Chapter 4 - Quantities in Chemical Formulas

Question 1

Law of definite proportions

Answer 1

law = statement about the consistency of observations
proportions = by mass of elements in a compound
compounds involve the consistent ratio of numbers of atoms of each element in a crystal lattice, or the same number of atoms of each element in a molecule

Question 2

Percent composition

Answer 2

experimental percent composition = these are based on observations collected in an experiment
theoretical percent composition = these are based on a chemical formula and the average atomic masses of the elements

Question 3

Discrepancy vs. error

Answer 3

discrepancy = a difference between a measured value and an accepted value
error = a process that causes variability in what should be a consistent measurement, or a quantification of the maximum expected variation in an instrument (these are unavoidable issues)

Question 4

Precision vs. accuracy

Answer 4

precision = degree to which repeated measurements under unchanged conditions show the same results
accuracy = degree of closeness of measurements of a quantity to that quantity’s true value

Question 5

The mole

Answer 5

a number (6.02 x 10^23) 
equal to the number of carbon-12 atoms in exactly 12 g of carbon-12

Question 6

Molar mass

Answer 6

molar mass of a substance = the mass of one mole of the fundamental particles of that substance
mass spectrometers can be used to measure the molar masses of elements
the molar mass of an element is equal to the average atomic mass in grams of that element

Question 7

Chemical formulas

Answer 7

empirical formula = simplest whole number ratio of elements, used for all lattice substances
molecular formula = actual number of atoms of each element in a molecular, is a whole number multiple of the empirical formula
the data used for calculating the empirical formula is the percent composition of the element

Question 8

Combustion analysis

Answer 8

a substance burned in a combustion analyzer produces oxides that are capture by absorbers in chemical traps
the initial and final masses of each trap indicate the masses of the oxides produced
these masses are then used in the calculation of the percent composition of the substance burned