my friend gave me his old iphone. He got a new one because he cant remember the password. Is there any way I can wipe the iphone when not knowing the passcode?

If you don’t know that passcode then you are going to have to factory rest you phone. To do this you will need to put the phone in restore mode by pressing the up volume then bottom then power until the connect to iTunes screen comes up. Next connect the phone to a computer that has iTunes. In iTunes you should see a window pop up saying restore or update and you want to hit restore. The restore will take a little bit of time, and when done everything will be erased off the phone, but the phone will still be locked to your Apple ID passcode unless you already had find my iPhone turned off. If you don’t have a computer with iTunes then you will need to take the phone into a apple store, you can make a appointment at https://getsupport.apple.com/

You will need to have your friend put in the Apple ID passcode, or have him go to find my on his phone and in his device list he will see the phone, when he taps on the phone he can hit remove this device, make sure he doesn’t hit erase device.