2.6 - Acids , Alkalis and Titrations

Question 1

What is the pH scale what are the different types of acids, and give an example for each?

Answer 1

Strongly acidic - pH 0-3 hydrochloric acid
Weakly acid - pH 4-6 ethanoic acid
Neutral - 7 sodium chloride
Weakly alkaline - 8-10 ammonia
Strongly alkaline - 11-14 sodium hydroxide

Question 2

How is pH measured?

Answer 2

Universal indicator is made from a mixture of indicators which change in colour in a gradual way over a range of pH values. It can be used a a solution or as papers. It changes through a variety of colours from pH 1 right up to pH 14 not entirely accurate.

Question 3

What are some common indicators and their colours in Acid and Alkalis

Answer 3

Litmus - Acid Red, Alkali blue
Methyl orange - Acid red, Alkali yellow
Phenolphthalein - Acid colourless, Alkali pink
Universal indicator - Acid red, Alkali blue

Question 4

What is a strong acid?

Answer 4

A strong acid completely ionises in water and thus releases a high concentration of H+

Question 5

What is a weak acid?

Answer 5

A weak acid is only partially ionised in water and thus releasing a much lower concentration of H+ ions

Question 6

What happens to Acids in water?

Answer 6

When acids are in water they dissociates to form hydrogen ions like:

HCL > H+ + CL-
HNO3 > H+ + NO3-
When measuring pH we are actually measuring the concentration of H+ ions in solution.

Question 7

What is the definition of Acids?

Answer 7

Substances that act as a source of Hydrogen ions (H+) in solution.

Question 8

What colour are different Acids and Alkalis on the pH scale?

Answer 8

Strong acids red
Weak acids orange
Strong alkalis purple
Weaker alkalis blue

Question 9

What are bases?

Answer 9

Bases are substances that neutralise acids by combining with hydrogen ions in them. Bases include metal oxide, metal hydroxide or ammonia (NH3)

Question 10

What are Alkalis?

Answer 10

Some bases dissolve in water to form solutions containing hydroxide ions.
Alkalis are a source of hydroxide (OH-) ions in solution.
Examples include sodium hydroxide pottasium hydroxide

Question 11

What are strong Alkalis?

Answer 11

A strong Alkali fully ionises in water a thus releases a high concentration of OH- ions

Question 12

What are weak Alkalis?

Answer 12

A weak alkali only partially ionises in water and thus releasing a much lower concentration of OH- ions

Question 13

What are Alkalis?

Answer 13

Some bases dissolve in water to form solutions containing hydroxide ions. Alkalis are a source of hydroxide (OH-) ions in solution. Examples of sodium hydroxide and potassium hydroxides. When sodium hydroxide is in water breaks apart to form sodium and hydroxide ions:

NaOH > Na+ + OH-
Another example would be ammonium reacts with water for for ammonium hydroxide ions alkalis have a pH greater than 7

Question 14

What are some examples of Alkaline solution?

Answer 14

There are other substances such as soluble metals carbonates that react with water to form hydroxide ions for example sodium carbonate and pottasium carbonate are both alkalis with a pH greater than 7. This is due to the OH- ions in the solution. Only some of the carbonate ions react wit water.

Question 15

What is a reacting acids with bases and alkalis?

Answer 15

Acids react with bases or alkalis in a neutralisation reaction.
Metal oxides such as copper oxide and magnesium oxide are bases. Copper(II) oxide reacts with hot dilute sulfuric acid in a neutralisation reaction to produce a solution of copper(II) sulfate and water

CuO + H2SO4 > CuSO4 +H20
Copper oxide ionic compound containing o2- ions h+ ions from acid been combined to O2- ions from base to form water.

Question 16

What are all the Neutralisation reactions?

Answer 16

Acid + Alkali > Salt + Water
Acid + metal oxide > salt + water
Acid + Metal hydroxide

Question 17

What are the definitions of acid and bases?

Answer 17

An acid as a proton (H+) donor.
A alkali/base as a proton (H+) acceptor (applied to insoluble and soluble bases.

Question 18

What happenes when Sodium hydroxide solution with dilute hydrochloric acid?

Answer 18

Sodium hydroxide solution (an alkali) reacts with a dilute hydrochloric acid to form sodium chloride and water.

NAOH + HCI > NaCl + H20
This is a neutralisation reaction. Sodium hydroxide and sodium chloride are both ionic compounds and so will be presented as ions in solution. HCl is an acid so will dissociate into H+ and Cl -

The Na+ and Cl- ions are the same on both sides of the equation and so are spectator ions.
OH- + H+ > H20
Ionic equation. All neutralisation reactions for an acid reacting with an alkali will have same ionic equation. This is because they all involve the OH- ions from alkali reacting with h+ ions from acid to form water.

Question 19

What is titration?

Answer 19

Titration can be used to follow the course of a neutralisation reaction between an acid and an alkali. Titration can be used to find out ow much of the acid/alkali reacts with a certain volume of acid/alkali.

Question 20

What is the method for titration?

Answer 20

The alkali is added to the acid from the burette until the indicator changed colour. Usually do a rough titration first in order to find out approximately how much alkali is required to neutralise the acid. For example if 22.5cm3 of alkali is required in the rough titration. Then do the experiment again but with 20cm3 of the alkali. Swirling conical flask to mix solutions. Then add the alkali very slowly until one drop of alkali causes the indicator to change from its acid to alkali colour. Then know the amount needed for neutralisation to within 1 drop this is quite precise.