シャドーイング練習: Exploring the pH Scale - 動画で英語スピーキングを学ぶ

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1
Lemon juice is acidic.
2
Pure water is neutral.
3
Many cleaning products are alkaline.
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But what do these terms mean and how do we measure the difference?
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The pH scale gives us a way to compare them and each step represents a much bigger change than you might expect.
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You'll see the pH scale displayed in several ways as colored bars, a dial, droplets, and a digital display.
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Each shows the same information in a different layout.
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For a closer look we'll use this vertical scale and work through the examples one by one.
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pH describes how acidic or alkaline a water -based solution is.
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The familiar scale runs from 0 to 14 although some solutions fall outside this range.
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At 25 degrees Celsius, 7 is neutral.
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Below 7 is acidic.
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Above 7 is alkaline, or basic.
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To understand what these numbers mean, we need to look at the particles in the solution.
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Water contains tiny amounts of hydrogen ions and hydroxide ions.
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Ions are particles with an electrical charge.
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In a neutral solution, hydrogen ions and hydroxide ions have equal concentrations.
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An acidic solution has a higher concentration of hydrogen ions than hydroxide ions.
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In an alkaline solution, the reverse is true.
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The lower the pH, the higher the hydrogen ion concentration.
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Each whole step represents a tenfold change.
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A solution at pH 3 has 10 times the hydrogen ion concentration of 1 at pH 4.
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Compared with a solution at pH 5, it has 100 times the hydrogen ion concentration.
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Move towards higher pH numbers, and hydrogen ion concentration decreases tenfold with each step.
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This makes pH a logarithmic scale.
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A difference of two pH units represents a hundred -fold change in hydrogen ion concentration.
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A difference of three units represents a thousand -fold change.
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The colors help us read the scale.
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They represent the colors produced by Universal Indicator, a mixture of dyes that changes color with pH.
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Universal Indicator generally shows reds and oranges in acidic solutions, green near neutral, and blues or purples in alkaline solutions.
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These are indicator colors, not necessarily the colors of the substances themselves.
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A calibrated pH meter measures pH electronically and displays a numerical reading.
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Let's work through the examples, starting at the acidic end.
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Their positions are approximate.
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The actual pH depends on the particular sample and its concentration.
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To test an unknown substance, we use suitable equipment.
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Never taste or touch.
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Battery acid appears at the extreme acidic end of our chart.
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Lead -acid car batteries contain sulfuric acid, which takes part in the reactions that produce an electric current.
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Battery acid is highly corrosive and can cause severe chemical burns.
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Next is stomach acid.
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Your stomach contains hydrochloric acid, which creates the acidic conditions needed by an enzyme called pepsin.
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Pepsin helps digest proteins in food.
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The acid also helps kill many swallowed microbes, while a protective mucus barrier helps shield the stomach lining.
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Lemon juice commonly has a pH around 2 to 3.
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Much of its acidity comes from citric acid
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which gives lemons their familiar sour taste grapefruit juice is also
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acidic commonly around ph3 it contains citric acid too the exact ph varies between fruits and can change as they ripen
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tomato ketchup is usually around ph4 acids from the tomatoes
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and added vinegar contribute to its tangy flavor the acidic conditions
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also help limit the growth of many microorganisms black coffee is commonly around pH 5.
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Several dissolved acids contribute to its acidity, and the exact pH depends on the beans and how the coffee is brewed.
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A substance does not have to taste like lemon juice to be acidic.
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Fresh milk is only slightly acidic, usually around pH 6 .5.
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As milk sours, bacteria convert milk sugar into lactic acid.
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This increases hydrogen ion concentration and lowers the pH.
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At pH 7, we reach our neutral reference, pure water at 25 degrees Celsius.
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Its hydrogen ion and hydroxide ion concentrations are equal.
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Neutral does not mean these ions are absent.
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Both are present in equal, very small amounts.
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Moving past 7, we enter the alkaline region.
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Seawater is slightly alkaline, with surface ocean water averaging around pH 8 .1.
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When the ocean absorbs carbon dioxide, chemical reactions increase hydrogen ion concentration and lower the pH.
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This is called ocean acidification.
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The term describes the decrease in pH, even though seawater remains alkaline.
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Around pH 9, we find borax dissolved in water.
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Borax is a mineral used in some cleaning products.
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Its solution is alkaline, with a typical pH around 9 .2.
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Milk of magnesia is around pH 10 to 11.
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Despite its name, it is not dairy milk.
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It contains magnesium hydroxide and is used as an antacid.
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The magnesium hydroxide reacts with excess stomach acid, reducing acidity.
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Household ammonia solution is often around pH 11.
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It consists of ammonia dissolved in water and is used in some cleaning products to help remove grease.
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Ammonia must never be mixed with bleach because the reaction can release dangerous gases.
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At pH 12, our example is dilute lye, a sodium hydroxide solution.
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This shows that even a relatively dilute solution can be highly alkaline.
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Its pH depends on how much sodium hydroxide is dissolved in a given volume of solution.
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Household chlorine bleach is another highly alkaline example, placed here near pH 13.
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It contains sodium hypochlorite and is formulated to remain alkaline.
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Its actual pH varies between products.
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Bleach should never be mixed with other cleaners.
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At the alkaline extreme, some drain cleaners contain concentrated sodium hydroxide.
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This reacts with fats and helps break down organic material in blocked pipes.
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Like battery acid at the opposite end of the scale, these products can cause severe chemical burns.
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Now compare two solutions, one at pH 3 and another at pH 5.
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Which has the higher hydrogen ion concentration?
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The solution at pH 3.
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How much higher?
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100 times.
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There are two steps between them, and each represents a factor of 10.
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There's one more distinction to remember.
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A low pH does not automatically mean an acid is classified as a strong acid.
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In chemistry, acid strength describes how readily an acid releases hydrogen ions in water.
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The pH also depends on its concentration.
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Citric acid is classified as a weak acid, even though lemon juice has a low pH.
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The pH scale helps us describe and compare solutions, from the food we eat to seawater and household products.
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At 25 degrees Celsius, below 7 is acidic,
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7 is neutral, and above 7 is alkaline and every whole step represents a tenfold change in hydrogen ion concentration.

