Name: how scientists test a hypothesis
Uploaded: 2020-09-03T13:38:25.000Z
Duration: 3 min 50 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.1.1

The Scientific Method

Il metodo scientifico è un approccio sistematico seguito da tutte le discipline scientifiche. Il metodo segue sei passaggi principali:fare un'osservazione, porre una domanda, costruire un'ipotesi, condurre esperimenti, interpretare i dati e, infine, derivarne una conclusione. Il metodo scientifico inizia con un'osservazione e una domanda per aiutare a capire quell'osservazione.

Per esempio, il chimico francese Antoine Lavoisier osservò i fenomeni di combustione. Formulò quindi una domanda per comprendere cosa succede quando qualcosa viene bruciato. Dove va la materia?

Il terzo passaggio del metodo scientifico è costruire un'ipotesi:un tentativo di spiegazione per l'osservazione in questione che vuole essere testata. Per rispondere alla domanda Dove va a finire la materia? Lavoisier ipotizzò che in una reazione chimica, la materia non venisse né creata, né distrutta.

Una buona ipotesi è anche verificabile o falsificabile. Un'ipotesi verificabile è quella che fa previsioni che possono essere confermate da sperimentazioni o osservazioni ripetute nel tempo. Un'ipotesi è falsificabile quando può essere confutata con la sperimentazione.

Il quarto passaggio nel metodo scientifico è la sperimentazione e la raccolta dei dati. Gli esperimenti sono osservazioni o misurazioni condotte in ambienti controllati, come temperatura, pressione o volume. Questo passaggio indaga in quale misura il mondo reale si adatti a quello previsto dall'ipotesi.

Alcuni esperimenti e osservazioni sono qualitativi:descrivono quindi come avviene un processo. Altri sono quantitativi:misurano o quantificano qualcosa riguardo al processo. Lavoisier verificò la sua ipotesi riscaldando il mercurio in un ambiente chiuso.

Questo portò alla formazione di una sostanza rossastra. Essendo i suoi esperimenti quantitativi, lo scienziato registrò attentamente la massa dei reagenti e dei prodotti sia nel sistema chiuso che separatamente. Il quinto passaggio è l'interpretazione e l'analisi dei dati:valutare se i risultati supportano o confutano l'ipotesi e se sono necessarie ulteriori sperimentazioni.

Lavoisier osservò che la massa totale del barattolo e il suo contenuto prima e dopo la reazione erano rimasti gli stessi, sebbene la massa del prodotto rosso fosse maggiore di quella del mercurio originale. Il passaggio finale consiste nel trarre una conclusione logica e decidere se accettare o rifiutare l'ipotesi. Se i risultati supportano l'ipotesi in modo significativo, allora questa è accettata.

L'ipotesi può anche essere sottoposta ad ulteriori test o perfezionata ponendo nuove domande, e conducendo nuovi esperimenti. Dai suoi esperimenti, Lavoisier concluse che, poiché la massa totale del barattolo era rimasta invariata durante la reazione, l'ossigeno nel barattolo si era combinato con il mercurio per formare il nuovo prodotto, ora noto come ossido di mercurio. Questa conclusione sosteneva fortemente la sua ipotesi sulla conservazione della massa:la massa totale degli oggetti rimane invariata durante il processo di combustione.

Tuttavia, se un'ipotesi viene confutata, gli scienziati possono formulare una nuova ipotesi, prendendo spunto dagli esperimenti falliti e ricominciando da capo. Anche se consideriamo il metodo scientifico come una serie di fasi, nuove informazioni o idee potrebbero indurre uno scienziato a tornare sui suoi passi e a modificare i passaggi in qualsiasi momento, durante il processo. Pertanto, il metodo scientifico è un processo iterativo.

il metodo scientifico

La chimica è una scienza empirica. Gli scienziati spesso pongono domande per comprendere la chimica nella vita di tutti i giorni e cercano risposte a queste domande. Per raggiungere questo obiettivo, gli scienziati seguono una serie definitiva di passaggi che insieme costituiscono il Metodo Scientifico. Questo approccio implica il fare osservazioni, porre domande, costruire ipotesi, condurre esperimenti, analizzare i risultati e giungere a una conclusione.

