The modal adverb 白
The modal adverb (语气副词) expresses subjective judgment or assurance toward an action.
The adverb 白 
is used when the action did not achieve the desired result and was done in vain in the speaker's opinion.
is used when the action did not achieve the desired result and was done in vain in the speaker's opinion. Pay attention
白 is placed before monosyllabic verbs that consist of one syllable.
Examples
超市没有牛奶，我白去了
There was no milk in the supermarket. I went there for nothing.
chāoshì méiyǒu niúnǎi, wǒ bái qù le
得不到签证的话，飞机票就白买了
If you don't get a visa, the plane ticket will be wasted
dé bú dào qiānzhèng de huà, fēijī piào jiù bái mǎi le
这里没有我需要的人，我算是白来了
There's no one I need to see here, I've come for nothing
zhèlǐ méiyǒu wǒ xūyào de rén, wǒ suànshì bái lái le
Adverbs can be reduplicated. In this case, it is followed either by a two-syllable verb or a monosyllabic verb with an object.
Pay attention
白白 can be followed by the particle 地 .
.Examples
我没有赢，白白费功夫了
I didn't win, so it was a waste of time
wǒ méiyǒu yíng, báibái fèi gōngfū le
没有人会把成功白白地送给你
No one will help you succeed without something in return
méi yǒu rén huì bǎ chénggōng báibái de sòng gěi nǐ