Mix Examples - Acids, Bases and Salts Questions in English

(C) Hydrochloric acid $(HCl)$ is a strong acid that dissociates completely in an aqueous solution.
The dissociation reaction is represented as: $HCl + H_{2}O \rightarrow H_{3}O^{+} + Cl^{-}$.
In a dilute aqueous solution,$HCl$ exists primarily as hydronium ions $(H_{3}O^{+})$ and chloride ions $(Cl^{-})$.
Therefore,the correct species present are $H_{3}O^{+}$ and $Cl^{-}$.

(D) The $pH$ scale measures the acidity or alkalinity of a solution.
For acids,as the concentration of $H^+$ ions increases,the $pH$ value decreases. Therefore,a lower $pH$ indicates a stronger acid,and a higher $pH$ indicates a weaker acid. Thus,statement $(ii)$ is correct.
For bases,as the concentration of $OH^-$ ions increases,the $pH$ value increases. Therefore,a higher $pH$ indicates a stronger base,and a lower $pH$ indicates a weaker base. Thus,statement $(iv)$ is correct.
Combining these,statements $(ii)$ and $(iv)$ are correct.

(A) Sodium carbonate $(Na_2CO_3)$ is formed by the neutralization reaction between carbonic acid $(H_2CO_3)$ and sodium hydroxide $(NaOH)$.
Carbonic acid $(H_2CO_3)$ is a weak acid.
Sodium hydroxide $(NaOH)$ is a strong base.
Since the salt is derived from a weak acid and a strong base,the resulting salt is basic in nature,having a $pH$ greater than $7$.

(B) Tooth enamel is composed of hydroxyapatite,which is a crystalline form of calcium phosphate,$Ca_3(PO_4)_2$.
Calcium phosphate is a salt formed by the reaction of a strong base,calcium hydroxide $Ca(OH)_2$,and a weak acid,phosphoric acid $H_3PO_4$.
Since it is a salt of a strong base and a weak acid,its nature is basic.

(C) $1$. The $pH$ paper turning yellowish-orange indicates that the soil solution is acidic (typically $pH$ range $5-6$).
$2$. To change the colour of the $pH$ paper to greenish-blue,we need a substance that is basic (alkaline),as basic solutions turn $pH$ paper towards blue/green $(pH > 7)$.
$3$. Lemon juice and vinegar are acidic. Common salt $(NaCl)$ is neutral.
$4$. An antacid is a mild base used to neutralize excess stomach acid,making it the correct choice to shift the $pH$ towards the basic range.

(D) The acidic strength of a substance depends on its ability to donate $H^+$ ions in an aqueous solution.
$1$. Hydrochloric acid $(HCl)$ is a strong acid that dissociates completely in water.
$2$. Acetic acid $(CH_3COOH)$ is a weak organic acid that dissociates partially in water.
$3$. Water $(H_2O)$ is amphoteric and acts as a very weak acid compared to the others.
Therefore,the increasing order of acidic strength is: Water < Acetic acid < Hydrochloric acid.

(A) When an acid reacts with a base,a neutralization reaction occurs.
This reaction is exothermic in nature,meaning heat is released,which causes the temperature of the solution to increase.
The products formed in this reaction are salt and water.
Therefore,both statement $(i)$ (temperature increases) and statement $(iv)$ (salt formation takes place) are correct.

(FALSE) False.
Acids like $HCl$ show acidic character only in the presence of water because water is required to dissociate $HCl$ molecules into $H^+$ (or $H_3O^+$) ions and $Cl^-$ ions.
In the absence of water,$HCl$ exists as covalent molecules and does not release $H^+$ ions,thus it does not exhibit acidic properties.

(TRUE) The statement is True.
According to the Arrhenius theory of acids,an acid is a substance that dissociates in water to produce hydrogen ions $(H^{+})$. Since $H^{+}$ ions are highly reactive and cannot exist independently in an aqueous solution,they immediately combine with water molecules $(H_{2}O)$ to form hydronium ions $(H_{3}O^{+})$.
Therefore,the reaction is represented as: $HCl + H_{2}O \rightarrow H_{3}O^{+} + Cl^{-}$.
Thus,acids produce $H_{3}O^{+}$ or $H^{+}(aq)$ ions in water.

