My interview special was to pose the question "what is the melting point of chocolate?" Then i would split them into groups of 3 to plan their investigation. They would have to choose the equipment from a selection, draw a diagram and explain their plan, then explain what safety precautions they are going to follow.
I gave them 10 compulsory mins on this, then once i had checked their plan they could start.
There are then many questions that can be asked in relation to recording, displaying, explaining and evaluating whilst all being based around an engaging tasty topic( though sadly they can't taste the choc as they are in a lab!!)
Take in some pre-prepared red cabbage water and get them to test various everyday chemicals for their pH. Make up some colour charts for them to compare it to. Milk looks especially lovely. Starter - give them each a small piece of lemon and some diluted sodium hydrogen carbonate to taste, get them to describe the difference in taste to each other. Mini plenary - guess the ph of various other chemicals e.g. shampoo, squash, saliva, oil etc. They could have acid/alkali double sided cards which they can hold up depending on what they think.
I had an interview on Thursday (I got the job!) where I was also given a free choice. 40 mins. I did a CSI type lesson with a couple of mini pracs, enabling the kids to figure out who dunnit! It was good because I could show that I was circulating, questioning each group rather than being stood at the front. It also didn't matter if they'd done the prac/skills stuff before because they were applying it to a new situation. Seemed to go down well.
Lots of luck! I have been teaching (Science) for 13 years and in that time been involved in the interview process, watching lessons etc. Whatever you do, get the kids doing things and all involved - I actually saw one interviewee do a "chalk and talk" type lesson where she got the kids copying off the board!! From what you have written it sounds like you are also a Science teacher - apologies for the following if you aren't! A skills type lesson is an excellent idea. What about something based on variables? You could plan to demo a practical and get kids to identify variables - lots of opportunity for writing answers on mini-whiteboards so all involved. Then maybe a task involving fair tests. Is that any help? Feel free to msg me if I can help any more!
Every other interview I have been to I have been given a topic to teach and planned accordingly. The lesson has generally been one within the topic the pupils are currently studying. So relatively straightforward format with a starter to assess prior knowledge.
BUT I have an interview next week where I teach a topic ofy choice. So it is effectively a stand alone lesson. I have no idea which topics have been covered prevoously etc. Worse still I have to plan an hour but only teach 20mins of it.
I just don't know where to start once I have picked a topic I will be fine. It's just so open ended.
The best I can come up with is to do a skills based lesson. Perhaps get them to plan an investigation