Acid, Base and Salt

Which of the following statements is/are correct?

• 1. All the bases are alkali.
• 2. All alkalis dissolve in water.
• 3. Alkalis are soapy to touch, bitter in taste and corrosive in nature.

Select the correct answer using the code given below :

[amp_mcq option1=”1 only” option2=”1 and 3 only” option3=”2 and 3 only” option4=”3 only” correct=”option3″]

Statement 1 is false. Bases are substances that can accept protons or donate electron pairs. Alkalis are a specific type of base – those that are soluble in water and dissociate to produce hydroxide ions (OH⁻). Therefore, all alkalis are bases, but not all bases are alkalis (because not all bases dissolve in water). Statement 2 is true by definition: Alkalis are precisely those bases that are soluble in water. Statement 3 is true: Alkalis have characteristic properties including feeling soapy/slippery to touch, having a bitter taste, and being corrosive.

An alkali is a base that is soluble in water. Thus, the set of alkalis is a subset of the set of bases. General properties of alkalis include slipperiness, bitter taste, and corrosiveness.

Examples of bases include metal oxides (like CuO), metal hydroxides (like NaOH), and ammonia (NH₃). Examples of alkalis include soluble metal hydroxides (like NaOH, KOH, Ca(OH)₂, NH₄OH). CuO is a base but not an alkali as it is insoluble in water.

Which of the following statements about universal indicator is/are true ?

• 1. It is a mixture of several indicators.
• 2. It shows different colours at different concentrations of hydrogen ions in solution.
• 3. It helps to determine the strength of given acid and base in titration.

Select the correct answer using the code given below :

[amp_mcq option1=”1 only” option2=”1 and 2 only” option3=”2 and 3 only” option4=”1, 2 and 3″ correct=”option2″]

Statement 1: A universal indicator is indeed a mixture of several different indicators (such as thymol blue, methyl red, bromothymol blue, thymol blue) to provide colour changes over a wide range of pH values. This statement is true.
Statement 2: The colour of a universal indicator changes gradually with the concentration of hydrogen ions (or hydronium ions) in the solution, covering the full pH scale (typically from pH 0-14). Different colours correspond to different pH values, which reflect different hydrogen ion concentrations. This statement is true.
Statement 3: While a universal indicator shows the pH throughout a titration, providing insight into how the pH changes with the addition of titrant (related to strength), it does not typically help determine the *strength* in the sense of quantitative concentration determination or finding a precise endpoint for volumetric analysis in titration. Specific indicators with sharp colour changes near the equivalence point are used for accurate titration. Universal indicator gives an approximate pH, which *can* give a general idea of strength (e.g., a strong acid causes a lower pH than a weak acid at the same concentration), but it’s not its primary use in quantitative titration analysis. Therefore, this statement is less accurate or potentially misleading in the context of standard titration procedures for determining strength (concentration). Considering the options, and the definite truth of statements 1 and 2, option B (1 and 2 only) is the most likely correct answer if statement 3 is considered not entirely true or imprecise for typical quantitative strength determination in titration.

– Universal indicator is a blend of multiple indicators.
– It provides a spectrum of colours corresponding to different pH levels.
– It is useful for estimating the pH of a solution but less so for precise titration endpoints.

The pH scale is a measure of the acidity or basicity of a solution, defined by the concentration of hydrogen ions. Strong acids/bases dissociate/ionise almost completely, leading to high/low H+ concentrations (low/high pH). Weak acids/bases only partially dissociate/ionise. Universal indicator colours range typically from red (strongly acidic) through orange, yellow, green (neutral), blue, indigo to violet (strongly alkaline).

Which one of the following oxides shows both acidic and basic behaviour?

[amp_mcq option1=”Zinc oxide” option2=”Copper oxide” option3=”Magnesium oxide” option4=”Calcium oxide” correct=”option1″]

Amphoteric oxides are oxides that show both acidic and basic properties. They react with acids to form salt and water, and also react with bases to form salt and water. Zinc oxide (ZnO) is a common example of an amphoteric oxide. It reacts with an acid like HCl: ZnO + 2HCl → ZnCl₂ + H₂O, and it reacts with a base like NaOH: ZnO + 2NaOH + H₂O → Na₂[Zn(OH)₄] (sodium tetrahydroxozincate).

Amphoteric oxides can react with both acids and bases.

