Teaching Chemistry

MN1988

Hello, I started this thread for chemistry teachers to share their experience. As an NQT any advice is appreciated.


I wanted to know how long does it take others to teach the mole and properties of gases including the mandatory experiment to measure the relative molecular mass of a volatile liquid?
I spent way too long on both of these last year and am rewriting my scheme of work

Pwpane

MN1988 wrote: »

Hello, I started this thread for chemistry teachers to share their experience. As an NQT any advice is appreciated.


I wanted to know how long does it take others to teach the mole and properties of gases including the mandatory experiment to measure the relative molecular mass of a volatile liquid?
I spent way too long on both of these last year and am rewriting my scheme of work

Students find this section very difficult. Even when they get it they can lose it again. I'd be inclined to give the bones of it at first, very few definitions etc and immediately apply it in making solutions and doing titrations.

So, a mole is a big group of molecules, use the Mr to figure it out, do examples. Concentration is how close together the molecules are in a solution, either how many molecules per litre or how many grams of them there are per litre - molecules x Mr = mass. Make some solutions, try short simple experiments then titrations.

Every chance you get use these ideas over and over throughout the rest of the course. At some stage when they're well used to the concept do the rest of the section.

Do the Mr experiment whenever suits you, or while you're doing the rest of the section - not when you're introducing the concept as it's too confusing. I always found that many students didn't understand the experiment till leaving cert year, if even then.

Sorry but I can't give you a timeline - I never measured how long it took. But the above is much shorter than teaching by the book. And much more effective. And much more enjoyable ☺

MN1988

Cheers that helps. I used simulations from phet to help get the concepts across but I spent about three weeks on these two chapters which I know was way too long. I done plenty of examples and felt they got it but was falling behind on the calendar. They're going to come up again over and over anyway as they're used in most other chapters. I will do the experiment at the end alright - I done it in the middle and it didn't work.


Another thing is I was given a question that I gave a bad answer for:
A mole of a gas occupies 22.4 litres, but if gases diffuse to fill their containers - what if a mole of a gas was in a 100 litre container? Wouldn't it diffuse to fill the volume of the container but just be less dense per cm3 ?

Pwpane

There's a horrendous amount in those chapters and the students just aren't mentally ready for it as they start chemistry. It can be enough to turn a lot of them off as it takes so long to drum it in at that stage and it's boring as hell. When their maths and logic skills are more developed they'll fly through it, particularly if they're well used to the basic concepts that Mr is the weight of a molecule and the the mole is a big group of them.

As for gases, that many molecules (1 mole) take up 22.4 L of space at S.T.P. The molecules will move to fill any space you put them in but they'll be at a different temperature and pressure. They have to do work to move apart - losing energy/heat and thus temp, and since there are fewer per cm3 they will exert lower pressure. So when their volume is no longer 22.4 L then their temp and pressure are no longer 273K or 1 atm either.

Look at it another way: if you want to put that many molecules of any gas in that amount of space at that temp (temp being a measure of how fast they are moving) then you'll have to use that amount of pressure to keep them there. Which is the same pressure that they're pushing back with.

You need to be very clear that 22.4 L (or 24 L at room temp/pressure) only works with gases when molecules are free to move and the substance can expand and contract easily. Students can miss that or forget, and start using 22.4 L with liquids or even solids. They often don't think about the state of a substance when they see it in a question.

kronsich

MN1988 wrote: »

Hello, I started this thread for chemistry teachers to share their experience. As an NQT any advice is appreciated.


I wanted to know how long does it take others to teach the mole and properties of gases including the mandatory experiment to measure the relative molecular mass of a volatile liquid?
I spent way too long on both of these last year and am rewriting my scheme of work

Do you have an iPad? If so, get molecule lab. It's great for teaching gas laws. Gas laws and the mole take ages to cover properly with all the calculations. The experiment only takes a double but that calculation can be tricky for the kids. For some reason, even my best kids have issues with the conversions between cm3 and m3 and keep getting the pvnrt calculations wrong.

Wouldn't worry about your scheme, usually plenty of time to cover the chemistry course in two years. I have LC biology this year too and that's a two year sprint through the syllabus.

MN1988

@Kronsich: I haven't an Ipad but I'm saving! simulations done through phet work just fine for now though. Cheers for the resource though, when I get an Ipad I'll look into it and compare with what I already have.

@Pwpane: Thank you very much, we were stuck on that for a long time and you explained it perfectly. As for starting on these chapters - I was sharing the class with another teacher who started on the atom chapters so I went with these. There wasn't much choice in it.

Corkgirl18

Would anyone have a year long 5th year scheme of work? Doing the PDE at the moment and teaching 5th year chemistry. I don't technically have a mentor teacher and have no idea how long I'm supposed to spend at each topic.

Or can anyone tell me what chapters are usually covered in 5th year? I'm supposed to get the majority of the practical experiments done this year.

Moody_mona

Corkgirl18 wrote: »

Would anyone have a year long 5th year scheme of work? Doing the PDE at the moment and teaching 5th year chemistry. I don't technically have a mentor teacher and have no idea how long I'm supposed to spend at each topic.

Or can anyone tell me what chapters are usually covered in 5th year? I'm supposed to get the majority of the practical experiments done this year.

The syllabus includes a suggested number of periods to use per topic.

kronsich

Yeah the suggested periods are on the syllabus. Check out pdst.ie in the chemistry section. Good resources for teaching the course. I definitely wouldn't be rushing to get all th practical work done. Just do the practicals as the topics come up.

I start with atomic theory, radioactivity and then on to acid bases, titrations to midterm. I then do organic from midterm to Xmas and if I have time I do the option. I teach parts of the mole early so they can do the titration calcs.

I'd generally leave things like stoichiometry, chem equilibrium, gas laws until sixth year as their maths skills will be better at this stage. To be honest, I would advise you to make your own scheme and have it as a working document that you can change each year depending on the class. I like to make sure we have an experiment most weeks as they expect chemistry to be very practical and the note taking and exam questions can get monotonous.

kronsich

BTW I wouldn't be overly worried about spending too much time on topics. Compared to biology, the course is short. Once they have notes, done the practicals and answered the exam questions, it's time to move on.