If I understand your intent, you want to change every URL in lines which begin with webURL =
to "www.google.com"? If so, you simply
$ sed -i.bak -r '/^webURL/{s/"[^"]+"/"www.google.com"/}' sampleText.txt
If you have a mixture of single and double quotes, you can use
$ sed -i.bak -r "/^webURL/{s/['\"][^'\"]+[\"']/\"www.google.com\"/}"
which will normalise to double quotes.