Chapter 8.3 - Trends In The Physical Properties Of Halogens Flashcards
Explain why chlorine has a lower boiling point than bromine. (2)
- chlorine has fewer electrons than bromine,
- weak van der waals forces between chlorine molecules
Suggest why iodide ions are stronger reducing agents than chloride ions (2)
- iodine ions are larger than chloride ions,
- the outer electron is less strongly held by the nucleus compared with that from a chloride ions
Explain why iodine has a higher melting point than fluorine. (2)
- iodine is a bigger molecule than fluorine,
- strong van der waals forces between molecules,
- more energy needed to overcome the forces
State the trend in electronegativity of the elements down Group VII. Explain this trend.
Trend
Explanation (3)
- decreases,
- shielding increases,
- weaker attraction by nuclear on electron pair in a covalent bond
State the trend in reducing ability of the halide ions down Group VII. (1)
Increases
Describe and explain the trend in the boiling points of the elements down Group VII from fluorine to iodine. (4)
- increases from fluorine to iodine,
- size of molecules increases,
- van der waals forces increase,
- more energy needed to break the forces
State and explain the trend in electronegativity down Group VII from fluorine to iodine.
Trend
Explanation (3)
- decreases,
- increase in shielding,
- weaker attraction by nucleus on electron pair in a covalent bond
State the trend in the boiling points of the halogens from fluorine to iodine and explain this trend.
Trend
Explanation (4)
- increases,
- Van der waals forces between molecules increase with size,
- more energy needed to overcome these forces
Which one of the following is not a correct trend down Group VII?
A The first ionisation energy of the atom decreases.
B The oxidising power of the element increases.
C The electronegativity of the atom decreases.
D The boiling point of the element increases.
B
State and explain the trend in electronegativity down Group VII from fluorine to iodine.
Trend
Explanation (3)
- decreases,
- atomic radius increases,
- shielding increases
- weaker attraction by nucleus on electron pair in a covalent bond
The boiling points of the halogens increase down Group VII because
A covalent bond strengths increase.
B bond polarities increase.
C the surface areas of the molecules increase.
D electronegativities increase
C
Which one of the following statements is correct?
A The first ionisation energies of the elements in Period 3 show a general decrease from
sodium to chlorine.
B The electronegativities of Group 2 elements decrease from magnesium to barium.
C The strength of the intermolecular forces increases from hydrogen fluoride to hydrogen chloride.
D The ability of a halide ion to act as a reducing agent decreases from fluoride to iodide
B
The boiling points of the halogens increase down Group VII because
A covalent bond strengths increase.
B bond polarities increase.
C the surface areas of the molecules increase.
D electronegativities increase
C
Which one of the following is not a correct trend down Group VII?
A The first ionisation energy of the atom decreases.
B The oxidising power of the element increases.
C The electronegativity of the atom decreases.
D The boiling point of the element increases.
B
Which of these species is the best reducing agent?
A Cl2
B Cl−
C I2
D I−
D
Which one of the following is the electron arrangement of the strongest reducing agent?
A 1s2 2s2 2p5
B 1s2 2s2 2p6 3s2
C 1s2 2s2 2p6 3s2 3p5
D 1s2 2s2 2p6 3s2 3p6 4s2
D
Which one of the following can act as an oxidising agent but not as a reducing agent?
A CH3CHO
B Fe2+
C I−
D MnO4-
D
The reaction between sodium iodide and concentrated phosphoric acid produces hydrogen iodide but no iodine. The reaction of sodium iodide with concentrated sulphuric acid produces mainly iodine. The difference in product occurs because, in comparison with sulphuric acid, phosphoric acid is
A the weaker acid.
B the stronger oxidising agent.
C the weaker oxidising agent.
D the stronger reducing agent
C
Write the simplest ionic equation for the reaction of chlorine with bromide ions. (1)
Cl2 + 2Br- = 2Cl- + Br2
Cl2 + 2Br- = 2Cl- + Br2
Give one observation that would be made during this reaction. (1)
Turns to yellow/orange/brown solution
In sunlight, chlorine can also oxidise water slowly to form oxygen. Write an equation for this reaction (2)
Equation
Oxidation state of chlorine in the reaction
2Cl2 + 2H2O = 4HCL + O2
-1
The following pairs of compounds can be distinguished by simple test-tube reactions.
