2 sentences for 空 (kōng — in vain)

1. 我们不能让他在这里空等。

   wǒ​men bù néng ràng tā zài zhè​lǐ kōng děng.

   We can't let him wait here for nothing.

   Source: Dong Chinese Dictionary

2. 尽管他费尽心机，到头还是一场空。

   jǐn​guǎn tā fèi​jìn​xīn​jī, dào​tóu hái​shi yī cháng kōng.

   Despite all his schemes, it all came to nothing in the end.

   Source: Dong Chinese Dictionary