(TRUE) True.
When an acid or a base is dissolved in water,it releases a significant amount of heat energy. This reaction is known as an exothermic process. Because of this,it is always recommended to add acid to water slowly with constant stirring,rather than adding water to a concentrated acid,to prevent the mixture from splashing out due to the sudden release of heat.

(B) The statement is False.
When diluting concentrated acids,the process is highly exothermic,meaning it releases a large amount of heat.
If water is added to concentrated acid,the heat generated may cause the mixture to splash out and cause severe acid burns.
Therefore,the correct procedure is to always add the concentrated acid slowly to a large volume of water with constant stirring,not the other way around.

(FALSE) The statement is False.
When an acid or a base is mixed with water,it undergoes a process called dilution.
Dilution is the process of adding water to a concentrated acid or base,which results in a decrease in the concentration of ions $(H_{3}O^{+}$ for acids or $OH^{-}$ for bases) per unit volume.
Therefore,the concentration of ions per unit volume decreases,not increases.

(B) The statement is False.
$A$ universal indicator is a mixture of several indicators that shows different colours at different concentrations of hydrogen ions $(H^+)$ in a solution.
It changes colour across the entire $pH$ scale,allowing us to determine the strength of an acid or a base.

(TRUE) True. The $pH$ scale is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. It typically ranges from $0$ to $14$,where $pH < 7$ indicates an acidic solution,$pH = 7$ indicates a neutral solution,and $pH > 7$ indicates an alkaline (basic) solution.

(FALSE) The statement is False.
The $pH$ of a solution is defined as the negative logarithm of the hydronium ion concentration,expressed as $pH = -\log[H_3O^+]$.
Because of the negative sign,as the concentration of hydronium ions $[H_3O^+]$ increases,the $pH$ value decreases.
Therefore,a higher hydronium ion concentration corresponds to a lower $pH$ value.

(TRUE) The statement is True.
Strong acids are those that completely dissociate in an aqueous solution to produce a high concentration of $H^+$ ions.
Weak acids are those that only partially dissociate in an aqueous solution,resulting in a lower concentration of $H^+$ ions.

(FALSE) The statement is False.
Acid rain is defined as rainwater that has a $pH$ of less than $5.6.$ This acidity is primarily caused by the presence of dissolved atmospheric pollutants such as sulfur dioxide $(SO_2)$ and nitrogen oxides $(NO_x)$,which react with water to form sulfuric acid and nitric acid,respectively.

(C) Non-metal oxides are acidic in nature. When a non-metal oxide reacts with a base,it undergoes a neutralization reaction to produce salt and water. For example,the reaction between carbon dioxide $(CO_2)$,which is a non-metal oxide,and calcium hydroxide $(Ca(OH)_2)$,which is a base,produces calcium carbonate $(CaCO_3)$ and water $(H_2O)$: $Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O$. Therefore,the correct product formed is a salt.

(B) When an acid reacts with a metal oxide,it undergoes a neutralization reaction to form salt and water.
Metal oxides are basic in nature.
Therefore,the general chemical equation is: $\text{Acid} + \text{Metal oxide} \longrightarrow \text{Salt} + \text{Water}$.
For example: $2HCl + CuO \longrightarrow CuCl_2 + H_2O$.

(C) When a base reacts with a metal,it produces a salt and releases $H_2$ (dihydrogen) gas.
For example,when sodium hydroxide $(NaOH)$ reacts with zinc $(Zn)$,it forms sodium zincate $(Na_2ZnO_2)$ and releases dihydrogen gas $(H_2)$.
The chemical equation is: $Zn + 2NaOH \rightarrow Na_2ZnO_2 + H_2 \uparrow$.

(D) Molarity $(M)$ is defined as the number of moles of solute dissolved per liter of solution.
Formula: $M = \frac{\text{moles of solute}}{\text{volume of solution in liters}}$
Given:
Moles of solute $(HCl)$ = $2 \ mol$
Volume of solution = $500 \ ml = 0.5 \ L$
Calculation:
$M = \frac{2 \ mol}{0.5 \ L} = 4 \ M$
Therefore,the molarity of the solution is $4 \ M$.

