Conditionally alternate code

I’m creating my portfolio site with individual client pages that are broken into sections. Each section has two columns: content and an image/media/slider etc.

I have it setup that each section is only displayed if the tag is added. e.g. the mobile section on the page wont be displayed if the post isn’t tagged ‘mobile’.

The problem is that each section is hard coded. How can I have the section layout be conditional if it’s the first, second, etc. so all the images don’t fall on the right side.

Here’s my reference sandbox: mykklemme.com/Code/portfolio-single.html