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Quizzes > Science > Chemistry

Test Your Chemistry Skills: Acid-Base Indicators Quiz

Think you can ace the acid or base test? Take the pH indicator quiz now!

Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
paper art acid base indicator quiz with test tubes pH scale color gradient on sky blue background

Are you ready to take on the ultimate acid or base test? Our interactive acid base indicator quiz helps students master pH indicators and color change patterns. Apply real-world scenarios to identify acids, bases, and neutral solutions using pH indicator test essentials. Tackle challenging chemistry acid base questions, fine-tune your skills, and track your progress step by step. Whether prepping for exams or lab work, this acid base indicator test adapts to your level. Explore an engaging acids and bases quiz and discover how to test if a solution is acidic or basic with confidence. Don't wait - jump into the acid or base test now and elevate your chemistry game!

Which of the following defines an Arrhenius acid?
A substance that produces hydroxide ions in water.
A substance that donates an electron pair.
A substance that accepts a proton from another substance.
A substance that increases the H+ concentration in aqueous solution.
An Arrhenius acid is defined as a substance that increases the concentration of H+ ions when dissolved in water. This definition applies specifically to aqueous solutions and is one of the classical definitions of acids. Arrhenius acids ionize to release protons, lowering the pH. Learn more on LibreTexts.
Which of the following describes an Arrhenius base?
A substance that donates protons to water.
A substance that increases hydrogen ion concentration.
A substance that accepts an electron pair.
A substance that increases hydroxide ion concentration in water.
An Arrhenius base is one that releases hydroxide ions (OH - ) when dissolved in water, increasing the OH - concentration. This distinguishes it from Bronsted-Lowry and Lewis definitions, which are broader. The presence of free hydroxide ions raises the pH. Read more on Arrhenius bases at LibreTexts.
What is the role of a pH indicator in acid-base chemistry?
To measure temperature changes.
To neutralize acids in a solution.
To adjust the pH to neutral.
To change color at a specific pH range, indicating acidity or basicity.
A pH indicator is a chemical that exhibits a distinct color change at a certain pH range, allowing visual determination of whether a solution is acidic or basic. Indicators contain weak acids or bases whose protonated and deprotonated forms differ in color. The transition range is characteristic of each indicator. See details on Chemguide.
What color does a universal indicator typically display at neutral pH?
Blue
Green
Yellow
Red
A universal indicator is a mixture of dyes that changes color over a wide pH range; at pH 7 (neutral), it appears green. This balanced transition reflects neither acidity nor basicity. The individual dyes in the mixture combine to yield that green color exactly at neutral pH. More on universal indicators at Wikipedia.
What color does litmus paper turn in an acidic solution?
Green
Blue
Yellow
Red
Litmus paper is a common indicator that turns red under acidic conditions (pH less than about 4.5). In basic solutions, it turns blue. Its simple color change makes it widely used for quick acidity tests. Read more about litmus on Britannica.
What color does litmus paper turn in a basic (alkaline) solution?
Blue
Orange
Red
Purple
Litmus paper turns blue in basic solutions (pH above about 8.3). This color change is the reverse of what is observed in acidic environments. The simplicity of red/blue makes litmus a convenient acid-base test. Learn about litmus at Chemicool.
What is the typical pH range of the pH scale used for aqueous solutions?
0 - 7
7 - 14
0 - 14
1 - 13
The pH scale for most aqueous solutions is defined from 0 to 14, representing the negative logarithm of hydrogen ion concentration. Values below 7 indicate acidity, values above 7 indicate basicity, and 7 is neutral. Although extreme solutions may fall slightly outside, 0 - 14 is the standard range. More on pH at Wikipedia.
Bromothymol blue changes from yellow to blue over which pH range?
pH 3.1 - 4.4
pH 6.0 - 7.6
pH 1.2 - 2.8
pH 8.2 - 10.0
Bromothymol blue is yellow in acidic conditions and turns blue in basic conditions, with its transition range around pH 6.0 - 7.6. Within this range, the ratio of protonated to deprotonated forms changes, altering its color. It is commonly used for titrations near neutrality. Reference on Chemguide.
Phenolphthalein is colorless below about pH 8.2 and turns what color above pH 10?
Colorless
Pink
Yellow
Orange
Phenolphthalein remains colorless in acidic to slightly basic solutions and turns pink to fuchsia in strongly basic solutions above pH 8.2 - 10.0. This sharp color change makes it ideal for titrations with endpoints in that range. Learn more on Chemguide.
Methyl orange changes from red to yellow over which pH range?
pH 6.0 - 7.6
pH 3.1 - 4.4
pH 1.0 - 2.5
pH 8.2 - 10.0
Methyl orange transitions from red in acidic solutions to yellow in neutral to basic ones over the pH range 3.1 - 4.4. It is commonly used for strong acid versus weak base titrations due to its low transition range. Details on Chemguide.
Which ion concentration increases when a base dissolves in water?
Na+
H?
Cl?
OH?
A base increases the concentration of hydroxide ions (OH?) when it dissolves in water, which raises the solution's pH. This is the hallmark of Arrhenius bases. Hydrogen ions (H+) decrease as OH? neutralizes them. See Khan Academy on bases.
Which of these is a strong acid?
Hydrochloric acid (HCl)
Carbonic acid (H?CO?)
Acetic acid (CH?COOH)
Hydrocyanic acid (HCN)
