Chemistry: Drying Agents and Gas Collection

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Questions and Answers

Which drying agent is considered neutral?

CaCl2 (correct)

H2SO4

CaO

NaOH

What type of delivery setup is appropriate for collecting dense gases such as CO2?

Downward delivery (correct)

Water displacement

Upward delivery

Direct exposure

Which acid is fully ionized in water and considered a strong acid?

H3PO4

CH3COOH

H2SO4 (correct)

H2CO3

What defines a weak acid in terms of ionization in water?

Partially ionizes to produce H+ ions Signup and view all the answers

Which of the following is NOT a strong acid?

H2CO3 Signup and view all the answers

What happens to HCl when dissolved in water?

It completely ionizes to produce H+ and Cl- ions. Signup and view all the answers

Which drying agent is classified as alkaline?

CaO Signup and view all the answers

Why is a funnel needed at the back of a setup producing NH3?

To prevent gas backflow, which may crack the test tube. Signup and view all the answers

What is the general formula for alkenes?

CnH2n Signup and view all the answers

Which of the following compounds is an example of an alkanoic acid?

CH3COOH Signup and view all the answers

What happens to the boiling point of compounds in a homologous series as the molecular size increases?

It increases Signup and view all the answers

What is the characteristic feature of homologous series that contributes to their similar chemical properties?

Same functional group Signup and view all the answers

Why are alkanes generally unreactive?

They have strong C-H and C-C bonds Signup and view all the answers

What product is majorly formed when an alkane reacts with halogen in excess?

Fully-substituted alkane Signup and view all the answers

In a homologous series, what trend occurs with volatility as molecular size increases?

Volatility decreases Signup and view all the answers

What is a key condition required for the substitution reaction of alkanes with halogens?

Presence of UV light or heat Signup and view all the answers

What happens to the viscosity of petroleum fractions as the molecular size increases?

Viscosity increases Signup and view all the answers

Which of the following correctly describes the state of hydrocarbons with more than 18 carbon atoms?

They are solids Signup and view all the answers

During the refining process of petroleum, what occurs to the longer hydrocarbons in the furnace?

They remain as liquids or solids Signup and view all the answers

In a fractionating tower, where do larger fractions with higher boiling points condense?

At lower, hotter levels Signup and view all the answers

Which of the following statements best describes the combustion of hydrocarbons?

Incomplete combustion increases with carbon content. Signup and view all the answers

What is the effect of molecular size on the volatility of hydrocarbons?

Volatility decreases with larger molecular sizes Signup and view all the answers

Which property of hydrocarbons changes as their molecular size increases, leading to a sootier flame during combustion?

Flammability decreases Signup and view all the answers

What is the primary result of vaporizing petroleum at around 400°C in the refining process?

Most hydrocarbons vaporize, while very long hydrocarbons remain Signup and view all the answers

What is the main purpose of cracking in chemistry?

To break down large molecules into smaller ones Signup and view all the answers

What are the required conditions for the cracking process?

Absence of air and high temperature Signup and view all the answers

How can the product gases from cracking be collected?

By displacement of water Signup and view all the answers

What observable change indicates that halogen solution has reacted during substitution?

The solution's color changes to colorless Signup and view all the answers

What happens to the first few cm³ of gas obtained during cracking?

It is discarded due to air composition Signup and view all the answers

Which of the following best describes the nature of the cracking reaction?

It is endothermic and absorbs heat Signup and view all the answers

What is the color of bromine in an aqueous solution?

Brown Signup and view all the answers

What is a precaution one must take after cracking the reaction is complete?

Remove the delivery tube before stopping heating Signup and view all the answers

What is the observable change when an alkene undergoes addition with halogen?

The halogen solution color changes from its original color to colourless. Signup and view all the answers

Which compound cannot undergo addition reactions due to its extra stability?

Benzene Signup and view all the answers

What is required in addition with cold, dilute KMnO4/H+ to produce a diol from an alkene?

