1. Testing Positive Ions

2. Starter Activity How do we identify hydrogen by chemical testing?
5 minutes
How do we identify hydrogen by chemical testing?
Why is being able to identify substances by their reactions useful?

3. In the real world
Scientists working in environmental monitoring, industry, medicine and forensic science need to analyse and identify substances
We can use a variety of tests for positive ions:
Precipitation Reactions
Flame Tests

4. Flame Tests When metals are placed into a flame they change colour.
Different metals give different colours to the flame, so flame tests can be used to identify the presence of a particular metal.

5. Use WJEC GCSE Chemistry p.29 to help you
SUPPORT
Use WJEC GCSE Chemistry p.29 to help you
Method
5 minutes
Put these steps in the correct order for how to do a flame test.
Record flame colour in table and repeat cleaning process and repeat
Dip a nichrome loop in Hydrochloric acid to clean
Put the nichrome loop with metal compound into a roaring Bunsen flame
Put the nichrome loop in a roaring Bunsen flame to clean
Put the nichrome loop into a metal compound
Dip the nichrome loop back in the acid

6. DOING A TEST
Different metal compounds produce different colours when they are put into a hot flame. The colour of the flame can be used to identify the metal ion present.
METHOD
A Put the Bunsen burner on the heat resistant mat. Adjust the flame so that the air hole is half open, producing a light blue flame.
B Clean the flame test loop - Dip the end into the hydrochloric acid, hold it in the flame, then dip it in a beaker of water.
C Dip the clean loop into one of the test crystals/solutions. Hold it in the edge of the flame. Observe and record the colour of the flame.

7. USE YOUR METHOD WE JUST DID
Results Table
10 minutes
Metal Ion
Ion Charge
Flame Colour
Lithium
Sodium
Potassium
Calcium
Barium
GOGGLES!! It may spit!

8. Metal Ion
Ion Charge
Flame Colour
Lithium
Li+
Crimson
Sodium
Na+
Yellow
Potassium K+
Lilac
Calcium
Ca2+
Red
Barium
Ba2+
Green

9. Flame Tests Substance Colour of Flame Lithium ions (Li +) Red flame
Sodium ions (Na+)
Yellow flame
Potassium ions (K+)
Lilac flame
Calcium ions (Ca2+)
Brick-red flame
Barium ions (Ba2+)
Apple-green flame

10. DOING A TEST JAR 1 JAR 2 JAR 4 JAR 3 Ca Na Cu SO4 K Cl K Cu Na NO3 Ca
Different metal compounds produce different colours when they are put into a hot flame. The colour of the flame can be used to identify the metal ion present.
There is a PROBLEM!!!
The labels of 4 chemical jars have been damaged. The lab technician is not really sure which chemicals are in each jar. She needs your help to identify the compounds. Test each one and write the correct symbol on each jar.
METHOD
A Put the Bunsen burner on the heat resistant mat. Adjust the flame so that the air hole is half open, producing a light blue flame.
B Clean the flame test loop - Dip the end into the hydrochloric acid, hold it in the flame, then dip it in a beaker of water.
C If an intense colour was seen when the loop was in the flame, the loop was not clean enough. Repeat step B if necessary.
D Dip the clean loop into one of the test crystals/solutions. Hold it in the edge of the flame. Observe and record the colour of the flame.
The technician is not sure if this chemical is calcium sulfate or copper sulfate
JAR 1
Is this chemical sodium chloride or potassium chloride? Let’s find out.
JAR 2 Ca Na Cu
SO4 K Cl
What’s this one? The technician is not sure if this chemical is potassium or sodium nitrate
JAR 3
JAR 4
The technician thinks this one is copper carbonate. Is she correct or is it calcium carbonate? K Cu Na
NO3 Ca
CO3

11. Teacher/technician notes
DOING A TEST
Teacher/technician notes
Place 4 jars with the following chemicals around the lab as a circuit. Write the anion names on ripped labels, which have the metal name part missing as on the sheet above. Items at each station:
A jar filled with the chemical to identify. Has ripped label.
Folded card (next sheet)
Spatula
Flame test wire
Concentrated hydrochloric acid in small beaker
Bunsen burner
Jar 1 - Contains calcium chloride. Flame colour = red
Jar Contains potassium nitrate. Flame colour = lilac
Jar Contains sodium chloride. Flame colour = bright orange.
Jar Contains copper sulfate. Flame colour = blue-green

12. JAR 1
JAR 2
JAR 3
JAR 4