理科の実験でよく見る「物質が水に溶ける」現象には、実はしっかりとした法則があるんだ。溶解度と再結晶を理解すれば、なぜ熱い砂糖水を冷やすと結晶ができるのか、計算問題も簡単に解けるようになるよ。
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Updated Apr 9, 2026
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溶解度の基本と再結晶のプロセス
1 / 6
溶解度と再結晶の基本概念
君たちが実験で使ったことがある食塩や砂糖、これらが水に溶ける量には実は限界がある。この限界を知ることで、物質を思い通りに取り出せるようになるんだ。
まず覚えておきたい用語がある。溶質（溶ける物質）、溶媒（溶かす液体）、溶液（混ざった全体）の3つだ。そして最も重要なのが溶解度で、これは100gの水に溶ける溶質の最大質量を表している。
質量パーセント濃度の計算も頻出だ。公式は「溶質の質量 ÷ 溶液の質量 × 100」。ここで注意したいのは、分母は溶液全体の重さということ。水だけの重さじゃないよ。
ここがポイント！ 溶解度は温度によって変わる。この性質を利用して物質を取り出すのが再結晶だ。
溶解度曲線の読み方
溶解度曲線は横軸が温度、縦軸が溶解度を表すグラフだ。このグラフを見れば、その物質がどんな性質を持っているかすぐにわかる。
硝酸カリウムのような物質は、温度が上がると溶解度が急激に増える。60℃では100gの水に109gも溶けるのに、20℃では32gしか溶けない。一方、塩化ナトリウム（食塩）は温度が変わってもあまり溶解度が変わらない。
この違いが、後で学ぶ再結晶の方法選択に直結している。グラフの傾きが急な物質ほど、温度を下げるだけで結晶がたくさん出てくるんだ。
テスト対策！ グラフから数値を読み取る問題では、目盛りをしっかり確認しよう。1目盛りがいくつを表すか見落とすと間違えるよ。
再結晶の2つの方法
再結晶は、一度溶かした物質を再び結晶として取り出す技術だ。不純物を取り除いて純粋な物質を得るためにも使われる。
方法は2つある。冷却法は高温で飽和水溶液を作ってから冷やす方法で、硝酸カリウムやミョウバンに適している。蒸発法は水を蒸発させる方法で、塩化ナトリウムのような物質に使う。
なぜ使い分けるかというと、硝酸カリウムは冷やすだけで溶解度が急激に下がるから結晶がどんどん出てくる。でも塩化ナトリウムは冷やしても溶解度があまり変わらないから、水を減らして強制的に結晶を出すんだ。
実験のコツ！ 再結晶では、どちらの方法を選ぶかが成功の鍵。溶解度曲線の傾きを見て判断しよう。
計算問題の解き方（基本編）
質量パーセント濃度の計算は、手順を覚えれば簡単だ。20gの砂糖を80gの水に溶かした場合、溶液全体は100gになる。だから濃度は20g ÷ 100g × 100 = 20%となる。
溶解度を使った計算では、比例の考え方が重要だ。水100gに64g溶ける物質なら、水50gには32g溶ける。「100g : 64g = 50g : x g」の式を作って解けばOK。
計算ミスを防ぐには、まず何を求めているかを明確にして、単位も忘れずに書くこと。特に水の量が100g以外の問題では、必ず比例計算が必要になる。
計算のポイント！ 溶液の質量 = 溶質の質量 + 溶媒の質量。この関係を忘れると計算が狂うよ。
再結晶計算と実戦対策
再結晶で出てくる結晶の量を計算する問題は、温度変化による溶解度の差がカギだ。60℃で109g溶けていた硝酸カリウムを20℃まで冷やすと、32gしか溶けていられない。だから109g - 32g = 77gの結晶が出てくる。
テストでよく出るポイントを整理しよう。溶解度の定義では「100gの水に」「最大」がキーワード。質量パーセント濃度では分母を間違えないこと。グラフ問題では目盛りの確認を忘れずに。
「硝酸カリウムは冷却、塩化ナトリウムは蒸発」の組み合わせは必須知識だ。なぜそうするのか、理由も説明できるようになっておこう。溶解度曲線の傾きの違いが根本原因だからね。
テスト必勝法！ 計算問題では、水の量が100gとは限らない。50gや200gの場合があるから、必ず比例計算を意識しよう。
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI companion is specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
Where can I download the Knowunity app?