For each pair, give a suitable reagent that could be added separately to each compound to distinguish between them.
Describe what you would observe in each case AgBr and AgI (3) Reagent: Observation with AgBr: Observation with AgI:
Reagent: concentrated sulfuric acid
Observation with AgBr: cream solid turns orange,
Observation with AgI: yellow solid turns black
The following pairs of compounds can be distinguished by simple test-tube reactions.
For each pair, give a suitable reagent that could be added separately to each compound to distinguish between them.
Describe what you would observe in each case HCl and HNO3 (3) Reagent: Observation with HCl: Observation with HNO3:
Reagent: silver nitrate
Observation with HCl: white ppt,
Observation with HNO3: remains colorless
The following pairs of compounds can be distinguished by simple test-tube reactions.
For each pair, give a suitable reagent that could be added separately to each compound to distinguish between them.
Describe what you would observe in each case
Aqueous silver nitrate and Aqueous sodium nitrate (3)
Reagent:
Observation with Aqueous silver nitrate:
Observation with Aqueous sodium nitrate:
Reagent: bromine water,
Observation with aqueous silver nitrate: no reaction,
Observation with Aqueous sodium nitrate: goes colorless
The following pairs of compounds can be distinguished by simple test-tube reactions.
For each pair, give a suitable reagent that could be added separately to each compound to distinguish between them.
Describe what you would observe in each case
Aqueous magnesium chloride and aqueous barium chloride
Reagent:
Observation with Aqueous MgCl:
Observation with BaCl:
Reagent: aqueous sulfuric acid,
Observation with MgCl: no reaction,
Observation with BaCl: white ppt
Which of these substances reacts most rapidly to produce a silver halide precipitate with acidified silver nitrate? A CH3Br B CH3Cl C CH3F D CH3l
D
A colourless solution contains a mixture of sodium chloride and sodium bromide.
Using aqueous silver nitrate and any other reagents of your choice, develop a procedure to prepare a pure sample of silver bromide from this mixture.
Explain each step in the procedure and illustrate your explanations with equations, where appropriate (6)
Stage 1:
- add silver nitrate,
- to form precipices of AgCl and AgBr,
- AgNO3 + NaCl = AgCl + NaNO3
- AgNO3 + NaBr = AgBr + NaNO3
Stage 2:
- add excess of dilute ammonia to the mixture of ppt,
- the silver chloride ppt dissolves,
- AgCl + 2NH3 = Ag(NH3)2 + Cl-
Stage 3:
- filter off the remaining silver bromide ppt,
- wash to remove soluble compounds and dry
Write an ionic equation for the reaction between chlorine and cold dilute sodium hydroxide solution.
Give the oxidation state of chlorine in each of the chlorine-containing ions formed. (2)
Cl2 + 2HO- = OCl- + Cl- + H2O
OCl- is +1
Cl- is -1
Several steps in the practical procedure were designed to ensure an accurate value for the percentage by mass of strontium chloride hexahydrate in the sample. (1)
Explain why the solution of strontium chloride was filtered to remove insoluble impurities before the addition of silver nitrate.
Would give a large mass of silver chloride
Test:
1. Add chlorine water to aqueous
potassium iodide solution.
Observation:
The colourless solution turned a brown color
Identify the species responsible for the brown colour in Test 1.
Write the simplest ionic equation for the reaction that has taken place in Test 1
State the type of reaction that has taken place in Test 1 (3)
-iodine,
Cl2 + 2I- —> 2Cl- + I2
-redox reaction
Write the simplest ionic equation for the reaction between chlorine and aqueous potassium bromide.
State what is observed when this reaction occurs (2)
Cl2 + 2Br− = 2Cl− + Br2
Solution goes orange/yellow to colorless
Chlorine displaces iodine from aqueous potassium iodide.
i) Write the simplest ionic equation for this reaction (1
Cl2 + 2I- = I2 + 2Cl-
Chlorine displaces iodine from aqueous potassium iodide.
Give one observation that you would make when this reaction occurs. (1)
Solution turns from colorless to brown/red brown solution
Consider the following reaction in which iodide ions behave as reducing agents.
Cl2(aq) + 2I–(aq) → I2(aq) + 2Cl–(aq)
In terms of electrons, state the meaning of the term reducing agent. (1)
Reducing agent is an electron donor
Consider the following reaction in which iodide ions behave as reducing agents.
