« 買ってもぅた | Main | 中学入試・・・・切手の問題 »

July 30, 2010

中学入試・・水溶液の問題

この問題、皆さんどう教えますか?・・・・小学生に。。。。

いま、ある物質Aがあります。この物質は、100gの水にそれぞれ以下のように溶けます。

 30度の水に80g
 80度の水に150g

問題1
 いま、80度の水に物質Aを溶けるだけ溶かしました(つまり飽和状態)。
 この”水溶液”300gに溶けている物質Aは何gですか?

  ・・・これは簡単。飽和水溶液量の濃度を考えればいいから、
    100gの水に150g溶けることから、濃度は
     150÷(150+100)×100=60%
    なので、300g×60%=180g

   答え:180g

問題は次。。。。。

問題2
 ”問題1で作った300gの水溶液”を30度まで冷やしました。
 結晶となって出てくる物質Aは何グラムですか?

 もともと、問題1の300gの水溶液に溶けている物質Aは180gなので
 そのときの水の量は120g。。。。
 ということは、30度の時に120gの水に溶ける物質Aの飽和量を考えて、180gから引けばいい。
 。。。。。なので、普通に考えて、30度の時の飽和濃度を考えて、
 80÷(80+100)×100=80/180×100≒44%
 120×44%=52.8g
 180-52.8=127.2g ☆できた!

と思ったら、大きな間違い。答えを見ると、こんな式でした

 100:80=120:x
 x=120×80÷100=96
 180-96=84
 答え:84g

おいおい!うちの娘はまだ比例方程式なんて習ってない!。。。比例式すらも習っていない。
じゃぁどうしよう。。。。
なるほど、「120×44%=52.8g」 ここが違う!
そもそも飽和水溶液量を考えているので、120gの水ではなく、
120gに溶けている物質Aを足した飽和水溶液量にかけなけばなりません。

 x=(120+x)×44%
 x=52.8÷0.56≒94.3
    ・・・ つまりこれが30度飽和水溶液120gに溶けている物質Aの量の近似値
 180-94.3=85.7

 答え:約85.7g

うーん、違う。。。。。皆さん、比例方程式なしの場合、どう教えますか?

|

« 買ってもぅた | Main | 中学入試・・・・切手の問題 »

「日記・コラム・つぶやき」カテゴリの記事

Comments

30℃のときは100gの水に80g溶けるわけですよね。
では120gのときは、100gの1.2倍あるので
80gも1.2倍溶けます、
よって96g溶けます。
したがって
180gから96gを引いて84gとなる。
の方が自然な考え方なのでは、
もしくは、20gには100gの5分の1なので80gの5分の1の16g溶けるとして、120gでは80g+16gで96gとけるとしては。

Posted by: | January 19, 2011 at 07:23 PM

Comment divorcer rapidement sans avocat droit divorce femme

Posted by: www.votredivorce.Net | March 10, 2013 at 10:25 PM

I really like your blog.. very nice colors & theme. Did you make this website yourself or did you hire someone to do it for you? Plz respond as I'm looking to design my own blog and would like to find out where u got this from. appreciate it

Posted by: castleclashgen.com | September 08, 2015 at 03:46 PM

Heya! I just wanted to ask if you ever have any trouble with hackers? My last blog (wordpress) was hacked and I ended up losing a few months of hard work due to no data backup. Do you have any methods to protect against hackers?

Posted by: http://castleclashgen.com/ | September 13, 2015 at 09:29 AM

This blog was... how do I say it? Relevant!! Finally I have found something which helped me. Appreciate it!

Posted by: Http://Nouvellesfrancaises.Hpage.Com/ | September 16, 2015 at 03:05 AM

It's very simple to find out any topic on web as compared to textbooks, as I found this paragraph at this site.

Posted by: code promo la redoute aout 2015 | September 16, 2015 at 05:08 PM

Great post. I was checking continuously this blog and I'm impressed! Extremely helpful info particularly the last part :) I care for such info much. I was seeking this particular information for a very long time. Thank you and best of luck.

Posted by: lasertest | October 15, 2015 at 02:51 PM

Very descriptive blog, I enjoyed that bit. Will there be a part 2?

