Illustrated Guide to Home Chemistry Experiments

186 DIY Science: Illustrated Guide to Home Chemistry Experiments

LABORATORY 1 0.2:

oBSERvE THE oxIdATIoN STATES of mANGANESE

Many elements can exist in several oxidation

states, which may differ noticeably in color.

In the introduction, we mentioned vanadium

as one such element. Manganese is another

element whose various oxidation states have

different colors, including MnO 4 – (+7, violet),

MnO 4 2– (+6, green), MnO 2 (+4, orange), Mn 2 O 3

(+3, violet), and Mn2+ (+2, pale pink).

RIREEqU d EqUIpmENT ANd SUppLIES

£ goggles, gloves, and protective clothing

£ test tubes (4)

£ test tube rack

£ graduated cylinder, 10 mL

£ dropper or beral pipette

£ stirring rod

£ potassium permanganate (kmno 4 ) solution, 0.01

m (50 mL)

£ sodium hydroxide solution, 1.0 m (8 mL)

£ sulfuric acid solution, 1.0 m (6 mL)

£ sodium bisulfite (NaHSo 3 ) solution, 0.01 m

(as required)

In this laboratory, we’ll begin with a solution of potassium
permanganate, in which manganese is in the +7 oxidation state,
and reduce the oxidation state to observe the color changes
associated with various oxidation states of manganese. To
achieve these changes in oxidation state, we’ll react potassium
permanganate with sodium bisulfite in neutral, basic (sodium
hydroxide), and acid (sulfuric acid) solutions, which are
represented by the equations shown in Table 10-2.

TABLE 10-2: Oxidation states of manganese

CUTIOA nS

Solutions of sodium hydroxide and sulfuric acid are

corrosive. Wear splash goggles, gloves, and protective

clothing.

z

Solution

Oxidation

stateIonColorEquation

Neutral +4MnO 2 orange2 MnO 4 – (aq) + 3 HSO 3 – + OH– ↔ 2 MnO 2 (s) + 3 SO 4 2–(aq) + 2 H 2 O(l)

Basic

(sodium hydroxide) +6MnO^4

2– green2 MnO 4 – (aq) + HSO 3 – + 3 OH– ↔ 2 MnO 4 2–(aq) + SO 4 2–(aq) + 2 H 2 O(l)

Acid (sulfuric acid)+2Mn2+ pink2 MnO 4 – (aq) + 5 HSO 3 – + H+ ↔ 2 Mn2+(aq) + 5 SO 4 2–(aq) + 3 H 2 O(l)