Help Difference between these grammatical constructions

I'm having trouble with expressions used to indicate things that occur at the same time.

First of all, what is the difference between ～うちに and ～際 ? Is it just that the first is used in more casual situations, and the second is used more formally?

Also, when using ～ところ/～ところに/～ところで/～ところを、how can you tell which particle needs to be used? I'm sure it's dependent on a clause in another part of the sentence, but I just can't figure it out.

Example practice sentences follow, I'll put in bold the right answer, which I basically got a 0% on.

大きいなあくびをしたところ（に・を・が）写真に撮られた。
よく眠っているところ（に・を・が）起こされた。
１０ページ書き終わったところ（に・を・で）、パソコンが動かなくなった。
引越しで忙しいところ（に・で・は）、国から友達が遊びにきた。
テストの答えがわかったところ（に・で・を）、終わりのバザーが鳴った。

Thank you!

alteregoivy said:

what is the difference between ～うちに and ～際 ? Is it just that the first is used in more casual situations, and the second is used more formally?

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～うちに is close to ～間に, not for "at a moment" but for "in/during a span."

涼しいうちに散歩してくる。
冷めないうちにお召し上がりください。

～際 is close to ～とき and mostly used for a concrete action.

こちらにお出での際は、是非お立ち寄りください。
×子供の際は、よく一緒に遊んでいた。
○子供のとき/頃は、よく一緒に遊んでいた。

alteregoivy said:

A
Also, when using ～ところ/～ところに/～ところで/～ところを、how can you tell which particle needs to be used? I'm sure it's dependent on a clause in another part of the sentence, but I just can't figure it out.
Example practice sentences follow, I'll put in bold the right answer, which I basically got a 0% on.
大きいなあくびをしたところ（に・を・が）写真に撮られた。
よく眠っているところ（に・を・が）起こされた。
１０ページ書き終わったところ（に・を・で）、パソコンが動かなくなった。
引越しで忙しいところ（に・で・は）、国から友達が遊びにきた。
テストの答えがわかったところ（に・で・を）、終わりのバザーが鳴った。

Click to expand...

That's a particle issue.

#1 the object of 撮られる
#2 when
#3,5 at the moment
#4 when/where

Toritoribe said:

～うちに is close to ～間に, not for "at a moment" but for "in/during a span."
涼しいうちに散歩してくる。
冷めないうちにお召し上がりください。
～際 is close to ～とき and mostly used for a concrete action.
こちらにお出での際は、是非お立ち寄りください。
×子供の際は、よく一緒に遊んでいた。
○子供のとき/頃は、よく一緒に遊んでいた。

Click to expand...

Thank you very much! I think I understand now.

Toritoribe said:

That's a particle issue.
#1 the object of 撮られる
#2 when
#3,5 at the moment
#4 when/where

Click to expand...

Ok... Then I think I need a recap on particles.

I thought that に is used for "when," rather than を, so I don't understand #2 still. Also, I still don't understand the difference between using で and に, as in between 3/5 and 4. Is で only ever used when the preceding verb is past tense (～ったところで）?

No, no, sorry for my too much abridging.

alteregoivy said:

I thought that に is used for "when," rather than を

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Right. When a clause is nominalized by とき, the particle に is used.

１０ページ書き終わったところで、パソコンが動かなくなった。
１０ページ書き終わったときに、パソコンが動かなくなった。

You can think these ところ as "a scene/situation in an action/movement."
～ところを is close to ～のを, the verb used in the main clause expresses the action of the subject of the whole sentence. The all example sentences are the descriptions about "me." In #1 and 2, the subjects of 撮られる and 起こされる are "I," whereas the subjects in the main clases in #3~5 are not "I"(パソコン, 友達, ブザー).

～ところで emphasizes that it's "just at the moment" than ～ところに. The action/movement in the main clause is done just at the point in/right after the action/movement expressed in the ところ-clause.

～ところに is close to ～ときに. In #4, a friend came to me when I was busy, not just at the moment I was busy.

alteregoivy said:

Is で only ever used when the preceding verb is past tense (～ったところで）?

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No. You can use ところで in a conditional sentence, too.

これから勉強しようというところで遊びに来られると、 すごく困る。