ACID AND REDOX

Question 1

Which element do all acids contain?

Answer 1

Hydrogen

Question 2

What happens when an acid is dissolved in water?

Answer 2

When an acid is dissolved in water, it releases hydrogen ions as protons, H+, into the solution

Question 3

What is the equation that shows hydrogen chloride gas dissolving to form an aqueous solution?

Answer 3

HCl (g) + aq ———–> H+ (aq) + Cl- (aq)

+aq shows the excess of water present

Question 4

What is an example of a strong acid?

Answer 4

Hydrochloric acid

Question 5

What happens to a strong acid when placed in an aqueous solution?

Answer 5

The strong acid releases all its hydrogen atoms into solution as H+ ions

It completely dissociates in an aqueous solution

Question 6

What happens to a weak acid when placed in an aqueous solution?

Answer 6

A weak acid only releases a small proportion of its available hydrogen atoms into solution as H+ ions.

It partially dissociates in aqueous solution.

Question 7

What is an example of a weak acid?

Answer 7

Ethanoic acid - Ch3COOH

Question 8

Why is ethanoic acid a weak acid?

Answer 8

A molecule of ethanoic acid contains 4 hydrogen atoms.

But only the hydrogen atom on the COOH group is released as H+

Question 9

What is a base?

Answer 9

A base neutralises an acid to form a salt

Question 10

What are example of bases?

Answer 10

Metal oxides
Metal hydroxides
Metal carbonates
Ammonia, NH3

Question 11

What is an Alkali?

Answer 11

An alkali is a base that dissolves in water releasing hydroxide ions (OH-) into the solution.

Question 12

What is the equation that shows alkali sodium hydroxide dissolving in water?

Answer 12

NaOH releases hydroxide ions as it dissolves in water

NaOH (s) + aq ——–> Na+ (aq) + OH- (aq)

Question 13

What is the formula of hydrochloric acid?

Answer 13

HCl

Question 14

What is the formula of sulfuric acid?

Answer 14

H2SO4

Question 15

What is the formula of nitric acid?

Answer 15

HNO3

Question 16

What is the formula of Ethanoic acid?

Answer 16

CH3COOH

Question 17

Name 4 common acids

Answer 17

Hydrochloric acid
Sulfuric acid
Nitric acid
Ethanoic acid

Question 18

Name 3 common metal oxide bases

Answer 18

MgO - Magnesium oxide
CaO - Calcium oxide
CuO - Copper oxide

Question 19

Name 3 common metal carbonate bases

Answer 19

Na2CO3 - Sodium carbonate
CaCO3 - Calcium carbonate
CuCO3 - Copper carbonate

Question 20

Name 3 common Alkali bases

Answer 20

NaOH - Sodium hydroxide
KOH - Potassium hydroxide
NH3 - Ammonia

Question 21

What are the products of a neutralisation of acid

Answer 21

Acid + metal oxide/hydroxide —-> Salt + water

Question 22

How do you form a salt from an acid?

Answer 22

The hydrogen in the acid is replaced by a metal or ammonium ion to form the salt

E.g. Hcl —–> NaCl

Question 23

What do you use to neutralise an acid?

Answer 23

A metal oxide or metal hydroxide

To form a salt and water only

Question 24

Acid + Alkali —->

Answer 24

Acid + Alkali —–> salt + water

Question 25

Carbonates neutralise acids to form...

Answer 25

salt + water + carbon dioxide gas

Question 26

Whats the differenc between a strong and a weak acid?

Answer 26

Strong acid fully dissociates in aqueous solution Weak acid partially dissociates in aqueous solution

Question 27

Neutralisation of an acid

Answer 27

The H+ ions react with a base to form a salt + water. H+ is replaced by metal or ammonium ions from base

Question 28

With alkalis, all reactants for neutralization are...

Answer 28

Aqueous

Question 29

What is a titration?

Answer 29

A titration is a technique used to accurately measure the volume of one solution that reacts exactly with another solution

Question 30

Titrations can be used for:

Answer 30

Finding the concentration of a solution Identification of unknown chemicals Finding the purity of a substance

Question 31

Why is finding the purity of a substance important?

Answer 31

Important for pharmaceuticals Just a tiny amount of impurity in a drug could cause a great deal of harm to a patient

Question 32

Volumetric flask typical tolerances

Answer 32

100cm^3 +/- 0.2cm^2 250cm^3 +/- 0.3cm^3

Question 33

Experimentally preparing standard solutions procedure:

Answer 33

Solid weighed + dissolved in beaker using less distilled water than needed to fill volumetric flask Transfer to volumetric flask + last traces rinsed into flask with distilled water Add distilled water dropwise until bottom of meniscus matches up with the mark Flask inverted slowly several times to mix, if not titration results will be inconsistent

Question 34

Pipette Typical tolerances

Answer 34

10 cm^3 +/- 0.04cm^3 25cm^3 +/- 0.06 cm^3 Burette: 50cm^3 +/- 0.1

Question 35

How is a burette measured and recorded?

Answer 35

Burette is recorded to the nearest half division, to 2dp (last 5 or 0)

Question 36

Acid - base titration procedure

Answer 36

Add measured volume one solution to conical flask with pipette Add other solutions to burette, recording initial reading Add few drops of indicator to conical flask Run solution from burette into conical flask, swirling it, until it reaches the end point Record first reading 1st titre carried out quickly to get approx, then repeat accurately adding solution dropwise as end point approached. Carry out until two accurate titres are concordant (within 0.1cm^3)

Question 37

What is the oxidation number of oxygen?

Answer 37

-2

Question 38

What is the oxidation number of hydrogen?

Answer 38

+1

Question 39

What is the oxidation state of fluorine?

Answer 39

-1

Question 40

What is the oxidation state of ions

Answer 40

Charge on the ions

Question 41

What are the special cases in oxidation numbers

Answer 41

H in metal Hydrides: -1 O in peroxides: -1 (02 ^2-) O boded to F: +2

Question 42

Reduction is

Answer 42

Gain of electrons | Decrease in oxidation numbers

Question 43

Oxidation is

Answer 43

Loss of electrons | Increase in oxidation numbers