Experiments on Properties of Acids
Properties of acids and bases are studied with the help of their reactions with
Litmus solution
Zinc and
Solid sodium carbonate.
Materials Required For All Experiments
Test tubes,
Dropper
Test tube stand and holder
Matchbox
Burner
Flat bottom flask
Beaker
Litmus paper/ solution (red & blue)
Thistle funnel
Glass rods
Zinc granules
Freshly made lime water
Dilute HCl
Dilute NaOH
Solid sodium carbonate
Let us know more about experiments.
Acids
Acids are compounds which when dissolved in the water yield hydronium ions as the only positively charged ions.
Strength of acid is decided by the basicity of the acid (basicity is the number of hydrogen ions present in the solution when acid is dissolved in water).
Eg. Nitric acid gives hydrogen ions and nitric ions and hydrogen ions react with water ions which gives hydronium ions.
An Experiment Of Litmus Test
Take two test tubes and label them as A and B
Take 10 ml of blue litmus in test tube A and 10 ml of red litmus solution in test tube B
Take the dropper filled with nitric acid and add a few drops of it in the test tube A and test tube B
Leave the solution for a few minutes
It is observed that the blue color of litmus in test tube A changes its color to red and it is observed that the red color of litmus solution in test tube B remains the same.
We conclude that acid turns the color of the litmus solution from blue to red
Experiment with Zinc
Take a dry and clean test tube
Place zinc granules in it
Fill it with liquid HCl submerging zinc granules and tilt it a little bit and fix it with properly in the cork
And place the bunsen burner and lit it
Close the mouth of the test tube with cork so that no vapor can escape
Leave the solution for 2-3 minutes it burns with a robust sound releasing a colorless and odorless gas
And if a burning match stick is brought near the mouth of the test tube it gives a pale blue flame with a pop sound.
The reaction of the given experiment:
Zn + 2HCl → ZnCl2+H2
Experiment With Solid Sodium Carbonate
Take one gram of solid sodium carbonate with some distilled water in a flat bottomed flask
Take a dry double bore fork and with thistle funnel which has a delivery tube fitted with it
Close the mouth of the flat flask with the dry double bore fork
Add 2 ml of hydrochloric gas
Colorless and odorless gas is liberated which is passed through lime water through the delivery tube
And it turns lime water milky
Na2CO3 + 2HCl →2NaCl+H20(l)+CO2(g)
Experiments on properties of Bases
Bases
Bases are the compounds which react with the acid to give salt and water (neutralization).
Alkalis are bases which can be dissolved in water and yield hydroxyl ions as the only negatively charged ions. eg calcium hydroxide gives calcium ion (positively charged) and hydroxyl ion (negatively charged) thus when alkalis dissolved in water gives hydroxyl ion
The strength of the base is given by the acidity of bases.
Note: all alkalis are bases but not all bases are alkalis
When sodium hydroxide reacts with hydrochloric acid it gives sodium chloride (salt) and water
An Experiment Of Litmus Test
Take two test tubes and label them as A and B
Fill test tube A with blue litmus solution and fill test tube A with red litmus solution (each 10 ml).
Use the dropper to add a few drops of calcium hydroxide in the solution in the test tube
Leave the solution for a few minutes
Observation: The red litmus solution in test tube A turns blue and the blue litmus solution in test tube B doesn't change its color.
Interference: we conclude that calcium hydroxide is basic in nature and bases turn from red litmus solution to blue litmus solution.
Experiment with Zinc
Take a dry and clean test tube
Place zinc granules in it
Fill it with liquid NaOH submerging zinc granules and tilt it a little bit and fix it properly in the cork
And place the bunsen burner and lit it
Close the mouth of the test tube with cork so that no vapor can escape
Leave the solution for 2-3 minutes it burns with a robust sound releasing a colorless and odorless gas
And if a burning match stick is brought near the mouth of the test tube it gives a pale blue flame with a pop sound.
The reaction of the given experiment:
2NaOH+Zn→Na2ZnO2+H2
Experiment With Solid Sodium Carbonate
Take one gram of Na2CO3 with some distilled water in a flat bottomed flask
Take a dry double bore fork and with thistle funnel which has a delivery tube fitted with it
Add dilute NaOH.
No reaction will take place.
Conclusions of Experiments
FAQs on Experiments on Properties Acids and Bases
1. What are some fundamental experiments to demonstrate the properties of acids and bases in a school laboratory?
Several key experiments can be performed to study the properties of acids and bases. These are central to the CBSE curriculum and help in understanding their chemical nature. Some important examples include:
Indicator Tests: Using litmus paper, phenolphthalein, or methyl orange to differentiate between acidic and basic solutions based on colour changes.
