3$. Balance $H$: Now there are $8$ atoms of $H$ on the left side $(4 \times 2)$,so place a coefficient of $4$ before $H_2$ on the right side: $3Fe(s) + 4H_2O(g) \rightarrow Fe_3O_4(s) + 4H_2(g)$.
The equation is now balanced.

(B) skeletal chemical equation is an unbalanced chemical equation in which the number of atoms of each element is not equal on both the reactant and product sides.
For example,the reaction $Mg + O_2 \rightarrow MgO$ is a skeletal equation because the number of oxygen atoms is not balanced.

(A) Electrolysis of water is a chemical change because it involves the decomposition of water $(H_2O)$ into hydrogen $(H_2)$ and oxygen $(O_2)$ gases using electricity,resulting in the formation of new substances.
Sodium chloride $(NaCl)$ is stable under sunlight and does not undergo a chemical change when exposed to it.

(A) When copper metal is heated in the presence of air (oxygen), it undergoes an oxidation reaction.
The copper reacts with oxygen to form copper $(II)$ oxide, which is represented by the chemical formula $CuO$.
This copper $(II)$ oxide forms a black-coloured coating on the surface of the copper metal.
The chemical equation for this reaction is: $2Cu(s) + O_2(g) \rightarrow 2CuO(s)$.

(N/A) The green iron salt is Ferrous sulphate heptahydrate $(FeSO_{4} \cdot 7H_{2}O)$. Upon strong heating, it loses water of crystallization and then decomposes into Ferric oxide $(Fe_{2}O_{3})$, which is black in colour, along with sulphur dioxide $(SO_{2})$ and sulphur trioxide $(SO_{3})$ gases.
$(b)$ This is a thermal decomposition reaction because a single reactant breaks down into multiple products upon the application of heat.

(N/A) Digestion of food involves the breakdown of complex food molecules into simpler substances,which is a decomposition reaction.
$(b)$ Combustion of coal involves the reaction of carbon with oxygen to form carbon dioxide,which is a combination reaction.

(A) Combination reaction: In this reaction,two or more reactants combine to form a single product $(2H_2 + O_2 \rightarrow 2H_2O)$.
$(b)$ Decomposition reaction: In this reaction,a single reactant breaks down into two or more simpler products under the influence of electricity $(2H_2O \xrightarrow{\text{electricity}} 2H_2 + O_2)$.

(N/A) No,oxidation or reduction cannot take place alone. This is because electrons lost during oxidation must be gained by another substance during reduction. Therefore,these processes always occur simultaneously. Such reactions are known as $Redox$ reactions.

(N/A) $(i)$ In the manufacturing of cement,quicklime $(CaO)$ is used,which is obtained by the thermal decomposition of limestone $(CaCO_3)$:
$CaCO_3(s) \xrightarrow{\text{Heat}} CaO(s) + CO_2(g)$
$(ii)$ In the manufacturing of photochromic glass,silver chloride $(AgCl)$ or silver bromide $(AgBr)$ is used,which undergoes photochemical decomposition in sunlight to form metallic silver,causing the glass to darken:
$2AgCl(s) \xrightarrow{\text{Sunlight}} 2Ag(s) + Cl_2(g)$
$2AgBr(s) \xrightarrow{\text{Sunlight}} 2Ag(s) + Br_2(g)$

(N/A) $(i)$ Decomposition reaction: The breakdown of complex organic matter into simpler substances by microorganisms is a decomposition process.
$(ii)$ Oxidation (Combustion) reaction: Burning of natural gas $(CH_4)$ in the presence of oxygen is an exothermic oxidation reaction, represented as: $CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O + \text{Heat}$.

(N/A) $(i)$ Corrosion (Oxidation reaction): Silver reacts with sulfur compounds in the air to form silver sulfide $(Ag_2S)$,which is black in color.
$(ii)$ Displacement reaction: Iron $(Fe)$ is more reactive than copper $(Cu)$,so it displaces copper from the copper sulphate $(CuSO_4)$ solution to form ferrous sulphate $(FeSO_4)$,which is green in color.

(N/A) $(i)$ The essential condition for the reaction $2 AgCl \rightarrow 2 Ag + Cl_{2}$ to occur is the presence of sunlight (photolytic decomposition).
$(ii)$ This reaction is used in black and white photography.

(A) The thermal decomposition of ferrous sulfate $(FeSO_{4})$ is a classic chemical reaction.
When heated,ferrous sulfate crystals lose water and then decompose to form ferric oxide $(Fe_{2}O_{3})$,sulfur dioxide $(SO_{2})$,and sulfur trioxide $(SO_{3})$.
The balanced chemical equation is:
$2 FeSO_{4} \xrightarrow{\text{Heat}} Fe_{2}O_{3} + SO_{2} + SO_{3}$

(N/A) The given reaction is a displacement reaction.
$(i)$ Metal $X$ is more reactive than metal $Y$.
$(ii)$ Metal $X$ is displacing metal $Y$ from its salt solution. According to the reactivity series,a more reactive metal displaces a less reactive metal from its salt solution. Therefore,$X$ is more reactive than $Y$.

