Group 7 Flashcards
Name the halogens, give their Color and physical state
• Fluorine= pale yellow= Gas
• Chlorine= Green= Gas
• Bromine= Red-brown= Liquid
• Iodine= Grey= Solid
Describe the trend in boiling points down Group 7
• Boiling points increase down the group
• Due to increase in strength of vander waals forces as size and relative mass of the of the molecule increases
Explain the trend in electronegativity down group 7
• Electronegativity decreases
• Larger atoms attract electrons less than smaller ones. This is because electrons are further from the nucleus and are shielded by more electrons
What happens when halogens react
They gain an electron
What is disproportionation?
A type of redox reaction in which there is mutual oxidation and reduction of the same element
What do halogens displace?
Less reactive halide ions from a solution
What type of halide does a halogen displace
A halide ion that is below it in the periodic table
What is the trend in oxidizing power as we go down group 7
Oxidizing power reduces
What happens when you mix chlorine gas with cold, dilute, aqueous sodium hydroxide
You get sodium chloride (I) solution. NaClO which is a common household bleach that kills bacteria
Give the uses of sodium chlorate (l) solution (bleach)
• Water treatment
• To bleach paper and textiles
• Clean toilets
Give the formula for chlorine and sodium hydroxide to make bleach
2NaOH(aq) + Cl2 (g) -> NaClO(aq) + NaCl(aq) + H2O(l)
What happens when you mix water with chlorine?
Chlorine undergoes disproportionation, you form chloride ions and chlorate(l) ions
What can chlorine do during sunlight
Chlorine can decompose to form chloride ions and oxygen
What are the benefits of treating water with chlorine?
•It kills disease causing micro organisms
•Some chlorine persists in the water and prevents reinfection further down the supply
•It prevents the growth of algae eliminating bad tastes and smells and removes discoloration caused by organic compounds
What are the risks of using chlorine to treat water?
• Chlorine gas is very harmful if breathed in because it irritates the respiratory system
• Liquid chlorine on the eyes or skin causes sever burns
• Chlorine reacts with organic compounds in water to form chlorinated hydrocarbons and many of these are carcinogenic (cancer-causing)
Describe the trend of reducing power down group 7
The reducing power of halides increases down the group
Explain the reason for the trend of reducing power down group 7
• Ions get bigger so the electrons are further away from the positive nucleus
• There are extra inner electron shells so there’s a greater shielding effect
• So further down the group the halide ion is, the easier it is to lose electrons and the greater the reducing power
What do all halides produce when they react with sulfuric acid
Hydrogen halide
Give the reaction of sodium fluoride and sodium chloride with sulfuric acid
• NaF(s) + H2SO4(l) -> NaHSO4(s) + HF(g)
• NaCl(s) + H2SO4(l) -> NaHSO4(s) + HCl(g)
Give the reaction of sodium bromide with sulfuric
• NaBr(s) + H2SO4(l) -> NaHSO4(s) + HBr(g)
• 2HBr(g) + H2SO4(l) -> Br2(g) + SO2(g) + 2H2O(l)
What is the difference between the results seen in hydrogen fluoride/hydrogen chloride and hydrogen bromide
• You’ll see misty fumes as the gas comes in contact with moisture in the air but HF/HCl aren’t strong enough reducing agents to reduce sulfuric acid so the reaction stops there
• HBr is a stronger reducing agent so it reacts with sulfuric acid in a redox reaction. (Musty fumes of hydrogen bromide) this reaction produces chocking fumes of SO2 and orange fumes of Br2
Give the equation of the reaction of NaI with sulfuric acid
• NaI(s) + H2SO4(l) -> NaHSO4(s) + HI(g)
• 2HI(g) + H2SO4(l) -> I2(s) + SO2(g) + 2H2O(l)
• 6HI(g) + SO2(g) -> H2S(g) + 3I2(s) + 2H2O(l)
What is used to test for haildes
Silver nitrate
Describe the process in which silver nitrate is used to test for halides
• Fist you add dilute nitric acid to remove ions which might interfere with the test
• Add a few drops of silver nitrate solution
• A precipitate is formed of the silver halide
E.g Ag+(aq) + X- -> AgX(s)
Give the results of each silver nitrate test for ions
• Fluoride F- : No precipitate
• Chloride Cl-: White precipitate
• Bromide Br-: Cream precipitate
• Iodide I-: Yellow precipitate
Describe the solubility of halides in ammonia
• Chloride Cl-: White precipitate, dissolves in dilute NH3(aq)
• Bromide Br-: Cream precipitate, dissolves in conc NH3(aq)
