pH experiments
15/07/2025
The pH set enables relating to the chemistry world – Acids and Bases, Acid rain, Action of a buffer solution and more.
BLT-202 USB/Bluetooth communication module
NUL-206 pH logger sensor
The lesson plan Common Acids and Bases experiment, presents us with the pH scale and how to determine the pH values of household substances.
The lesson plan Acid rain experiment, describes the acid rain phenomenon by producing carbon dioxide and dissolving it in water.
The lesson plan Action of a Buffer Solution experiment, describes buffer solutions which are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. Many life forms thrive only in a relatively narrow pH range. An example of a buffer solution is blood.
The pH lesson plans can be found in Chemistry experiments page in this site.
Acids and Bases
Acids and bases are chemical opposites that neutralize each other. Acids are substances that increase the concentration of hydrogen ions (H+) in solution, while bases increase the concentration of hydroxide ions (OH-).
Acids are substances that donate protons (H+) or increase the concentration of hydrogen ions (H+) in water.
Examples of acids are: hydrochloric acid (HCl), sulfuric acid (H2SO4), citric acid in fruits (C₆H₈O₇), and acetic acid in vinegar ( C2H4O2).
Bases are substances that accept protons (H+) or increase the concentration of hydroxide ions (OH-) in water.
Examples of bases are: sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia (NH3), and many metal oxides.
When acids and bases react, they neutralize each other, forming a salt and water.
Indicators are substances that change color depending on the pH of the solution, helping to identify acids and bases.
The pH scale is logarithmic and it shows the hydrogen ion [H+] concentration in a solution, so acidity can be expressed using this scale that goes from 0 to 14. Neutral solutions have a pH 7, acidic solutions pH is less than 7 and basic solutions pH is more than 7.
Many common household solutions contain acids and bases which play an essential role in our everyday lives.
In Common Acids and Bases experiment you will study the acidity and basicity of daily common solutions using a pH sensor. You will determine the pH values of household substances such as lemon juice, vinegar, soda, black coffee, tap water, milk, soapy solution, baking soda.
Acid rain
Acid rain is a phenomenon associated with the development of urban and industrial areas. It is created by the incorporation of chemical compounds such as carbon dioxide, sulfur dioxide and nitrogen oxides to rain water. These compounds are emitted by car's exhausts, factories and thermoelectric centrals.
When these oxides are in contact with humidity in the atmosphere, they are transformed into secondary polluting agents which form solutions of Carbon, Sulfuric and Nitric acid. Rain carries these compounds to the Earth’s surface, deposits them on the soil and in water bodies.
The persistent fall of acid rain damages lakes, rivers and underground waters, causing the death of fish and other organisms in aqueous ecosystems. It acidifies and demineralizes soils, damages forests, national parks and reserves and causes low producing crops. Also, the acidity of the water deteriorates archeological zones, historical monuments, buildings and metallic structures. The dimension of the damage depends on the degree of acidity.
In Acid rain experiment, we produce CO2, one of the gases responsible for acid rain by using vinegar and baking soda. Baking soda is sodium bicarbonate (NaHCO3) and the key ingredient of vinegar is acetic acid (CH3COOH).
CH3COOH(aq) + NaHCO3(s) ð CO2(g) + H2O(l) + CH3COONa(aq)
Carbon dioxide (CO2) reacts reversibly with water (H2O) and produces carbonic acid (H2CO3), a weak acid which dissociated into hydronium (H3O+) and bicarbonate (HCO3-) ions. This reaction occurs when acid rain forms:
2H2O(l) + CO2(g) ó H2CO3(aq) + H2O(l) ó H3O+(aq) + HCO3–
You will quantify the variation in the pH induced in the water after the carbon dioxide is dissolved in it.
In chemical equations, (s), (l), (g), and (aq) denote the physical state of a substance: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous (dissolved in water). These symbols are placed in parentheses after the chemical formula of a substance to indicate its state.
In chemistry, a buffer is a system, usually an aqueous (water) solution, which resists having its pH changed when an acid or a base is added to it.
Buffer Solutions
Buffer solutions are used as means of keeping pH at a nearly constant value in a wide variety of chemical applications. Many life forms thrive only in a relatively small pH range. An example of a buffer solution is blood.
There are two common kinds of buffer solutions: those that contain a weak acid plus one of its salts (e.g., acetic acid plus sodium acetate) and solutions that contain a weak base plus one of its salts (e.g., ammonia plus ammonium chloride).
There is equilibrium in a solution between a weak acid, HA, and its conjugate base, A- :
HA + H2O H3O+ + A−
- When hydrogen ions (H+) are added to the solution, the equilibrium moves to the left, as there are hydrogen ions (H+ or H3O+) on the right-hand side of the equilibrium expression.
- When hydroxide ions (OH-) are added to the solution, the equilibrium moves to the right, as hydrogen ions are removed in the reaction (H+ + OH- → H2O).
Thus, in both cases, some of the added reagent is consumed in shifting the equilibrium in accordance with Le Chatelier's principle and the pH changes by less than it would if the solution was not buffered.
Through Action of a Buffer Solution activity, we shall discover the main characteristics of such mixtures. The first part of the experiment will allow us to study how water reacts to the addition of an acid or a base.
In the second part, the experiment will be repeated using this time an aqueous solution with a buffer (Alka Seltzer).
Alka-Seltzer is a combination of citric acid (weak acid) and sodium bicarbonate (salt) used for the relief of heartburn, acid indigestion, and stomach aches.