(N/A) When copper is heated in air,it reacts with oxygen to form copper$(II)$ oxide,which is a black-colored substance.
Equation: $2Cu(s) + O_2(g) \xrightarrow{\text{Heat}} 2CuO(s)$
$(b)$ When the product obtained (copper$(II)$ oxide) is heated in hydrogen gas,it undergoes a reduction reaction to form copper metal and water.
Equation: $CuO(s) + H_2(g) \xrightarrow{\text{Heat}} Cu(s) + H_2O(l)$
The black coating turns brown as copper metal is formed.

(N/A) $(i)$ The colour of the precipitate formed is yellow.
$(ii)$ The compound precipitated is lead iodide,which has the chemical formula $PbI_{2}$.

(N/A) $(i)$ The balanced chemical equation is:
$2KI(aq) + Pb(NO_3)_2(aq) \to PbI_2(s) \downarrow + 2KNO_3(aq)$
$(ii)$ This is a double displacement reaction. Since an insoluble solid (precipitate) is formed,it is also classified as a precipitation reaction.

(N/A) $KCl(aq) + AgNO_3(aq) \to AgCl(s) \downarrow + KNO_3(aq)$
In this reaction, potassium chloride reacts with silver nitrate to form silver chloride, which is an insoluble white precipitate, and potassium nitrate.

(A-D) The chemical reaction is: $KCl(aq) + AgNO_3(aq) \rightarrow AgCl(s) + KNO_3(aq)$.
$(a)$ Double displacement reaction: The ions $K^+$ and $Ag^+$ exchange their partners to form new products.
$(b)$ Precipitation reaction: An insoluble white solid, silver chloride $(AgCl)$, is formed as a precipitate.

(N/A) Aluminium is more reactive than iron. Therefore,it displaces iron from the ferrous sulphate solution in a displacement reaction.
The chemical reaction is as follows:
$2Al(s) + 3FeSO_4(aq) \to Al_2(SO_4)_3(aq) + 3Fe(s)$
Due to this reaction,the aluminium metal of the can is consumed to form aluminium sulphate,which leads to the formation of holes in the can.

(B) combustion reaction is classified as an oxidation reaction because it involves the addition of oxygen to a substance or the removal of hydrogen from it.
In most combustion processes,the fuel reacts with oxygen to form oxides,which is a fundamental characteristic of oxidation.
For example,the combustion of methane is represented as:
$CH_{4}(g) + 2O_{2}(g) \rightarrow CO_{2}(g) + 2H_{2}O(l)$
In this reaction,oxygen is added to carbon and hydrogen,confirming it as an oxidation process.

(N/A) To test for hydrogen gas,bring a burning matchstick or a burning splinter near the mouth of the test tube from which the gas is being evolved.
If the gas is hydrogen,it will burn with a characteristic '$pop$' sound,which is caused by the rapid combustion of hydrogen in the presence of oxygen.

(N/A) $FeSO_{4} \cdot 7H_{2}O$ crystals are green in colour. Upon heating,they first lose their water of crystallisation and turn white (anhydrous $FeSO_{4}$). On further heating,they decompose to form ferric oxide $(Fe_{2}O_{3})$,which is reddish-brown in colour,along with sulphur dioxide $(SO_{2})$ and sulphur trioxide $(SO_{3})$ gases.
Step $1$: Loss of water of crystallisation:
$FeSO_{4} \cdot 7H_{2}O(s) \xrightarrow{\Delta} FeSO_{4}(s) + 7H_{2}O(g)$
(Green) (White)
Step $2$: Decomposition of anhydrous ferrous sulphate:
$2FeSO_{4}(s) \xrightarrow{\Delta} Fe_{2}O_{3}(s) + SO_{2}(g) + SO_{3}(g)$
(Reddish-brown)

(N/A) The smell and taste of food containing fats and oils change because they get oxidized when exposed to air,leading to a condition known as $Rancidity$.
Process: $Rancidity$.
Two ways to slow down this process are:
$1$. Storing food in airtight containers to prevent contact with oxygen.
$2$. Flushing nitrogen gas into food packets (like chips) to replace oxygen and prevent oxidation.

(N/A) When hydrated copper sulphate $(CuSO_4 \cdot 5H_2O)$ is heated,the five molecules of water of crystallisation are lost,and the blue-coloured crystals turn into a white anhydrous powder.
If we add water back to this white powder,the blue colour reappears due to the re-formation of hydrated copper sulphate.
The chemical equation is:
$CuSO_4 \cdot 5H_2O (s) \xrightarrow{\text{Heat}} CuSO_4 (s) + 5H_2O (g)$
(Blue) $\quad \quad \quad \quad \quad \quad \quad \quad$ (White)

(N/A) When gypsum $(CaSO_4 \cdot 2H_2O)$ is heated at $373 \, K$,it loses three-fourths of its water of crystallization and forms Plaster of Paris $(CaSO_4 \cdot \frac{1}{2}H_2O)$.
The chemical equation for this reaction is:
$CaSO_4 \cdot 2H_2O(s) \xrightarrow{373 \, K} CaSO_4 \cdot \frac{1}{2}H_2O(s) + 1\frac{1}{2}H_2O(g)$

