Some Basic Concepts Of Chemistry Test 1

The prefix used for 10^-18 is: atto-

One atomic mass unit is equal to 1.66×10⁻²⁷kg. It is equal to 1/12th of the mass of an atom of carbon-12. It is abbreviated as amu.

Base system means fundamental physical quantities and there are 9 fundamental physical quantities but only 7 have units so number of base SI units is 7.

The SI unit of time, the second, symbols, is easy enough to define, but time itself can only be defined in reference to other quantities.

Cisplatin is particularly effective against testicular cancer. Taxol (paclitaxel) is a mitotic inhibitor used in cancer chemotherapy. AZT is used for helping AIDS victims.

• Two or more atoms combine to give molecules.
• The atoms of different elements are present in a compound in a fixed and definite ratio.
• These two are correct by concepts of chemistry.

Here 6.65 is the coefficient and 10⁴ is the exponent.

• Luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye.
• The SI unit of luminous intensity is the candela, an SI base unit.

3256, This number has four non zero numbers. That's why it has four significant figures.

The SI unit for measuring an electric current is the ampere, which is the flow of electric charge across a surface at the rate of one coulomb per second. Electric current is measured using a device called an ammeter.

The rules of determining the number of significant figures:

• Zeroes between nonzero digits are significant.
• Leading zeros to the left of the first nonzero digits are not significant.
• Trailing zeroes that are also to the right of a decimal point in a number are significant.

Number of Significant figures in 0.001520 are 4.

Precision indicates how closely repeated measurements match each other. Since both the values are close to each other, they are precise and since their is a difference between the mean value and true value, they are not accurate.

• Amount of Substance is also called as material quantity. The amount of substance refers to a standards-defined quantity that measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles.
• The amount of substance appears in thermodynamic relations such as the ideal gas law, and in stoichiometric relations between reacting molecules as in the law of multiple proportions. The unit symbol of the amount of substance is mole.

6.26 & 0.00267 contains 3 significant figures while 5.8 has two significant figures and 0.03 contains least that is 1.

• Precision indicates how closely repeated measurements match each other.
• Accuracy indicates how closely a measurement matches the correct or expected value.

The answer is 5 because all non zero digits and zero between the non zero digits are significant.

Here, the decimal has to be moved four places to the right side and hence -4 is the exponent in the scientific notation.

Let atomic weight of element X is x and that of element Y is y.

During addition, the result cannot have more digits to the right of the decimal point than either of the original numbers. Since there is only 1 digit after the decimal point in 0.8 so the result 7.48 round off we will get 7.5. 

Molecular mass: The sum of the atomic masses of all the atoms in a molecule of a substance is called the molecular mass of the molecule.

Generally we use relative atomic masses of atoms for calculating the molecular mass of 1 mole of any molecular or ionic substances.

Molecular formula of glucose is C₆H₁₂O₆

► Atomic mass of H = 1

► Atomic mass of C = 12

► Atomic mass of O = 16

► Molecular mass of C₆H₁₂O₆ = 12 (Atomic mass of Hydrogen) + 6(Atomic mass of carbon) + 6(Atomic mass of oxygen)

= 12 × 1 + 6 × 12 + 6 × 16

= 12 + 72 + 96 = 180 u.