The preparation, properties, structure, and reactions of material substances
Explicación
Chemistry is the branch of science concerned with the preparation, properties, structure, and reactions of material substances.
During the eighteenth century
Explicación
Modern chemistry took shape in eighteenth-century Europe after earlier alchemical traditions had been introduced by the Arabs. Alchemy and iatrochemistry were more prominent during 1300–1600 CE.
Rasayan Shastra, Rastantra, Ras Kriya, or Rasvidya
Explicación
Ancient Indian chemistry was known by names such as Rasayan Shastra, Rastantra, Ras Kriya, and Rasvidya, and covered areas including metallurgy, medicine, cosmetics, glass, and dyes.
By adding tin and arsenic
Explicación
Harappans increased copper hardness by using tin and arsenic. Their technological achievements also included baked and glazed pottery, faience, and forged metal objects.
They consist of indivisible particles called Paramãnu
Explicación
Acharya Kanda proposed that substances consist of eternal, indestructible, spherical, indivisible particles called Paramãnu, which could combine into pairs or triplets through unseen forces.
Anything that has mass and occupies space
Explicación
Matter is defined as anything that has mass and occupies space. The other properties may apply to some matter but do not define it.
Developing drugs such as cisplatin and taxol for cancer therapy
Explicación
Chemistry contributes to healthcare by developing drugs, including cisplatin and taxol for cancer therapy. AZT is another chemical drug used to help AIDS patients.
Because chlorofluorocarbons contribute to stratospheric ozone depletion
Explicación
Safer alternatives have been developed because chlorofluorocarbons contribute to depletion of stratospheric ozone. Methane and carbon dioxide remain separate greenhouse-gas concerns.
As elements and compounds
Explicación
Pure substances are classified further into elements and compounds. Mixtures, in contrast, contain two or more pure substances in variable proportions.
Its components are uniformly distributed throughout
Explicación
A homogeneous mixture has a uniform composition because its components are distributed evenly throughout. A non-uniform composition characterizes a heterogeneous mixture.
Distillation
Explicación
Distillation separates mixture components by using differences in boiling points. Filtration, for example, separates suitable solids from fluids based on particle size or insolubility.
Its elements are combined in a definite ratio and require chemical methods for separation
Explicación
A compound contains different elements in a definite ratio and can be separated into simpler substances only by chemical methods. Mixture components remain physically combined and may be separated by physical methods.
Boiling point
Explicación
Boiling point is a physical property that can be measured without producing a new substance. Flammability, rusting, and reaction with acid involve chemical change.
A liquid has a volume of 250 millilitres
Explicación
A quantitative observation includes a numerical value and its unit, such as 250 millilitres. The other observations describe qualities without necessarily giving numerical measurements.
Kelvin
Explicación
The kelvin is the SI base unit for thermodynamic temperature. The mole measures amount of substance, while the joule is not an SI base unit.
4.0 kg m⁻³
Explicación
Density is mass divided by volume: ρ = 2.0 kg ÷ 0.5 m³ = 4.0 kg m⁻³. Mass is the numerator in this relationship, not the density itself.
68°F
Explicación
Using F = (9/5)C + 32 gives F = (9/5)(20) + 32 = 68°F. The Celsius-to-Kelvin relationship is a different conversion.
Mass is the amount of matter and remains constant, whereas weight is gravitational force and can vary with location
Explicación
Mass describes the amount of matter and remains constant, while weight is the gravitational force acting on an object and can change with location. Therefore, they are distinct physical quantities.
N × 10ⁿ, where N ranges from 1.000… to 9.999…
Explicación
Scientific notation expresses a number as N × 10ⁿ, with N ranging from 1.000… to 9.999… and n an integer.
The leading zeros are not significant, but the captive and terminal zeros are significant
Explicación
Zeros before the first non-zero digit are not significant, while the zero between non-zero digits and terminal zeros to the right of the decimal point are significant.
Precise but not accurate
Explicación
The measurements are close to one another, so they are precise, but they disagree substantially with the accepted value, so they are not accurate.
15.3
Explicación
For addition, the result cannot have more digits to the right of the decimal point than the least precise measurement. Since 3.2 has one decimal place, the result is 15.3.
Multiply by conversion factors equal to one and cancel units algebraically
Explicación
Dimensional analysis uses unit factors equal to one, chosen so unwanted units cancel and the desired units remain.
172,800 seconds
Explicación
Multiplying 2 × 24 × 60 × 60 gives 172,800 seconds.
The total mass remains unchanged, although the substances may change
Explicación
The law states that matter cannot be created or destroyed, so total mass remains constant even though chemical reactions can produce different substances.
Natural and synthetic cupric carbonate contain the same elements in identical mass percentages
Explicación
A compound follows definite proportions when it contains the same elements in the same mass proportions regardless of its source. Both natural and synthetic cupric carbonate contain 51.35% copper, 9.74% carbon, and 38.91% oxygen by mass.
