mod_rewrite

I am using Apache 2.0.54 as reverse proxy.The proxy is not hiding the
actual url present in the query string.I am thinking to rewrite the
url present in query string with w.r.t proxy.

configuration is like this

ProxyPass / http://kinka.co.in:7700
ProxyReversePass / http://kinka.co.in:7700

Now i am seeing the url in browser like this
http://kinka.co.in:7700?backurl=http://ratnakar.co.in:7701
Here you can see the proxy is not hiding the url in query string.the
url http://ratnakar.co.in:7701 should be hiden by proxy.

Can i use rewrite rule to hide the actual url in query string.If yes
then can any one provide me an example to achieve this.

TIA
Ravi