Hydrochloric acid (HCl) is classified as a strong acid because it dissociates completely in aqueous solution, releasing all its protons. Weak acids like acetic acid only partially dissociate. The strength is determined by the equilibrium constant for dissociation. More at Wikipedia.
Which of these is a weak base?
Ammonia (NH?)
Calcium hydroxide (Ca(OH)?)
Sodium hydroxide (NaOH)
Potassium hydroxide (KOH)
Ammonia (NH?) is a weak base because it does not fully protonate in water, establishing an equilibrium between NH? and NH??. Strong bases like NaOH and KOH dissociate completely to produce OH? ions. The strength relates to the base dissociation constant, Kb. Read on LibreTexts.
What is the pH of a 0.01 M HCl solution?
1
7
2
12
Hydrochloric acid (HCl) is a strong acid, so 0.01 M HCl fully dissociates to produce 0.01 M H?. The pH is given by -log[H?] = -log(0.01) = 2. Calculation details at Khan Academy.
Which indicator is most suitable for a titration between a strong acid and a strong base?
Alizarin yellow R
Phenolphthalein
Methyl orange
Congo red
In titrations of strong acid with strong base, the equivalence point is around pH 7. Phenolphthalein transitions from colorless to pink around pH 8.2 - 10, giving a sharp end point just above neutral. It is widely used because the color change is clear. See selector guide on Chemguide.
Which indicator is best for titrating a weak base with a strong acid?
Bromothymol blue
Thymolphthalein
Methyl orange
Phenolphthalein
When titrating a weak base with a strong acid, the equivalence point is below pH 7. Methyl orange, with its transition range of pH 3.1 - 4.4, provides a clear color change near that acidic endpoint. Phenolphthalein, which changes at higher pH, would not detect that end point effectively. Details on Chemguide.
At the half-equivalence point in the titration of a weak acid with a strong base, the pH equals:
pKa of the acid
pKb of the base
7
pKw - pKa
At the half-equivalence point, half of the weak acid has been converted to its conjugate base, making [A?] = [HA]. The Henderson-Hasselbalch equation simplifies to pH = pKa. This principle is widely used to find pKa values experimentally. Henderson-Hasselbalch on Khan Academy.
During titration of acetic acid with NaOH, what is the pH at the equivalence point?
Cannot be determined
Less than 7
Greater than 7
Equal to 7
At the equivalence point of a weak acid (like acetic acid) titrated with a strong base, the conjugate base (acetate) hydrolyzes to produce OH - , making the solution basic. Therefore, the pH is greater than 7. Details at LibreTexts.
What is the approximate pKa of phenolphthalein, given its color change occurs around pH 9.7?
9.7
5.0
7.4
4.0
The pKa of an indicator approximates the midpoint of its transition range. Phenolphthalein changes color around pH 8.2 - 10.0, giving a midpoint of about 9.7. This pKa corresponds to when half of the indicator is protonated. Chemguide reference.
Which indicator would you choose for the first equivalence point in the titration of carbonic acid (pKa1 ? 6.35)?
Cresol red
Thymol blue (second range)
Phenolphthalein
Bromothymol blue
The first equivalence point of carbonic acid occurs around pH 6.35. Bromothymol blue, with a transition range of pH 6.0 - 7.6, brackets this point well, giving a clear color change. Other indicators change outside this range. See polyprotic titrations on Chemguide.
Why does a universal indicator consist of a mixture of several indicators?
To provide a smooth color change over a wide pH range.
To lower the cost of the indicator solution.
To reduce temperature dependence.
To increase sensitivity at a single pH.
A universal indicator is composed of multiple individual indicators, each with different pKa values, to cover a broad pH range from 1 to 14. This mixture yields a continuous gradient of colors rather than a single sharp change. It allows approximate pH determination across the entire scale. More on universal indicators.
What molecular change causes the color transition in phenolphthalein under basic conditions?
Liquid crystal formation changes structure.
Oxidation of the aromatic ring occurs.
Deprotonation alters conjugation, shifting absorbance.
Micelle formation in solution.
In basic conditions, phenolphthalein loses protons, which changes the extent of conjugation in its molecular structure. This altered conjugation shifts the wavelength of light absorbed, producing a pink color. Protonation state directly affects the chromophore. Mechanism on LibreTexts.
Using the Henderson-Hasselbalch equation, what is the pH of a buffer with 0.10 M acetic acid (pKa = 4.76) and 0.10 M acetate?
4.76
5.76
7.00
3.76
When [HA] = [A?], the Henderson-Hasselbalch equation (pH = pKa + log[A?]/[HA]) simplifies to pH = pKa. Here the concentrations are equal, so pH = 4.76. This is a fundamental buffer property. See KHAN Academy.
What is the name of the technique that measures absorbance changes of an indicator to determine a titration endpoint?
Conductometric titration
Spectrophotometric titration
Potentiometric titration
Gravimetric titration
Spectrophotometric titration involves monitoring the absorbance of an indicator or analyte as titration proceeds. The endpoint is identified by a sudden change in absorbance at a specific wavelength. It is useful when visual observation is difficult. More at Wikipedia.
Which electronic transition is primarily responsible for the visible color change in most pH indicators?
? ? ?* transition in conjugated systems
d ? d transition in transition metals
n ? ?* transition in alkanes
? ? ?* transition in saturated bonds
Most organic pH indicators rely on ? ? ?* transitions within conjugated systems. Protonation or deprotonation alters the conjugation length, shifting the absorbance wavelength into or out of the visible region. This shift causes the observed color change. Explanation on LibreTexts.
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Study Outcomes