(C) In an aqueous solution at $25^{\circ}C$,the concentration of hydronium ions $[H_3O^+]$ and hydroxide ions $[OH^-]$ are related by the water dissociation constant,$K_w = [H_3O^+][OH^-] = 10^{-14}$.
For a neutral solution,$[H_3O^+] = [OH^-] = 10^{-7} \; M$.
An acidic solution is defined as a solution where the concentration of hydronium ions is greater than the concentration of hydroxide ions.
Therefore,for an acidic solution,$[H_3O^+] > 10^{-7} \; M$ and $[H_3O^+] > [OH^-]$.

(C) The $pH$ scale ranges from $0$ to $14$.
Solutions with a $pH$ value less than $7$ are acidic,while solutions with a $pH$ value greater than $7$ are basic.
The higher the $pH$ value above $7$,the more basic the solution is.
Comparing the given values: $11.5 > 10.6 > 9.3 > 8.2$.
Therefore,the solution with $pH = 11.5$ is the most basic.

(C) The $pH$ scale is a measure of the hydrogen ion concentration in a solution.
$S.P.L. Sorensen$ introduced the $pH$ scale in $1909$.
The scale typically ranges from $0$ to $14$ at $25^{\circ}C$.
The $pH$ scale is specifically defined for aqueous solutions,where water acts as the solvent.
Therefore,the statement that the $pH$ scale is applicable to only non-aqueous solutions is incorrect.

(C) The $pH$ of an aqueous solution is a measure of the hydrogen ion concentration.
While $pH$ paper and universal indicators provide an approximate value by showing a color change,they are subject to human error in color interpretation.
$A$ $pH$ meter is an electronic device that measures the potential difference between two electrodes immersed in the solution.
This provides a precise,digital,and accurate reading of the $pH$ value,making it the standard instrument for exact measurements.

(B) An antacid is a substance that neutralizes stomach acidity.
$Mg(OH)_{2}$,also known as milk of magnesia,is a mild base used as an antacid to treat indigestion and heartburn by neutralizing excess $HCl$ in the stomach.
$NaCl$ is a neutral salt.
$HCl$ and $H_{2}SO_{4}$ are strong acids.

(D) The $pH$ of a solution is defined as $pH = -\log[H^+]$.
For a solution with $pH \, 8$,the concentration of hydrogen ions is $[H^+]_1 = 10^{-8} \, M$.
For a solution with $pH \, 11$,the concentration of hydrogen ions is $[H^+]_2 = 10^{-11} \, M$.
Since $pH + pOH = 14$ at $25^{\circ}C$,the $pOH$ values are:
For $pH \, 8$,$pOH = 14 - 8 = 6$,so $[OH^-]_1 = 10^{-6} \, M$.
For $pH \, 11$,$pOH = 14 - 11 = 3$,so $[OH^-]_2 = 10^{-3} \, M$.
The ratio of basicity is the ratio of hydroxide ion concentrations: $\frac{[OH^-]_2}{[OH^-]_1} = \frac{10^{-3}}{10^{-6}} = 10^3 = 1000$.
Therefore,the solution with $pH \, 11$ is $1000$ times more basic than the solution with $pH \, 8$.

(C) strong acid is an acid that completely dissociates into its ions in an aqueous solution.
Among the given options,$Acetic$ $acid$ $(CH_3COOH)$,$Citric$ $acid$,and $Oxalic$ $acid$ are organic acids,which are generally weak acids.
$Nitric$ $acid$ $(HNO_3)$ is a mineral acid that dissociates completely in water,making it a strong acid.
Therefore,the correct option is $C$.

(D) $NH_{3}$ (Ammonia) is a weak base because it does not completely dissociate into ions in an aqueous solution. When it reacts with water,it accepts a proton $(H^{+})$ to form ammonium $(NH_{4}^{+})$ and hydroxide $(OH^{-})$ ions,but this reaction is reversible and does not go to completion. Therefore,it is classified as a weak base.

(C) The ionic product of water $(K_w)$ at $25^{\circ}C$ is given by the expression: $K_w = [H^+][OH^-] = 10^{-14}$.
Taking the negative logarithm on both sides:
$-\log(K_w) = -\log([H^+][OH^-]) = -\log(10^{-14})$.
$pK_w = -(\log[H^+] + \log[OH^-]) = 14$.
Since $pH = -\log[H^+]$ and $pOH = -\log[OH^-]$,we get:
$pH + pOH = 14$.

