Ph Of Acids And Bases

MATERIALS REQUIRED:

Apparatus: Test tubes, test tube stand, droppers or glass rod, pH paper/universal indicator, standard colour chart, glazed white tile

Chemical compounds: HCl, ethanoic acid (acetic acid/vinegar), lemon juice, distilled water, and sodium bicarbonate solution.

THEORY

1. pH is the measure of the concentration of hydrogen ion in the solution.

2. pH is defined as the negative logarithm of the concentration of hydrogen ion in a solution at room temperature (298 K).

3. The hydrogen ion concentration (H⁺) for an acidic solution is always less than 7 on the pH scale.

4. The hydrogen ion concentration of a basic solution is always greater than 7 on pH scale.

5. The hydrogen ion concentration of a neutral solution is 10 mol/L. Therefore, its pH is 7.

6. The pH of a solution can be measured by using a pH paper, universal indicator or pH meter.

PROCEDURE

1. Pour the given solution in separate clean and dry test tubes marked as A, B, C, D, E, and F and place them in the test tube stand, as shown in the figure below:

2. Take six strips of pH paper and place them on a tile.

3. Place a drop of each test solution on the six strips of the pH paper using a dropper.

4. Note the colour of the pH paper and compare it with the colour chart of the pH paper.

5. Record the pH value corresponding to the colour.

6. Similarly, using a new dropper each time perform the same experiment with the remaining test samples using a new strip of pH paper.

7. Record your observations in the observation table below.

OBSERVATION TABLE

RESULT

1. The pH of dilute solutions of hydrochloric acid, ethanoic acid and lemon juice is less than 7, and therefore, they are acids.

2. The pH of dilute solutions of sodium hydroxide and, sodium bicarbonate is more than 7, and therefore, these solutions are bases.

3. The pH of water is 7 and therefore, it is neutral.

PRECAUTIONS

1. The acids and bases solution should be used with care.

2. Use distilled water for preparing solutions.

3. Use only standard colour charts for finding the pH value.

4. Do not touch the pH paper with dirty and wet hands.

5. Keep the pH paper away from fumes produced during a chemical reaction.

pH is the measure of acidity or alkalinity of a sample. The pH is defined as the negative logarithm of the hydrogen ion concentration in mole per liter.

•For acidic solution, pH < 7

•For basic/alkaline solution, pH > 7

•For neutral solution, pH = 7

The solution can be divided into three classes,i.e., acid, base and neutral solution :

1. Acid: Any substance that gives H⁺ ions when dissolved in water is called “acid.”Generally, they have a pH less than 7 in pH scale. Example HCl, HNO_3, etc

2. Base: Any substance that gives OH^- ions when dissolved in water is called as “base.”They have a pH more than 7 in pH scale. Example NaOH, NH₄OH,etc

3. Neutral: The solutions with an equal concentration of H⁺ and OH^-ions are called neutral solutions. They have a pH of 7in pH scale. Example: water

Natural indicators are Litmus and Turmeric.

Synthetic indicators are Phenolphthalein and methyl orange

Universal indicator is a homogenous mixture which is prepared by mixing some common indicators. It has pH ranging from 1-14 to indicate acidity or alkalinity of solutions.

Example: pH scale is a universal indicator. If we put a pH paper in lemon solution, then the reddish color of the paper turns “yellow” as shown in the picture below.

pH of rainwater < 7 due to the dissolution of acidic gases like NO₂andSO_2.

The soap solution is basic hence have a pH>7.

The Stomach consists of HCL in gastric juice which is acidic, hence the pH of the stomach is comparable to the pH of HCL which is 2.

The hyperacidity is a condition in which the pH of the stomach reaches a pH <2.5. This happens due to higher secretion of HCl in the stomach which make the stomach more acidic.

The antacid is the remedy for hyperacidity because they are basic which helps to balance the ph of the stomach. Example: milk of magnesia, Sodium bicarbonate.

Dil HCl is an acid as it furnishes hydrogen ion in the solution and therefore has a ph less than 7

HCL(aq) → H⁺ (aq)+ CL^- (aq)

Dil. NaOH, on the other hand, is base as it furnishes hydroxyl ions in solution and therefore has pH greater than 7.

NaOH(aq) → Na⁺ (aq)+OH^- (aq)

It is a weak base because it ionizes partially in solution.

NH₄ OH(aq) ↔ NH₄⁺ (aq)+OH^- (aq)

CO₂ in soda water bottle exists as carbonic acid. On opening the bottle, CO₂ escapes out. Therefore, the concentration of carbonic acid decreases and pH increases.

On heating, a solution the pH of the medium get shifts to the right side in the scale in a temperature increase because of the ability of a solution to ionizer increases and so the concentration of H⁺ ions increases in the solution.
The pH scale is given below:

Acids shows acidic behavior when they are dissolved in water, i.e., are aqueous. Thus, No change occurs to litmus paper when dry HCl gas is used.

The blue litmus paper will turn red .This is because the litmus paper is wet and therefore H⁺ (aq) ions are released by HCl gas.

