Muskan Shafi Education Content Expert
Education Content Expert
Strong and Weak Acids are the two major types of Acids based on ion dissociation in water. Acids are chemical compounds that donate a hydrogen ion (H+) to other substances.
- Strong Acids are acids that dissociate completely into their constituent ions when dissolved in water.
- Weak Acids are acids that do not dissociate their constituent ions completely in water.
- Stronger acids can produce higher concentrations of hydrogen ions and can be fully ionized in an acidic suspension.
- The concentration of hydrogen ions is less in weak acids.
- pH is a quantitative measurement of the alkalinity or acidity present in a solution.
- pH value of strong acids is lower than that of weak acids.
Given below is an experiment for Comparing the pH of Solutions of Strong and Weak Acids of the Same Concentration.
Read More: Importance of pH in Everyday Life
Key Terms: Strong Acid, Weak Acid, pH, Solutions, Hydrogen Ions, Dissociation, Acids, pH Indicator, pH Paper, Universal Indicator
What are Strong and Weak Acids?
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Acids are chemical substances that donate positive hydrogen ions (H+) to another compound which is usually a base. On the basis of Ion Dissociation, Acids can be classified into two major types namely:
- Strong Acids
- Weak Acids
Strong Acids
- Strong Acids are defined as those acids that dissociate their H+ ions completely in water.
- They dissociate into their hydrogen ions and anions when combined with water.
- In chemistry, there are only seven strong acids.
- Examples of Strong Acids are Hydrochloric Acid, Chloric Acid, Sulfuric Acid, etc.
Strong and Weak Acids
Weak Acids
- Weak Acids are defined as those acids that dissociate into their ions partially in the water.
- They have a pH range of 2 to 7.
- Weak acids have a higher pH than strong acids at the same concentration.
- Examples of Weak Acids are Formic Acid, Acetic Acid, Benzoic Acid, Hydrofluoric Acid, etc.
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How to Compare the pH of Solutions of Strong and Weak Acids of the Same Concentration?
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Stronger Acids are the acids that produce or donate higher concentrations of hydrogen ions. They dissociate completely into their constituent ions in water or an aqueous solution. On the other hand, weak acids produce a less concentration of hydrogen ions and dissociate partially. At the same concentration, Weak Acids have a higher pH than Strong Acids.
Here is an experiment that aims at Comparing The pH of Solutions of Strong and Weak Acids of The Same Concentration.
Aim
Comparing the pH of Solutions of Strong and Weak Acids of the Same Concentration
- Strong Acid: Hydrochloric Acid (HCl)
- Weak Acid: Acetic Acid (CH3COOH)
Materials Required
- 0.1 M HCl
- 0.01 M HCl
- 0.1 M CH3COOH
- 0.01 M CH3COOH
- Test Tubes
- Glass Rod
- Universal Indicator Solution
Procedure for Determining pH Using pH Paper
The procedure for determining the pH using pH paper is as follows:
- First, with the help of the glass rod, take 2-3 drops of solutions of the given concentration on pH paper.
- Check the change in color of the pH paper.
- Now, match the color of the pH paper with the standard pH indicator chart.
- Note down the pH of the samples accordingly.
Procedure for Determining pH Using Universal Indicator
The procedure for determining the pH using Universal Indicator is as follows:
- First, take out dry 5 test tubes and fill them with 5 mL of each solution of various concentrations.
- Now, using a dropper, drop 2-3 drops of universal indicator in each test tube.
- Keep a note of the change in the color of the test tubes.
- Next, compare the color of the solution with a standard pH indicator chart.
- Lastly, note down the pH of the samples.
Read More: pH Formula
Precautions
One must make sure to follow the given precautions during the experiment:
- Handle the test tubes very carefully.
- Do not add too much of indicators.
- pH paper should be clean.
- Make sure that the color of the solution in the test tube and the pH paper color exactly match the standard pH indicator chart.
Observation
Note down the observations made in a tabular format:
| Sample | Color on pH Paper | Color in Solution | Approximate pH Value | pH = – log[H3O+] |
|---|---|---|---|---|
| 0.1M HCl | - | - | - | - |
| 0.01M HCl | - | - | - | - |
| 0.001M HCl | - | - | - | - |
| 0.0001M HCl | - | - | - | - |
| 0.00001M HCl | - | - | - | - |
Viva Voice
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Given below are some important viva questions related to the experiment on Comparing the PH of Solutions of Strong and Weak Acids of the Same Concentration.
Ques. What is a Universal Indicator?
Ans. Universal Indicator is a kind of pH indicator solution designed to identify the pH of a solution over a wide range of values.
Ques. What is pH?
Ans. pH is a scale that helps to determine whether a given solution is alkaline or acidic in nature. It is dependent on the concentration of hydrogen or hydronium ions.
Ques. Explain the effect of dilution on pH.
Ans. On dilution, the pH of the acidic solution increases while the pH of the basic solution decreases.
Ques. Give the pH Range for Acidic and Basic Solutions.
Ans. pH values range from 0 to 14 as follows:
- pH < 7: Acidic Solution
- pH> 7: Basic Solution
- pH = 7: Neutral Solution
Ques. Define pH Indicator Chart.
