Mix Examples - Acids, Bases and Salts Questions in English

(N/A) $(i)$ Antacids are mild bases.
$(ii)$ During indigestion,the stomach produces excess hydrochloric acid,which causes pain and irritation. Antacids are chemical substances that neutralize this excess acid,thereby providing relief from stomach ache.

(N/A) Bases that are soluble in water are known as alkalies.
All alkalies are bases,but not all bases are alkalies.
Examples include sodium hydroxide $(NaOH)$ and potassium hydroxide $(KOH)$.

(B) The $pH$ scale ranges from $0$ to $14$.
Substances with a $pH$ value less than $7$ are acidic.
Substances with a $pH$ value equal to $7$ are neutral.
Substances with a $pH$ value greater than $7$ and up to $14$ are basic (alkaline).
Therefore,the range for the identification of a base is $7-14$.

(N/A) Chloride of lime,commonly known as bleaching powder,has the chemical formula $CaOCl_{2}$ (calcium oxychloride).
In contrast,calcium chloride has the chemical formula $CaCl_{2}$.
Chemically,chloride of lime contains an oxygen atom bonded to calcium and chlorine,whereas calcium chloride is a simple salt of calcium and chlorine.

(N/A) Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt.
For example, hydrated copper sulphate is represented as $CuSO_{4} \cdot 5H_{2}O$.
In this formula, the $5H_{2}O$ signifies that there are five molecules of water present as water of crystallisation for every one formula unit of copper sulphate.

(N/A) Chemical name: Sodium carbonate.
Chemical formula: $Na_{2}CO_{3} \cdot 10H_{2}O$.
Washing soda is chemically known as sodium carbonate decahydrate,which contains $10$ molecules of water of crystallization.

(B) The $pH$ of a solution decreases with an increase in the concentration of $H^{+}(aq)$ ions.
This is because $pH$ is defined as the negative logarithm of the hydrogen ion concentration,expressed as $pH = -\log[H^{+}]$.
As the concentration of $H^{+}(aq)$ ions increases,the value of the negative logarithm increases,which mathematically results in a lower $pH$ value.
Therefore,a higher concentration of $H^{+}(aq)$ indicates higher acidity and a lower $pH$ value.

(N/A) When dilute $HCl$ reacts with sodium hydrogen carbonate $(NaHCO_3)$,the gas evolved is carbon dioxide $(CO_2)$.
The chemical reaction is: $NaHCO_3 + HCl \rightarrow NaCl + H_2O + CO_2 \uparrow$.
This gas is recognized by passing it through lime water $(Ca(OH)_2)$. It turns the lime water milky due to the formation of insoluble calcium carbonate $(CaCO_3)$.

(B) Olfactory indicators are substances whose smell or odour changes in acidic or basic media.
These indicators are useful for visually impaired students as they can detect the change in the nature of a substance through their sense of smell.
Examples include onion,vanilla extract,and clove oil.

(A) $HCl$ is a strong acid,which means it undergoes complete dissociation in an aqueous solution to produce a high concentration of $H^{+}$ ions.
In contrast,$CH_{3}COOH$ (acetic acid) is a weak acid,which undergoes only partial dissociation in an aqueous solution.
Therefore,for the same molar concentration,the $HCl$ solution will have a significantly higher concentration of $H^{+}$ ions compared to the $CH_{3}COOH$ solution.

(N/A) When an active metal reacts with hydrochloric acid $(HCl)$,hydrogen gas $(H_2)$ is liberated.
To test for this gas,bring a burning candle or a matchstick near the mouth of the test tube or jar containing the gas.
The hydrogen gas burns with a characteristic '$pop$' sound,which confirms its presence.

(B) Hydrogen ions $(H^{+})$ cannot exist independently in an aqueous solution because they are highly reactive.
They immediately combine with water $(H_{2}O)$ molecules to form hydronium ions $(H_{3}O^{+})$.
Therefore,hydrogen ions are always represented as $H^{+}(aq)$ or as hydronium ions $(H_{3}O^{+})$.

