1. Review: Lab Exam

2. 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

3. 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

4. Acid, base or neutral?
Base

5. Acid, base or neutral?
Neutral

6. Acid, base or neutral?
Acid

7. 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

8. Water or no water?
Water!

9. 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

10. Which ones have chloride ions?
YES
YES
YES
YES

11. 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

12. Which one has sulfate ions?
HERE

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

14. 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

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

16. 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

17. Protein or no protein?
Protein
Protein
No protein

18. 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

19. Glucose or no glucose?
No glucose
glucose
glucose
glucose

20. 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

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

22. Practice

23. 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

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

25. 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