The pH measures the amount of hydrogen ions in a solution. Basic solutions have low concentrations of hydrogen ions, while acidic solutions have high concentrations of hydrogen ions. The pH of solutions can be altered by adding acids and bases. Acids lower the pH while bases raise the pH. If you blindly mix an acid with water, you are unlikely to add the correct amount. If you put too much acid into a solution, you will have to use a base to raise the pH once again. To avoid wasting acids and bases, use a simple calculation to determine exactly how much acid you need.
Obtain a strong acid, such as hydrochloric acid, hydrobromic acid and nitric acid, designated HCl, HBr and HNO_3, respectively. Strong acids have an extremely high concentration of hydrogen ions. Hydrogen ions make a solution acidic, while hydroxide ions make a solution basic.
Obtain the concentration of hydrogen ions, also known as molarity, in your strong acid. If you don’t have the concentration, then you likely have the pH of the solution. If you have the pH, convert from pH to molarity by using the following equation:
Molarity = 10^-[pH]
If you have a number higher than 1, you likely made an error. However, if you have a very strong acid, its pH may be less than zero and yield a concentration more than 1. This resulting value is the molarity of the solution. Molarity is the amount of moles of acid per liter of solution. For example, if your solution has 0.5 molarity, then there is only 0.5 mol of acid per 1 L. Calculate molarity using this formula:
Molarity = moles of acid ÷ liters of solution
Find the molarity of your water sample using the same method.
Convert your target pH value into molarity using the equation in the previous step.
Calculate how much acid you need to obtain the pH level of your target value. Work this out using the following formula:
M_1V_1 + M_2V_2 = M_3(V_1 + V_2)
In this equation, “M_1” is the molarity of the acid, “V_1” is the volume of the acidic solution, “M_2” is the molarity of the water and “V_2” is the volume of the water. Converting this equation to solve for “V_1” yields the following equation:
V_1 = (M_3V_2 – M_2V_2)/(M_1 – M_3).
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About the Author
Charles Alex Miller began writing professionally in 2010. He currently writes for various websites, specializing in the sciences. He is a full-time employee in the chemicals and environmental sciences industry.
pH, commonly used for water measurements, is a measure of acidity and alkalinity, or the caustic and base present in a given solution. It is generally expressed with a numeric scale ranging from 0-14. The value 7 represents neutrality. The numbers on the scale increase with increasing alkalinity, while the numbers on the scale decrease with increasing acidity.
Each unit of change represents a tenfold change in acidity or alkalinity. The pH value is also equal to the negative logarithm of the hydrogen-ion concentration or hydrogen-ion activity.
Combination pH Sensors
The most common method of measuring pH is to use an electrochemical pH sensor. Combination pH sensors are a type of electrochemical pH sensor that feature both a measuring electrode and a reference electrode. The measuring electrode detects changes in the pH value while the reference provides a stable signal for comparison.
A high impedance device, known as a pH meter, is used to display the millivolt signal in pH units. Combination pH sensor technology can be used to build different products, including laboratory pH sensors and industrial or process pH sensors.
Differential pH SensorsCompared with a typical combination pH probe, differential pH sensors work slightly differently. While combination pH sensors have 2 electrodes, a measuring and a reference electrode, differential pH sensors have 3 electrodes. In the differential design, 2 electrodes measure pH differentially with respect to a third metal ground electrode. This design has the advantage of preventing reference fouling, making it ideal for industrial applications like wet scrubbers.
Laboratory pH Sensors
Combination pH sensors in 12mm glass and plastic bodies are commonly referred to as laboratory style sensors. These sensors work well in light duty applications such as education and research, environmental sampling, and pool monitoring. While the basic design is the same, features like the sensor fill, junctions, and cables can be changed to fit different application needs.
Process pH Sensors
Combination pH sensors can also be built in larger, sturdier bodies with process connections (like NPT threads) built in. These sensors are commonly referred to as process pH sensors, and they are well-suited for continuous monitoring of pH. Process pH sensors are typically mounted in a pipe, submerged in a tank, or used as part of an insertion assembly.
How much acid do I add to lower pH?
Aim to bring your pH down to just below the optimal range. This should be enough muriatic acid to bring your alkalinity down to normal. In general, 20 ounces of acid will lower the alkalinity in a 10,000 gallon by 10 ppm.
How much acid do I add to my pool to lower pH?
Using Muriatic Acid as a pH Reducer For an average-sized pool (think 15,000 to 20,000 gallons), you'll need about a quart of muriatic acid. If your pool is much larger or much smaller than average, you should check with your pool professional.
How much hydrochloric acid to reduce pH?
Reading pH levels If the pH readings of your pool water have reached 8.4 or higher, the amount of acid that you use should be 180ml for 10,000 liters, 540ml for 30,000 liters, 900ml for 50,000 liters, and 1.8 liters for 100,000 liters of water.
How do you calculate the pH needed to change acid?
Using the formula (equation) pH = -log10[H+] we can calculate the pH of solutions with varying H+ concentrations and plot these values on a graph. Increasing [H+] decreases pH. Higher [H+] gives a lower pH. Decreasing [H+] increases pH.