Mix Examples - Acids, Bases and Salts Questions in English

(B) The $pH$ scale is a logarithmic scale used to measure the acidity or alkalinity of a solution.
$pH = -\log[H^+]$.
As the $pH$ value decreases,the concentration of hydrogen ions $[H^+]$ increases,making the solution more acidic.
Since $2 < 4$,the solution with $pH = 2$ has a higher concentration of $H^+$ ions compared to the solution with $pH = 4$.
Therefore,a solution with $pH = 2$ is more acidic than a solution with $pH = 4$.

(C) The $pH$ scale ranges from $0$ to $14$.
Solutions with a $pH$ less than $7$ are acidic,while solutions with a $pH$ greater than $7$ are basic.
As the $pH$ value increases above $7$,the concentration of hydroxide ions $(OH^-)$ increases,making the solution more basic.
Since $12 > 9$,the solution with $pH$ $12$ has a higher concentration of $OH^-$ ions than the solution with $pH$ $9$.
Therefore,a solution with $pH$ $12$ is more basic than a solution with $pH$ $9$.

(D) Blue litmus paper turns red in an acidic solution.
According to the $pH$ scale,acidic solutions have a $pH$ value less than $7$.
Therefore,the $pH$ range for an acidic solution is between $0$ and $7$.
Option $D$ is the correct answer.

(C) The $pH$ scale ranges from $0$ to $14$.
$pH$ paper (universal indicator) changes color based on the acidity or alkalinity of a solution.
$A$ pink or red color on $pH$ paper indicates a strongly acidic solution.
Among the given options,$pH = 2$ represents a strongly acidic solution,which would turn the $pH$ paper pink.
$pH = 7$ is neutral,while $pH = 8$ and $pH = 10$ are basic.

(B) The $pH$ scale ranges from $0$ to $14$.
$A$ $pH$ value of $7$ indicates that the solution is neutral.
Universal indicator or $pH$ paper shows a green or light green colour at $pH$ $7$.
Acidic solutions (below $pH$ $7$) turn the paper towards red/orange/yellow,while basic solutions (above $pH$ $7$) turn it towards blue/purple.

(A) $pH$ paper changes color based on the acidity or alkalinity of a solution.
$pH$ paper turns blue or purple in basic (alkaline) solutions,where the $pH$ value is greater than $7$.
Among the given options,$10$ is the only value greater than $7$,indicating a basic solution.
Therefore,the correct answer is $10$.

(B) The human body is highly sensitive to changes in $pH$. Most of the physiological processes and biochemical reactions in the human body occur within a narrow $pH$ range of $7.0$ to $7.8$. If the $pH$ of the body fluids,such as blood,deviates significantly from this range,it can lead to serious health complications.

(A) The stomach secretes gastric juice,which contains hydrochloric acid $(HCl)$.
This acid creates an acidic environment with a low $pH$ (typically between $1.5$ and $3.5$).
Pepsin is a digestive enzyme that breaks down proteins into smaller peptides.
It is secreted in its inactive form,pepsinogen,and requires this low $pH$ environment to be converted into its active form,pepsin,to function effectively.

(D) Antacids are basic substances used to neutralize excess acid in the stomach.
$Mg(OH)_{2}$ (Magnesium hydroxide),$Al(OH)_{3}$ (Aluminum hydroxide),and $NaHCO_{3}$ (Sodium bicarbonate) are all mild bases that react with excess $HCl$ in the stomach to neutralize it.
$HCl$ (Hydrochloric acid) is an acid itself,which is responsible for causing acidity in the stomach.
Therefore,$HCl$ cannot be used as an antacid.

(B) The $pH$ of soil is a critical factor for plant growth and fertility.
Most plants grow best in soil that is slightly acidic to neutral.
The ideal $pH$ range for most fertile agricultural land is generally considered to be between $6.5$ and $7.3$.
If the soil is too acidic or too alkaline,essential nutrients become unavailable to the plants,hindering their growth.

(A) When soil becomes too acidic,it is not suitable for the growth of plants.
To neutralize the acidity,farmers add basic substances to the soil.
Lime (calcium oxide or calcium hydroxide) is a basic chemical commonly used for this purpose.
It reacts with the excess acid in the soil to form neutral salts and water,thereby restoring the soil pH to a level suitable for plant growth.

(A) The $pH$ scale is used to measure the acidity or alkalinity of a substance.
- $A$ $pH$ value of $7$ is considered neutral.
- $A$ $pH$ value less than $7$ indicates an acidic nature.
- $A$ $pH$ value greater than $7$ indicates a basic (alkaline) nature.
- For soil,a $pH$ range of $6.5$ to $7.3$ is generally considered neutral or optimal for most plants.
- Therefore,soil with a $pH$ value less than $6.5$ is considered acidic.

(A) Soil acidity is often caused by the accumulation of hydrogen ions or the presence of acidic fertilizers.
To neutralize acidic soil,a basic substance is added.
Lime (calcium oxide or calcium hydroxide) is a common alkaline material used in agriculture to raise the $pH$ of the soil,effectively neutralizing the acidity.
Therefore,the correct option is $A$.

(B) Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate.
Its chemical formula is $CaSO_4 \cdot 2H_2O$.
When gypsum is heated at $373 \ K$,it loses water molecules and becomes calcium sulfate hemihydrate,which is known as Plaster of Paris $(CaSO_4 \cdot \frac{1}{2}H_2O)$.

(C) Tooth decay starts when the $pH$ of the mouth falls below $5.5$.
This happens because bacteria present in the mouth produce acids by degrading sugar and food particles remaining in the mouth after eating.
These acids corrode the tooth enamel,which is made of calcium hydroxyapatite (a crystalline form of calcium phosphate),the hardest substance in the body.