You can download the app in the Google Play Store and in the Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
Most popular content in 化学
Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.6/5
App Store
4.7/5
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
溶解度の基本と再結晶のプロセス
理科の実験でよく見る「物質が水に溶ける」現象には、実はしっかりとした法則があるんだ。溶解度と再結晶を理解すれば、なぜ熱い砂糖水を冷やすと結晶ができるのか、計算問題も簡単に解けるようになるよ。
溶解度と再結晶の基本概念
君たちが実験で使ったことがある食塩や砂糖、これらが水に溶ける量には実は限界がある。この限界を知ることで、物質を思い通りに取り出せるようになるんだ。
まず覚えておきたい用語がある。溶質（溶ける物質）、溶媒（溶かす液体）、溶液（混ざった全体）の3つだ。そして最も重要なのが溶解度で、これは100gの水に溶ける溶質の最大質量を表している。
質量パーセント濃度の計算も頻出だ。公式は「溶質の質量 ÷ 溶液の質量 × 100」。ここで注意したいのは、分母は溶液全体の重さということ。水だけの重さじゃないよ。
ここがポイント！ 溶解度は温度によって変わる。この性質を利用して物質を取り出すのが再結晶だ。
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溶解度曲線の読み方
溶解度曲線は横軸が温度、縦軸が溶解度を表すグラフだ。このグラフを見れば、その物質がどんな性質を持っているかすぐにわかる。
硝酸カリウムのような物質は、温度が上がると溶解度が急激に増える。60℃では100gの水に109gも溶けるのに、20℃では32gしか溶けない。一方、塩化ナトリウム（食塩）は温度が変わってもあまり溶解度が変わらない。
この違いが、後で学ぶ再結晶の方法選択に直結している。グラフの傾きが急な物質ほど、温度を下げるだけで結晶がたくさん出てくるんだ。
テスト対策！ グラフから数値を読み取る問題では、目盛りをしっかり確認しよう。1目盛りがいくつを表すか見落とすと間違えるよ。
Sign up to see the contentIt's free!
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再結晶の2つの方法
再結晶は、一度溶かした物質を再び結晶として取り出す技術だ。不純物を取り除いて純粋な物質を得るためにも使われる。
方法は2つある。冷却法は高温で飽和水溶液を作ってから冷やす方法で、硝酸カリウムやミョウバンに適している。蒸発法は水を蒸発させる方法で、塩化ナトリウムのような物質に使う。
なぜ使い分けるかというと、硝酸カリウムは冷やすだけで溶解度が急激に下がるから結晶がどんどん出てくる。でも塩化ナトリウムは冷やしても溶解度があまり変わらないから、水を減らして強制的に結晶を出すんだ。
実験のコツ！ 再結晶では、どちらの方法を選ぶかが成功の鍵。溶解度曲線の傾きを見て判断しよう。
Sign up to see the contentIt's free!
Access to all documents
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Join milions of students
計算問題の解き方（基本編）
質量パーセント濃度の計算は、手順を覚えれば簡単だ。20gの砂糖を80gの水に溶かした場合、溶液全体は100gになる。だから濃度は20g ÷ 100g × 100 = 20%となる。
溶解度を使った計算では、比例の考え方が重要だ。水100gに64g溶ける物質なら、水50gには32g溶ける。「100g : 64g = 50g : x g」の式を作って解けばOK。
計算ミスを防ぐには、まず何を求めているかを明確にして、単位も忘れずに書くこと。特に水の量が100g以外の問題では、必ず比例計算が必要になる。
計算のポイント！ 溶液の質量 = 溶質の質量 + 溶媒の質量。この関係を忘れると計算が狂うよ。
Sign up to see the contentIt's free!
Access to all documents
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Join milions of students
再結晶計算と実戦対策
再結晶で出てくる結晶の量を計算する問題は、温度変化による溶解度の差がカギだ。60℃で109g溶けていた硝酸カリウムを20℃まで冷やすと、32gしか溶けていられない。だから109g - 32g = 77gの結晶が出てくる。
テストでよく出るポイントを整理しよう。溶解度の定義では「100gの水に」「最大」がキーワード。質量パーセント濃度では分母を間違えないこと。グラフ問題では目盛りの確認を忘れずに。
「硝酸カリウムは冷却、塩化ナトリウムは蒸発」の組み合わせは必須知識だ。なぜそうするのか、理由も説明できるようになっておこう。溶解度曲線の傾きの違いが根本原因だからね。
テスト必勝法！ 計算問題では、水の量が100gとは限らない。50gや200gの場合があるから、必ず比例計算を意識しよう。
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI companion is specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
Where can I download the Knowunity app?
You can download the app in the Google Play Store and in the Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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Most popular content in 化学
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Students love us — and so will you.
4.6/5
App Store
4.7/5
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user