• Iodide I-: yellow precipitate, insoluble in con NH3(aq)
What is another name for positive ions
Cations
Describe the sodium hydroxide test for positive ions
• You can use dilute sodium hydroxide solution (NaOH) to help you identify group 2 ions
• Add NaOH dropwise to a test tube containing the metal ion solution and observe the precipitate that forms
• Keep adding the NaOH until it is in excess. Record any changes that you see
State the results from the dilute sodium hydroxide test
• Magnesium, Mg2+, with OH- forms slight white precipitate but with excess OH- forms white precipitate
• Calcium, Ca2+ with OH- forms slight white precipitate but with excess OH- forms slight white precipitate
• Strontium, Sr2+ with OH- forms slight white precipitate but with excess OH- forms slight white precipitate
• Barium, Ba2+ with OH- there is no change but with excess OH- there is still no change
Describe how to use Red litmus paper and NaOH to test for ammonium ions and ammonia gas
• Ammonia gas is alkaline so you can test for it using damp piece of red litmus paper
• Litmus paper must be damp so ammonia gas can dissolve
• If ammonia is present, litmus paper will turn blue
• If hydroxide ions in a solution containing ammonium ions it will react to produce ammonia gas and water
• This can be used to test for ammonium ions
• NH4+(aq) + OH-(aq) -> NH3(g) + H2O(l)
Give examples of negative ions (anions)
Halide ions, hydroxide ions, sulfate ions and carbonate ions
Describe the flame test for group 2 ions
• Dip a niche one wire loop in concentrated hydrochloride acid
• Then dip the wire loop in concentrated hydrochloride acid
• Hold the loop in the unknown compound
• Hold the loop in the clear blue part of the Bunsen burner flame
• Observe the color change in the flame
• Calcium= brick red, Strontium= red, Barium= pale green
Describe the test for sulfates with HCL and barium chloride
Add a little hydrochloride acid followed by barium chloride solution. If a white precipitate of barium sulfate forms, the original compound contained a sulfate
Describe the pH indicator test for hydroxides
• Dip a piece of red litmus paper into the solution
• If hydroxide ions are present, the paper will turn blue
Describe how hydrochloric acid can help Detect Carbonates
• When you Add hydrochloride acid a solution containing carbonate ions will fizz
• This is because the carbonate ions react with the hydrogen ions in the acid to give carbon dioxide
• You can test for carbon dioxide using limewater
• Carbon dioxide turns limewater cloudy just bubble the gas through a test tube of lime water
• If the limewater turns cloudy, your solution contains carbonate ions
WhaT type of agents are halogens and halide ions
Halide ions are reducing agents and halogens are oxidizing agents
Why is fluorine the strongest oxidizing agent?
It is the smallest halogen atom as it has the fewest electron shells so outermost electrons are closer to the nucleus. This means greater shielding effect and the outermost electron have a stronger attraction to the positive nucleus making it easier to gain an electron
What is the rule of halide ions and halogen molecules?
Halogen molecules have an oxidation state of zero and can be reduced to halide ions. Halide ions have an oxidation state of -1 and can be oxidized to halogens
Suggest why excess is used
To ensure all the halide ions are removed from the solution
what are the major products formed when chlorine reacts with cold dilute, aqueous sodium hydroxide
NaCl and NaClO
Which property increases down group 7
boiling point
Chlorine has a low boiling point because the forces between its molecules are weak, explain how these forces arise between molecules
- Random movement of electrons create a dipole
- Induces a dipole in the neighboring molecule
- These temporary dipoles attract
What type of reaction is the reaction with chlorine and water
equilibrium reaction
Why is chlorine still used in water despite its toxicity
Health benefits outweigh the risks, only used in small/ low concentrations
Give the formula for the reaction of sodium bromide with sulfuric acid
2NaBr + 2H2SO4 = Na2SO4 + Br2 + SO2 + 2H2O
Explain the uses of the reagents involved in the testing of halides with silver nitrate
• Nitric acid removes ions that may give other precipitates with silver nitrate
• Silver nitrate produces precipitates with halides
• Ag+ (aq) + Cl- (aq) -> AgCl(s)
• NH3 dissolves AgCl
• AgCl(s) + 2NH3(aq) -> Ag(NH3)2+(aq) + Cl-(aq)
