Investigating Acidity and Basicity Using a pH Probe
Dot-Point 1: conduct a practical investigation to measure the pH of a range of acids and bases
Dot-Point 6: calculate the pH of the resultant solution when solutions of acids and/or bases are diluted or mixed
Introduction
If the pH of a solution is known, the [H+][H^+] can be calculated as:
[H⁺] = 10^(-pH)The acidity or basicity of substances can be quantified using the pH scale, ranging from 0 (highly acidic) to 14 (highly basic). This investigation uses a pH probe to measure the pH of a variety of household and laboratory substances, including acids, bases, and neutral solutions. A pH probe works by detecting the electrical potential generated by hydrogen ion concentration in a solution, enabling accurate pH measurements.
Aim
To measure the pH of a range of solutions, including laboratory acids and bases, and common household substances, using a pH probe.
Materials
pH meter with probe and power adaptor
Distilled water (pH 7)
Test tubes (9) and test tube rack
Solutions:
0.1M Hydrochloric acid (HCl)
0.1M Sodium hydroxide (NaOH)
0.1M Ammonia solution
Soft drink
Red wine
Orange juice
Aspirin (dissolved in water)
Soapy water
Oven cleaner
Distilled water for rinsing the probe
25 mL measuring cylinder
Labels and marker
Procedure
Setup the pH Meter
Connect the pH probe to the pH meter and attach the power adaptor to a power supply.
Turn on the pH meter and verify its calibration.
Calibrate the Probe
Rinse the pH probe with distilled water.
Calibrate the probe using buffer solutions of known pH values (e.g., pH 4.0, 7.0, 10.0).
Prepare the Solutions
Measure 25 mL of each substance (HCl, NaOH, ammonia, soft drink, red wine, orange juice, aspirin solution, soapy water, oven cleaner) into separate labelled test tubes.
Measure pH of Solutions
Submerge the cleaned pH probe into Test Tube 1 (0.1M HCl).
Record the pH displayed on the meter.
Rinse the probe thoroughly with distilled water.
Repeat Measurements
Repeat the above steps for the other test tubes, rinsing the probe between each measurement to avoid cross-contamination.
Results
The following table shows the expected pH ranges for each substance tested.
Analysis
Acidic Solutions: Substances like HCl, soft drink, orange juice, and aspirin showed low pH values, indicating high concentrations of H₃O⁺ ions.
Neutral Solution: Distilled water maintained a pH of ~7, serving as a reference point.
Basic Solutions: NaOH, ammonia, and oven cleaner displayed high pH values, reflecting high concentrations of OH⁻ ions.
Household Acids and Bases: pH values varied significantly across common substances, showing practical applications of acid-base chemistry in everyday life.
Conclusion
This investigation effectively demonstrated how a pH probe can measure the pH of a wide variety of substances, from laboratory acids and bases to household items. Results aligned with theoretical expectations based on the chemical composition of the solutions. This technique highlights the importance of pH in fields ranging from household maintenance (e.g., oven cleaners) to food and beverages (e.g., soft drinks and wine).