Copper oxide (CuO), Magnesium oxide (MgO), and Calcium oxide (CaO) are typically basic oxides formed by metals. They react with acids but generally do not react with bases. For instance, MgO + 2HCl → MgCl₂ + H₂O, but MgO does not react with NaOH. Other examples of amphoteric oxides include Al₂O₃, PbO, SnO, etc.

The equivalent weight of Ba(OH)₂ is (given, atomic weight of Ba is 137·3)

[amp_mcq option1=”85·7″ option2=”137·3″ option3=”154·3″ option4=”171·3″ correct=”option1″]

The correct answer is A) 85·7.

The equivalent weight of a base is calculated as its molar mass divided by its acidity (the number of replaceable hydroxide ions, OH⁻).
The molar mass of Ba(OH)₂ is calculated as:
Atomic weight of Ba + 2 * (Atomic weight of O + Atomic weight of H)
= 137.3 + 2 * (16.0 + 1.0)
= 137.3 + 2 * 17.0
= 137.3 + 34.0
= 171.3 g/mol
Ba(OH)₂ is a strong base with two replaceable OH⁻ ions, so its acidity is 2.
Equivalent weight = Molar mass / Acidity = 171.3 g/mol / 2 = 85.65 g/equivalent.
Rounding to one decimal place gives 85.7 g/equivalent, which matches option A.

Equivalent weight is a concept historically used in chemistry, particularly in stoichiometry and acid-base titrations. It represents the mass of a substance that reacts with or is equivalent to a certain amount of another substance (e.g., one mole of hydrogen ions). For bases, it’s the mass that reacts with one mole of H⁺ ions or provides one mole of OH⁻ ions.

Two reactants in a flask at room temperature are producing bubbles of a gas that turn limewater milky. The reactants could be

[amp_mcq option1=”zinc and hydrochloric acid” option2=”magnesium carbonate and hydrochloric acid” option3=”methane and oxygen” option4=”copper and dilute hydrochloric acid” correct=”option2″]

The reaction between magnesium carbonate and hydrochloric acid produces carbon dioxide gas, which turns limewater milky.

Carbonates and bicarbonates react with acids to produce carbon dioxide gas (CO₂), water, and a salt. CO₂ gas, when bubbled through limewater (calcium hydroxide solution), reacts to form insoluble calcium carbonate, which appears as a milky precipitate.

The reaction in option B is: MgCO₃(s) + 2HCl(aq) → MgCl₂(aq) + H₂O(l) + CO₂(g).
Option A produces hydrogen gas (Zn + 2HCl → ZnCl₂ + H₂), which does not turn limewater milky.
Option C (methane and oxygen) is combustion, which doesn’t occur simply by mixing at room temperature and requires ignition.
Option D (copper and dilute hydrochloric acid) does not react as copper is less reactive than hydrogen.

The paste of a white material in water is used to maintain a fractured bone fixed in place. The white material used is called

[amp_mcq option1=”bleaching powder” option2=”plaster of Paris” option3=”powder of zinc oxide” option4=”lime powder” correct=”option2″]

The correct option is B) plaster of Paris.

Plaster of Paris is calcium sulfate hemihydrate (CaSO₄·½H₂O). When mixed with water, it forms calcium sulfate dihydrate (gypsum, CaSO₄·2H₂O), which is a hard solid. This property makes it ideal for creating casts to immobilize fractured bones, allowing them to heal properly.

Bleaching powder is primarily used for disinfection and bleaching. Zinc oxide is used in various applications including cosmetics, paints, and as a mild antiseptic. Lime powder (calcium oxide or hydroxide) is used in construction, agriculture, and chemical industries. Only plaster of Paris has the specific property of setting into a hard mass upon mixing with water which is used for medical casts.

In the reaction between hydrogen sulphate ion and water
HSO₄⁻ + H₂O → H₃O⁺ + SO₄²⁻
the water acts as

[amp_mcq option1=”an acid” option2=”a base” option3=”a salt” option4=”an inert medium” correct=”option2″]

The correct option is B) a base.

In the given reaction, HSO₄⁻ + H₂O → H₃O⁺ + SO₄²⁻, the hydrogen sulphate ion (HSO₄⁻) donates a proton (H⁺) to water (H₂O). According to the Brønsted-Lowry acid-base theory, an acid is a proton donor and a base is a proton acceptor. Since water accepts a proton from HSO₄⁻ to form H₃O⁺, water is acting as a base in this specific reaction.

