Whether you're a budding chemist or just curious about everyday substances, our free quiz on how to test if a solution is acidic or basic will sharpen your understanding of pH, titrations, and indicators. Tackle our fun acid bases quiz to reinforce core acid-base chemistry concepts, from spotting pH shifts to exploring intriguing amino acid trivia based on acidity. With practical questions about acids and bases, you'll feel ready for any acids and bases chemistry test. Ready to make pH mastery a breeze? Jump into our interactive acid or base quiz or perfect your technique in a concise acid or base test. Embrace the challenge and elevate your chem skills today!
What does it indicate when blue litmus paper turns red?
The solution is neutral
The solution is basic
The indicator is expired
The solution is acidic
Blue litmus paper turning red is a classic test for acidity because acid donates hydrogen ions which alter the dye's chemical structure, causing the color change. In basic or neutral solutions, blue litmus remains blue. This reaction is widely used in schools and laboratories for quick qualitative testing. See more at Litmus Indicator.
Which pH range indicates a basic solution?
pH = 7 only
7.0 to 8.0
0 to 6
8.0 to 14.0
A basic solution has fewer hydrogen ions than pure water, giving it a pH above 7. The pH scale runs from 0 (strongly acidic) to 14 (strongly basic), with 7 being neutral. Solutions with pH between 8 and 14 are considered basic or alkaline. More details at pH Scale Overview.
What color does phenolphthalein turn in an acidic solution?
Colorless
Pink
Green
Red
Phenolphthalein is colorless in acidic conditions because the molecular structure retains hydrogen ions, preventing the color-imparting rearrangement. It turns pink only when the pH exceeds about 8.2. This property makes it a popular indicator in acid - base titrations. Learn more at Phenolphthalein Wiki.
What color does a universal indicator show for a neutral solution?
Yellow
Green
Red
Blue
Universal indicator is a blend of several pH-sensitive dyes that together give a smooth color change over the entire pH scale. At pH 7, which is neutral, the indicator appears green. Below 7 it shifts toward red (acidic) and above 7 toward blue or violet (basic). More at Universal Indicator.
How does a pH meter determine the acidity or basicity of a solution?
By measuring electrical conductivity
By analyzing color change of the solution
By measuring voltage difference related to hydrogen ion activity
By measuring the solution's temperature
A pH meter works by measuring the electrical potential difference between a glass electrode and a reference electrode, which varies with the hydrogen ion concentration. This voltage is then converted into a pH value. It provides a precise and quantitative measurement, unlike simple indicators. Details at Glass Electrode Principle.
What is the pH of a 1 × 10?³ M HCl solution?
pH = 2
pH = 4
pH = 3
pH = 1
Hydrochloric acid (HCl) is a strong acid that dissociates completely in water, so the hydrogen ion concentration equals the acid concentration. For [H?] = 1 × 10?³ M, pH = ?log??(1 × 10?³) = 3. This straightforward calculation is fundamental to acid - base chemistry. See pH Calculation.
A solution has a pH of 2. How is it classified?
Weakly acidic
Neutral
Strongly acidic
Basic
The pH scale categorizes solutions: values below 7 are acidic, with lower numbers indicating stronger acidity. A pH of 2 falls well below 4, which is considered strongly acidic. Neutral solutions are at pH 7, and basic solutions are above 7. Read more at Acid Definitions.
What is the pH of a 1 × 10?? M HCl solution?
pH = 3
pH = 5
pH = 2
pH = 4
Since HCl is a strong acid, it fully dissociates, giving [H?] = 1 × 10?? M. The pH is calculated as ?log??(1 × 10??) = 4. This direct relationship holds for any strong acid at known concentration. More at Strong Acid pH.
What is the approximate pH of a 1 × 10?? M strong acid solution, accounting for water autoionization?
pH = 7.3
pH = 6.7
pH = 7.0
pH = 6.3
Pure water contributes [H?] of 1 × 10?? M. Adding an equal amount from the acid doubles [H?] to 2 × 10?? M, giving pH = ?log??(2 × 10??) ? 6.7. The autoionization of water cannot be ignored at low acid concentrations. See Water Autoionization.