Posted by: lasertest | October 16, 2015 at 03:13 PM

For that prices you may additionally prepared your wallet on this means that you're going to create.

Posted by: The Limo Rental Mystery | October 19, 2015 at 04:20 PM

All the necessary file maintenance. On top of best cheap wweb hosting that exaactly happening. Many webmasters plan to party again soon.These appear corporate email accounts, web server. He doesn't get yelled at for this reason wwe recommend a partnerA Powered by WordPress. Join San Diego for a hodt who's page takes ages to load. But this does is to both FedEx and pay for what specifics you will result in nearly the ame price as those families vying for cash.

Posted by: top web hosting service | October 19, 2015 at 04:57 PM

Greetings! Quick question that's entirely off topic. Do you know how to make your site mobile friendly? My site looks weird when browsing from my iphone 4. I'm trying to find a theme or plugin that might be able to fix this issue. If you have any recommendations, please share. Cheers!

Posted by: jurassic world hack | October 20, 2015 at 01:43 PM

I could not resist commenting. Well written!

Posted by: day nau an tphcm | October 22, 2015 at 03:39 PM

A great deal of people in the group that is nootropic paradoxically combination materials that promote other neurotransmitter / hormones. 's Wort

Posted by: nootropic stack for adhd | October 22, 2015 at 07:48 PM

It's like asking "when does going to church a crime. Since gender is determined by the father and not the mother, the "failure" to produce a male child was actually Henry's failure. 22 Coming before she's got excited or begun to enjoy sex.

Posted by: Allphimsex.Com | October 22, 2015 at 10:24 PM

Terrific work! That is the kind of info that should be shared across the net. Shame on Google for now not positioning this publish higher! Come on over and visit my web site . Thank you =)

Posted by: 24 hour emergency locksmith | October 24, 2015 at 03:11 PM

I like what you guys are usually up too. This type of clever work and reporting! Keep up the amazing works guys I've added you guys to our blogroll.

Posted by: World of Warships Aimbot | October 26, 2015 at 07:49 AM

This piece of writing is in fact a good one it helps new net users, who are wishing in favor of blogging.

Posted by: Getting Rid Of Sunspots | October 27, 2015 at 03:09 PM

Hi there everyone, it's my first pay a quick visit at this web page, and post is in fact fruitful in support of me, keep up posting these types of posts.

Posted by: wolfteam hack | October 28, 2015 at 09:23 AM

Dabei kannst du dir das Wahrsagen on the internet als eine Reise vorstellen, bei der deine Vergangenheit ebenso aufgesucht wird wie deine Gegenwart und Zukunft.

Posted by: kartenlegen kostenlos Neue portale | October 28, 2015 at 09:29 AM

First off I want to say superb blog! I had a quick question that I'd like to ask if you don't mind. I was curious to find out how you center yourself and clear your thoughts before writing. I have had a difficult time clearing my thoughts in getting my thoughts out. I do enjoy writing but it just seems like the first 10 to 15 minutes tend to be lost simply just trying to figure out how to begin. Any suggestions or hints? Cheers!

Posted by: fat diminisher system review | October 28, 2015 at 03:41 PM

Hurrah! At last I got a blog from where I be capable of genuinely obtain helpful data regarding my study and knowledge.

Posted by: fat diminisher system pdf | October 28, 2015 at 06:11 PM

I used to be recommended this web site through my cousin. I'm not positive whether this submit is written by way of him as nobody else know such certain about my trouble. You are wonderful! Thanks!

Posted by: fat diminisher system reviews | October 29, 2015 at 01:28 AM

Post a comment



(Not displayed with comment.)




TrackBack

TrackBack URL for this entry:
http://app.cocolog-nifty.com/t/trackback/10194/49013920

Listed below are links to weblogs that reference 中学入試・・水溶液の問題:

» 75日で1ランク上の高校に合格した学習法 [教えたい]
75日あれば、どんなお子様でも 公立【第一志望校】へ逆転合格することは可能です... [Read More]

Tracked on August 01, 2010 at 07:07 AM

« 買ってもぅた | Main | 中学入試・・・・切手の問題 »