Molybdenum

Reaction of molybdenum with acids

Mo(VI) is reduced to Mo(IV) by ascorbic acid. The reaction is fast [3].

Reaction of molybdenum with air

At room temperature, molybdenum does not react with oxygen, O₂. If heated to red heat, the trioxide molybdenum(VI) oxide, MoO₃, is formed.

2 Mo(s) + 3 O₂(g)

2 MoO₃(s)

Reaction of molybdenum with glycols

Mo(VI) is reduced to Mo(IV) by glycols [3].

Glycols	Reductive coefficient (x 10^-7 M^-1·s^-1)
Ethylene glycol Diethylene glycol Triethylene glycol Tetraethylene glycol PEG	1.06 22.5 2.25 1.80 2.55

Reductive coefficients for glycols adapted from [3].

Reaction of molybdenum with halogens

Molybdenum reacts directly with fluorine, F₂, at room temperature, forming molybdenum(VI) fluoride, MoF₆.

Mo(s) + 3 F₂(g)

MoF₆(l) [colourless]

Under controlled conditions, molybdenum reacts with chlorine, Cl₂, forming molybdenum(V) chloride, MoCl₅.

2 Mo(s) + 5 Cl₂(g)

2 MoCl₅(s) [black]

Reaction of molybdenum with monosaccharides

Mo-ions complexes with monosaccharides. The complexes of D-glucose, D-fructose, D-galactose, D-mannose, D-ribose and D-xylose are as seen below [2]. (a) is best fitted with D-glucose and D-xylose, (b) with D-galactose, (c) with D-ribose and (d) with D-mannose [2].

Fig. 1: Mo-complexes with D-glucose, D-fructose, D-galactose, D-mannose, D-ribose and D-xylose adapted from [2]. (a) is best fit with D-glucose and D-xylose, (b) with D-galactose, (c) with D-ribose and (d) with D-mannose.

Hydrolysis of the complexes changes the concentration of H⁺ in the solution, giving a decrease in pH. The complexes shown i fig 1 all hydrolysis over time [2], D-xylose being the most stable of the complexes and the first to reach equilibrium [2]. During the hydrolysis Mo(VI) is reduced to Mo(IV) by the monosaccharides under acidic conditions [3].

Monosaccharide		Reductive coefficient (x 10^-6 M^-1·s^-1)
Hexoses	D-fructose	3.17
	D-galactose	0.34
	D-glucose	0.41

Reductive coefficients for monosaccharides adapted from [3].

Reaction of molybdenum with sulfide

Mo(VI) is precipitated by sulfide in 0.4 M hydrochloric acid

MoO₄²⁻(aq) + 3 S²⁻(aq) + 8 H⁺(aq)

MoS₃(s) [brown/black] + 4 H₂O(l)

The precipitate can be dissolved by sodium disulfide

2 MoS₃(s) + S₂²⁻(aq)

2 MoS₄²⁻(aq)

Mo(VI) as ammonium molybdate is precipitated by hydrogen sulfide in the presence of ammonia:

MoO₄²⁻(aq) + 4 H₂S(aq) + 2 NH₄⁺(aq)

(NH₄)₂MoS₄(s) [red] + 4 H₂O(l)

Reaction of molybdenum with nucleotides

Mo(VI) is reduced to Mo(IV) by L-cysteine. Reductive coefficient = 1.26·10^-4 M^-1·s^-1 [3]

Reaction of molybdenum with sulfide

Mo(VI) is precipitated by sulfide in 0.4 M hydrochloric acid

MoO₄²⁻(aq) + 3 S²⁻(aq) + 8 H⁺(aq)

MoS₃(s) [brown/black] + 4 H₂O(l)

The precipitate can be dissolved by sodium disulfide

2 MoS₃(s) + S₂²⁻(aq)

2 MoS₄²⁻(aq)

Mo(VI) as ammonium molybdate is precipitated by hydrogen sulfide in the presence of ammonia:

MoO₄²⁻(aq) + 4 H₂S(aq) + 2 NH₄⁺(aq)

(NH₄)₂MoS₄(s) [red] + 4 H₂O(l)

Reaction of molybdenum with water

At room temperature, molybdenum does not react with water.

Quantitative analysis

Method 3500-Mo C Inductively Coupled Plasma Method [7]. A portion of the sample is digested in a combination of acids. The digest is aspirated into an 8,000 K argon plasma where resulting light emission is quantified for 30 elements simultaneously.

Method limit of detection in water = 0.002 mg/L
Method limit of detection in soil = 1.00 mg/kg