Ph Of Acids And Bases Class 10th Science Lab Manual CBSE Solution

Class 10th Science Lab Manual CBSE Solution
Lab Experiment 1a
  1. pH value of dilute hcl/dilute hydrogen carbonate/dilute ethanoic acid/lemon juice using…
Viva Questions
  1. What is pH?
  2. What are the different characteristics of the solution (by pH), explain them and give two…
  3. Give two examples of natural and synthetic Indicator:
  4. Using any for indicator differentiate acid, base and neutral solution?…
  5. What is a Universal indicator, Give one example?
  6. What is the pH of rainwater?
  7. What is the pH of soap solution?
  8. What is the pH of the stomach?
  9. What is Hyperacidity. Give any two examples of an antacid?
  10. What according to you should be the pH of dil. HCl and dil. NaOH solution? Observe and…
  11. Why NH4OH is a weak base?
  12. On opening the soda water bottle the dissolved CO2 comes out. Would the ph of the solution…
  13. What happens to the ph of the solution when we increase the temperature of the solution?…
  14. Dry litmus paper does not show any color change when brought to dry HCl gas. Why?…
  15. If a wet blue litmus paper is brought closer to dry HCl gas, what changes will you observe…
  16. Why does lime water turn milky when CO2 gas is passed through it?…
  17. Why do we use Zinc granules for the test in the lab?
  18. Why do metal displace hydrogen from dilute acids?
  19. Do all metals displace hydrogen gas from dilute acids?
  20. What would happen when dil. HCl and dil. NaOH are mixed in equal amounts? Write the…
  21. Why hydrogen gasan explosion?
  22. Write the reaction of zinc with dil — sulphuric acid.
  23. What is the difference between a strong acid and a weak base?
  24. What will happen to a lighted candle if it is brought near the mouth of a gas jar…
  25. What will be the color of blue litmus paper on bringing it in contact with a drop of dil.…
Lab Experiment 1b
  1. AIM:Studying the properties of acids (HCl) by their reaction with(i) Litmus solution…
Lab Experiment 1c
  1. AIM :Studying the properties of bases (NaOH) by their reaction with(i) Litmus solution…

Lab Experiment 1a
Question 1.

AIM:

To find the pH of the following samples by using pH paper/universal indicator:

(a) Dilute hydrochloric acid (HCl)

(b) Dilute sodium hydroxide (NaOH) solution

(c) Dilute ethanoic acid (CH3COOH) solution

(d) Lemon juice

(e) Water

(f) Dilute hydrogen carbonate (NaHCO3) solution


Answer:

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.



Viva Questions
Question 1.

What is pH?


Answer:

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



Question 2.

What are the different characteristics of the solution (by pH), explain them and give two examples each?


Answer:

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, HNO3, 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



Question 3.

Give two examples of natural and synthetic Indicator:


Answer:

Natural indicators are Litmus and Turmeric.

Synthetic indicators are Phenolphthalein and methyl orange



Question 4.

Using any for indicator differentiate acid, base and neutral solution?


Answer:



Question 5.

What is a Universal indicator, Give one example?


Answer:

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.




Question 6.

What is the pH of rainwater?


Answer:

pH of rainwater < 7 due to the dissolution of acidic gases like NO2andSO2.



Question 7.

What is the pH of soap solution?


Answer:

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



Question 8.

What is the pH of the stomach?


Answer:

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.



Question 9.

What is Hyperacidity. Give any two examples of an antacid?


Answer:

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.



Question 10.

What according to you should be the pH of dil. HCl and dil. NaOH solution? Observe and explain your findings.


Answer:

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)



Question 11.

Why NH4OH is a weak base?


Answer:

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

NH4 OH(aq) ↔ NH4+ (aq)+OH- (aq)



Question 12.

On opening the soda water bottle the dissolved CO2 comes out. Would the ph of the solution increase or decrease as the gas comes out? Explain your answer?


Answer:

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.



Question 13.

What happens to the ph of the solution when we increase the temperature of the solution? Explain?


Answer:

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:



Question 14.

Dry litmus paper does not show any color change when brought to dry HCl gas. Why?


Answer:

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.



Question 15.

If a wet blue litmus paper is brought closer to dry HCl gas, what changes will you observe and Why?


Answer:

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.



Question 16.

Why does lime water turn milky when CO2 gas is passed through it?


Answer:

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



Question 17.

Why do we use Zinc granules for the test in the lab?


Answer:

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



Question 18.

Why do metal displace hydrogen from dilute acids?


Answer:

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)



Question 19.

Do all metals displace hydrogen gas from dilute acids?


Answer:

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



Question 20.

What would happen when dil. HCl and dil. NaOH are mixed in equal amounts? Write the equation also?


Answer:

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



Question 21.

Why hydrogen gasan explosion?


Answer:

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



Question 22.

Write the reaction of zinc with dil — sulphuric acid.


Answer:


Zn(s) + H2SO4(dil) → ZnSO4 + H2(gas)



Question 23.

What is the difference between a strong acid and a weak base?


Answer:

Strong acids are those who completely dissociates into ions.

HCl(aq) → H+ (aq) + Cl(aq)



Question 24.

What will happen to a lighted candle if it is brought near the mouth of a gas jar containing hydrogen gas?


Answer:

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



Question 25.

What will be the color of blue litmus paper on bringing it in contact with a drop of dil. NaOH?


Answer:

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.




Lab Experiment 1b
Question 1.

AIM:

Studying the properties of acids (HCl) by their reaction with

(i) Litmus solution (Blue/Red)

(ii) Zinc metal (Zn)

(iii) Solid sodium carbonate (Na2CO3)


Answer:

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.



Lab Experiment 1c
Question 1.

AIM :

Studying the properties of bases (NaOH) by their reaction with

(i) Litmus solution (Blue/Red)

(ii) Zinc metal (Zn)

(iii) Solid sodium carbonate (Na2CO3)


Answer:

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.


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