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このレッスンの語彙とスピーキングのポイント

このスピーキングレッスンは、動画「Exploring the pH Scale」を教材にしています。 繰り返し出てくる語は次のとおりです：ion, acid, solution, alkaline, hydrogen。 この動画には、シャドーイング用の文が99文、単語が1062語あります。 音声の長さは7:43です。 話す速さは1分あたり約138語で安定しており、シャドーイングしやすいペースです。 英語の頻出3,000語に含まれる単語は64%だけなので、語彙は難しめです。

この動画の重要語彙

動画に出てくる覚えておきたい単語15語を、発音と意味つきで紹介します。

単語発音意味
acid 名詞/ˈæsɪd/酸
concentration 名詞/ˌkɑn.sənˈtɹeɪ.ʃən/集中, 集中力
hydrogen 名詞/ˈhaɪdɹəd͡ʒ(ə)n/水素
ion 名詞/ˈaɪ.ɑn/イオン
neutral 形容詞/ˈnuː.tɹəl/中立の
juice 名詞/d͡ʒuːs/汁, 樹液
lemon 名詞/ˈlɛmən/檸檬, レモン
compare 動詞/kəmˈpɛɚ/比べる, 比較する
stomach 名詞/ˈstʌmək/胃, 胃袋
depend 動詞/dɪˈpɛnd/依存する
sodium 名詞/ˈsəʊ.di.əm/ナトリウム
substance 名詞/ˈsʌbstəns/物質
indicator 名詞/ˈɪn.dɪˌkeɪ.tə(ɹ)/インジケータ, インジケーター
bleach 名詞/bliːt͡ʃ/漂白剤
contribute 動詞/kənˈtɹɪb.jut/貢献する

注意したい発音

  • 「sh」と「zh」の音: concentration /ˌkɑn.sənˈtɹeɪ.ʃən/, shield /ˈʃild/, distinction /dɪˈstɪŋkʃən/, acidification /əˌsɪdɪfɪˈkeɪʃən/, magnesia /ˌmæɡˈniʒə/
  • 長い単語（アクセントの位置に注意）: concentration /ˌkɑn.sənˈtɹeɪ.ʃən/, indicator /ˈɪn.dɪˌkeɪ.tə(ɹ)/, necessarily /ˌnɛs.əˈsɛɹ.ə.li/, electrical /ɪˈlɛktɹɪkəl/, numerical /n(j)uːˈmɛɹ.ɪ.kəl/

日本語話者が苦手な音：

  • /r/ と /l/ の区別 — /l/ は舌先を歯茎につけ、/r/ はどこにもつけない: neutral /ˈnuː.tɹəl/, particle /ˈpɑɹtək(ə)l/, necessarily /ˌnɛs.əˈsɛɹ.ə.li/, electrical /ɪˈlɛktɹɪkəl/, mineral /ˈmɪn.ə.ɹəl/
  • /v/ — /b/ にならないように、上の歯を下唇に当てる: vary /ˈvɛəɹi/, reverse /ɹɪˈvɝs/, vertical /ˈvɝ.tɪ.kəl/, protective /pɹəˈtɛk.tɪv/, convert /kənˈvɝt/
  • /f/ — 「フ」ではなく、上の歯と下唇で出す: fold /ˈfəʊld/, flavor /ˈfleɪvə/, tenfold /ˈtɛnfoʊld/, classify /ˈklæs.əˌfaɪ/, acidification /əˌsɪdɪfɪˈkeɪʃən/

この動画での練習方法

  1. まず声を出さずに動画を最後まで聞き、知らない単語をメモします。
  2. 通常の速度で一文ずつシャドーイングし、話し手のリズムに合うまで繰り返します。
  3. 自分の声を録音して元の音声と比べます。acid, concentration, hydrogenなどの単語に特に注意しましょう。

シャドーイングとは？英語上達に効果的な理由

シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。

シャドーイングのやり方: ステップ別の完全ガイドを読む →