  1. Interpret pH Indicator Color Shifts -

    Learn how common acid - base indicators change color across different pH values to recognize acids and bases at a glance.

  2. Differentiate Acids and Bases -

    Accurately classify substances as acids or bases by observing the color transitions of indicators in various solutions.

  3. Apply Acid or Base Test Techniques -

    Perform pH indicator tests by selecting the proper indicator and carrying out step-by-step procedures in simulated lab scenarios.

  4. Analyze Real Lab Scenarios -

    Evaluate acid - base reactions and predict indicator outcomes based on solution composition and pH level.

  5. Optimize Indicator Selection -

    Choose the most suitable pH indicator for a given acid or base test by understanding each indicator's transition range.

  6. Reinforce Acid - Base Concepts -

    Solidify your grasp of pH theory, indicator chemistry, and acid - base equilibrium through targeted quiz questions.

Cheat Sheet

  1. pH Scale Fundamentals -

    The pH scale measures hydrogen ion concentration, defined as pH = - log10[H+], with values below 7 indicating acids and above 7 indicating bases (source: IUPAC). Remember "pH > 7 means basic" by thinking "big number, basic." Mastering this concept is key for any acid or base test.

  2. Indicator Color-Change Ranges -

    Different indicators switch colors at specific pH ranges; for example, phenolphthalein changes from colorless to pink between pH 8.2 and 10.0, while methyl orange shifts from red to yellow between pH 3.1 and 4.4 (source: NIST). A handy mnemonic is "PO = Pink in Over-7." Knowing these ranges is essential for the acid base indicator quiz.

  3. Strong Acid-Base Titration Curves -

    In a titration of HCl with NaOH, the equivalence point occurs at pH 7, producing a sharp inflection on the titration curve (source: University Chemistry texts). Phenolphthalein is ideal here, since it turns pink just past pH 7. Mastering this helps you ace both lab scenarios and the acid or base test.

  4. Weak Acid/Base Equilibrium Calculations -

    For a weak acid like acetic acid (Ka ≈ 1.8×10❻❵), use an ICE table to find [H+] ≈ √(Ka·C₀). Similarly, for a weak base, apply Kb and solve for [OH - ] (source: ACS journal fundamentals). Being confident with these calculations will boost your score on the pH indicator test.

  5. Buffer Solutions & Henderson-Hasselbalch -

    A buffer of acetic acid and acetate maintains pH via pH = pKa + log([A - ]/[HA]), where pKa for acetic acid is 4.76 (source: CRC Handbook). Remember "pH is the pKa plus the ratio tale." Understanding buffers is crucial when tackling advanced chemistry acid base questions.

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