Review: Lab Exam

Tests You will be identifying an unknown liquid You need to know how to interpret the results for the following tests: Litmus paper Cobalt chloride paper Silver nitrate Barium chloride Electrical conductivity Biurets solution Benedict’s solution Iodine

Litmus paper Litmus paper is used to test for the nature of the substance (acid, base or neutral) Red litmus paper Blue litmus paper Nature Red -> Red Blue -> Red Acid Blue -> Blue Neutral Red -> Blue Base

Acid, base or neutral? Base

Acid, base or neutral? Neutral

Acid, base or neutral? Acid

Cobalt Chloride Paper Cobalt chloride paper is used to test for the presence of water If water is present: turns pink If water is not present: stays blue

Water or no water? Water!

Snakes nibbled creepily Silver Nitrate Silver nitrate is used to test for the presence of chlorine ions (Cl-) If chloride ions are present: precipitate forms If chloride ions are not present: stays clear Snakes nibbled creepily

Which ones have chloride ions? YES YES YES YES

Boredom causes suffering Barium Chloride Barium chloride is used to test for the presence of sulfate ions (SO42-) If sulfate ions are present: precipitate forms If sulfate ions are not present: stays clear Boredom causes suffering Or Bored, cranky students

Which one has sulfate ions? HERE

NOTE Your substance will not have both chloride and sulfate ions It can only have one or the other Or neither

Electrical Conductivity Electrical conductivity is used to test for the presence of ions in water In other words need to see if the liquid can conduct electricity If the liquid conducts = light turns on If the liquid does not conduct = light stays off

Electrical Conductivity What does electrical conductivity tell us? Only electrolytes conduct: Acids, bases and salts Distilled water and ethanol do not conduct

Biuret’s Solution Biuret’s solution is used to test for the presence of protein If protein is present: turns dark blue/purple If protein is not present: stays lighter blue

Protein or no protein? Protein Protein No protein

Benedict’s Solution Benedict is so sweet! Benedict’s = glucose Benedict’s solution is used to test for the presence of glucose If glucose is present: turns green or orange/red and cloudy If glucose is not present: stays clear light blue Benedict is so sweet! Benedict’s = glucose

Glucose or no glucose? No glucose glucose glucose glucose

Iodine Test Iodine is used to test for the presence of starch If starch is present: black/blue If starch is not present: stays orange/yellow

Starch or no starch? No starch: 1,2,3,7,8 Starch: 5,6 and 4?

Practice

What do you have? Unknown: Is basic (litmus turns blue and conducts) Silver nitrate Barium chloride Unknown: Is basic (litmus turns blue and conducts) Contains sulfate ions

What do you have? Unknown contains: Protein Glucose No starch Biuret’s Benedict’s Unknown contains: Protein Glucose No starch Iodine

Tip If there is distilled water available – use it to create a negative control for Biuret’s Not always easy to tell the difference between lighter blue and the darker blue/purple