Cl2(aq) + 2I–(aq) → I2(aq) + 2Cl–(aq)
Deduce the half-equation for the conversion of chlorine into chloride ions. Explain why iodide ions are stronger reducing agents than chloride ions. (3)
Cl2 + 2e- = 2Cl-
Iodine ions are larger than chlorine ions,
Electrons lost from iodide ion are less strongly held by the nucleus compared with that lost from a chloride ion
One of these products is a colourless, odourless gas and the other is an acidic solution that reacts with silver nitrate solution to give a white precipitate.
Write an equation for the reaction of chlorine with water in bright sunlight.
Name the white precipitate and state what you would observe when an excess of aqueous ammonia is added to it. (3)
Cl2 + 2H2O = 4HCl + O2
- Silver chloride only
- the ppt would dissolve
Identify the two reagents that could be used in a test to confirm that the solutions contained chloride ions, not bromide ions. State what would be observed on addition of each reagent Reagent 1: Observation 1: Reagent 2: Observation 2:
Reagent 1: silver nitrate
Observation 1: white ppt
Reagent 2: aqueous ammonia
Observation 2: colorless solution
The presence of halide ions in solution can be detected by adding silver nitrate solution and dilute nitric acid.
State the purpose of the nitric acid in this test. (1)
To ensure that other ions do not interfere
Explain how the addition of an ammonia solution can be used to confirm that a precipitate is silver bromide. (2)
- Concentrated ammonia,
- ppt dissolves
The addition of silver nitrate solution followed by dilute aqueous ammonia can be used as a test to distinguish between chloride and bromide ions. For each ion, state what you would observe if an aqueous solution containing the ion was tested in this way.
Observations with chloride ions:
Observations with bromide ions: (4)
Observations with chloride ions:
- white ppt,
- soluble in ammonia,
Observation with bromide ions:
- cream ppt
- insoluble in ammonia
Write an equation for the reaction between chlorine and cold, dilute aqueous sodium hydroxide. Give two uses of the resulting solution.
Equation:
Use1:
Use2: (3)
Equation: Cl2 + 2NaOH = NaCl + NaOCl + H2O
Use1: bleach,
Use2 : kills bacteria
When using silver nitrate to test for the presence of chloride ions in an aqueous solution, it is important to add another reagent to prevent interference by any carbonate ions which would form a white precipitate of Ag2CO3
Identify this other reagent. (1)
HNO3
When using silver nitrate to test for the presence of chloride ions in an aqueous solution, it is important to add another reagent to prevent interference by any carbonate ions which would form a white precipitate of Ag2CO3
Write an equation to show how this other reagent reacts with sodium carbonate. (1)
2HNO3 + Na2CO3 = 2NaNO3 + CO2 + H2O
The presence of some halide ions in solution can be detected using aqueous silver nitrate and aqueous ammonia
Identify a halide ion which, on addition of aqueous silver nitrate, forms a precipitate that is insoluble in concentrated aqueous ammonia (1)
I-
The presence of some halide ions in solution can be detected using aqueous silver nitrate and aqueous ammonia
Identify a halide ion which cannot be detected using these reagents (1)
F-
Describe what you would observe when aqueous silver nitrate, followed by dilute aqueous ammonia, is added to separate aqueous solutions of sodium chloride and sodium bromide (4)
With NaCl: white ppt, soluble in ammonia
With NaBr: cream ppt, insoluble in ammonia
State the trend in the oxidising abilities of the elements down Group VII from chlorine to iodine.
Explain how this trend can be shown by displacement reactions between halogens and halide ions in aqueous solutions. (7)
-oxidizing ability decreases down the group,
Cl2 + 2Br- = 2Cl- + Br2
-Br2 red brown liquid
Cl2 + 2I- = 2Cl- + I2
-I2 black solution
Br2 + 2I- = 2Br- + I2
-redbrown/ yellow solution goes black solid
Write an equation for the reaction between chlorine gas and dilute aqueous sodium hydroxide. Name the two chlorine-containing products of this reaction and give the oxidation state of chlorine in each of these products.