Osservazione e domanda

Il primo passo nel metodo scientifico è osservare un fenomeno nel mondo fisico. Successivamente, viene posta una domanda per comprendere meglio quel fenomeno. Ad esempio, la domanda potrebbe essere: “Cosa congela più velocemente, l’acqua normale o l’acqua con aggiunta di sale?”

Ipotesi

Il passo successivo è quello di formulare una spiegazione per quella particolare osservazione. Questo tentativo di interpretazione di un insieme di osservazioni che funge da guida per comprendere il fenomeno osservato viene chiamato ipotesi. Ad esempio, per la domanda precedente, un’ipotesi potrebbe suggerire che l’aggiunta di sale alteri il punto di congelamento dell’acqua normale.

Gli scienziati spesso utilizzano ricerche e letteratura precedenti per iniziare le loro indagini e formulare un'ipotesi che potrebbe essere verificata attraverso esperimenti. Un’ipotesi forte è sia verificabile che falsificabile. È considerata verificabile se può essere dimostrata corretta e falsificabile se può essere smentita: in questo caso lo scienziato deve modificare o scartare l'ipotesi.

Sperimentazione

Il terzo passo consiste nel progettare e condurre esperimenti per verificare la validità dell'ipotesi. Gli esperimenti sono misurazioni e osservazioni effettuate in condizioni controllate. Alcune osservazioni ed esperimenti sono qualitativi (descrivono come avviene un processo), mentre molti sono quantitativi (misurano o quantificano qualcosa riguardo al processo). Per verificare l'ipotesi dell'acqua salata, lo scienziato può prendere due bicchieri con la stessa quantità di acqua, a temperatura ambiente, e aggiungere un cucchiaio di sale a uno dei bicchieri per poi riporli entrambi nel congelatore. Lo stato dell'acqua in ogni bicchiere può essere osservato ogni 15 minuti e si può calcolare il tempo impiegato da ogni bicchiere d'acqua per congelarsi completamente.

Il disegno sperimentale è un passaggio fondamentale del metodo scientifico. È necessario prestare attenzione nel controllare il numero di fattori variabili in modo da poter monitorare l'effetto di un fattore specifico in questione.

Analisi dei Risultati e Conclusione

Il passo successivo è analizzare i risultati degli esperimenti e concludere se questi risultati convalidano o meno l'ipotesi. Se la conclusione è positiva, allora l’ipotesi viene accettata e potrebbe essere sottoposta a ulteriori sperimentazioni per rispondere a nuove domande. Quando un’ipotesi viene smentita, se ne può proporre una nuova e il processo continua.

Nell’esempio dell’acqua salata, i risultati indicano che l’acqua salata impiega più tempo a congelarsi rispetto all’acqua normale. Ciò fornisce la conclusione che l’acqua salata si congela a una velocità più lenta rispetto all’acqua semplice. Pertanto, i risultati convalidano l’ipotesi.

Questo testo è adattato da <a href="https://openstax.org/books/chemistry-2e/pages/1-1-chemistry-in-context">Openstax, Chimica 2e, Sezione 1.1: Il Metodo Scientifico.</a>

Il metodo scientifico

La chimica è una scienza empirica. Gli scienziati spesso pongono domande per comprendere la chimica nella vita di tutti i giorni e cercano risposte a queste domande. A...

Education

Didattica

JoVE Core

Chimica

Introduction: Matter and Measurement

Introduzione: Materia e Misurazione

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

how scientists test a hypothesis

Chemistry uses the scientific method to turn observations into testable answers. Scientists begin by observing a phenomenon in the physical world and then asking a question about it. This process helps explain everyday chemistry through evidence.

A question leads to a hypothesis, which is a tentative explanation for what is being observed. Scientists often use earlier research and published literature to shape that idea. A strong hypothesis must be testable, meaning it can be supported by evidence, and falsifiable, meaning it can also be proven wrong.

The next step is experimentation. Scientists design and carry out experiments under controlled conditions to test the hypothesis. These tests can include qualitative observations, which describe how a process happens, and quantitative measurements, which record how much or how long something changes.

