쉐도잉 연습: Exploring the pH Scale - 영상으로 영어 말하기 배우기
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1
Lemon juice is acidic.
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Pure water is neutral.
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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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이 레슨의 어휘와 말하기 포인트
이 말하기 레슨은 영상 “Exploring the pH Scale”을(를) 바탕으로 합니다. 가장 자주 반복되는 단어는 다음과 같습니다: ion, acid, solution, alkaline, hydrogen. 이 영상에는 섀도잉할 문장 99개와 단어 1062개가 있습니다. 말하는 구간의 길이는 7:43입니다. 화자는 분당 약 138단어의 일정한 속도로 말해서 섀도잉하기에 편한 속도입니다. 영어에서 가장 많이 쓰이는 3,000단어에 속하는 단어가 64%뿐이라 어휘가 어려운 편입니다.
이 영상의 핵심 어휘
영상에 나오는 익혀 둘 만한 단어 15개를 발음, 뜻과 함께 정리했습니다.
| 단어 | 발음 | 뜻 |
|---|---|---|
| acid 명사 | /ˈæsɪd/ | 산 |
| concentration 명사 | /ˌkɑn.sənˈtɹeɪ.ʃən/ | 집중, 집중력 |
| hydrogen 명사 | /ˈhaɪdɹəd͡ʒ(ə)n/ | 수소 |
| ion 명사 | /ˈaɪ.ɑn/ | 이온 |
| neutral 형용사 | /ˈnuː.tɹəl/ | 중립의 |
| juice 명사 | /d͡ʒuːs/ | 즙 |
| lemon 명사 | /ˈlɛmən/ | 레몬 |
| compare 동사 | /kəmˈpɛɚ/ | 비교하다, 비유하다 |
| stomach 명사 | /ˈstʌmək/ | 위, 위장 |
| depend 동사 | /dɪˈpɛnd/ | 의존하다, ...에 달려 있다 |
| sodium 명사 | /ˈsəʊ.di.əm/ | 나트륨, 소듐 |
| substance 명사 | /ˈsʌbstəns/ | 물질 |
| indicator 명사 | /ˈɪn.dɪˌkeɪ.tə(ɹ)/ | 인디케이터, 지시약 |
| bleach 명사 | /bliːt͡ʃ/ | 표백제 |
| react 동사 | /ɹiːˈækt/ | 반응하다 |
주의할 발음
- “sh”와 “zh” 소리: concentration /ˌkɑn.sənˈtɹeɪ.ʃən/, shield /ˈʃild/, distinction /dɪˈstɪŋkʃən/, acidification /əˌsɪdɪfɪˈkeɪʃən/, magnesia /ˌmæɡˈniʒə/
- 긴 단어 — 강세 위치에 주의: concentration /ˌkɑn.sənˈtɹeɪ.ʃən/, indicator /ˈɪn.dɪˌkeɪ.tə(ɹ)/, necessarily /ˌnɛs.əˈsɛɹ.ə.li/, electrical /ɪˈlɛktɹɪkəl/, numerical /n(j)uːˈmɛɹ.ɪ.kəl/
한국어 화자가 어려워하는 소리:
- /f/ — ㅍ(/p/)으로 바꾸지 말고 윗니를 아랫입술에 대기: fold /ˈfəʊld/, flavor /ˈfleɪvə/, tenfold /ˈtɛnfoʊld/, classify /ˈklæs.əˌfaɪ/, acidification /əˌsɪdɪfɪˈkeɪʃən/
- /v/ — ㅂ(/b/)과 구별하기: vary /ˈvɛəɹi/, reverse /ɹɪˈvɝs/, vertical /ˈvɝ.tɪ.kəl/, protective /pɹəˈtɛk.tɪv/, convert /kənˈvɝt/
- /z/ — ㅈ이 아니라 성대를 울리는 /s/: enzyme /ˈɛn.zaɪm/, dissolve /dɪˈzɑlv/, magnesium /ˌmæɡˈnizi.əm/, microorganism /ˌmaɪ.kɹoʊˈɔɹ.ɡəˌnɪz.m̩/
이 영상으로 연습하는 방법
- 먼저 말하지 않고 영상을 끝까지 듣고 모르는 단어를 적어 둡니다.
- 보통 속도로 한 문장씩 섀도잉하고, 화자의 리듬과 맞을 때까지 반복합니다.
- 자신의 목소리를 녹음해 원본과 비교하고, acid, concentration, hydrogen 같은 단어에 특히 주의합니다.
쉐도잉이란? 영어 실력을 빠르게 키우는 과학적 방법
쉐도잉(Shadowing)은 원래 전문 통역사 훈련을 위해 개발된 언어 학습 기법으로, 다언어 학자인 Dr. Alexander Arguelles에 의해 대중화된 방법입니다. 핵심 원리는 간단하지만 매우 강력합니다: 원어민의 영어를 들으면서 1~2초의 짧은 지연으로 즉시 소리 내어 따라 말하는 것——마치 '그림자(shadow)'처럼 화자를 따라가는 것입니다. 문법 공부나 수동적인 청취와 달리, 쉐도잉은 뇌와 입 근육이 동시에 실시간으로 영어를 처리하고 재현하도록 훈련합니다. 연구에 따르면 이 방법은 발음 정확도, 억양, 리듬, 연음, 청취력, 말하기 유창성을 크게 향상시킵니다. IELTS 스피킹 준비와 자연스러운 영어 소통을 원하는 분들에게 특히 효과적입니다.