Does God hear our prayers for mercy on behalf of others?

Abraham approached him and said, "Will you destroy both innocent and guilty alike? Suppose you find fifty innocent people there within the city—will you still destroy it, and not spare it for their sakes? Surely you wouldn't do such a thing, destroying the innocent with the guilty. Why, you would be treating the innocent and the guilty exactly the same! Surely you wouldn't do that! Should not the Judge of all the earth do what is right?" [The Lord responds that he will not destroy the city. Abraham persists, reducing the number to 45, then 40, 30, 20 and finally ten]. And the Lord said, "Then, for the sake of the ten, I will not destroy it."

Genesis 18:23-31 NLT

In the days before their fiery judgment, the citizens of Sodom and Gomorrah probably had no idea that their neighbor Abraham was agonizing with God over their fate. Abraham saw the need for justice, but he also begged God to show them his mercy. He asked God to spare the city for just a handful of righteous people, and God agreed. In addition, God sent his angels to protect Lot's innocent family and get them out of harm's way. But as Sodom and Gomorrah's destruction illustrates, there's a limit to his mercy, for the God of justice will not let sin go unpunished forever. Just as he listened to righteous Abraham long ago, God will listen to your cries for justice and your pleas for mercy. In the end, God will do what is right.
From The One Year Book of Bible Prayers (Tyndale House), entry for March 25