Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 7: Problem 73

When a solution of white phosphorous in \(\mathrm{CS}_{2}\) is poured over saw dust, the latter catches fire spontaneously on blowing air upon it because (a) \(\mathrm{CS}_{2}\) is volatile (b) \(\mathrm{CS}_{2}^{-}\) is inflammable (c) \(\mathrm{P}\) is reactive (d) Ignition temperature of white \(\mathrm{P}\) is low

Short Answer

Expert verified
The saw dust catches fire spontaneously because white phosphorous (P) is extremely reactive and has a low ignition temperature, making it ignite easily on exposure to air.

Step by step solution

01

Understanding the Reaction

The exercise presents a scenario where a solution of white phosphorous in carbon disulfide (CS2) is poured over saw dust. When air is blown over the mixture, the saw dust catches fire spontaneously. To solve which is the correct reason, it's important to consider the chemical properties of both white phosphorous and carbon disulfide.
02

Evaluate the Choices

Evaluate each option in the context of the reaction described. (a) Volatility of CS2 would aid in its rapid evaporation but does not explain ignition. (b) CS2 is indeed flammable, but its anion CS2- isn't mentioned in the context of the reaction. (c) White phosphorous is known to be reactive, especially when exposed to air. (d) White phosphorous has a very low ignition temperature, which means it can catch fire at room temperature when exposed to air.
03

Identify the Correct Reason

The correct reason for the saw dust catching fire must relate to the component that reacts with oxygen in the air. White phosphorous (P) is extremely reactive and has a very low ignition temperature which allows it to spontaneously ignite in the presence of air. This is more likely the cause of the spontaneous fire than the volatility or flammability of CS2.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

White Phosphorous Reactivity
White phosphorous is a highly reactive element, particularly when it comes in contact with atmospheric oxygen.

Its reactivity stems from its structure; it exhibits a P4 tetrahedral molecule, which is strain-riddled and therefore highly reactive. When exposed to air, white phosphorous spontaneously ignites, which is why it must be stored underwater or in inert atmospheres to prevent unwanted reactions.

The reactivity is such that it can cause combustible materials like sawdust to catch on fire without an external ignition source, simply by being in close proximity to the reactive phosphorous.
Ignition Temperature of White Phosphorous
Ignition temperature refers to the lowest temperature at which a substance will spontaneously catch fire without an external source of ignition. For white phosphorous, this temperature is very low, at about 30°C (86°F), which is well below room temperature.

This low ignition temperature makes white phosphorous unique and especially dangerous, as it can spontaneously combust upon contact with air. It explains why in chemical reactions, even at room temperature, white phosphorous can be the primary cause of ignition when other factors are present.
Flammability of Carbon Disulfide
Carbon disulfide, or CS2, is a highly volatile and flammable liquid. Its volatility means it easily evaporates at room temperature, creating a flammable atmosphere above the liquid. This flammable vapor can ignite easily with a flame or spark; however, it requires such an external ignition source to combust.

In contrast to white phosphorous, carbon disulfide's flammability is not the primary cause of the spontaneous fire in the exercise. Instead, it acts as a solvent for white phosphorous and helps in distributing it over a surface, such as sawdust, which then ignites due to the extreme reactivity of white phosphorous.
Chemical Reactions with Oxygen
Oxygen is a key player in combustion reactions. In the presence of oxygen, flammable substances can undergo rapid oxidation, releasing energy in the form of heat and light—what we observe as fire.

White phosphorous reacts with oxygen to form phosphorus pentoxide in a highly exothermic reaction. The energy released from this reaction is sufficient to cause nearby flammable materials, like sawdust, to ignite spontaneously. This type of chemical reaction demonstrates the importance of oxygen in combustion and the need for careful handling of substances that can react so vigorously with it.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Which has maximum number of allotropes here? (a) \(\mathrm{S}\) (b) \(\mathrm{O}\) (c) Se (d) \(\mathrm{Te}\)

What is the Haber's process? (a) The synthesis of hydrazine, \(\mathrm{N}_{2} \mathrm{H}_{4}\) (b) The synthesis of nitric acid, \(\mathrm{HNO}_{3}\) (c) The isolation of \(\mathrm{N}_{2}\) from the atmosphere (d) The synthesis of ammonia, \(\mathrm{NH}_{3}\)

In \(\mathrm{H}_{4} \mathrm{P}_{2} \mathrm{O}_{7}\) the oxidation state of P-atom and basicity of the acid are respectively? (a) \(+5,3\) (b) \(+5,4\) (c) \(+4,5\) (d) \(+3,3\)

Which one of the following is used in the industrial preparation of nitric acid by Ostwald's process? (a) \(\mathrm{NH}_{3}\) (b) \(\mathrm{N}_{2} \mathrm{O}_{5}\) (c) \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) (d) \(\mathrm{N}_{2}\)

White phosphorus \(\left(\mathrm{P}_{4}\right)\) has (1) \(\operatorname{six} \mathrm{P}-\mathrm{P}\) sigma bonds (2) four \(\mathrm{P}-\mathrm{P}\) single bonds (3) four lone pairs of electrons (4) PPP angle of \(60^{\circ}\) (a) \(1,2,3\) (b) \(2,3,4\) (c) \(\mathrm{N}_{2} \mathrm{O}_{4}\) (d) \(1,3,4\)
See all solutions

Recommended explanations on Chemistry Textbooks

Chemistry Branches

Read Explanation

The Earths Atmosphere

Read Explanation

Chemical Reactions

Read Explanation

Inorganic Chemistry

Read Explanation

Organic Chemistry

Read Explanation

Kinetics

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free