Equation:
Name of product 1:
Oxidation state of chlorine in product 1:
Name of product 2:
Oxidation state of chlorine in product 2: (5)
Equation: Cl2 + 2NaOH = NaCl + NaOCl + H2O
Name of product 1: sodium chloride,
Oxidation state of chlorine in product 1: -1
Name of product 2: sodium chlorate
Oxidation state of chlorine in product 2: +1
The reaction of aqueous bromide ions with aqueous silver nitrate followed by the addition of concentrated aqueous ammonia
Observation with aqueous silver nitrate:
Equation:
Observation with concentrated aqueous ammonia:
Observation with silver nitrate: cream ppt
Equation: Br- + Ag+ = AgBr
Observation with ammonia: precipitate dissolves
The reaction of solid potassium bromide with concentrated sulphuric acid
Observation 1:
Observation 2:
1: orange/brown gas
2: white choking gas
Write an equation for the redox reaction that occurs when potassium bromide reacts with concentrated sulphuric acid (2)
2H+ + H2SO4 + 2Br– → SO2 + Br2 + 2H2O
Test:
Add silver nitrate solution to aqueous potassium chloride solution.
Observation:
The colourless solution produced a white precipitate
Name the species responsible for the white precipitate in Test 2.
Write the simplest ionic equation for the reaction that has taken place in Test 2
State what would be observed when an excess of dilute ammonia solution is added to the white precipitate obtained in Test 2. (3)
-white ppt is silver chloride,
Ag+ + Cl- —> AgCl
-white ppt dissolves
-colorless solution
State why the silver nitrate solution is acidified when testing for iodide ions. (1)
To remove ions that react with the silver nitrate
Explain why dilute hydrochloric acid is not used to acidify the silver nitrate solution in
this test for iodide ions. (1)
-HCl would form a white ppt
Chlorine and bromine are both oxidising agents.
Define an oxidising agent in terms of electrons (1)
Gains electrons
How can the addition of an aqueous solution of chlorine be used to distinguish between aqueous solutions of sodium bromide and sodium iodide?
State any observations you would make and write equations for the reactions occurring (4)
Cl2 to Br- : yellow to orange/red/brown
2Br- + Cl2 —> 2CL- + Br2
Cl2 to I- : black solution formed
2I- + Cl2 —> 2Cl- + I2
This question is about sodium chloride.
A student Carried out some test tube reactions starting with sodium bromide solution. The student recorded these observations
Reagent 1:
Sodium bromide solution = cream ppt
Reagent 2:
Sodium bromide solution = yellow solution
Identify reagent 1 and reagent 2 (2)
Reagent 1: silver nitrate
Reagent 2: chlorine
A student added few drops of concentrated sulfuric acid to solid sodium bromide
Give 2 observations that the students would make
Write an Ionic equation for the redox reaction (4)
Observation: choking gas, orange gas
Equation: SO4^-2 + 2Br- + 4H+ —> SO2 + Br2 + 2H2O
Test:
Add concentrated sulfuric acid to solid potassium chloride.
Observation:
The white solid produced misty white fumes which turned blue lit as paper to red
Write the simplest ionic equation for the reaction that has taken place in test 3
Identify the species responsible for the misty fumes produced in test 3 (2)
H2SO4 + 2Cl- —> 2HCl + SO4^-2
HCl
Br2 + H2O = HBrO + H+ +Br-
Use le chateliers principle to explain by this equilibrium moves to the right when sodium hydroxide solution is added to a solution containing dissolved bromine
- Sodium hydroxide neutralizes the acid,
- the equilibrium shifts to the right to oppose the loss of products
Explain why bromide ions react differently from chloride ions (2)
- Br- ions are bigger than Cl- ions,
- therefore Br- ions are more easily oxidized
Cl2 + H2O = H+ + Cl- + HClO
Give the formula of the species responsible for the pale green color in the solution of chlorine in water
Use le chateliers principle to explain why the green color disappears when sodium hydroxide is added to the solution (3)
Cl2 gives the green color,
NaOH reacts with the acid,
Equilibrium shifts from left to right
A different student said that when concentrated sulfuric acid was added to one of the sodium halides, a gas with the smell of bad eggs would be produced
Identify the sodium halide that forms a gas with a bad smell (1)
NaI/ sodium iodide
Identify the halides from the observations recorded:
A : yellow solid and misty fumes
B : brown fumes and misty fumes
C : misty fumes (3)
A: NaI
B: NaBr
C: NaCl
