Testing Positive Ions

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?

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

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.

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

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.

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!

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

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

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

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 2 - Contains potassium nitrate. Flame colour = lilac Jar 3 - Contains sodium chloride. Flame colour = bright orange. Jar 4- Contains copper sulfate. Flame colour = blue-green

JAR 1 JAR 2 JAR 3 JAR 4