Accuracy vs Precision Chemistry Quiz

In isotope notation, the mass number is written as a superscript and the atomic number as a subscript to the left of the element symbol. This clearly identifies both properties.

Oxygen has an atomic number of 8 and a mass number of 16. Subtracting gives 8 neutrons, which explains isotope composition.

Isotopes are atoms of the same element with identical numbers of protons but different numbers of neutrons, resulting in different mass numbers.

Oxygen isotopes are written with the mass number as a superscript and atomic number as a subscript. Oxygen-16, 17, and 18 all share atomic number 8.

The abbreviation for atomic mass unit is amu. It is used to express atomic and molecular masses on a relative scale.

Atomic mass is a weighted average based on isotope masses and their natural abundances. This explains why atomic masses are often decimals.

Carbon’s atomic mass is calculated using its isotopes’ masses and abundances. The result, 12.011 amu, reflects the dominance of carbon-12 with a small contribution from carbon-13.

Error represents the difference between the value obtained from an experiment and the accepted or true value. It shows how far the experimental result deviates from what is expected. Subtracting the accepted value from the experimental value preserves whether the result is higher or lower than expected, which is useful for analysis.

Percent error measures how large the error is relative to the accepted value. Taking the absolute value ensures the error is positive, regardless of direction. Dividing by the accepted value and multiplying by 100 converts the result into a percentage, allowing easy comparison of accuracy across different experiments.

Accuracy describes how close a measured value is to the true or accepted value. A measurement can be precise but inaccurate if it is consistently wrong. Accuracy focuses on correctness, not repetition or detail, and is essential when validating experimental results against known standards.

Precision refers to how close repeated measurements are to each other. It reflects consistency rather than correctness. Measurements can be very precise but inaccurate if they are consistently far from the true value. Precision is influenced by measurement technique and instrument reliability.

Leading zeros are not significant because they only indicate the position of the decimal point. In 0.00073, only the digits 7 and 3 carry meaningful measurement information. Therefore, the number has two significant figures.

All nonzero digits are considered significant figures. In the number 8765, each digit contributes to the measured value, and there are no placeholder zeros. This results in four significant figures.

Zeros between nonzero digits and trailing zeros to the right of a decimal are significant. In 0.05730, the digits 5, 7, 3, and the trailing zero are all significant, giving four significant figures.

The International System of Units (SI) defines base units for fundamental quantities. These include meter for length, kilogram for mass, kelvin for temperature, second for time, mole for amount of substance, candela for luminous intensity, and ampere for electric current.

SI prefixes represent powers of ten. From smallest to largest, they increase in value from pico (10⁻¹²) to nano, micro, milli, centi, deci, kilo, and finally mega (10⁶). Ordering them correctly is essential for unit conversions.

Density describes how much mass is packed into a given volume. It is calculated by dividing mass by volume. This formula allows comparison of substances regardless of sample size and explains why some objects float or sink.

The Kelvin scale starts at absolute zero, so converting from Celsius requires adding 273. This maintains correct spacing between temperature units while shifting the zero point to reflect absolute thermal energy.

As temperature increases, particles move faster and spread farther apart. This increases volume without changing mass, resulting in a decrease in density for most substances.

One joule equals 0.239 calories, and one calorie equals 4.184 joules. This conversion reflects the relationship between SI energy units and older heat-based units used in chemistry and biology.

Democritus proposed that matter is made of tiny, indivisible particles called atoms. He believed atoms could not be destroyed or divided, an idea that laid philosophical groundwork for modern atomic theory.

Dalton stated that elements consist of identical atoms, compounds form from atoms in whole-number ratios, and chemical reactions rearrange atoms without changing one element into another. This theory explained conservation of mass and chemical behavior.

An electron is a negatively charged subatomic particle with extremely small mass compared to protons. Its mass is about 1/1840 that of a proton, making it significant in charge but negligible in atomic mass.

A proton is a positively charged subatomic particle found in the nucleus. It has a relative mass of 1 and determines the atomic number of an element, which defines the element’s identity.

A neutron is a neutral subatomic particle located in the nucleus. It has nearly the same mass as a proton and contributes to atomic mass and stability but does not affect charge.

J.J. Thomson discovered electrons using cathode-ray tubes. He proposed the plum pudding model, suggesting electrons were embedded in a positively charged sphere.

Eugen Goldstein discovered canal rays, which traveled opposite cathode rays. These rays were made of positively charged particles, contributing to the understanding of atomic structure.

James Chadwick discovered the neutron. This discovery explained discrepancies in atomic mass and helped refine the nuclear model of the atom.

Rutherford’s experiment showed most alpha particles passed through gold foil, while a few deflected sharply. This proved atoms are mostly empty space with a small, dense, positively charged nucleus.

The number of neutrons is found by subtracting the atomic number from the mass number. This works because the mass number equals protons plus neutrons.