(N/A) When an acid is diluted,the concentration of hydrogen ions $(H^+)$ per unit volume decreases.
Since $pH$ is defined as the negative logarithm of the hydrogen ion concentration $(pH = -\log[H^+])$,a decrease in the concentration of $H^+$ ions leads to an increase in the $pH$ value of the solution.

(A) Normal rain water has a $pH$ of about $5.6$ due to the dissolution of atmospheric $CO_2$ forming weak carbonic acid.
When the $pH$ of rain water drops below $5.6$,it is considered to be acid rain.
This occurs due to the presence of pollutants like oxides of sulfur and nitrogen in the atmosphere.

(N/A) When dilute hydrochloric acid $(HCl)$ reacts with zinc $(Zn)$,it produces zinc chloride $(ZnCl_2)$ and releases hydrogen gas $(H_2)$.
The chemical equation for this reaction is: $Zn(s) + 2HCl(aq) \rightarrow ZnCl_2(aq) + H_2(g)$.
The gas evolved is hydrogen gas,and its molecular formula is $H_2$.

(N/A) The acidic character of $HCl$ is due to the presence of $H^+$ ions.
In the absence of water,$HCl$ molecules do not dissociate to produce $H^+$ ions.
Since the litmus paper is dry and the $HCl$ gas is also dry,there is no medium for the dissociation of $HCl$ into ions.
Therefore,the litmus paper does not change its colour.

(D) $HCl$ is a strong acid because it undergoes complete dissociation in an aqueous solution,releasing a high concentration of $H^+$ ions.
In contrast,acetic acid is a weak acid that undergoes only partial dissociation in water,resulting in a lower concentration of $H^+$ ions for the same molar concentration.
Therefore,due to the higher degree of ionization,$HCl$ exhibits stronger acidic properties.

(N/A) When zinc granules are heated with sodium hydroxide solution,a chemical reaction occurs in which hydrogen gas is evolved and a salt called sodium zincate is formed.
The balanced chemical equation for this reaction is:
$Zn(s) + 2NaOH(aq) \longrightarrow Na_2ZnO_2(aq) + H_2(g)$
The main product formed in this reaction is sodium zincate $(Na_2ZnO_2)$.

(N/A) universal indicator is a mixture of several indicators that exhibits a range of different colours over a wide range of $pH$ values.
It is used to determine the strength of an acid or a base in a solution by indicating the concentration of hydrogen ions $(H^+)$ present.
By comparing the colour produced with a standard $pH$ colour chart,one can estimate the approximate $pH$ value of the solution.

(N/A) Tooth enamel is made up of $Calcium \text{ } phosphate$ (specifically, $Hydroxyapatite$, a crystalline form of $Calcium \text{ } phosphate$).
It gets corroded when the $pH$ of the mouth falls below $5.5$.
Bacteria present in the mouth produce acids by the degradation of sugar and food particles remaining in the mouth after eating.
To prevent tooth decay, one should use toothpaste, which is generally basic, to neutralize the excess acid produced in the mouth.

(N/A) The acidic character of a substance is due to the presence of $H^{+}$ ions.
In the case of dry $HCl$ gas,there is no water present to facilitate the dissociation of $HCl$ molecules into $H^{+}$ and $Cl^{-}$ ions.
Since $H^{+}$ ions are responsible for the acidic property of changing the colour of litmus paper,the absence of these ions in dry $HCl$ means the litmus paper will not change colour.

(N/A) When an acid is dissolved in water,it dissociates to produce $H^{+}$ ions (hydrogen ions).
These $H^{+}$ ions act as charge carriers in the solution.
Since the movement of ions is responsible for the flow of electric current,the aqueous solution of an acid conducts electricity.

