Worksheets and lesson ideas to challenge students aged 11 to 16 to think hard about halogens and displacement (GCSE and Key Stage 3)
GCSE activity about the use of chlorine on the battlefield. Students read Dulce et Decorum Est a poem by Wilfred Owen describing the use of chlorine on the battlefield. The poem finishes with the ironic line, Dulce et decorum est Pro patria mori (it is sweet and fitting to die for one’s country). Students consider what this poem tells us about the chemistry of chlorine and other halogens. It can be interesting to explain the chemistry here – chlorine dissolves in the moisture of the lungs and eyes and then reacts with the water to form HCl. HCl then damages living cells – mainly through protein denaturation. The video above can be used instead of, or in addition to, the text. (PDF)
Displacement reactions – a role play
A great way to help students understand displacement reactions is to model what is happening at the molecular level using students and mini-white boards. This helps students to zoom! First start with demonstrating the displacement reaction so students can see the colour changes involved. Then introduce the theory. Now, to see if students understand, ask them to devise their own way of representing the reaction through a role play or, you could simply model this at the front of the class using selected students.
sodium bromide + chlorine –> sodium chloride + bromine
Take four students. Give each student a mini white board and then label them e.g. Na, Br, Cl, Cl, You may or may not want to add charges and colours. Ask the students to pair up according to the equation and then ‘start the reaction’. Depending on the class you may want to show the ions dissociating in the first stage (students holding Na and Br move apart) before they react with the diatomic halogen. Obviously, there are lots of opportunities here to introduce misconceptions but also huge potential to help students appreciate what is happening in the test tube. This is also a great way to make student thinking visible.
If students have devised their own role plays, get a few groups to present to the class and ask their peers to spot the misconception, provide WWW and EBIs.