Chemistry Concepts Quiz

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Questions and Answers

State the element in Period 3 that has the highest first ionisation energy.

Argon / Ar

Explain why the TlCl2 + ion has the shape that you have drawn in part (f)(i).

Two bonds (pairs of electrons) repel equally.

Explain why CF4 has a bond angle of 109.5°.

4 bonding pairs of electrons around carbon repel equally.

Explain how the electron pair repulsion theory can be used to deduce the shape of PF3.

PF3 has a tetrahedral/trigonal pyramidal shape with a bond angle of 107°. Signup and view all the answers

Explain why magnesium has a higher melting point than sodium.

Mg2+ has a higher charge than Na+. Signup and view all the answers

Write an equation for the reaction of sulfur(IV) oxide with water.

SO2 + H2O → H+ + HSO3 - Signup and view all the answers

Write an equation for the reaction between phosphorus(V) oxide and magnesium oxide.

P4O10 + 6MgO → 2Mg3(PO4)2 Signup and view all the answers

Write an equation for the reaction of magnesium with titanium(IV) chloride.

2Mg + TiCl4 → 2MgCl2 + Ti Signup and view all the answers

Explain why calcium has a higher melting point than strontium.

Calcium has delocalized electrons that are closer to the cations. Signup and view all the answers

Write the simplest ionic equation for the reaction of acidified barium chloride with sulfate ions.

Ba2+ + SO4 2- → BaSO4 Signup and view all the answers

Write the equation for the reaction of sodium bromide with concentrated sulfuric acid and explain why bromide ions react differently from chloride ions.

2NaBr + 2H2SO4 → Na2SO4 + Br2 + SO2 + 2H2O Signup and view all the answers

Discuss how to prepare a pure sample of silver bromide from a mixture of sodium chloride and sodium bromide.

Add silver nitrate to form AgCl and AgBr precipitates, then dissolve AgCl with dilute ammonia. Signup and view all the answers

Write an ionic equation for the reaction between chlorine and cold dilute sodium hydroxide solution.

Cl2 + 2HO- → OCl- + Cl- + H2O Signup and view all the answers

State how to test a sample of water for chloride ions.

Add silver nitrate, observe a white precipitate. Signup and view all the answers

Deduce the half-equation for the formation of hydrogen sulfide from concentrated sulfuric acid.

SO4 2− + 10H+ + 8e - → H2S + 4H2O Signup and view all the answers

State why silver nitrate solution is acidified when testing for iodide ions.

To react with/remove ions that would interfere with the test. Signup and view all the answers

Explain why dilute hydrochloric acid is not used to acidify the silver nitrate solution.

HCl would form a white precipitate with silver nitrate. Signup and view all the answers

Describe the method to prepare a solution containing a known mass of MHCO3.

Weigh the sample, add water, stir to dissolve, transfer to volumetric flask, make up to the mark. Signup and view all the answers

Explain how ions are accelerated, detected and their abundance determined in a TOF mass spectrometer.

Ions accelerate due to attraction to a negatively charged plate, detected by gaining electrons. Signup and view all the answers

Write a half-equation for the reduction of chlorate(I) ions to chlorine in acidic conditions.

2ClO− + 4H+ + 2e− → Cl2 + 2H2O Signup and view all the answers

Write an overall equation for the redox reaction of chlorate(I) ions with hydrochloric acid.

ClO− + Cl− + 2H+ → Cl2 + H2O Signup and view all the answers

What is observed when sodium chlorate(l) is added to potassium iodide?

The solution goes brown. Signup and view all the answers

Give one reason why bond enthalpy from your calculations differs from literature values.

Data book values derive from multiple compounds, not just one. Signup and view all the answers

Suggest improvements to the method and analysis for more accurate enthalpy change determinations.

Use better insulation, improved temperature recording, and advanced result analysis. Signup and view all the answers

Write a half-equation for the conversion of NO2 − in an acidic solution into NO.