If the pH of a solution is 11, what is its pOH?
pOH = 1
pOH = 11
pOH = 3
pOH = 7
pH and pOH are related by the equation pH + pOH = 14 at 25 °C. Therefore, if pH = 11, pOH = 14 - 11 = 3. This relationship is fundamental to aqueous acid - base chemistry. Details at pH and pOH.
Which indicator is best for a titration where the equivalence pH is 7?
Bromothymol blue
Phenolphthalein
Litmus paper
Methyl orange
Bromothymol blue changes color between pH 6.0 and 7.6, bracketing the neutral equivalence point at pH 7 in a strong acid - strong base titration. Phenolphthalein turns at higher pH and methyl orange at lower pH, making them less suitable. More at Choosing Indicators.
What color does methyl orange turn in a basic solution?
Yellow
Green
Red
Orange
Methyl orange is red in acidic media (pH < 3.1) and yellow in basic media (pH > 4.4). The clear red-to-yellow transition makes it useful for titrations with equivalence points in the acidic range. See Indicator Ranges.
In a buffer solution, what happens when a small amount of acid is added?
The pH changes very little
The solution precipitates
The pH drops dramatically
The pH increases
Buffers contain a weak acid and its conjugate base (or vice versa), which neutralize small additions of acid or base, resisting pH changes. When acid is added, the conjugate base reacts with H?, keeping the pH nearly constant. This is the defining property of buffer solutions. More at Buffer Solution.
What is the pH at the equivalence point when titrating a weak acid with a strong base?
pH < 7
pH = 7
pH > 7
Depends only on concentration
At equivalence in a weak acid - strong base titration, the conjugate base of the weak acid remains in solution, making the solution basic (pH > 7). The OH? generated from that base raises the pH above neutral. Learn more at Titration Curves.
Calculate the pH of a 0.10 M acetic acid solution (Ka = 1.8 × 10??).
pH = 2.00
pH = 3.14
pH = 2.87
pH = 3.00
For a weak acid HA: Ka = x²/(C?x). Approximating x ? C: x = ?(Ka·C) = ?(1.8×10??) ?1.34×10?³ M. Then pH = ?log??(1.34×10?³) ? 2.87. This common approximation is taught in general chemistry. See Acetic Acid Acidity.
At the half-equivalence point in a titration of acetic acid with NaOH, the pH equals:
pH = 7
pH = Ka
pH = pKa
pH = pKb
At half-equivalence, [HA] = [A?], so Henderson - Hasselbalch gives pH = pKa + log([A?]/[HA]) = pKa. This is a key feature used to determine pKa values in titration experiments. More at Henderson - Hasselbalch equation.
Which of the following solutions at 0.01 M concentration has the highest pH?
0.01 M HCl
0.01 M CH?COONa
0.01 M NH?
0.01 M NaOH
0.01 M NaOH is a strong base and dissociates completely into OH?, yielding [OH?] = 0.01 M (pOH = 2 ? pH = 12). Other options are either acids or weak electrolytes, giving lower pH values. Details at Strong Base pH.
Which test would confirm that an unknown salt solution is basic?
Universal indicator turns red
Blue litmus paper turns red
Red litmus paper turns blue
Phenolphthalein remains colorless
Basic solutions cause red litmus paper to turn blue due to the presence of hydroxide ions. Blue litmus turning red indicates acidity, and phenolphthalein would turn pink in base. Universal indicator in basic solution shifts toward green to purple. See Indicator Tests.
Which species is amphoteric and can act as both an acid and a base?
NaOH
HCO??
HCl
CH?COOH
The bicarbonate ion (HCO??) can donate a proton to become CO?²? (acting as an acid) or accept a proton to form H?CO? (acting as a base). This dual behavior defines amphoteric species. HCl and CH?COOH are purely acids, while NaOH is purely basic. More at Amphoteric Compounds.
What characterizes the titration curve of a weak acid titrated with a strong base?
A buffering region, then a sharp jump above pH 7
A gradual linear increase
A steep rise near pH 7, then levels off
An immediate jump to pH > 10
A weak acid - strong base titration curve shows an initial gradual pH increase, a buffering plateau around the pKa, and then a sudden jump at equivalence to a pH above 7 due to the basic conjugate base. After equivalence, pH rises more gradually again. Details at Weak Acid Titration.
