Acids and Bases - Acids and Bases

Question 1

What are acids?

Answer 1

Acids are substances which composes of one or more HYDROGEN atoms chemically bonded to one, or a group of, non-metal atoms. eg H2SO4 is made up of 2 H atoms bonded to the sulphate group SO4 ^2-

Question 2

What happens to an acid in water?

Answer 2

It will dissociate into its ions, meaning that it will separate into its IONS. Eg HCl in water -> H ions, and Cl ions

Question 3

How do strong acids differ from weak acids?

Answer 3

Strong acids will COMPLETELY dissociate, releasing ALL Hydrogen ions when in contact with water.
Weak acids do not completely dissociate and only release SOME of their hydrogen ions in water, some remain as neutral particles.

Question 4

Examples of strong and weak acids

Answer 4

Laboratory acids like HCl, H2SO4, HNO3

Organic acids like acetic (in vinegar), citric acids are weak acids.

Question 5

What do bases do?

Answer 5

Remove Hydrogen ions from a solution

Question 6

What are bases usually?

Answer 6

Metal oxides, metal hydroxides, metal carbonates or metal hydrogen carbonates.

Question 7

What is a base called if it does dissolve in water?

Answer 7

An alkali

Question 8

What ions do alkali dissociate into?

Answer 8

Hydroxide ions.

Question 9

What is the difference between strong alkalis and weak alkalis?

Answer 9

Strong alkalis COMPLETELY dissociate in water.
Weak alkalis do not completely dissociate and only release a small number of hydroxide ions. Some remain as neutral particles.

Question 10

Which group of the periodic table are strong alkalis?

Answer 10

Any of the group 1 metals eg Na, Li…

Question 11

What is the difference between weak/strong and concentrated/diluted acids or bases?

Answer 11

The STRENGTH of an acid/alkali does not change depending on concentration. Concentration is HOW MANY acid/alkali particles in per unit volume of water.

The REACTIVITY of an acid/alkali is determined by the concentration of ions in the solution.

Question 12

What is the pH scale used to represent?

Answer 12

The concentration of acids and bases

Question 13

What is the pH a measure of?

Answer 13

The concentration of hydrogens in a SOLUTION. The more hydrogen ions present, the more acidic the solution.

Question 14

Each unit on the pH scale represents a _____ change in acidity

Answer 14

The pH scale is logarithmic so each unit on the pH scale represents a TENFOLD change in acidity. ie pH of 4 is 10x more acidic than pH of 5, and 100x more acidic than pH of 6

Question 15

What are the indicators for pH?

Answer 15

-Litmus: Litmus indicator SOLUTION turns red in acidic solutions and blue in alkaline solutions.
Blue litmus paper turns red in an acidic solution and remain blue in neutral/alkali solution. Red litmus turns blue when in alkali but stays red in acidic/neutral solutions.

-Universal indicator: many different colour changes, from red for strong acids to dark purple for strong bases. Green is neutral

Question 16

What is the important difference between litmus and universal indicator?

Answer 16

Litmus DOES NOT tell you HOW STRONG the acid or alkali is whereas the universal indicator does.

Question 17

Describe the neutralisation reaction

Answer 17

It is when a base cancels out the effects of the acid because a neutral solution is made if the right amount of acid and base is added together.

Question 18

When hydrogen ions collide with hydroxide ions what is produced?

Answer 18

Water!!

Question 19

How are salts formed?

Answer 19

When an acid is neutralised by a base (metals, bases or carbonates).

Acid + base -> salt + water

Question 20

What are salts?

Answer 20

Ionic substances composed of a positively charged metal ions and a negatively charged non-metal ion.

Question 21

Properties of salts

Answer 21

• relatively High melting points

- many are soluble in water

Question 22

How are salts made? (Soluble salts)

Answer 22

1. Heat acid til 70°C. Do not boil acid.
2. Add insoluble base until saturated.
3. Allow beaker to cool.
4. Fold filter paper and place in funnel. Place funnel into beaker
5. Pour down in filter paper and allow to filter through
6. Place beaker full of water on to tripod
7. Place evaporating dish on top of this beaker and pour solution from other beaker into evaporating basin
8. Gently heat until solution has reduced by half
9. Leave dish to cool. Move to a warm place and observe over a few days.

Question 23

How to make salts using soluble bases or soluble carbonates

Answer 23

If the base or carbonate is soluble, then you cannot tell if the acid has been used up because excess solids will dissolve even after the acid has been neutralised, of if a colourless liquid base or carbonate is used, it will just form a colourless solution with the acid.

Therefore, an indicator must be used to determine when neutralisation occurs.
NEUTRAL SOLUTION/EQUAL AMOUNTS

Question 24

Reaction between an acid and a metal hydroxide?

Answer 24

Acid + metal hydroxide –> metal salt + water

Question 25

Reaction between an acid and a metal oxide?

Answer 25

Acid + metal oxide –> metal salt + water

Question 26

Reaction between an acid and a metal carbonate?

Answer 26

Acid + metal carbonate –> salt + carbon dioxide + water

Question 27

Reaction between an acid and a metal?

Answer 27

Acid + metal –> salt + hydrogen

Question 28

Reaction between an acid and a metal hydrogen-carbonate?

Answer 28

Acid + metal carbonate –> salt + carbon dioxide + water

Question 29

Properties of salts (2)

Answer 29

• High melting points

- Generally soluble in water

Question 30

Properties of alkalis

Answer 30

Alkalis turn fats and oils into soluble soap

• feel soapy
• taste bitter.

Question 31

How do we know if CO2 is produced?

Answer 31

Bubbles

use limewater test.