The law of multiple proportions
Explicación
The masses of Y that combine with a fixed mass of X are in the small whole-number ratio 2:6, or 1:3, demonstrating the law of multiple proportions.
They contain equal numbers of molecules
Explicación
Avogadro’s law states that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.
Matter consists of atoms that combine in fixed ratios, and chemical reactions rearrange rather than create or destroy atoms
Explicación
Dalton proposed that matter is composed of atoms, compounds contain atoms in fixed ratios, and reactions rearrange conserved atoms. Later discoveries showed that atoms are divisible, but this was not part of Dalton’s original theory.
It could not explain the laws of gaseous volumes or why atoms combine
Explicación
Dalton’s theory accounted for the laws of chemical combination but did not explain the laws of gaseous volumes or the reasons atoms combine.
One-twelfth of the mass of one carbon-12 atom
Explicación
One atomic mass unit, or u, is exactly one-twelfth of the mass of a carbon-12 atom. Hydrogen was an earlier arbitrary reference, not the modern definition.
It is a weighted mean based on the relative abundances of the element’s naturally occurring isotopes
Explicación
Average atomic mass accounts for both isotope masses and their natural relative abundances, so it is a weighted mean rather than simply one isotope’s mass.
M = Σᵢ nᵢAᵢ
Explicación
The molecular mass is found by multiplying each element’s atomic mass by the number of its atoms in the molecule and summing the results: M = Σᵢ nᵢAᵢ.
Sum the atomic masses represented by its formula unit to obtain its formula mass
Explicación
Ionic substances such as sodium chloride are described by formula units rather than discrete molecules. Their formula mass is the sum of the atomic masses represented in the formula unit.
Exactly 6.02214076 × 10²³ specified elementary entities
Explicación
The mole is the SI unit of amount of substance and contains exactly 6.02214076 × 10²³ specified entities. Molarity, in contrast, describes concentration.
N_A equals 6.02214076 × 10²³ mol⁻¹
Explicación
The Avogadro constant is N_A = 6.02214076 × 10²³ mol⁻¹. The unit mol⁻¹ distinguishes it from the dimensionless number of entities in one mole.
Its numerical value is the same, but it is expressed in grams per mole instead of u
Explicación
Molar mass is the mass of one mole and is expressed in g mol⁻¹. Its numerical value matches the corresponding mass expressed in atomic mass units.
The mass of the element divided by the molar mass of the compound, multiplied by 100
Explicación
Mass percentage compares an element’s mass contribution with the compound’s molar mass and multiplies by 100. A mole fraction instead compares numbers of moles.
An empirical formula gives the simplest atom ratio, while a molecular formula gives the actual atoms in one molecule
Explicación
The empirical formula represents the simplest whole-number ratio of atoms. The molecular formula represents the actual number of each atom in one molecule.
Assume a 100 g sample of the compound
Explicación
Assuming a 100 g sample makes each percentage numerically equal to the corresponding mass in grams. These masses are then converted to moles and simplified into a whole-number ratio.
The quantitative amounts of reactants and products involved
Explicación
Stoichiometry calculates quantitative relationships, such as the masses or volumes of reactants and products. Balancing an equation establishes ratios but does not itself calculate these amounts.
Changing coefficients while keeping subscripts unchanged
Explicación
Coefficients may be adjusted to obtain equal numbers of each type of atom on both sides. Subscripts must remain unchanged because changing them changes the substances involved.
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)
Explicación
The balanced equation is CH₄ + 2O₂ → CO₂ + 2H₂O. It has one carbon, four hydrogen, and four oxygen atoms on each side.
The reaction cannot continue because that reactant is exhausted
Explicación
The limiting reagent is consumed first and therefore determines the maximum amount of product. Once it is exhausted, further reaction cannot occur.
Moles of the component divided by total moles of all components
Explicación
Mole fraction uses the component’s moles divided by the total moles of every component in the solution. Moles per litre is molarity, not mole fraction.
0.25 M
Explicación
Molarity equals moles of solute divided by litres of solution: 0.50 mol ÷ 2.0 L = 0.25 M.
M₁V₁ = M₂V₂
Explicación
For dilution, the amount of solute remains constant, giving the relationship M₁V₁ = M₂V₂. The initial and final concentration-volume products are equal.
Moles of solute per kilogram of solvent
Explicación
Molality is defined as the number of moles of solute present in one kilogram of solvent. It differs from molarity, which uses the volume of the entire solution.
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What does chemistry study in material substances?
Preparation, properties, structure, and reactions.
During which years did chemistry develop mainly as Alchemy and Iatrochemistry?
1300–1600 CE.
When did modern chemistry take shape in Europe?
In the eighteenth century.
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