A clear example is the freezing of plain water and salt water. A scientist can place equal amounts of room-temperature water into two glasses, add salt to one glass, and put both in a freezer. By checking the glasses every 15 minutes and recording the time until each one freezes, the scientist can compare the results while keeping other variables controlled.

After the experiment, the results are analyzed and used to form a conclusion. If the data support the hypothesis, it may be accepted and tested further with new questions. If the hypothesis is not supported, a new one can be proposed and the process begins again. In the salt-water example, the results show that salt water freezes more slowly than plain water, so the hypothesis is validated.

How Scientists Test a Hypothesis

scientific laws and theories

How Science Explains Laws and Theories

Scientific laws and scientific theories describe science in two different ways. A law is a concise verbal or mathematical statement that summarizes many experimental observations. It describes or predicts aspects of the natural world that stay the same under the same conditions. A scientific theory is different because it explains why natural events happen. It is a unifying principle that gives a well-supported and testable explanation for a broad set of observations. Strong theories are the...

the scientific method

Chemistry uses the scientific method to turn observations into testable answers. Scientists begin by observing a phenomenon in the physical world and then asking a question about it. This process helps explain everyday chemistry through evidence. A question leads to a hypothesis, which is a tentative explanation for what is being observed. Scientists often use earlier research and published literature to shape that idea. A strong hypothesis must be testable, meaning it can be supported by...

physical and chemical properties of matter

physical-and-chemical-properties-of-matter

Distinguishing Physical and Chemical Changes

Matter can be identified by its properties, which are the features that help us tell one substance from another. These properties fall into two main groups: physical properties and chemical properties. Understanding the difference helps explain how matter changes. A physical property is a feature of matter that is not linked to a change in chemical composition. Examples include density, color, hardness, melting point, boiling point, and electrical conductivity. Some physical properties can be...

what is energy?

Energy Forms and Conservation

Energy is a property of matter that appears in many forms. On Earth, most energy starts with the Sun. Plants capture light energy from the Sun and use photosynthesis to turn it into chemical energy. That stored energy can then move through living things and materials in several ways. People get energy from plant foods, and wood or coal, which come from fossilized plants, can be burned to produce heat and electricity. Energy is defined as the ability to do work. Work happens when a force moves...

classifying matter by state

States of Matter and Their Properties

States of matter help describe how matter behaves in chemistry. Matter is anything that has mass and takes up space. It is found everywhere, including air, water, soil, mountains, and even our bodies. The three common states on Earth are solid, liquid, and gas. A solid has a definite shape and a definite volume. Its particles, such as atoms or molecules, are packed very closely together and held in place by strong forces, so they only vibrate slightly. This tight arrangement makes solids...

measurement: standard units

Measurement: SI Units and Conversions

Measurement gives three kinds of information: a number, a unit, and an estimate of uncertainty. The number shows size or magnitude. The unit gives a standard for comparison. The uncertainty reflects possible error in the measurement. Numbers can be written in more than one way. A value may appear in decimal form or in scientific notation, which is also called exponential notation. For example, the maximum take-off weight of a Boeing 777-200ER airliner is 298,000 kilograms, or 2.98 × 10^5 kg. <br...

classifying matter by composition

Matter: Elements, Compounds, and Mixtures

Matter can be grouped by composition into pure substances and mixtures. A pure substance has a constant composition throughout and uniform properties. For example, any sample of sucrose has the same composition and the same physical properties, such as melting point, color, and sweetness, no matter where it is isolated from. A mixture contains two or more kinds of matter in varying amounts. Its parts can be separated by physical changes, such as evaporation. The components keep their own...

measurement: derived units

SI Units, Density, and Property Types

SI units and derived units help describe physical properties in chemistry. The International System of Units, or SI system, uses agreed-upon base units for seven fundamental properties: length, mass, time, temperature, electric current, amount of substance, and luminosity. Units made by combining these base units are called SI-derived units. Speed is one example. If distance is measured in meters and time in seconds, the derived unit for speed is meters per second, or m/s. Miles per hour is...

