Chapter 4

Question 1

What is ionic equation ? What does it show ? How do you write one ?

Answer 1

When solutions of different ionic substances are mixed, precipitation sometimes occurs.
An ionic equation shows how ionic substances react as independent ions in solutions.

Separate all ionic aqueous substances into ions
Identify spectator ions ( those present on both sides ) and remove them.

Question 2

What happens when ionic solids dissolve in water ?

Answer 2

The ions become surrounded by water molecules and
become hydrated (or ‘solvated’).
 - O atoms in water molecules are attracted to the
cation.
 + H atoms in water molecules are attracted to the
anion.

The ions are separated and behave independently:
NaCl (s) → Na + (aq) + Cl - (aq)

Ionic solids dissolve in water when the attraction between the polar
water molecules and the ions is sufficient to overcome the attraction
between the ions in the solid lattice.
In solution the individual ions are surrounded by water molecules and
are independent of each other.

Question 3

Are all alkali metals and nitrates ( examples of ionic solids ) soluble or insoluble ?

Answer 3

Soluble

Question 4

Formula for common acids : Hydrochloric, sulphuric, nitric and ethanoic acids

Answer 4

HCl, H2SO4, HNO3 and CH3COOH

Question 5

Formula for common alkalis : sodium hydroxide, potassium hydroxide and ammonia

Answer 5

NaOH, KOH, NH3

Question 6

What do acids release in aqueous solution ?

Answer 6

H+ ions. All acids contain a hydrogen atom which can be lost from the molecule as H+ ions.

Question 7

What do alkalis release in aqueous solution ?

Answer 7

OH- ions.

Question 8

Acid definition

Answer 8

Substance that produces hydrogen ions in solution. H+ donors

Question 9

Base definition

Answer 9

Substance that neutralises an acid to produce a salt. H+ acceptors.

Question 10

Alkali definition

Answer 10

A soluble base that dissolves in water to form hydroxide ions. H+ acceptors

Question 11

What are the 4 different types of bases ?

Answer 11

Hydroxides, oxides, carbonates and ammonia.

Question 12

What is a strong acid ?

Answer 12

Good donors of H+ ions, fully dissociate in aqueous solution ( water )

Question 13

What is a weak acid ?

Answer 13

Bad donors of H+ ions, partially dissociate in aqueous solution ( water )

Question 14

Salt definition

Answer 14

It is the product of a reaction where by H+ ions are replaced by metal or ammonium ions.

Question 15

Neutralisation definition

Answer 15

A chemical reaction in which an acid and a base react together to produce a salt

Question 16

Neutralisation equation

Answer 16

Reaction of H+ and OH– to form H2O

Question 17

Name the products when an acid reacts with :
Base
Alkali
Metal
Carbonate

Answer 17

Salt + Water
Salt + Water
Salt + Hydrogen
Salt + Water + Carbon dioxide

Question 18

How to calculate percentage error ?

Answer 18

( uncertainty in measurement / actual measurement ) x 100

Question 19

How do you make a standard solution and carry out a titration ?

Answer 19

1) Calculate the amount of solid required and weigh it out
2) Place solid in beaker and dissolve in small volume of solvent
3) Transfer solution to volumetric flask using funnel
4) Rinse breaker and rod into volumetric flask
5) Fill volumetric flask to just below the graduation mark using a wash bottle
6) Use teat pipette to carefully add solvent to bring level up to the mark
7) Stopper the flask and invert to ensure thorough mixing

Using a burette : rinse equipment with solution you are using
Always use funnel to fill burette but remove it afterwards
After taking initial reading run the solution into the conical flask whilst swirling it until colour appears to be changing then add drop wise until one more makes the colour change permanently.
Read burette from bottom of miniscus quoting to 2dp
Need at least 2 concordant results ( within 0.10cm3 of each other )

Question 20

Titration calculations method

Answer 20

Write balanced equation
Calculate moles of one substance using info in question
Calculate moles of other substance using ratio
Calculate concentration using c = n/v

Question 21

Oxidation number rules

Answer 21

1) Oxidation number of atoms in elements is always zero
2) Group 1 = +1, Group 2 = +2
3) Zn = +2, Al = +3, F = -1
4) H = +1 ( except when in groups 1, 2 or with Al )
5) Oxygen = -2 ( except with F and in peroxides )
6) Chlorine = -1 ( except when with O and F )

Question 22

Oxidation numbers in a compound

Answer 22

Have to add up to zero

Question 23

Oxidation numbers in an ion

Answer 23

The sum of all the oxidation numbers is equal to the charge on the ion.

Question 24

Naming compounds using oxidation numbers

Answer 24

Roman numerals are used to indicate the magnitude of the oxidation number when an element may have compounds/ions with different oxidation numbers

Question 25

Using oxidation number to decide whether oxidation or reduction has taken place

Answer 25

If element becomes more positive during reaction, it has been oxidised so it has lost electrons.
If element becomes less positive during reaction, it has been reduced so it has gained electrons.

Question 26

Oxidation and Reduction in terms of electrons

Answer 26

OILRIG
Oxidation is loss of electrons
Reduction is gain of electrons

Question 27

How you work out oxidation numbers and how they change in reactions

Answer 27

i). Ignore the multipliers in the equation (equations don’t even need to be
balanced!!!)
ii). Use what you know to work out what you don’t know.
iii). Use total oxidation numbers to help you work out unknown oxidation numbers
iv). Clearly state what the starting and finishing oxidation numbers are.