I live in an apartment and have always had scalding water in all faucets. I am now getting only lukewarm water in the kitchen. My kitchen faucet hot water knob becomes loose and I have to tighten the screw in the top. Could that have affected the temp of the water coming out of the faucet?

No all faucets don't. Many do in a shower, but not all even there. Outside of a shower I can't remember even seeing one.