Ans. pH Indicator Chart is a universal chart that displays the resultant color with the corresponding pH value.
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Things to Remember
- Acids are chemical substances that produce positive hydrogen ions (H+) in water.
- Acids are divided into Strong Acids and Weak Acids on the basis of ion dissociation in water.
- Strong acids are acids that dissociate completely into their ions in the water.
- Weak acids are acids that dissociate partially into their ions in water.
- pH scale is used to measure the acidity or alkalinity of a solution.
- Weak acids tend to have a higher pH than strong acids at the same concentration of the solution.
Previous Years’ Questions
- pH-scale was proposed by…
- The pH range for phenolphthalein is…
- The pH value of an acid is 5 and its concentration is 1 M… (Manipal 2004)
- The pH value of human blood is about… (AIIMS 1996)
- The pH value of 1×10−4 M NaOH solution is… (AFMC 2009)
- If pH of a solution decreases from 5 to 2, then it is…
- B2H6 reacts with (CH3)3N to produce… (UPSEE 2019)
- The pH value of 0.001 M aqueous solution of NaCl is…
- The pH of a solution prepared by mixing 2.0 mL of HCl solution…
- The pH of rainwater is approximately… (JEE Main 2019)
Sample Questions
Ques. State a few examples of Strong and Weak Acids. (3 Marks)
Ans. Strong acids are defined as acids that dissociate completely into their constituent ions such as
- Chloric Acid (HClO3)
- Hydrobromic Acid (HBr)
- Hydrochloric Acid (HCl)
- Hydroiodic Acid (HI)
- Nitric Acid (HNO3)
- Perchloric Acid (HCLO4)
- Sulfuric Acid (H2SO4)
Weak acids are defined as acids that do not dissociate completely into the constituent ions such as
- Formic Acid (HCOOH)
- Benzoic Acid (C6H5COOH)
- Sulfurous Acid (H2SO3)
- Nitrous Acid (HNO2)
- Acetic Acid (CH3COOH)
- Phosphoric Acid (H3PO4)
- Oxalic Acid (C2H2O4)
- Hydrofluoric Acid (HF)
Ques. What is the difference between strong and weak acid solutions with the same pH? (2 Marks)
Ans. On comparing the pH of strong and weak acid solutions of equal concentration, it can be said that stronger acids can produce higher concentrations of hydrogen ions and can be fully ionized in an aqueous solution while the concentration of hydrogen ions in weak acids is lower. However, weak acids have a higher pH than strong acids at the same concentration in the solution.
Ques. Can weak and strong acids have the same pH? (2 Marks)
Ans. Yes, weak and strong acids can have the same pH. However, the weak acid would need to be concentrated more. The pH of a solution is determined by the concentration of hydrogen ions in the solution. A strong acid's contribution of hydrogen ions is proportionate to its concentration.
Ques. State some properties of Strong and Weak Acids. (3 Marks)
Ans. The properties of strong and weak acids are as follows:
Properties of Strong Acids
- They dissociate into their hydrogen ions and anions on dissolving with water.
- It means all its molecules break in a solution.
- They need not have high corrosive power.
Properties of Weak Acids
- They have a greater pH than strong acids at the same level of concentration.
- They have less values for Ka in comparison to strong acids.
- Their pH range is from 2 to 7.
Ques. What is the difference between a strong acid and concentrated acid? (2 Marks)
Ans. In an aqueous solution, a strong acid completely dissociates to generate H3O+ ions, whereas a weak acid only partially does so. A concentrated acid, on the other hand, is one in which the concentration of H3O+ ions in an aqueous solution is extremely high.
Ques. What is the difference between Acid Strength and pH? (2 Marks)
Ans. The pH of a solution is less than 7, indicating that it is acidic. When the pH of a solution exceeds 7, it is classified as basic. The strength of the acid or base in a solution determines the pH of the solution. The relative strengths of acids and bases can thus be determined by measuring the pH of dilute solutions.
Ques. What is the pH of a weak acid? (2 Marks)
Ans. pH of a weak acid should be less than 7 (not neutral), and it's usually lower than a strong acid's. There are some exceptions to this rule. For example, the pH of a 1 mM solution of hydrochloric acid is 3.01, but the pH of a 1 mM solution of hydrofluoric acid is equally low, at 3.27.
Ques. Does higher pH mean strong acid? (2 Marks)
Ans. The concentration of hydrogen ions in a solution is measured by pH. Strong acids, such as hydrochloric acid, have a pH of 0 to 1 at the doses used in laboratories. The lower the pH, the higher the concentration of hydrogen ions in the solution. Thus, a higher pH does not indicate a strong acid as weak acids tend to have a higher pH than strong acids at the same concentration.
Ques. Why do Weak Bases have lower pH? (2 Marks)
Ans: Weak acids and bases have a higher H+ saturation than stronger acids because they are less fully neutralized and hence have more hydrogen ions in the solution. When you use a larger H+ concentration in the formula, you get a low pH level.
Ques. How is pH related to the Strength of an Acid? (1 Mark)
Ans. pH value is inversely proportionate to the acid's strength. The ionization and pH reduction of acid are related to its strength. The acidity increases as the pH decreases.
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