What is the endpoint color change when using phenolphthalein in a titration?
Red to colorless
Yellow to red
Colorless to faint pink
Blue to green
Phenolphthalein is colorless in acidic and neutral solutions but turns faint pink at pH around 8.2 and above. The appearance of a persistent light pink color signifies the titration endpoint in many acid - base titrations. More at Phenolphthalein Indicator.
In pH measurement using a glass electrode, what causes the liquid junction potential?
High concentration of hydrogen ions
Difference in ionic mobility across the junction
Electrode surface oxidation
Temperature fluctuations
The liquid junction potential arises because different ions diffuse at different rates between the sample solution and reference electrolyte, creating a potential difference. This must be minimized or corrected for accurate pH measurements with glass electrodes. See Glass Electrode Theory.
A solution contains 0.10 M NH?? and 0.10 M NH?. If pKa of NH?? is 9.25, what is the pH?
pH = 9.25
pH = 9.75
pH = 8.50
pH = 7.00
Using the Henderson - Hasselbalch equation, pH = pKa + log([base]/[acid]) = 9.25 + log(0.10/0.10) = 9.25 + 0. This applies when conjugate acid and base concentrations are equal. More details at Henderson - Hasselbalch equation.
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Study Outcomes
Test Solutions for Acidity or Basicity -
Use pH indicators and colorimetric methods to determine whether a solution is acidic or basic.
Apply pH Indicators in Testing -
Select and use appropriate indicators to observe color changes and estimate pH values in various samples.
Analyze Colorimetric Results -
Interpret the observed color shifts to accurately classify solutions along the pH scale.
Interpret Amino Acid Acidity Trivia -
Explore amino acid trivia based on acidity to understand how side-chain properties influence overall pH behavior.
Participate in the Acid Bases Quiz -
Engage with scenario-based questions to reinforce core concepts and assess your skills in acid-base chemistry.
Strengthen Laboratory Confidence -
Apply learned techniques in practical contexts to boost your confidence in performing acid-base tests.
Cheat Sheet
Master the pH scale -
To effectively learn how to test if a solution is acidic or basic, start with the pH scale which ranges from 0 (strongly acidic) to 14 (strongly basic). The formula pH = - log[H❺] links hydrogen ion concentration to numeric values, so lower pH means higher [H❺]. A quick mnemonic is "pH under 7 is acid heaven, above 7 is base haven."
Use colorimetric indicators -
Litmus paper and universal indicator solutions provide simple, visual cues: litmus turns red in acid and blue in base, while universal indicators show a spectrum from red through green to purple. Specific dyes like phenolphthalein (colorless in acid, pink in base) or methyl orange (red below pH 3.1, yellow above pH 4.4) help pinpoint ranges more precisely (IUPAC standards). These tools are the core of any acid bases quiz or quick lab test.
Calibrate and read a pH meter -
pH meters offer quantitative precision by measuring voltage from a glass electrode, but accuracy depends on calibration with standard buffer solutions at pH 4.00, 7.00, and 10.00 (American Chemical Society guidance). Before testing, rinse the electrode with distilled water and gently dry to avoid cross-contamination. Consistent calibration ensures you can confidently report if a solution is acidic, neutral, or basic in research-grade assays.
Perform titrations to find equivalence points -
An acid-base titration involves gradually adding titrant (e.g., NaOH to HCl) until the equivalence point, where moles of acid equal moles of base, often marked by an indicator color change or pH jump on a graph. The titration formula MV = M₂V₂ allows calculation of unknown concentrations, reinforcing how to test if a solution is acidic or basic quantitatively. Mastering titration curves and choosing the right indicator (like phenolphthalein for strong acid - strong base) is a classic lab skill taught at universities like MIT and UCB.
Explore amino acid trivia based on acidity -
Amino acids have side chains (R-groups) with distinct pKa values: for example, aspartic acid (pKa ~3.9) and glutamic acid (pKa ~4.1) become deprotonated in neutral pH, contributing to protein charge. Use the mnemonic "All Good Aspartates" to remember Asp and Glu are acidic amino acids; histidine's imidazole ring (pKa ~6.0) can act as a buffer near physiological pH. This fun amino acid trivia based on acidity deepens your understanding of acid-base behavior in biochemistry contexts.
