Shadowing Practice: Exploring the pH Scale - Learn English Speaking with Video
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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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Vocabulario y notas de pronunciación para esta lección
Esta lección de conversación se basa en el vídeo “Exploring the pH Scale”. Las palabras que más se repiten: ion, acid, solution, alkaline, hydrogen. Este vídeo tiene 99 frases y 1062 palabras para practicar shadowing. La parte hablada dura 7:43. El hablante mantiene un ritmo constante de unas 138 palabras por minuto, cómodo para el shadowing. Solo el 64 % de las palabras está entre las 3.000 más comunes del inglés, por lo que el vocabulario es exigente.
Vocabulario clave de este vídeo
15 palabras del vídeo que vale la pena aprender, con su pronunciación y significado:
| Palabra | Pronunciación | Significado |
|---|---|---|
| acid sustantivo | /ˈæsɪd/ | ácido |
| concentration sustantivo | /ˌkɑn.sənˈtɹeɪ.ʃən/ | concentración |
| hydrogen sustantivo | /ˈhaɪdɹəd͡ʒ(ə)n/ | hidrógeno |
| ion sustantivo | /ˈaɪ.ɑn/ | ion, ión |
| neutral adjetivo | /ˈnuː.tɹəl/ | neutral |
| juice sustantivo | /d͡ʒuːs/ | zumo, jugo |
| lemon sustantivo | /ˈlɛmən/ | limón, citrón |
| compare verbo | /kəmˈpɛɚ/ | comparar, parangonar |
| stomach sustantivo | /ˈstʌmək/ | estómago |
| depend verbo | /dɪˈpɛnd/ | depender/pender (de), ser dependiente (de) |
| sodium sustantivo | /ˈsəʊ.di.əm/ | sodio |
| household adjetivo | /ˈhaʊshoʊld/ | casero, hogareño |
| commonly adverbio | /ˈkɑmənli/ | comúnmente |
| substance sustantivo | /ˈsʌbstəns/ | sustancia, substancia |
| indicator sustantivo | /ˈɪn.dɪˌkeɪ.tə(ɹ)/ | señalizador |
Phrasal verbs que vas a escuchar
| Palabra | Significado |
|---|---|
| break down verbo | descomponerse, averiarse |
Pronunciación a tener en cuenta
- Los sonidos de “sh” y “zh”: concentration /ˌkɑn.sənˈtɹeɪ.ʃən/, shield /ˈʃild/, distinction /dɪˈstɪŋkʃən/, acidification /əˌsɪdɪfɪˈkeɪʃən/, magnesia /ˌmæɡˈniʒə/
- Palabras largas — cuida el acento: concentration /ˌkɑn.sənˈtɹeɪ.ʃən/, indicator /ˈɪn.dɪˌkeɪ.tə(ɹ)/, necessarily /ˌnɛs.əˈsɛɹ.ə.li/, electrical /ɪˈlɛktɹɪkəl/, numerical /n(j)uːˈmɛɹ.ɪ.kəl/
Sonidos difíciles para hispanohablantes:
- s + consonante al inicio — sin añadir una “e” delante: stomach /ˈstʌmək/, swallow /ˈswɑ.loʊ/
- /v/ — no es /b/: los dientes tocan el labio inferior: vary /ˈvɛəɹi/, reverse /ɹɪˈvɝs/, vertical /ˈvɝ.tɪ.kəl/, protective /pɹəˈtɛk.tɪv/, convert /kənˈvɝt/
- /z/ — sonora, no /s/: enzyme /ˈɛn.zaɪm/, dissolve /dɪˈzɑlv/, magnesium /ˌmæɡˈnizi.əm/, microorganism /ˌmaɪ.kɹoʊˈɔɹ.ɡəˌnɪz.m̩/
Cómo practicar con este vídeo
- Escucha el vídeo entero una vez sin hablar y anota las palabras que no conoces.
- Haz shadowing frase por frase a velocidad normal, repitiendo cada una hasta que tu ritmo coincida con el del hablante.
- Grábate y compara con el original, prestando atención a palabras como acid, concentration, hydrogen.
¿Qué es la Técnica de Shadowing?
Shadowing es una técnica de aprendizaje de idiomas respaldada por la ciencia, desarrollada originalmente para la formación de intérpretes profesionales y popularizada por el políglota Dr. Alexander Arguelles. El método es simple pero poderoso: escuchas audio en inglés nativo y lo repites en voz alta de inmediato, como una sombra que sigue al hablante con solo 1-2 segundos de retraso. A diferencia de la escucha pasiva o los ejercicios de gramática, el shadowing obliga a tu cerebro y músculos de la boca a procesar y reproducir simultáneamente patrones de habla reales. Las investigaciones muestran que mejora significativamente la precisión de la pronunciación, la entonación, el ritmo, el habla conectada, la comprensión auditiva y la fluidez al hablar, convirtiéndola en una de las metodologías más efectivas para la preparación del IELTS Speaking y la comunicación en inglés en el mundo real.