Yes, but there's a catch to the keychain; see below.
The following is all for Yosemite (I had version 10.10.3).
To see wifi networks you've connected to from your iOS devices:
- On your OSX device (eg your Mac), make sure you are logged in to iCloud (via System Preferences).
- Open the Keychain Access app desribed above.
- On the left, in the Keychains box, click "iCloud".
- In the main display, click on "Kind" to sort all entries by kind.
- All the wifi networks will now be listed together with the kind "AirPort network password".
To view a wifi password:
- Double click one of the displayed entries (or right-click it and select Show Info).
- Click the checkbox next to "Show Password".
- Enter your iCloud password.
You have to enter the iCloud password you had when you first connected to that network. If you have since changed your iCloud password, your current iCloud password won't work. There won't even be an error message: after you click OK, no password will be displayed, that's all.
This is obviously a bad problem: who can remember their old iCloud passwords? It's sad that Apple hasn't fixed this yet.
Personally, I get around the problem by using 1Password (https://agilebits.com) whenever I change my iCloud password. 1Password keeps a log of all my previously created passwords with their creation dates; so, I look at the Keychain Access entry's "Date Modified", and then in 1Password I choose the last iCloud password I created before that date.