(N/A) $(i)$ The $pH$ range of a base is greater than $7$ and up to $14$.
$(ii)$ The strength of a base depends on the concentration of $OH^{-}$ ions in the solution. Therefore,the strength of a basic solution can be increased by increasing the concentration of $OH^{-}$ ions.

(N/A) strong base is a base that completely dissociates into its ions in an aqueous solution. An example of a strong base is $NaOH$ (Sodium hydroxide).
$A$ weak base is a base that partially dissociates into its ions in an aqueous solution. An example of a weak base is $Mg(OH)_2$ (Magnesium hydroxide or Milk of magnesia).

(N/A) $(i)$ Washing soda contains $10$ molecules of water of crystallisation $(Na_2CO_3 \cdot 10H_2O)$. Plaster of Paris contains $1/2$ molecule of water of crystallisation $(CaSO_4 \cdot 1/2H_2O)$.
$(ii)$ These water molecules are known as water of crystallisation.

(N/A) Acids ionize in an aqueous medium to produce hydrogen ions $(H^+)$. These hydrogen ions cannot exist independently; they combine with water molecules to form hydronium ions $(H_3O^+)$. Since the presence of these ions is essential for exhibiting acidic properties,acids only show acidic behavior in the presence of water.
Chemical equation:
$H^+ + H_2O \to H_3O^+$
These hydrogen ions are represented as $H^+(aq)$ or hydronium ions $(H_3O^+)$.

(N/A) When $CO_2$ is passed through lime water in limited amount,the lime water turns milky due to the formation of insoluble white precipitates of calcium carbonate.
The chemical reaction is as follows:
$Ca(OH)_2(aq) + CO_2(g) \to CaCO_3(s) \downarrow + H_2O(l)$

(N/A) When $CO_{2}$ is passed through lime water in excess,the initially formed white precipitate of calcium carbonate $(CaCO_{3})$ reacts further with $CO_{2}$ and water to form calcium hydrogen carbonate,which is soluble in water.
The chemical reaction is as follows:
$Ca(OH)_{2}(aq) + 2CO_{2}(g) \to Ca(HCO_{3})_{2}(aq)$
In this reaction,the insoluble $CaCO_{3}$ (formed when $CO_{2}$ is passed in limited amounts) dissolves due to the formation of soluble calcium hydrogen carbonate.

(B) Dilution should always be performed by adding concentrated acid to water,never by adding water to concentrated acid.
This is because the process of dissolving a concentrated acid in water is highly exothermic.
If water is added to concentrated acid,the large amount of heat generated can cause the mixture to splash out,potentially causing severe acid burns.
Therefore,one should always add acid to water slowly while stirring the solution constantly to dissipate the heat.

(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) $(i)$ When sodium hydrogen carbonate $(NaHCO_3)$ is heated, it decomposes to form sodium carbonate $(Na_2CO_3)$, water $(H_2O)$, and carbon dioxide $(CO_2)$ gas.
$(ii)$ The balanced chemical equation for the thermal decomposition of sodium hydrogen carbonate is:
$2NaHCO_3(s) \xrightarrow{\Delta} Na_2CO_3(s) + H_2O(l) + CO_2(g)$

(N/A) Bleaching powder is prepared by the action of chlorine gas $(Cl_2)$ on dry slaked lime $[Ca(OH)_2]$.
The chemical reaction is:
$Ca(OH)_2 + Cl_2 \to CaOCl_2 + H_2O$
Bleaching powder smells strongly of chlorine because it reacts with carbon dioxide $(CO_2)$ present in the atmosphere,which leads to the liberation of free chlorine gas.

(N/A) Bleaching powder is prepared by the action of chlorine gas $(Cl_{2})$ on dry slaked lime $[Ca(OH)_{2}]$.
The chemical reaction is as follows:
$Ca(OH)_{2} + Cl_{2} \rightarrow CaOCl_{2} + H_{2}O$
$(i)$ Bleaching powder does not dissolve completely in water because it contains some amount of unreacted lime $[Ca(OH)_{2}]$,which is insoluble in water. Due to the presence of this unreacted lime,the solution appears milky or leaves a residue when dissolved in water.

