Ch. 4: Compounds and Stoichiometry Flashcards
Given the molar mass of a substance, how is the gram equivalent weight determined? What is the gram equivalent weight?
Gram equivalent weight = molar mass / n
n is the number of particles of interest produced or consumed per molecule of the compound in the reaction.
For example, to produce 1 equivalent of hydrogen ions from H2CO3 then n=2 because one molecule of H2CO3 donates 2 hydrogen ions.
The gram equivalent weight of a compound is the mass (g) that provides one mole of the particle of interest.
If the amount of a compound in a reaction is known how is the number of equivalents determined?
Equivalents = mass of compound known (g) / gram equivalent weight (g)
What is the measurement of normality (N)?
Normality is a measure of concentration in equivalents/L.
If hydrogen ion concentration is being discussed then a 1 N solution of acid contains a concentration of hydrogen ions equal to 1 mole per liter. A 2 N solution of acid contains a concentration of 2 moles of hydrogen ions per liter.
In a 1 N HCl solution, the molarity of HCl is 1 M because it is a monoprotic acid. In a 1 N H2CO3 solution, the molarity of H2CO3 is 0.5 M because it is a diprotic acid.
How is molarity converted to normality?
molarity = normality / n
n = number of protons, hydroxide ions, electrons, or ions produced or consumed by the solute.
What is the formula for determining percent composition of an element by mass?
Percent composition = (mass of element in formula / molar mass of entire formula) x100
Given molar mass and percent composition of element, what are the TWO methods of determining the molecular and empirical formula?
Method 1:
- Determine number of moles of each element assuming a 100g sample
- Find simplest whole ratio by dividing the number of moles by the smallest number obtained from the previous step
- Convert number to whole number by multiplying by integer => Empirical Formula
- Divide molar mass by empirical formula weight. The resulting value is what you multiply the empirical formula with to get the molecular formula (page 119)
Method 2:
- Multiply the molar mass by the given percentages to find mass of each element present in one mole of the compound
- Divide this number by the the atomic weight of each element to find whole ratio of elements => Molecular Formula
- Reduce the subscript ratio (if possible) to find the empirical formula
What are combination reactions?
Two or more reactants forming one product
A + B -> C
What are decomposition reactions?
A single reactant breaks down into two or more products
A -> B + C
What conditions result in decomposition reactions?
High heat, high-frequency radiation, electrolysis
What are combustion reactions?
Hydrocarbon + O2 -> CO2 + H2O
This involves oxidation of the hydrocarbon.
What are single-displacement reactions? Common example?
When an atom or ion in a compound is replaced by an atom or ion of another element.
A + BC -> B + AC
Common example: Redox reaction!!
What are double displacement reactions?
Two different compounds swap places with each other to form two new compounds
AB + CD -> AC + BD
What are neutralization reactions?
They are a type of double displacement reaction that involves an acid and base forming a salt and water
HCl + NaOH -> NaCl + H2O
How many liters is equal to 1 mole of any ideal gas at STP?
22.4 L
Given grams of starting material, how is the limiting reagent of a reaction determined?
- Determine the number of moles for each reactant using their molar mass
- Determine the mole ratio.
- Compare the calculated ratio to the real ratio.