Reaction with Metals: Observing the reaction of an acid (like HCl) with an active metal (like zinc) to produce hydrogen gas.
Reaction with Metal Carbonates: Testing the reaction of an acid with a metal carbonate (like sodium carbonate) to observe the effervescence of carbon dioxide gas.
Neutralisation Reaction: Demonstrating the reaction between an acid and a base, using an indicator to see the point where they neutralise each other to form salt and water.
2. How can you experimentally test if a given solution is acidic or basic using litmus paper?
The litmus test is a simple and definitive way to identify the nature of a solution. To perform the experiment:
Take a strip of blue litmus paper and dip it into the unknown solution. If the colour changes to red, the solution is acidic.
Take a strip of red litmus paper and dip it into the unknown solution. If the colour changes to blue, the solution is basic.
If there is no colour change in either the blue or red litmus paper, the solution is likely neutral.
3. What is the expected outcome of an experiment reacting an acid with an active metal like zinc?
When an acid reacts with an active metal, it results in the formation of a salt and the liberation of hydrogen gas. For example, in an experiment with hydrochloric acid and zinc granules, you will observe:
Bubbles of a colourless, odourless gas forming on the surface of the zinc metal. This is hydrogen (H₂) gas.
The general reaction is: Acid + Metal → Salt + Hydrogen Gas.
To confirm the gas is hydrogen, you can bring a burning splint near the mouth of the test tube. The gas will extinguish the flame with a characteristic 'pop' sound.
4. What are the most important safety precautions to take while performing experiments with acids and bases?
Safety is crucial when handling acids and bases as they can be corrosive. Key precautions include:
Always wear safety goggles to protect your eyes from splashes.
Handle strong acids like HCl and strong bases like NaOH with extreme care, preferably wearing gloves.
When diluting an acid, always add the acid to water slowly, never the other way around, to prevent splashing due to an exothermic reaction.
Use small quantities of chemicals for experiments to minimise risk.
Ensure the apparatus, like test tubes and droppers, is clean and not interchanged between different chemicals to avoid unwanted reactions.
5. Why does an aqueous solution of an acid conduct electricity, but a pure acid sample (like pure acetic acid) does not?
This phenomenon is explained by the concept of ionisation. An acid's ability to conduct electricity depends on the presence of mobile ions.
In its pure state, an acid consists of neutral molecules and lacks free-moving ions, so it cannot conduct electricity.
When an acid is dissolved in water (forming an aqueous solution), it dissociates or ionises to produce charged ions. For example, HCl in water forms H⁺ and Cl⁻ ions.
These mobile ions in the aqueous solution are free to move and carry an electric current, making the solution an electrolyte.
6. What is a neutralisation reaction, and how can you demonstrate it experimentally using phenolphthalein?
A neutralisation reaction is a chemical reaction in which an acid and a base react quantitatively with each other to form a salt and water. To demonstrate this:
Take a small amount of a basic solution (e.g., sodium hydroxide, NaOH) in a test tube.
Add one or two drops of phenolphthalein indicator. The solution will turn pink, indicating its basic nature.
Now, add an acidic solution (e.g., hydrochloric acid, HCl) drop by drop while gently shaking the test tube.
The point at which the pink colour just disappears is the neutralisation point. At this stage, the base has been completely neutralised by the acid.
7. Why does the reaction of an acid with a metal carbonate produce a brisk effervescence, and how can you identify the gas produced?
The brisk effervescence observed is due to the rapid release of a gas. The reaction is: Acid + Metal Carbonate → Salt + Water + Carbon Dioxide.
The gas responsible for the effervescence is carbon dioxide (CO₂).
To identify this gas, you can perform the limewater test. Pass the evolved gas through a test tube containing limewater (a solution of calcium hydroxide, Ca(OH)₂). If the limewater turns milky or cloudy, it confirms the presence of carbon dioxide. This is due to the formation of insoluble calcium carbonate (CaCO₃).
8. How could you design an experiment to compare the relative strengths of two acids, such as hydrochloric acid (HCl) and acetic acid (CH₃COOH)?
To compare the strengths of acids, you need to assess their degree of ionisation. A stronger acid ionises more completely, leading to a higher concentration of H⁺ ions. Here are two possible experiments:
Comparing Reaction Rates: React equal volumes and concentrations of both acids with identical pieces of an active metal like magnesium ribbon. The stronger acid (HCl) will produce hydrogen gas much more rapidly (faster bubbling) than the weaker acid (acetic acid).
Comparing Electrical Conductivity: Use a conductivity meter to measure the electrical conductivity of aqueous solutions of both acids (of the same concentration). The stronger acid, HCl, will show higher conductivity because it produces more ions in the solution.