(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.

(C) $NH_{4}Cl$ is a salt formed by the reaction of a strong acid $(HCl)$ and a weak base $(NH_{4}OH)$.
When $NH_{4}Cl$ dissolves in water, it undergoes hydrolysis.
The $NH_{4}^+$ ion reacts with water to produce $H_3O^+$ ions, which makes the solution acidic.
Since the solution is acidic, the concentration of $H^+$ ions increases, resulting in a $pH$ value of less than $7$ $(pH < 7)$.

(A) The $pH$ of a solution is calculated using the formula $pH = -\log[H^+]$.
For $pH = 2$,the concentration of hydrogen ions $[H^+]$ must be $10^{-2} \, M = 0.01 \, M$.
$(A)$ $0.01 \, M \, HCl$: $HCl$ is a strong monoprotic acid,so $[H^+] = 0.01 \, M$. Thus,$pH = -\log(0.01) = 2$.
$(B)$ $0.02 \, M \, HCl$: $[H^+] = 0.02 \, M$,so $pH = -\log(0.02) \approx 1.7$.
$(C)$ $0.01 \, M \, H_2SO_4$: $H_2SO_4$ is a strong diprotic acid,so $[H^+] = 2 \times 0.01 = 0.02 \, M$. Thus,$pH = -\log(0.02) \approx 1.7$.
$(D)$ $0.02 \, M \, H_2SO_4$: $[H^+] = 2 \times 0.02 = 0.04 \, M$,so $pH = -\log(0.04) \approx 1.4$.
Therefore,the correct option is $A$.

(B) Given that the $pH$ of the solution is $8$.
We know that $pH + pOH = 14$ at $25^{\circ}C$.
Therefore,$pOH = 14 - pH = 14 - 8 = 6$.
The relationship between $pOH$ and $[OH^{-}]$ is given by $pOH = -\log[OH^{-}]$.
So,$6 = -\log[OH^{-}]$,which implies $\log[OH^{-}] = -6$.
Taking the antilog,we get $[OH^{-}] = 10^{-6} \, M$ or $1 \times 10^{-6} \, M$.

(C) The $pH$ value is inversely proportional to the concentration of hydrogen ions $[H^+]$.
As the $pH$ value decreases,the concentration of $[H^+]$ ions increases,which means the acidity of the solution increases.
Given $pH$ values are: $A = 1.9, B = 2.5, C = 2.1, D = 3.0$.
Comparing these values: $1.9 < 2.1 < 2.5 < 3.0$.
Since lower $pH$ indicates higher acidity,the order of acidity is $A > C > B > D$.
This is equivalent to $D < B < C < A$.

(B) solution is basic if its $pH > 7$.
The $pH$ is calculated using the formula $pH = -\log[H_{3}O^{+}]$.
For option $A$: $pH = -\log(10^{-5}) = 5$ (Acidic).
For option $B$: $pH = -\log(10^{-12}) = 12$ (Basic).
For option $C$: $pH = -\log(10^{-7}) = 7$ (Neutral).
For option $D$: $pH = -\log(10^{-4}) = 4$ (Acidic).
Since $12 > 7$,the solution with $[H_{3}O^{+}] = 10^{-12} \; M$ is basic.

(C) The poison of a honeybee is a complex mixture of various compounds.
One of the primary components responsible for the pain and inflammatory response is a peptide called $Melittin$.
$Melittin$ is the main constituent of bee venom, accounting for about $50\%$ of its dry weight.
It acts as a potent inflammatory agent and causes the release of histamine, leading to pain and swelling at the site of the sting.

(A) Lemon juice contains citric acid,which is a weak organic acid.
When lemon juice is dissolved in water,it releases hydrogen ions $(H^+)$,which makes the aqueous solution acidic in nature.
Therefore,the correct option is $A$.

