Acids, Alkalis and Salt Preparation

Question 1

Color of methyl orange in acids and alkalis:

Answer 1

Acids: red
Alkalis: yellow

Question 2

Color of litmus in acids and alkalis:

Answer 2

Acids: red
Alkalis: blue

Question 3

Color of phenolphthalein in acids and alkalis:

Answer 3

Acids: colorless
Alkalis: pink

Question 4

Examples of bases (general):

Answer 4

Metal oxides
Metal hydroxides
Ammonia (NH₃)

Question 5

The reaction for ammonia dissolving in water:

Answer 5

NH₃ + H₂O ↔ NH₄+1 + OH-1

Question 6

Why do we not use universal indicator for titration?

Answer 6

Because it gives us a range of colors and changes gradually between them. We would not be able to see a clear endpoint for the titration.

Question 7

What is salt?

Answer 7

When the metal replaces the hydrogen from an acid, the compound formed is a salt

Question 8

Write the general equations for reaction between bases (+carbonates) and acids:

Answer 8

Metal oxide + acid ➡ salt + water

Metal hydroxide + acid ➡ salt + water

Metal carbonate + acid ➡ salt + carbondioxide + water

Question 9

Steps for making an insoluble salt:

Answer 9

• React two aqueous solutions of soluble salts
• Filter the solution
• Insoluble salt (residue) from the filter paper
• Wash it with distilled water 2-3 times to get rid of the excess reactant and the by-product
• Dry it in a warm oven

Question 10

Steps for making a soluble salt (not sodium…ammonium):

Answer 10

• React an acid with an excess of solid
• Warm the acid
• Filter excess of solid from the solution
• Crystallization: heat until concentrated, dip a glass rod in the hot solution, cool solution
• Filter the crystals
• Dry the crystals in a warm oven

Question 11

Why do we need to add an excess of solid to acid when making a soluble salt?

Answer 11

If the solution is in excess, it will contaminate the salt solution as it cannot be easily separated from the salt solution.

Question 12

Why is titration used for sodium…ammonium salts and not the other method?

Answer 12

These salts are highly soluble in water, it’ll dissolve in water and you can’t tell whether neutralization has completed or dissolving is going on

Question 13

Define acid and alkali according to the Lowry-Bronsted theory

Answer 13

Acid: proton donor
Alkali: proton acceptor

Question 14

Define acid and alkali according to the Arrhenius theory

Answer 14

Acid: Produces H+ ions in solution

Alkali: Produces OH- ions in solution

Question 15

What is the hydroxonium ion:

Answer 15

H₃O+