(N/A) $(i)$ $A$ hydrated salt is a crystalline salt molecule that is loosely attached to a specific number of water molecules,known as water of crystallisation.
$(ii)$ Two examples of white hydrated salts are:
$1$. Washing soda: $Na_{2}CO_{3} \cdot 10H_{2}O$
$2$. Gypsum: $CaSO_{4} \cdot 2H_{2}O$

(N/A) $(i)$ Sodium acetate $(CH_{3}COONa)$ is formed from the reaction between:
Acid: $CH_{3}COOH$ (Acetic acid)
Base: $NaOH$ (Sodium hydroxide)
$(ii)$ Ammonium chloride $(NH_{4}Cl)$ is formed from the reaction between:
Acid: $HCl$ (Hydrochloric acid)
Base: $NH_{4}OH$ (Ammonium hydroxide)

(N/A) $Na_{2}CO_{3} \cdot 10H_{2}O$ is known as Sodium carbonate decahydrate (Washing soda).
$Na_{2}CO_{3}$ is known as Anhydrous sodium carbonate (Soda ash).
The $10H_{2}O$ represents the water of crystallisation.
Significance of $10H_{2}O$: It is a fixed number of water molecules present in one formula unit of a salt. It is responsible for the specific crystalline shape and,in some cases,the colour of the salt.
The term used for these water molecules is 'water of crystallisation'.

(N/A) The substance is Copper sulphate pentahydrate, with the formula $CuSO_{4} \cdot 5H_{2}O$.
When heated, the blue-coloured hydrated copper sulphate crystals lose their water of crystallisation and turn into white anhydrous copper sulphate $(CuSO_{4})$.
This is a reversible physical change. Upon cooling, the anhydrous salt absorbs moisture from the atmosphere or the water vapour present in the test tube to regain its water of crystallisation, thereby returning to its original blue colour.

(N/A) The metal is aluminium $(Al)$.
Aluminium oxide $(Al_{2}O_{3})$ is an amphoteric oxide,meaning it reacts with both acids and bases.
Reaction with dilute sulphuric acid:
$Al_{2}O_{3}(s) + 3H_{2}SO_{4}(aq) \longrightarrow Al_{2}(SO_{4})_{3}(aq) + 3H_{2}O(l)$
Reaction with dilute sodium hydroxide solution:
$Al_{2}O_{3}(s) + 2NaOH(aq) + 3H_{2}O(l) \longrightarrow 2Na[Al(OH)_{4}](aq)$ (Sodium aluminate)

(N/A) $(i)$ The acid should be added slowly to the water with constant stirring. This is because the process of dissolving a concentrated acid in water is highly exothermic. If water is added to a concentrated acid,the heat generated may cause the mixture to splash out and cause burns. Adding acid to water allows the large volume of water to absorb the heat generated.
$(ii)$ This process is called dilution.

(A) $X$ is Sodium hydrogen carbonate $(NaHCO_3)$.
$Y$ is Carbon dioxide $(CO_2)$.
$Z$ is Sodium carbonate $(Na_2CO_3)$.
When $NaHCO_3$ is heated, it decomposes to form sodium carbonate, water, and carbon dioxide:
$2NaHCO_3(s) \xrightarrow{\text{Heat}} Na_2CO_3(s) + H_2O(l) + CO_2(g)$
When $CO_2$ is passed through lime water $[Ca(OH)_2]$, it forms calcium carbonate, which makes the solution milky:
$Ca(OH)_2(aq) + CO_2(g) \rightarrow CaCO_3(s) + H_2O(l)$

(N/A) Chemically,marble is $CaCO_3$ (calcium carbonate). When exposed to the atmosphere for a long time,it reacts with acidic pollutants like $SO_2$ and $NO_2$ present in the air,which dissolve in rainwater to form acids (acid rain).
These acids react with the calcium carbonate of the marble to form soluble salts,which are then washed away by rain,leading to the slow corrosion of the statues.
The chemical reaction is as follows:
$CaCO_3(s) + H_2O(l) + CO_2(g) \rightarrow Ca(HCO_3)_2(aq)$

