Ch 22 - (Chemical analysis) Flashcards
What are anions?
Negatively charged non - metal ions are known as anions
What are the major tests for anions?
- Carbonate ions (CO32-)
- Halide ions (Cl-, Br-, I-)
- Sulfate ions (SO42-)
- Sulfite ions (SO32-)
What is the ion for carbonate?
CO32-
What is the test for carbonate ion?
- add dilute acid
- bubble the gas through limewater
- limewater turns cloudy if carbonate ion is present
What should the observation be for a positive test for carbonate ion?
- fizzing \ effervescence
- CO2 is produced
- White precipitate of calcium carbonate
What is the chemical equation for the test of carbonate ions?
CO32- (aq) + 2H+ (aq) —> CO2 (g) + H2O (l)
CO2 (g) + Ca(OH)2 (aq) –> CaCO3 (s) + H2O (l)
White precipitate limewater turns cloudy
What are halide ions?
- negative ions
- anions formed by elements in Group 7
What is the test for halide ions?
- acidify the sample with nitric acid
- add silver nitrate solution, AgNO3
- silver halide precipitate
What is the word and symbol equation for the reaction between potassium chloride and silver nitrate?
Word:
Potassium chloride + silver nitrate –> potassium nitrate + silver chloride
Symbol:
KCl (aq) + AgNO3 –> KNO3 (aq) + AgCl (s)
What is the observation for the reaction between potassium chloride and silver nitrate?
chloride ions form white precipitate
What is the word and symbol equation for the reaction between potassium bromide and silver nitrate?
Word:
Potassium bromide + silver nitrate –> potassium nitrate + silver bromide
Symbol:
KBr (ag) + AgNO3 (aq) –> KNO3 (aq) + AgI (s)
What is the observation for the reaction between potassium bromide and silver nitrate?
bromide ion forms a cream precipitate of silver bromide
What is the word and symbol equation for the reaction between potassium iodide and silver nitrate?
Word:
Potassium iodide + silver nitrate –> potassium nitrate + Silver iodide
Symbol:
KI (aq) + AgNo3 (aq) –> KNO3 (aq) + AgI (s)
What is the observation for the reaction between potassium iodide and silver nitrate?
Iodide ions form a yellow precipitate of silver iodide
What is the ion for sulfate?
SO42-
What is the test for sulfate ion?
- acidify the sample with dilute hydrochloric acid
- add a few drops of barium chloride solution
What is the symbol equation for reaction of barium reacting with sulfate?
Ba 2+ (aq) + SO42- (aq) –> BaSO4 (s)
What is the ion for sulfite?
SO3 2-
What is the test for sulfite ion?
- add dilute acid
- warm the mixture gently
- bubble the gas released through potassium manganate (VII) solution
- potassium manganate (VII) solution changes from purple to colorless if sulfate ion is present.
What is an ammonium ion?
NH 4+
What is the test for ammonium ions?
- gently warming a solution with the ions and sodium hydroxide solution
- source of hydroxide solution OH-
- releases ammonia gas which turns damp red litmus paper
- cations in aqueous solution can be identified by colour of precipitate they form
- Transition metals produce hydroxides with distinctive colours
What happens if ammonia solution and metal hydroxide are added togteher?
It form a metal hydroxide precipitate
What happens if excess ammonia solution is added to metal hydroxides?
- some precipitate may re-dissolve
- that’s why few drops are very slowly dropped
How do u test metal ion with ammonia?
- add a few drops of ammonia solution
- record any color changes or precipitates formed
- add excess ammonia solution
- record any color changes to precipitates
What happens if precipitate is formed from sodium hydroxide or ammonia solution?
Hydroxide is insoluble in water
What are 3 metal ions that for white precipitate?
- Aluminium ions (Al3+)
- Calcium ions (Ca2+)
- Zinc ions (Zn2+)
What happens when calcium ions are tested with NaOH or ammonia?
- White precipitate of calcium hydroxide does not dissolve in excess sodium hydroxide solution
- precipitate of zinc hydroxide and aluminum hydroxide dissolve in excess sodium hydroxide solution
What happens when zinc ions are tested with NaOH or ammonia?
- White precipitate of zinc hydroxide dissolves in excess ammonia solution
- White precipitate or aluminum hydroxide does not dissolve in excess ammonia solution
What is the flame test used for?
- identify metal cations by color of flame
- ions with diff metals hv diff color
How do you do flame test for metal ions?
- dip loop of unreactive metal wore such as nichrome or platinum in concentrated acid
- hold in blue flame, with no color change
- test will work only with one type of ion
- cleans the wire loop and avoid contamination
How is the flame test carried out?
- small sample is produced in unreactive metal wire loop such as nichrome or platinum
- dip loop in solid sample, place in blue flame
What was the flame color for metal ion test?
- Lithium (Li+) - Crimson
- Sodium (Na+) - Yellow
- Potassium (K+) - Lilac
- Calcium (Ca2+) - Red
- Barium (Ba2+) - Apple green
- Copper (Cu2+) - Blue green
What gasses are identified in the test?
- Ammonia
- Carbon dioxide
- Chlorine
- Hydrogen
- Oxygen
- Sulfur dioxide
What is ammonia?
Gas with characteristics sharp chocking smell that turn damp red litmus paper blue
How do u test for ammonia?
- hold litmus paper near mouth of test tube
- avoid touching sides of test tube to prevent traces of sodium hydroxide
How do u test for carbon dioxide?
- bubbling gas through aqueous solution of limewater (calcium hydroxide)
- if CO2 present, limewater is cloudy
How is the test for chlorine gas?
- use of litmus paper
- if it is present, damp blue litmus paper will turn red and then be bleached White
- it turns red as acids are produced when chlorine comes in contact with water
- chlorine has sharp chocking smell
- Shud be handled in fume cupboard due to toxicity
What is the test for hydrogen gas?
- holding a burning splint at open end of a test tube of a gas
- if hydrogen present, it produ es a squeaky pop
- put splint only in mouth
What is the test for oxygen?
- places a glowing splint inside test tube of gas
- if age is oxygen it relights
What is the test for sulfur dioxide?
- sharp chocking smell
- sulfur dioxide involves bubbling gas through an acidified solution of potassium manganate (VII)
- if present, it changes from purple to colorless