Lime water(Ca(OH)₂) react with CO₂ to form an insoluble precipitate of calcium carbonateCaCO₃which turns water milky.

Zinc granules have increased surface area so that reaction occurs fast.

Metals displace hydrogen from dilute acids because they are more reactive than hydrogen. Metals lose electrons from which the hydrogen ions from acids accept, and hydrogen gas is liberated.

2HCl → 2H⁺+ 2Cl^-

Mg → Mg²⁺+ 2 e^-

2H⁺+ 2e^- → H₂(gas)

No, only the metal which is above hydrogen in the reactivity series can displace hydrogen from dilute acids.

Whenever acid reacts with base the reaction is said to be neutralization reaction. As a result salt and water will be formed.

NaOH +HCL → NaCl +H₂O

Hydrogen gas burns with an explosion because Hydrogen gas has the highest calorific value with low ignition temperature.

Zn(s) + H₂SO₄(dil) → ZnSO₄ + H₂(gas)

Strong acids are those who completely dissociates into ions.

HCl(aq) → H⁺ (aq) + Cl^–(aq)

The candle extinguishes with a pop sound and the gas burn with a pale blue film.

Blue litmus paper does not undergo any change in color on bringing it in contact with a drop of dil. NaOH as it is basic.

MATERIALSREQUIRED

ApparatusRequired: Test tubes, test tube stand, test tube holder, cork, droppers, beaker, litmus (red and blue), Zn metal granules.

ChemicalRequired: Solid sodium carbonate, dil. HCL.

THEORY

1. Acids turn blue litmus red and do not affect red litmus. As HCl is an acid, it will turn blue litmus solution red.

2. HCl reacts with zinc metal, to forms a salt, zinc chloride (ZnCl₂) and hydrogen gas (H₂) is liberated.

3. Hydrogen gas burns in air with a pop sound.

4. HCL reacts with sodium carbonate (aqueous/solid) to liberate carbon dioxide (CO₂) which turns lime water milky. When an excess of CO₂ is passed through the solution, the milkiness disappears.

PROCEDURE

1.Litmustest

Take 1 ml dil. HCl in two test tubes each. Mark them ‘A’ and ‘B’ and put them in a test tube stand. Add blue litmus in a test tube ‘A’ and red litmus in a test tube ‘B’ Observe the colour change in both.
2.ReactionwithZnmetal

Take a test tube and add zinc granules to it. Add to it dil. HCl. Place a cork with a fine jet on the mouth of the test tube. Bring a lighted matchstick near the mouth of the fine jet after some time and observe.

3.Na₂CO₃test

Take a small amount of sodium carbonate in a test tube and add dil. HCL dropwise.

Pass the gas evolved through lime water and observe changes.

4. Note the observation in the observation table.

OBSERVATIONTABLE

RESULT

1. HCI being acid turns blue litmus red.

2. It releases H₂ gas on reaction with Zn metal.

3. It liberates CO₂ gas on reaction with Na₂CO₃.

PRECAUTIONS

1. HCI is corrosive in nature, therefore, handle it with care.

2. Use small quantities of the chemical compounds.

3. Use zinc granules, otherwise, the reaction will occur very slowly.

MATERIALS REQUIRED:

Apparatus: Test tubes, test tube holder, test tube stand and droppers.

Chemical compounds : Dil. NaOH, red and blue litmus solutions, zinc metal, sodium carbonate

THEORY:
Bases: Bases are the substance which furnishes hydroxide ions in a solution.

1. NaOH is a base. Base turn red litmus solution to blue and does not affect blue litmus solution.

2. On reacting with zinc metal, NaOH forms sodium zincate and hydrogen gas is liberated.

3. NaOH does not react with solid or aqueous Na₂CO₃.

PROCEDURE :

1.Litmus test:

(i) Take about 5mL of NaOH in two test tubes and mark them as ‘A’ and ‘B.’ Put both the test tubes in a test tube stand.
(ii) Add blue litmus in a test tube ‘A’ and red litmus in a test tube ‘B.
(iii) Note the observation in the observation table.

2.Reaction with Zn metal:
(i) Take a test tube and zinc granules to it.
(ii) Add NaOH solution to it and place a cork with a fine jet on the mouth of the test tube.
(iii) Bring a lighted matchstick near the mouth of the fine jet and observe the mouth of the fine jet and observe.
(iv) Note the observation in the observation table.

3.Na₂CO₃ test:
(i) Take a small amount of sodium carbonate in a test tube and add sodium hydroxide solution.
(ii) Note the observation in the observation table.

OBSERVATION TABLE :

RESULT:

1. NaOH turns red litmus solution to blue and does not affect the blue litmus solution.

2. On reaction with Zn metal, Zn atom being more reactive undergo displacement reaction to form sodium zincate and H₂ gas is liberated.

3. NaOH does not undergo a chemical reaction with Na₂CO₃.

PRECAUTIONS :

1. NaOH is corrosive in nature, therefore use with care.

2. Use small quantities of the chemicals in the test tube.

3. A fine jet should be taken from the test tube for burning hydrogen.