Water is an amphoteric substance, meaning it can act as both an acid and a base depending on the substance it reacts with. When reacting with a stronger acid (like HCl), water acts as a base. When reacting with a base (like NH₃), water acts as an acid. In this reaction with HSO₄⁻, which can act as either an acid or a base but is acting as an acid here (donating H⁺), water acts as a base.

Vinegar is

[amp_mcq option1=”5-8% solution of acetic acid in water” option2=”5-8% solution of carbonic acid in water” option3=”5-8% solution of ethanol in water” option4=”10-15% solution of propionic acid in water” correct=”option1″]

Vinegar is a common acidic liquid produced through the fermentation of ethanol.

Vinegar is an aqueous solution of acetic acid (CH₃COOH). The concentration of acetic acid in most commercially available vinegars ranges from 5% to 8%, although some types may have higher concentrations (up to 20%).

The fermentation process typically involves two steps: alcoholic fermentation of sugars into ethanol by yeasts, followed by oxidation of ethanol to acetic acid by acetic acid bacteria (Acetobacter). Vinegar is used in cooking, preservation, and cleaning.

Which one of the following is the correct order of pH for the given substances?

[amp_mcq option1=”Coffee < Lemon juice < Milk of magnesia < Blood" option2="Milk of magnesia < Blood < Coffee < Lemon juice" option3="Lemon juice < Blood < Milk of magnesia" option4="Lemon juice < Coffee < Blood < Milk of magnesia" correct="option4"]

The pH scale measures the acidity or basicity of a solution. A pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is basic (alkaline). The lower the pH, the more acidic the substance. The higher the pH, the more basic the substance.
Approximate pH values for the given substances:
– Lemon juice: pH is typically around 2-2.5 (highly acidic).
– Coffee: pH is typically around 4.5-5 (acidic).
– Blood: pH is slightly alkaline, maintained within a narrow range of 7.35-7.45.
– Milk of magnesia (Magnesium hydroxide, Mg(OH)₂ suspension): A base, pH is typically around 10-11 (basic).
Ordering these substances from most acidic (lowest pH) to most basic (highest pH):
Lemon juice (pH ~2) < Coffee (pH ~5) < Blood (pH ~7.4) < Milk of magnesia (pH ~10.5). Checking the options, option D follows this order.

– Lower pH values indicate higher acidity.
– Higher pH values indicate higher basicity (alkalinity).
– Pure water has a neutral pH of 7.

pH is defined as the negative logarithm of the hydrogen ion concentration ($pH = -\log_{10}[H^+]$). The pH scale is logarithmic, meaning a difference of 1 pH unit represents a tenfold difference in acidity or basicity. Body fluids like blood have specific pH ranges that must be maintained for proper physiological function.

Consider the following statements:
While diluting concentrated nitric acid solution

• the concentration of [H₃O⁺] ions/ volume increases
• water must be added slowly to concentrated acid
• acid must be added slowly to water

Which of the statements given above is/are correct?

[amp_mcq option1=”1, 2 and 3″ option2=”1 and 2 only” option3=”3 only” option4=”2 and 3 only” correct=”option3″]

Let’s evaluate each statement:
1. the concentration of [H₃O⁺] ions/ volume increases: When diluting a concentrated acid by adding water, the *volume* of the solution increases significantly. While the total amount of H₃O⁺ ions might increase slightly due to more complete ionization in a more dilute solution, the increase in volume is much larger, leading to a *decrease* in the concentration of H₃O⁺ ions per unit volume. This statement is incorrect.
2. water must be added slowly to concentrated acid: Adding water to concentrated acid is a highly exothermic process. Adding water directly to concentrated acid can generate a large amount of heat rapidly, causing the water to boil and potentially splash corrosive acid out of the container. This is a dangerous procedure. This statement is incorrect.
3. acid must be added slowly to water: The correct and safe way to dilute concentrated acid is to add the concentrated acid slowly, drop by drop, to a large volume of water while stirring constantly. This method allows the heat generated by the exothermic reaction to be absorbed by the larger volume of water, preventing dangerous temperature increases and splashing. This statement is correct.
Based on the analysis, only statement 3 is correct.

– Dilution of concentrated acid is a highly exothermic process.
– Always add acid to water, not water to acid, for safety.
– Dilution decreases the concentration of hydronium ions.

The rule “Add Acid to Water, like A&W Root Beer” is a mnemonic to remember the correct dilution procedure. Stirring is important to ensure even distribution of heat and reactants. Wearing appropriate safety gear like goggles and gloves is essential when handling concentrated acids.