(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) Calcium carbonate reacts with hydrochloric acid to form calcium chloride,water,and carbon dioxide:
$CaCO_{3} + 2HCl \rightarrow CaCl_{2} + H_{2}O + CO_{2}$
$(b)$ Calcium oxychloride (bleaching powder) reacts with hydrochloric acid to form calcium chloride,water,and chlorine gas:
$CaOCl_{2} + 2HCl \rightarrow CaCl_{2} + H_{2}O + Cl_{2}$
$(c)$ Sodium hydroxide reacts with zinc to form sodium zincate and hydrogen gas:
$2NaOH + Zn \rightarrow Na_{2}ZnO_{2} + H_{2}$

(N/A) The given reactions are neutralization reactions where an acid reacts with a base to form salt and water.
$(i)$ $HNO_{3} + NaOH \rightarrow NaNO_{3} + H_{2}O$. Here,$A$ is $NaNO_{3}$ (Sodium nitrate).
$(ii)$ $H_{2}SO_{4} + Ca(OH)_{2} \rightarrow CaSO_{4} + 2H_{2}O$. Here,$B$ is $H_{2}SO_{4}$ (Sulphuric acid).
$(iii)$ $HCl + KOH \rightarrow KCl + H_{2}O$. Here,$C$ is $KOH$ (Potassium hydroxide).

(N/A) $(i)$ The purpose of developing the $pH$ scale was to quantify the concentration of $H^{+}$ or $OH^{-}$ ions in a solution.
$(ii)$ The $pH$ range for acidic solutions is $0$ to less than $7$.
$(iii)$ Acid rain is defined as rain water with a $pH$ value of less than $5.6$. When this acidic water flows into rivers and lakes,it lowers the $pH$ of the aquatic environment,making it difficult for aquatic organisms to survive.

(D) $(i)$ Between hydrochloric acid and acetic acid of the same concentration,acetic acid will produce a lower concentration of $H^{+}$ ions because it is a weak acid that does not ionize completely in water.
$(ii)$ Acetic acid is the weak acid.
$(b)$ If someone is suffering from acidity,$I$ would suggest a baking soda solution to cure it. Baking soda is a mild base (sodium bicarbonate) that neutralizes the excess hydrochloric acid produced in the stomach,thereby providing relief.

(N/A) $(i)$ Antacids are formulated based on the principle of neutralisation reaction to treat acidity.
$(ii)$ Toothpastes are basic in nature,which help in neutralising the excess acid produced in the mouth,thereby preventing tooth decay.
$(iii)$ Milkmen add a small amount of baking soda to milk to neutralise the lactic acid produced,which helps in preventing the milk from souring quickly.

(N/A) The salt formed by the reaction of carbonic acid $(H_{2}CO_{3})$ and sodium hydroxide $(NaOH)$ is sodium carbonate,with the formula $Na_{2}CO_{3}$.
$(b)$ The chlor-alkali process involves the electrolysis of brine $(NaCl$ solution$)$,which produces sodium hydroxide $(NaOH)$,chlorine gas,and hydrogen gas. The basic substance formed is sodium hydroxide $(NaOH)$.
$(c)$ Sodium hydrogen carbonate $(NaHCO_{3})$,also known as baking soda,is added to cakes. Upon heating,it releases carbon dioxide gas,which makes the cakes fluffy.

(N/A) $(i)$ Soda ash: Anhydrous sodium carbonate; $Na_{2}CO_{3}$
$(ii)$ Blue vitriol: Copper$(II)$ sulphate pentahydrate; $CuSO_{4} \cdot 5H_{2}O$
$(iii)$ Baking soda: Sodium hydrogen carbonate; $NaHCO_{3}$