Sodium molybdate

Key takeaways

Sodium molybdate belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sodium molybdate to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sodium molybdate from memory before moving on to harder problems.

Reference excerpt

Sodium molybdate, Na2MoO4, is useful as a source of molybdenum. This white, crystalline salt is often encountered as the dihydrate, Na2MoO4·2H2O.

Structure

In aqueous solution, sodium molybdate features dissociated sodium ions and tetrahedral molybdate (MoO2−4), which adopts a sulfate-like structure. The solid dihydrate material has a complex structure typical for alkali metal salts of oxyanions. The MoO2−4 subunits are tetrahedral with Mo-O distances near 178 pm.

Preparation Dissolution of MoO3 in sodium hydroxide at 50–70 °C followed by crystallizing the filtered product. If crystallized below 10 °C, the decahydrate forms. Above 10 °C, the dihydate crystallizes. The anhydrous salt is obtained by heating this product at 100 °C.

MoO 3 + 2 NaOH + H 2 O ⟶ Na 2 MoO 4 ⋅ 2 H 2 O {\displaystyle {\ce {MoO3 + 2NaOH + H2O -> Na2MoO4*2H2O}}}

Uses The agriculture industry uses 500 tons per year as a fertilizer. In particular, its use has been suggested for treatment of whiptail in broccoli and cauliflower in molybdenum-deficient soils. However, care must be taken because at a level of 0.3 ppm sodium molybdate can cause copper deficiencies in animals, particularly cattle. It is used in industry for corrosion inhibition, as it is a non-oxidizing anodic inhibitor. The addition of sodium molybdate significantly reduces the nitrite requirement of fluids inhibited with nitrite-amine, and improves the corrosion protection of carboxylate salt fluids. In industrial water treatment applications where galvanic corrosion is a potential due to bimetallic construction, the application of sodium molybdate is preferred over sodium nitrite. Sodium molybdate has the advantage in that the dosing of lower ppm's of molybdate allow for lower conductivity of the circulating water. Sodium molybdate at levels of 50-100 ppm offer the same levels of corrosion inhibition as sodium nitrite at levels of 800+ ppm. By utilizing lower concentrations of sodium molybdate, conductivity is kept at a minimum and thus galvanic corrosion potentials are decreased.

Reactions When treated with sodium borohydride, molybdate is reduced to molybdenum(IV) oxide:

Na 2 MoO 4 + NaBH 4 + 2 H 2 O ⟶ NaBO 2 + MoO 2 + 2 NaOH + 3 H 2 {\displaystyle {\ce {Na2MoO4 + NaBH4 + 2H2O -> NaBO2 + MoO2 + 2NaOH + 3H2}}}

Sodium molybdate reacts with the acids of dithiophosphates:

Na 2 MoO 4 + ( RO ) 2 PS 2 H ⟶ [ MoO 2 ( S 2 P ( OR ) 2 ) 2 ] {\displaystyle {\ce {Na2MoO4 + (RO)2PS2H -> [MoO2(S2P(OR)2)2]}}}

with R = Me, Et which further reacts to form [MoO3(S2P(OR)2)4].

Safety Sodium molybdate supports the biosynthesis of molybdoenzymes, which are found in all higher forms of life. The LC50 for freshwater fish ranges from 60 to 7630 mg/L. The toxicity of soluble molybdate to marine organisms has also been reported.

References

Illustrations

Worked examples

Example 1 — a first encounter with Sodium molybdate

Start with the simplest possible case. Write down what Sodium molybdate claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sodium molybdate before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sodium molybdate ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sodium molybdate

In research: Sodium molybdate appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sodium molybdate in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sodium molybdate is common in secondary-school and first-year university syllabi. It links to neighbouring topics Corrosion inhibitors, Dietary minerals, Inorganic compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Sodium molybdate outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Sodium molybdate in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sodium molybdate means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sodium molybdate out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sodium molybdate in simple terms?

Sodium molybdate, Na2MoO4, is useful as a source of molybdenum. This white, crystalline salt is often encountered as the dihydrate, Na2MoO4·2H2O.

Why does Sodium molybdate matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sodium molybdate?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sodium molybdate.