Twice the amount of water and [O] compared to the double bonds in the alkene. Signup and view all the answers

When testing for unsaturation, what color change occurs when an alkene interacts with cold, dilute KMnO4/H+?

Purple to clear. Signup and view all the answers

What happens to the layers formed during an addition reaction involving aqueous halogen and an alkene?

Two immiscible layers of solution are formed. Signup and view all the answers

What should NOT be used to synthesize a diol from alkenes due to potential further oxidation?

Cold dilute KMnO4/H+ Signup and view all the answers

What is the general outcome when an alkene reacts with halogen in an addition reaction?

Formation of a dihaloalkane. Signup and view all the answers

If more than one double bond is present in an alkene during an addition reaction with halogen, what adjustment must be made?

Double the amount of halogen needed. Signup and view all the answers

Study Notes

Drying Agents

Calcium Chloride (CaCl2): Neutral drying agent, no specific acid or base preference.
Calcium Oxide (CaO): Alkaline drying agent, ineffective for acidic gases like HCl and CO2.
Sulfuric Acid (H2SO4): Acidic drying agent, ineffective for alkaline gases like NH3.

Common Gas Collection Set-Ups

Upward Delivery: Suitable for lighter gases (e.g., NH3).
Downward Delivery: Used for denser gases (e.g., CO2).
Water Displacement: Effective for gases not soluble in water (e.g., H2).
Precaution: A funnel is needed when producing NH3 to prevent back suction that may crack the test tube.

Acid-Base Definitions

Neutral Definition: Acid concentration [H+] equals base concentration [OH-]; pH of 7 only at 25°C.
Strong Acids: Fully ionize in water (e.g., HCl, HNO3, H2SO4).
Weak Acids: Partially ionize in water (e.g., H2SO3, H2CO3).

Hydrocarbon States and Properties

1-4 Carbon Atoms: Exist as gases.
5-17 Carbon Atoms: Liquid state.
>18 Carbon Atoms: Solid state.
Physical Properties: Increased molecular size leads to higher boiling points, increased viscosity, decreased volatility and flammability.

Petroleum Refining Process

Step 1: Vaporization at 400°C; small hydrocarbons become gases while larger remain liquid/solid.
Step 2: Separation in a fractionating tower; heavier fractions settle, lighter fractions rise.
Step 3: Fractional condensation occurs where lighter hydrocarbons condense higher in the tower.

Hydrocarbon Combustion

Complete Combustion: Occurs with sufficient oxygen, producing CO2 and H2O.
Incomplete Combustion: Limited oxygen results in carbon monoxide and soot production.

Homologous Series

Definition: Family of compounds with similar chemical properties and gradual physical property changes due to increased molecular size.
General Formulas:
- Alkanes: CnH2n+2
- Alkenes: CnH2n
- Alkanols: CnH2n+1OH
- Alkanoic Acids: CnH2n+1COOH

Chemical Reactions of Alkanes

Combustion and Substitution: Generally unreactive due to strong C-H and C-C bonds.
Substitution with Halogens: Requires UV light or heat to initiate bond breaking with varying products based on halogen excess.

Chemical Reactions of Alkenes

Cracking: Breaking down larger molecules into smaller ones under high temperature and absence of air; collected via water displacement.
Addition Reactions: Test for unsaturation.
- With Halogens: Observable color change from halogen solution to colorless upon reaction.
- With Cold, Dilute KMnO4/H+: Purple to colorless, indicating unsaturation.

Precautions in Reactions

Heat catalyst instead of paraffin to avoid rapid vaporization.
Discard initial gas to eliminate atmospheric air contamination.
Remove delivery tube before stopping heat to prevent back suction of water.

Summary of Chemical Testing

Unsaturation Test: Only alkenes change the color of KMnO4 from purple to colorless; reactions produce diols under basic conditions without further oxidation interference.

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Description

This quiz covers key topics in chemistry regarding drying agents, gas collection methods, and acid-base definitions. Understand how different agents function and their suitability for various gases, as well as the properties of hydrocarbons. Test your knowledge on these essential concepts.