Properties of Acids

Advertisements

Topics

  • Properties of Acids
  • Physical properties of Acids
  1. Taste
  2. Physical state
  3. Effect on skin
  4. Colours of indicators
  • Chemical properties of Acids
  1. Reaction with active metals
  2. Reaction with bases - Neutralisation
  3. Decomposition of hydrogen carbonates and carbonates
  4. Decomposition of sulphites and bisulphites
  5. Decomposition of sulphides
  6. Reaction with chlorides and nitrates
  7. Reaction with metal oxide

INDICATORS:-

Natural indicator:-

A natural Indicator is a type of indicator that can be found naturally and can determine whether the substance is acidic or basic in nature.

Examples:-

  • Litmus
  • Turmeric
  • Red Cabbage Juice
  • Onion
  • Vanilla

Synthetic indicators:-

A synthetic indicator is a man-made chemical substance used to determine the pH of another substance.

Examples:-

  • Methyl orange
  • Phenolphthalein

Universal Indicators:-

A universal indicator is a pH Indicator made of a solution of several compounds that exhibits several smooth colour changes over a wide range of pH values to indicate the acidity or alkalinity of solutions.

Indicator

Original colour

Acid

Base

Red litmus

Red

No change

Blue

Blue litmus

Blue

Red

No change

Turmeric

Yellow

No change

Reddish brown

Red cabbage juice

Purple

Reddish

Greenish yellow

Phenolphthalein

Colourless

Colourless

Pink

Methyl orange

Orange

Red

Yellow

Onion

n/a

No change

Smell vanishes

Vanilla

n/a

No change

Smell vanishes

 

 

CONCEPT OF pH SCALE:-

In the pH scale, ‘p’ stands for ‘potenz’. Potenz is a German word which means ‘power’ or ‘potential’. Here, ‘H’ stands for hydrogen ion. Thus, pH means the potential of hydrogen or the power of hydrogen.

The strength of an acid or base depends upon the hydrogen ion concentration. If the concentration of hydrogen ion is greater than hydroxide ion, the solution is called acidic. If the concentration of hydrogen ion is smaller than the hydroxide ion, the solution is called basic. If the concentration of hydrogen ion is equal to the concentration of hydroxide ion, the solution is called a neutral solution.

pH is a measure of hydrogen ion concentration, a measure of the acidity or alkalinity of a solution.

The pH scale usually ranges from 0 to 14. Aqueous solutions at 25°C with a pH less than 7 are acidic, while those with a pH greater than 7 are basic or alkaline. A pH level of 7.0 at 25°C is defined as ‘Neutral’.

 

 

Reactions

REACTION OF ACID & BASES WITH METALS:-

When an acid reacts with a metal, hydrogen gas is evolved, and a corresponding salt is formed.

Given below is the reaction of Zinc Granules with Dilute sulphuric acid

  • Set the apparatus as shown in Fig.

  • Take about 5 mL of dilute sulphuric acid in a test tube and add a few pieces of zinc granules.

  • What do you observe on the surface of zinc granules?

  • Pass the gas being evolved through the soap solution.

  • Why are bubbles formed in the soap solution?

  • Take a burning candle near a gas-filled bubble.

Observation:-

  • Bubble formation takes place inside the test tube.

  • The gas passes through the delivery tube into the soap solution, forming soap bubbles.

  • We hear a pop sound when a burning candle is taken near the gas-filled bubble. This is because the soap bubbles are filled with hydrogen gas.

 

Acid + Metal → Salt + Hydrogen gas

 

 

2NaOH(aq) + Zn(s) → Na2ZnO2(s) + H2(g)

Examples:-

Magnesium reacts with Hydrochloric acid, forms Magnesium Chloride, and liberates Hydrogen gas.

 

Mg + 2HCl → MgCl2+ H2

When a base reacts with a metal, hydrogen gas is evolved, and salt is formed, with a negative ion composed of the metal and oxygen.

 

Examples:-

When Aluminium reacts with Sodium hydroxide, it forms Aluminium Hydroxide and liberates Hydrogen gas.

2Al + 2NaOH + 6H2O → 2Na+ +2[Al(OH)4]- + 3H2

REACTION OF ACID WITH METAL CARBONATE AND METAL HYDROGEN CARBONATES:-

  • Take two test tubes, and label them as A and B.
  • Take about 0.5 g of sodium carbonate (Na2CO3) in test tube A and about 0.5 g of sodium hydrogen carbonate (NaHCO3) in test tube B.
  • Add about 2 mL of dilute HCl to both the test tubes
  • Pass the gas produced in each case through lime water (calcium hydroxide solution)

OBSERVATION:-

  • When HCL is added to sodium carbonate, carbon dioxide gas is liberated.
  • When this gas is passed through lime water, a white precipitate of calcium carbonate is formed
  • When we pass carbon dioxide gas through lime water, then calcium carbonate is formed.

Ca(OH)2(s)+CO2(g)→CaCO3(s)+H2O(l)

On passing the excess carbon dioxide, we get the calcium bicarbonate.

CaCO3(s) + H2O(l) + CO2(g) → Ca(HCO3)2(aq)

When an acid reacts with a metal carbonate or metal hydrogen carbonate, it gives salt, carbon dioxide gas and water.

Metal carbonate/Metal hydrogen carbonate + Acid → Salt + Carbon dioxide + Water

Example:-

Calcium carbonate + Sulfuric acid Calcium sulfate + Water + Carbon Dioxide

CaCO3+ H2SO4 → CaSO4+ H2O + CO2

REACTION OF ACIDS WITH METAL OXIDES:-

Metal oxide + Acid → Salt + Water

Metal oxides react with acid to form salt and water.

2HCl+ Na2O → 2NaCl + H2O

Hydrochloric acid reacts with sodium oxide to form sodium chloride (salt) and H2O.

REACTION OF BASE WITH NON-METAL OXIDES:-

Non-metallic oxides are acidic in nature, therefore, react with a base to form salt and water.

Non-metallic Oxide + Base → Salt + Water

Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)

Calcium hydroxide, when it reacts with carbon dioxide, produces calcium carbonate and water.

 

REACTION OF ACID AND BASES:-

Acid, when it reacts with a base, produces salt and water

Acid + Base Salt + Water

HCl + NaOH → NaCl + H2O

When an acid or a base is dissolved in water, they dissociate into ions.

For example,

  • When hydrochloric acid is dissolved in water, it gets dissociated into ions such as protons (H+ions) and Cl-ions as follows:
  • HCl + H2O → H3O++ Cl-
  • As there is an increase in the protons in the aqueous solutions, the solution is acidic in nature.
  • Similarly, when NaOH is dissolved in water, it gets dissociated as,
  • NaOH + H2O → Na++ OH-+ H2O
  • As there is an increase in the hydroxyl ions in the solution, the solution is basic in nature.
  • Basic aqueous solution is called alkali.

 

 

If you would like to contribute notes or other learning material, please submit them using the button below.

Video Tutorials

We have provided more than 1 series of video tutorials for some topics to help you get a better understanding of the topic.

Series 1


Series 2


Series 3


Advertisements
Share
Notifications



      Forgot password?
Use app×