白 (bái) doesn't only mean "white." When added before a verb it means to do that verb "in vain" or "with no effect." In a certain way, you can think of 白 as not being just "white" but also "blank," like when you do something for a long time without thinking, and you're just going through the motions. It's like doing something with a "blank" mind.
Structure with just 白
All you have to do is but 白 before the verb.One important thing to note is that 白 is usually used with mono-syllabic words, like 帮, 做, 学 etc. You cannot put a 地 after 白.
Examples
- 白 花 了 一 百 块 钱，这 件 衣服 不 能 穿。 I just wasted a hundred kuai. I can't even wear these clothes.
- 他 不 回来 吃饭 了？！我 这些 菜 白 做了。 He's not coming back to eat？！I made all this food for nothing.
- 你 一 句 汉语 都 不 会 说，白 学 了 这么 长 时间。 You can't speak even one sentence in Chinese, wasting all of that time studying.
- 我 去 的 时候 他 不 在 家， 所以 我 白 跑 了 一 趟。 He wasn't home when I got there, so I wasted all of that time going over there.
- 不好意思， 让 你 白 忙 了 一 个 早上，我们 老板 今天 来 不了 了。 Sorry to make you work this whole morning for nothing. Our boss just said that he couldn't come today.
Structure with 白白
白 can also be replaced with 白白, and they are basically the same, though 白白 has a stronger emphasis on the "wasted effort." 白白 also is usually paired with a disyllabic word, like 帮助, 准备, 学习 etc. Unlike 白, 白白 can be used with a 地.
Examples
- 明天 不 考 中文， 小王 白白 准备 了 一 天。 There's not a Chinese test tomorrow. Little Wang studied the whole day in vain.
- 他 没有 来，我 在 飞机场 白白 等 了 他 四 个 小时。 He hasn't come. I wasted four hours at the airport waiting for him.
- 她 白白 学 了 十 年 的 英语， 她 看得懂 英文，但是 连 简单 的 对话 都 不 会 说！ She spent ten years fruitlessly studying English. She can read English, but she can't even speak a simple sentence.
Sources and further reading
- 现代汉语八百词 (p.58)
- Chinese Grammar - Broken down into 100 items - Basic and Intermediate Levels (汉语语法百项讲练 - 初中级) (p.160-161)