dimensional analysis

Using Conversion Factors to Cancel Units

Dimensional analysis is a method for using conversion factors to cancel units and solve measurement problems. It is also called the factor label method. The main rule is that units must be treated the same way as the numbers attached to them. A conversion factor is a ratio of two equal quantities written in different units. For example, 1 meter is equal to 1.0936 yards. That relationship can be used to build a factor that converts one unit into the other. When a value is multiplied or divided...

uncertainty in measurement: accuracy and precision

uncertainty-in-measurement-accuracy-and-precision

Measurement Error: Reading Results Correctly

Measurement error affects how scientists judge the quality of their results. Repeated measurements help show whether results are precise and accurate. A measurement is precise when repeated values are very similar. A measurement is accurate when it is very close to the true or accepted value. Precise values agree with each other, while accurate values agree with the true value. A pharmaceutical quality control chemist can use this idea to check machines that dispense 500 mL of cough syrup. The...

uncertainty in measurement: reading instruments

uncertainty-in-measurement-reading-instruments

Measurement Uncertainty and Significant Figures

Measurement uncertainty and significant figures show how carefully a value can be read from an instrument. Counting is different. If the number of objects does not change during counting, the result is exact. Defined quantities are exact too. For example, 1 foot is exactly 12 inches, 1 inch is exactly 2.54 centimeters, and 1 gram is exactly 0.001 kilograms. Most other measurements are not exact because the measuring process has limits. The result depends on the device used and on the person...

uncertainty in measurement: significant figures

uncertainty-in-measurement-significant-figures

Significant Figures and Rounding Rules

Significant figures and rounding rules help students report measurements with the right level of certainty. A measurement includes every digit that was actually measured, including the last uncertain digit. That is why a value can look simple but still carry useful information about the tool used to measure it. Zero can also be significant when it is part of a measured value. For example, if a scale reads 140 pounds to the nearest pound, the 1, 4, and 0 are all significant. Reporting...

key terms and concepts

Explore how scientists use observations, hypotheses, controlled experiments, and data analysis to test ideas, using a salt water freezing example.

How Scientists Test a Hypothesis | JoVE K12

chemistry

JoVE Core: Chimica illustra concetti chiave di chimica attraverso video animazioni concise e di immediata comprensione. Inoltre, i video della sezione "scienziati in azione" mostrano procedure metodologiche realizzate da ricercatori provenienti dai migliori laboratori internazionali.

Virginia  Standards of Learning

HIgh School

Earth Science

ES.1

ES.1.a

ES.1.f

Life Science

LS.1

LS.1.a

LS.1.f

Physical Science

PS.1

PS.1.f

Physics

PH.1

PH.1.f

Texas Essential Knowledge and Skills

High School

CHEM.1

CHEM.1.A

CHEM.1.H

Florida Department of Education

Nature of Science

SC.912.N.1

SC.912.N.1.1

SC.912.N.1.2

SC.912.N.2

SC.912.N.2.1

PHYS.4

PHYS.4.A

PHYS.4.B

Chemistry and Physics

IPC.4

IPC.4.A

Scientific Laws and Theories

Scientific Laws

In science, a law is defined as a concise, verbal or mathematical, statement that summarizes a vast number of experimental observations. ...

Chemistry is an empirical science. Scientists often pose questions to understand the chemistry in everyday life and seek answers to these questions. To ...

Classifying Matter by State

Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air, ...

Classifying Matter by Composition

Matter: Pure Substances and Mixtures
According to its composition, the matter can be classified into two broad categories &mdash; pure substances and ...

The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

Elements: Chemical Symbols and Isotopes

A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is ...

Use models to explain how the scientific understanding of atomic structure has evolved.

Radioactivity and Nuclear Equations

Nuclear chemistry is the study of reactions that involve changes in nuclear structure. The nucleus of an atom is composed of protons and, except for ...

Types of Radioactivity

The most common types of radioactivity are &#945; decay, &#946; decay, &#947; decay, neutron emission, and electron capture.
Alpha (&#945;) decay is the ...

Nuclear Stability

Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10&#8722;15 meters, a nucleus is ...

Nuclear Binding Energy

The difference between the calculated and experimentally measured masses is known as the mass defect of the atom. In the case of helium-4, the mass defect ...