(B) Washing soda is chemically known as sodium carbonate decahydrate $(Na_2CO_3 \cdot 10H_2O)$.
When dissolved in water, it undergoes hydrolysis.
Sodium carbonate is a salt of a strong base (sodium hydroxide, $NaOH$) and a weak acid (carbonic acid, $H_2CO_3$).
Due to the presence of a strong base, the resulting aqueous solution is basic in nature, which turns red litmus paper blue.

(D) Robert Boyle was the first scientist to define acids and bases based on their chemical properties. He observed that acids have a sour taste,change the color of litmus from blue to red,and react with metals to release hydrogen gas. Bases,on the other hand,were defined by their bitter taste,soapy feel,and ability to turn red litmus blue.

(B) The properties of acids are as follows:
$1$. Acids are sour to taste.
$2$. Acids turn blue litmus paper red,not red litmus paper blue. Turning red litmus paper blue is a property of bases.
$3$. Acids react with bases to form salt and water,which is known as a neutralization reaction.
$4$. Acids react with active metals to release $H_{2}$ gas.
Therefore,the statement 'They turn moist red litmus paper blue' is incorrect.

(A) Acids are substances that release $H^+$ ions in an aqueous solution.
According to the chemical properties of acids,they have the ability to change the color of blue litmus paper to red.
This reaction occurs because the acidic nature of the solution neutralizes the basic dye present in the litmus paper,resulting in a color change to red.
Therefore,moist blue litmus paper turns red in the presence of an acid.

(D) When an acid reacts with a base, the hydrogen ions $(H^+)$ from the acid combine with the hydroxide ions $(OH^-)$ from the base to form water $(H_2O)$.
The remaining ions form a salt.
This process is known as a neutralisation reaction.
The general equation is: $\text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water}$.

(B) When an acid reacts with a metal,it produces a metal salt and releases $H_2$ gas.
For example,the reaction between zinc and dilute hydrochloric acid is:
$Zn(s) + 2HCl(aq) \rightarrow ZnCl_2(aq) + H_2(g)$
Therefore,the gas released is dihydrogen $(H_2)$.

(C) The acid-base theory of ionization was proposed by Svante Arrhenius in $1884$.
According to the Arrhenius theory,an acid is a substance that dissociates in water to produce hydrogen ions $(H^+)$,and a base is a substance that dissociates in water to produce hydroxide ions $(OH^-)$.
Therefore,the correct option is $C$.

(C) According to the Arrhenius theory,a base is defined as a substance that dissociates in water to produce hydroxide ions $(OH^-)$ as the only negative ions.
For example,sodium hydroxide $(NaOH)$ dissociates in water as follows:
$NaOH(aq) \rightarrow Na^+(aq) + OH^-(aq)$
Therefore,the correct option is $C$.

(B) Acids produce hydrogen ions $(H^{+})$ in the presence of water. Since $H^{+}$ ions cannot exist alone,they combine with water molecules $(H_{2}O)$ to form hydronium ions $(H_{3}O^{+})$.
Therefore,the reaction is: $H^{+} + H_{2}O \rightarrow H_{3}O^{+}$.
Thus,$H_{3}O^{+}$ is known as the hydronium ion.

(B) According to the Arrhenius theory,an acid is a substance that dissociates in water to increase the concentration of hydrogen ions $(H^{+})$.
When an acid is dissolved in water,it releases $H^{+}$ ions,which immediately combine with water molecules to form hydronium ions $(H_{3}O^{+})$.
However,the fundamental definition states that acids produce $H^{+}$ ions in aqueous solution.

(A) Caustic soda is the common name for sodium hydroxide, which has the chemical formula $NaOH$.
When $NaOH$ is dissolved in water, it undergoes complete ionization to produce sodium ions $(Na^+)$ and hydroxide ions $(OH^-)$.
The dissociation reaction is represented as: $NaOH_{(s)} \xrightarrow{H_2O} Na^+_{(aq)} + OH^-_{(aq)}$.
Therefore, the ions produced are $Na^+_{(aq)}$ and $OH^-_{(aq)}$.

(B) The Bronsted-Lowry theory,proposed independently by Johannes Nicolaus Bronsted and Thomas Martin Lowry in $1923$,defines an acid as a proton $(H^+)$ donor and a base as a proton $(H^+)$ acceptor. Therefore,the fundamental basis of this theory is the transfer of protons between chemical species.