NO2− + e− + 2H+ → NO + H2O Signup and view all the answers

Write an overall ionic equation for the reaction of NO2 − in an acidic solution with I−.

2NO2− + 2I− + 4H+ → I2 + 2NO + 2H2O Signup and view all the answers

Study Notes

Ionisation Energy

Argon (Ar) in Period 3 has the highest first ionisation energy due to its large number of protons, resulting in a strong nuclear charge, while maintaining the same electron shielding as other elements in the period.

Molecular Shape and Repulsion

The TlCl2+ ion exhibits a geometry where bond pairs of electrons repel equally to maximize distance between them.
CF4 has a bond angle of 109.5° because it has four bonding pairs around carbon, which repel equally and are arranged as far apart as possible.

Electron Pair Repulsion Theory

In PF3, phosphorus (P) has five outer shell electrons, leading to three bonding pairs and one lone pair, resulting in a trigonal pyramidal shape with a bond angle decreased to 107°.
Lone pairs repel more strongly than bonding pairs.

Melting Points

Magnesium (Mg) has a higher melting point than sodium (Na) due to Mg2+ having a greater charge compared to Na+, increasing the strength of electrostatic attraction.
Calcium has a higher melting point than strontium (Sr) because it has delocalised electrons closer to cations, leading to stronger attraction between cations and delocalised electrons.

Reactions with Acids

Sulfur(IV) oxide (SO2) reacts with water to form hydrogen ions and bisulfite ions: SO2 + H2O → H+ + HSO3-.
Phosphorus(V) oxide reacts with magnesium oxide: P4O10 + 6MgO → 2Mg3(PO4)2.
The reaction of magnesium with titanium(IV) chloride yields titanium and magnesium chloride: 2Mg + TiCl4 → 2MgCl2 + Ti.

Ionic Equations

The simplest ionic equation for the reaction of barium chloride with sulfate ions is: Ba2+ + SO4 2- → BaSO4.
The half-equation for the formation of hydrogen sulfide from sulfuric acid is: SO4 2− + 10H+ + 8e− → H2S + 4H2O.

Chloride Tests

Testing for chloride ions involves adding silver nitrate (AgNO3) to yield a white precipitate: Ag+ + Cl− → AgCl.
To test for iodide ions, silver nitrate is acidified to prevent interference from other ions: HCl adds a precipitate that complicates the test.

Iodide Reaction and Observations

Sodium bromide reacts with sulfuric acid to form sodium sulfate, bromine, sulfur dioxide, and water: 2NaBr + 2H2SO4 → Na2SO4 + Br2 + SO2 + 2H2O. Bromide ions, larger than chloride ions, are oxidized more readily.
A solution of sodium chlorate(I) added to potassium iodide turns brown due to the formation of iodine (I2) from the oxidation of iodide ions (I−).

Determining Enthalpy and Bond Enthalpy

Mean bond enthalpy values can differ from calculated values because they are averaged from various compounds, not just a single type.
To improve the accuracy of enthalpy measurements, methods can include better insulation, extended temperature recording prior to reaction, and extrapolating data for temperature corrections.

Half-Equations for Reactions

Reduction of chlorate(I) ions in acidic conditions can be represented as: 2ClO− + 4H+ + 2e− → Cl2 + 2H2O.
Overall ionic reaction of chlorate(I) ions with hydrochloric acid: ClO− + Cl− + 2H+ → Cl2 + H2O.

Ionic Reactions with NO2 −

Conversion of nitrate ions (NO2−) in acidic solutions into nitric oxide (NO): NO2− + e− + 2H+ → NO + H2O.
Overall ionic reaction of NO2− with iodide ions (I−) produces iodine, nitric oxide, and water: 2NO2− + 2I− + 4H+ → I2 + 2NO + 2H2O.

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Description

Test your understanding of key chemistry concepts related to ionization energy, molecular shapes, and bond repulsion. This quiz covers fundamental principles that are essential for mastering chemistry. Each question encourages you to explain your reasoning clearly.