Radioactive Decay and Radiometric Dating

Radioactivity is a spontaneous disintegration of an unstable nuclide and is a random process, as all the nuclei in the sample do not decay simultaneously. ...

Nuclear Fission

Many heavier elements with smaller binding energies per nucleon can decompose into more stable elements that have intermediate mass numbers and larger ...

Nuclear Power

Controlled nuclear fission reactions are used to generate electricity. Any nuclear reactor that produces power via the fission of uranium or plutonium by ...

Nuclear Fusion

The process of converting very light nuclei into heavier nuclei is also accompanied by the conversion of mass into large amounts of energy, a process ...

Nuclear Transmutation

Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with ...

Use models to compare nuclear reactions including alpha decay, beta decay and gamma decay; nuclear fusion and nuclear fission.

PS.Chm.1.2

Atomic Orbitals

An atomic orbital represents the three-dimensional regions in an atom where an electron has the highest probability to reside. The radial distribution ...

The Pauli Exclusion Principle

The arrangement of electrons in the orbitals of an atom is called its electron configuration. We describe an electron configuration with a symbol that ...

The Energies of Atomic Orbitals

In an atom, the negatively charged electrons are attracted to the positively charged nucleus. In a multielectron atom, electron-electron repulsions are ...

The Aufbau Principle and Hund's Rule

To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and ...

electron-configuration-of-multielectron-atoms

Electron Configuration of Multielectron Atoms

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the ...

Use models to explain how electrons are distributed in atoms.

PS.Chm.1.3

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Atomic Mass

Atoms &mdash; and the protons, neutrons, and electrons that compose them &mdash; are extremely small. For example, a carbon atom weighs less than 2 ...

Molar Mass

The identity of a substance is defined not only by the types of atoms or ions it contains but by the quantity of each type of atom or ion. For example, ...

Use the Periodic Table as a model to predict the relative properties of elements based on the pattern of valence electrons in the outermost energy levels of atoms.

PS.Chm.2.1

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

Ionic radius is the measure used to describe the size of an ion. A cation always has fewer electrons and the same number of protons as the parent atom; it ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



This process can be either ...

Construct an explanation to infer the atomic size, reactivity, electronegativity, and ionization energy of an element based on its position in the Periodic Table.

PS.Chm.2.2

Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Lewis Symbols and the Octet Rule

Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

The Born-Haber Cycle

Lattice Energy&#xA0;

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a ...

trends-in-lattice-energy-ion-size-and-charge

Trends in Lattice Energy: Ion Size and Charge

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure ...

Covalent Bonding and Lewis Structures

Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual ...

Electronegativity

Whether a bond is nonpolar or polar covalent is determined by a property of the bonding atoms called electronegativity.&#xA0;

Electronegativity values of ...

bond-polarity-dipole-moment-and-percent-ionic-character

Bond Polarity, Dipole Moment, and Percent Ionic Character

Bond Polarity

The absolute value of the difference in electronegativity (&Delta;EN) of two bonded atoms provides a rough measure of the polarity to be ...

lewis-structures-of-molecular-compounds-and-polyatomic-ions

Lewis Structures of Molecular Compounds and Polyatomic Ions

To draw Lewis structures for complicated molecules and molecular ions, it is helpful to follow a step-by-step procedure as outlined:


	Determine the ...

Resonance

The Lewis structure of a nitrite anion (NO2&minus;) may actually be drawn in two different ways, distinguished by the locations of the N-O and N=O ...

Formal Charges

In some cases, there are seemingly more than one valid Lewis structures for molecules and polyatomic ions. The concept of formal charges can be used to ...

Exceptions to the Octet Rule

Many covalent molecules have central atoms that do not have eight electrons in their Lewis structures. These molecules fall into three categories:


	...

Bond Energies and Bond Lengths

Stable molecules exist because covalent bonds hold the atoms together. The strength of a covalent bond is measured by the energy required to break it, ...

Analyze and interpret data to explain the mechanisms and properties of the two main types of intramolecular (ionic and covalent) bonds.

PS.Chm.3.1

Analyze the structure of atoms and isotopes.

How Scientists Test a Hypothesis

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