(A) The $pH$ values of the given substances are as follows:
$1$. Vinegar is a dilute solution of acetic acid,which is acidic,so its $pH$ is approximately $2.5$.
$2$. Human blood is slightly basic,with a $pH$ range of approximately $7.35$ to $7.45$,so it matches $pH = 7.4$.
$3$. Washing soda $(Na_2CO_3)$ is a salt of a strong base and a weak acid,making its aqueous solution basic with a $pH$ of approximately $12$.
$4$. Pure water is neutral,so its $pH$ is $7.0$.
Therefore,the correct matching is $(1-b), (2-a), (3-d), (4-c)$.

(D) When a red ant bites,it injects an acidic liquid into the skin.
This liquid contains $Formic \ acid$ (also known as $Methanoic \ acid$,with the chemical formula $HCOOH$).
This acid causes irritation,pain,and a burning sensation at the site of the bite.
Therefore,the correct option is $D$.

(C) Melittin is the principal active component of honeybee venom ($Apis$ $mellifera$).
It is a basic polypeptide consisting of $26$ amino acid residues.
Its primary structure is $Gly-Ile-Gly-Ala-Val-Leu-Lys-Val-Leu-Thr-Thr-Gly-Leu-Pro-Ala-Leu-Ile-Ser-Trp-Ile-Lys-Arg-Lys-Arg-Gln-Gln-NH_2$.
Therefore,the correct option is $C$.

(C) $H_{2}SO_{4}$ is a strong diprotic acid that dissociates completely in an aqueous solution according to the following equation:
$H_{2}SO_{4} \rightarrow 2H^{+} + SO_{4}^{2-}$
Since $H^{+}$ ions react with water to form hydronium ions $(H_{3}O^{+})$,the reaction can be represented as:
$H_{2}SO_{4} + 2H_{2}O \rightarrow 2H_{3}O^{+} + SO_{4}^{2-}$
From the stoichiometry of the reaction,$1$ mole of $H_{2}SO_{4}$ produces $2$ moles of $H_{3}O^{+}$.
Therefore,for a $1\,M$ solution of $H_{2}SO_{4}$,the concentration of $H_{3}O^{+}$ will be $2 \times 1\,M = 2\,M$.

(A) Acids are classified as strong or weak based on the extent of their ionization in an aqueous solution.
Strong acids are those that completely dissociate into ions in water (e.g.,$HCl$,$H_2SO_4$).
Weak acids are those that only partially dissociate into ions in water (e.g.,$CH_3COOH$,$H_2CO_3$).
Therefore,the correct basis for this classification is the degree of ionization.

(A) salt solution has a $pH$ greater than $7$ if it is a salt of a weak acid and a strong base.
$CH_3COONa$ is a salt formed from a weak acid (acetic acid,$CH_3COOH$) and a strong base (sodium hydroxide,$NaOH$).
When dissolved in water,it undergoes hydrolysis to form a basic solution,resulting in a $pH > 7$.
$NH_4Cl$ and $NH_4NO_3$ are salts of a strong acid and a weak base,resulting in an acidic solution $(pH < 7)$.
$NaCl$ is a salt of a strong acid and a strong base,resulting in a neutral solution $(pH = 7)$.

(C) $NaOH$ is a strong base that dissociates completely in water as follows:
$NaOH \rightarrow Na^+ + OH^-$
Given the concentration of $NaOH$ is $1 \times 10^{-5} \; M$,the concentration of $OH^-$ ions $[OH^-]$ is $1 \times 10^{-5} \; M$.
We know that $pOH = -\log[OH^-]$.
$pOH = -\log(1 \times 10^{-5}) = 5$.
Using the relation $pH + pOH = 14$ at $25^{\circ}C$:
$pH = 14 - pOH = 14 - 5 = 9$.
Therefore,the $pH$ of the solution is $9$.

(D) $HCl$ is a strong acid that dissociates completely in water as: $HCl \rightarrow H^+ + Cl^-$.
Given the concentration of $HCl$ is $10^{-4} \; M$,the concentration of $H^+$ ions is $[H^+] = 10^{-4} \; M$.
The $pH$ of the solution is calculated as: $pH = -\log[H^+] = -\log(10^{-4}) = 4$.
Using the relationship $pH + pOH = 14$ at $25^{\circ}C$,we find $pOH = 14 - pH$.
Therefore,$pOH = 14 - 4 = 10$.

(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 $C$.

(B) salt formed by the neutralization of a weak acid and a strong base will be basic in nature.
$Na_{2}CO_{3}$ is formed by the reaction between carbonic acid $(H_{2}CO_{3})$,which is a weak acid,and sodium hydroxide $(NaOH)$,which is a strong base.
$NH_{4}Cl$ is formed from a weak base $(NH_{4}OH)$ and a strong acid $(HCl)$.
$NaCl$ is formed from a strong acid $(HCl)$ and a strong base $(NaOH)$.
$KNO_{3}$ is formed from a strong acid $(HNO_{3})$ and a strong base $(KOH)$.

(A) $NH_{4}Cl$ (Ammonium chloride) is formed by the neutralization reaction between $NH_{4}OH$ (Ammonium hydroxide) and $HCl$ (Hydrochloric acid).
$NH_{4}OH$ is a weak base,while $HCl$ is a strong acid.
Therefore,$NH_{4}Cl$ is a salt of a strong acid and a weak base.

(B) strong acid is one that completely dissociates into its ions in an aqueous solution. Examples include $HCl$,$H_2SO_4$,and $HNO_3$.
$A$ weak acid is one that only partially dissociates into its ions in an aqueous solution. Acetic acid $(CH_3COOH)$ is a classic example of a weak acid because it does not ionize completely in water.
Therefore,the correct option is $B$.