(N/A) When chlorine gas is passed through dry slaked lime,it reacts to form bleaching powder (calcium oxychloride) and water.
The chemical equation is:
$Ca(OH)_2 + Cl_2 \to CaOCl_2 + H_2O$

(N/A) Potato chips manufacturers flush bags with nitrogen gas to create an unreactive environment,which prevents the oxidation of fats and oils,thereby stopping the chips from becoming rancid.
$(b)$ Iron articles lose their shine because they react with moisture and oxygen present in the atmosphere to form a layer of hydrated iron oxide,a process known as corrosion or rusting.
$(c)$ Foods should be kept in airtight containers to minimize their exposure to oxygen and moisture,which helps in preventing oxidation and slowing down the growth of microorganisms,thus keeping the food fresh for a longer period.

(N/A) Zinc is more reactive than copper; therefore,it will displace copper from $CuSO_4$. This reaction will take place.
$(b)$ Iron is less reactive than zinc; therefore,it cannot displace zinc from zinc sulphate. This reaction will not take place.
$(c)$ Zinc is more reactive than iron; therefore,it will displace iron from $FeSO_4$. This reaction will take place.

(N/A) chemical reaction involving a change in colour can be observed when lead nitrate solution reacts with potassium iodide solution. The reaction mixture changes from colourless to a yellow precipitate.
The balanced chemical equation is:
$Pb(NO_3)_2(aq) + 2KI(aq) \rightarrow PbI_2(s) + 2KNO_3(aq)$
In this reaction,lead$(II)$ iodide $(PbI_2)$ is formed as a yellow precipitate.

(N/A) change in temperature occurs during an exothermic reaction, where heat is released into the surroundings.
Example: The reaction between zinc granules and dilute sulphuric acid.
Chemical equation: $Zn(s) + H_2SO_4(aq) \rightarrow ZnSO_4(aq) + H_2(g) + \text{Heat}$

(N/A) Formation of a precipitate occurs when two aqueous solutions react to form an insoluble solid product,known as a precipitate.
Example: The reaction between barium chloride and sodium sulphate results in the formation of a white precipitate of barium sulphate.
Chemical equation:
$BaCl_{2}(aq) + Na_{2}SO_{4}(aq) \rightarrow BaSO_{4}(s) + 2NaCl(aq)$

(N/A) $(i)$ Electricity (Electrolytic decomposition):
$2H_{2}O(l) \xrightarrow{\text{Electric current}} 2H_{2}(g) + O_{2}(g)$
$(ii)$ Heat (Thermal decomposition):
$CaCO_{3}(s) \xrightarrow{\text{Heat}} CaO(s) + CO_{2}(g)$
$(iii)$ Sunlight (Photolytic decomposition):
$2AgCl(s) \xrightarrow{\text{Sunlight}} 2Ag(s) + Cl_{2}(g)$

(B) The correct statement is that copper can displace silver from silver nitrate solution,but silver cannot displace copper from copper sulphate solution.
This is because copper is more reactive than silver,as per the reactivity series of metals.
$A$ more reactive metal can displace a less reactive metal from its salt solution.
The chemical reaction is: $Cu(s) + 2AgNO_3(aq) \rightarrow Cu(NO_3)_2(aq) + 2Ag(s)$.

(N/A) $(i)$ $(a)$ At the anode,oxygen gas is evolved.
$(b)$ At the cathode,hydrogen gas is evolved.
$(ii)$ The amounts of gases collected in the two test tubes are not of the same volume because water $(H_2O)$ consists of hydrogen and oxygen in a molar ratio of $2:1$. Thus,twice as much hydrogen gas is produced compared to oxygen gas.
$(iii)$ This reaction is an electrolytic decomposition reaction.
$(iv)$ Pure water is a poor conductor of electricity. Salt water is used to act as an electrolyte,allowing electricity to pass through the solution to facilitate the decomposition of water.

(N/A)

Displacement reactions	Double displacement reactions
$1.$ In these reactions, a more active element displaces a less active element from its salt solution.	$1.$ In these reactions, there is an exchange of ions between two reactants.
$2.$ These reactions are usually slow and take longer time for their completion.	$2.$ These reactions are usually fast and take place instantaneously.
$3.$ During these reactions, a change of color usually takes place. Example: $Fe(s) + CuSO_4(aq) \to FeSO_4(aq) + Cu(s)$ (Blue to Light green).	$3.$ During these reactions, precipitates are usually formed. Example: $AgNO_3(aq) + NaCl(aq) \to AgCl(s) \downarrow + NaNO_3(aq)$ (White precipitate).

(B) is the most reactive element.
Reason: $B$ displaces both $A$ and $C$ from their respective compounds,which indicates that $B$ has a higher reactivity than both $A$ and $C$.
$(b)$ $C$ is the least reactive element.
Reason: $C$ is displaced by both $A$ and $B$ in the given chemical reactions,which indicates that $C$ has the lowest reactivity among the three.
$(c)$ These are displacement reactions.
Reason: In each reaction,a more reactive element displaces a less reactive element from its compound.