1.1 - Formulae of compounds and ions

Question 1

How do you work out the formula of an ionic compound?

Answer 1

1) Write out the symbols and ions within the compound
2) Balance the ions so that the total charge of the compound is 0 (compounds are neutral)
3) Write the formula out without the charges and write the number of ions on the bottom right of the element.

Question 2

Work out the ionic formula of sodium sulfide.

Answer 2

Ions are Na+ and s2-
We need 2 NA+ ions for every S2-
Na2S

Question 3

What is an oxidation number?

Answer 3

Number of electrons that need to be added to or taken away from an element to make it neutral.

Question 4

What are the 6 oxidation rules?

Answer 4

1) The oxidation number of an uncombined element is 0
2) the sum of oxidation numbers in a compound is zero, in an ion its equal to its charge
3) In group 1 and 2 metals, the on is +1 and +2
4) Oxygen is -2 unless with fluorine
5) The on of hydrogen is +1 in compounds apart from in metal hydrides
6) The most electronegative element is given the negative oxidation number

Question 5

What can oxidation numbers show?

Answer 5

Used in redox reactions to show which species has been oxidised and reduced.

Question 6

How do you write a balanced equation?

Answer 6

1) write word equation
2) write symbols and formulae
3) balance equation by multiplying formula
4) add state symbols (g,aq,l,s)

Question 7

What are ionic equations?

Answer 7

Looking at the charges of elements to see where the reactions are taking place, to simplify a formula.

Question 8

Water

Answer 8

H20

Question 9

Carbon dioxide

Answer 9

CO2

Question 10

Sulfur dioxide

Answer 10

SO2

Question 11

Methane

Answer 11

CH4

Question 12

Hydrochloric acid

Answer 12

HCl

Question 13

Sulfuric acid

Answer 13

H2SO4

Question 14

Nitric acid

Answer 14

HNO3

Question 15

Ethanoic acid

Answer 15

CH3CO2H

Question 16

Ammonia

Answer 16

NH3

Question 17

Ammonium chloride

Answer 17

NH4Cl

Question 18

Sodium hydroxide

Answer 18

NaOH

Question 19

Sodium chloride

Answer 19

NaCl

Question 20

Sodium carbonate

Answer 20

Na2CO3

Question 21

Sodium hydrogencarbonate

Answer 21

NaHCO3

Question 22

Sodium sulfate

Answer 22

Na2SO4

Question 23

Copper II oxide

Answer 23

CuO

Question 24

Copper II sulfate

Answer 24

CuSO4

Question 25

Calcium hydroxide

Answer 25

Ca(OH)2

Question 26

Calcium carbonate

Answer 26

CaCO3

Question 27

Calcium chloride

Answer 27

CaCl2

Question 28

Ammonium

Answer 28

NH4-

Question 29

Hydrogen

Answer 29

H+

Question 30

Lithium

Answer 30

Li+

Question 31

Potassium

Answer 31

K+

Question 32

Sodium

Answer 32

Na+

Question 33

Silver

Answer 33

Ag+

Question 34

Barium

Answer 34

Ba2+

Question 35

Calcium

Answer 35

Ca2+

Question 36

Magnesium

Answer 36

Mg2+

Question 37

Copper (II)

Answer 37

Cu2+

Question 38

Iron (II)

Answer 38

Fe2+

Question 39

Iron (III)

Answer 39

Fe3+

Question 40

Aluminium

Answer 40

Al3+

Question 41

Bromide

Answer 41

Br-

Question 42

Chloride

Answer 42

Cl-

Question 43

Fluoride

Answer 43

F-

Question 44

Iodide

Answer 44

I-

Question 45

Hydrogencarbonate

Answer 45

HCO3-

Question 46

Hydroxide

Answer 46

OH-

Question 47

Nitrate

Answer 47

NO3-

Question 48

Oxide

Answer 48

O2-

Question 49

Sulfide

Answer 49

S2-

Question 50

Carbonate

Answer 50

CO3 2-

Question 51

Sulfate

Answer 51

SO4 2-

Question 52

Phosphate

Answer 52

PO4 3-

Question 53

What does it mean if a positive ion has formed?

Answer 53

If there are fewer electrons than protons the ion is positively charged.

Question 54

What does it mean if a negative ion has formed?

Answer 54

If the result is an atom with more electrons than protons, the ion is negatively charged.