Two Actions at Once: пока
When two actions happen at the same time, use the conjunction пока (while). It introduces a temporal clause describing an ongoing situation.
| while | пока |
You can place the пока clause at the beginning or in the middle of the sentence. Remember to separate the clauses with a comma.
| We are starting the experiment while the liquid in the flask is cold. | Мы начинаем эксперимент, пока жидкость в колбе холодная. |
| While I am mixing these liquids, a chemical reaction is going on. | Пока я смешиваю эти жидкости, идёт химическая реакция. |
Setting Limits: пока не
To state that an action continues until a certain event happens, use пока не.
| until | пока не |
Don't let the не fool you—it does not make the clause negative! Instead, it acts as a boundary marking exactly when the first action will stop. The verb following пока не is usually perfective, as it refers to a specific result being achieved.
| We will heat the solution in the flask until it becomes dark blue. | Мы будем нагревать раствор в колбе, пока он не станет синим. |
| The student must not mix dangerous substances until he asks the teacher. | Студент не должен смешивать опасные вещества, пока не спросит учителя. |
In the Laboratory
Let's put this grammar to work in the lab. When observing an experiment (эксперимент), you will often need to combine these temporal conjunctions with other complex clauses to describe exactly how a solution (раствор) or substance (вещество) behaves.
| The solution that is in the flask changes color while it boils. | Раствор, который находится в колбе, меняет цвет, пока он кипит. |
| The scientist does not trust the new experiment until the liquid starts to boil. | Учёный не доверяет новому эксперименту, пока жидкость не начнёт кипеть. |
| Why can't we rest until we finish this important experiment? | Почему мы не можем отдыхать, пока не закончим этот важный эксперимент? |