Unit 3 Test Notes Flashcards
What is a limiting reagent?
The reactant that is completely consumed in a chemical reaction and determines how much product will be formed.
What is an excess reagent?
A reactant that is still present after the reaction goes to completion, in larger quantity than required.
In the reaction 2 Gc + 4 Cc + M → Sm, which reactant is the limiting reagent?
Marshmallows are the limiting reagent because there are not enough of them to use up all the other reactants.
How can companies reduce costs related to reactants?
By choosing the most expensive reactant to be the limiting reagent, ensuring none is wasted.
True or False: Complete combustion releases less energy per mole of fuel than incomplete combustion.
False
What is the first step in calculating the limiting reagent when given two quantities of reactants?
Use mole ratios to determine the Limiting and Excess Reagents.
Fill in the blank: If you have 6.0 mol of O2, you need _______ mol of CH4 to use it up.
3.0
What is the limiting reagent if you have 2.8 mol of titanium (IV) chloride and 5.4 mol of magnesium?
To be determined through calculations.
What mass of methanol can be produced from 9.80 g of carbon monoxide and 1.30 g of hydrogen?
To be determined through stoichiometric calculations.
What is the general overview of steps for a limiting reagent problem?
- Convert masses to moles
- Find Limiting Reagent
- Use Limiting Reagent to find required substance
- Convert to mass of required substance.
In the combustion of magnesium, if 6.73 g of magnesium and 8.15 g of oxygen are available, what must be identified?
The limiting reagent and the mass of magnesium oxide produced.
Fill in the blank: Complete combustion requires an _______ of oxygen.
excess
What is stoichiometry?
The relationship between mass and amount of reactants and products in a chemical reaction.
Stoichiometry is essential for calculating the masses of substances involved in chemical reactions.
What do the coefficients in a chemical equation represent?
The mole ratio of one chemical to another in the reaction.
This ratio is crucial for determining how much of each reactant is needed or produced.
What is the general outline for calculating masses in a chemical reaction?
Mass Compound A → Mole Compound A → Mole Compound B → Mass Compound B
This process involves converting mass to moles and using mole ratios.
In the reaction CO2 + 2 LiOH → Li2CO3 + 2 H2O, what is the first step to determine the mass of lithium hydroxide required?
Convert mass of compound given into moles.
This step is necessary to relate the mass of CO2 to the moles of LiOH.
What is the mass of nitrogen produced by the decomposition of sodium azide in the airbag example?
87.5 g.
This mass is used to determine how much sodium azide is needed to produce that amount of nitrogen.
What is a stoichiometric amount?
The predicted amount of a reactant, relative to another reactant, that will react according to the balanced chemical equation.
In stoichiometric reactions, all reactants are used up without any remaining.
True or False: When stoichiometric amounts of reactants are available for a chemical reaction, some reactants will remain when the reaction is complete.
False.
If stoichiometric amounts are used, all reactants should be consumed by the end of the reaction.
What happens when non-stoichiometric amounts of reactants are combined?
One reactant remains when the reaction is complete.
This is a common situation in chemical reactions where reactants are not perfectly balanced.
Fill in the blank: The study of the mass and amount relationships between reactants and products in a chemical reaction is called _______.
[stoichiometry]
What is the balanced chemical equation for the reaction that inflates an automobile airbag?
2 NaN3(s) → 2 Na(s) + 3 N2(g)
This reaction shows the decomposition of sodium azide to produce nitrogen gas.
What is the final step to determine the mass of lithium hydroxide from moles?
Convert moles of required compound given into mass.
This step completes the calculation by translating moles back into mass.
What is the definition of yield in a chemical reaction?
The amount of product obtained in a chemical reaction.
Define theoretical yield.
The amount of product we predict will be obtained in a chemical reaction based on stoichiometric calculations.
Define actual yield.
The amount of product that is actually obtained at the end of a laboratory procedure.
True or False: The actual yield in a chemical reaction is often greater than the theoretical yield.
False.
List some reasons why the actual yield may be less than the theoretical yield.
- Transfer of solutions
- Filtering precipitates
- Splattering during heating
- Forming undesired byproducts
What does percentage yield compare?
The actual yield in a chemical reaction to the theoretical yield.
Why do chemists report the percentage yield?
To determine how efficient or successful the reaction is at converting reactants into products.
Calculate the percentage yield if the theoretical yield is 10.0 kg and the actual yield is 9.0 kg.
90%
Percentage Yield = (Actual Yield / Theoretical Yield) x 100
In the reaction CO2 (g) + 3 H2 (g) → CH3OH(l) + H2O(g), what is the actual yield of methanol if 20.0 g of hydrogen produced 102.0 g of product?
Calculate percentage yield using the actual yield of 102.0 g and the theoretical yield based on stoichiometric calculations.
Fill in the blank: Limiting reagent: _______ , Excess reagent: _______.
[key learning term].
What is the empirical formula?
A formula that shows the simplest whole-number ratio of elements in a compound.
What is the molecular formula?
A formula that shows the element symbols and exact number of each type of atom in a molecular compound.
In what cases can the empirical and molecular formula be the same?
When the empirical formula represents the actual number of atoms in the compound.
If CH3 is the empirical formula, what is a possible molecular formula of this compound?
C2H6 or C3H9, etc.
What does percentage composition indicate?
The proportion of masses of the elements in a compound.
What are the steps to determine the empirical formula?
- Determine the mass of each element in the sample.
- Calculate the amount of each element in moles.
- Determine the simplest ratio of the elements in the compound.
How do you handle fractions when determining empirical formulas?
Multiply to get a whole number ratio or round to the nearest whole number if within 0.05.
What does the molar mass tell us in relation to the molecular formula?
It tells us how many atoms are in a molecule.
What is the empirical formula of a compound with a % composition of 21.6% sodium, 33.3% chlorine, and 45.1% oxygen?
To be determined through calculations.
What is the ratio of hydrogen to oxygen in hydrogen peroxide?
1:1.
What is the molar mass of hydrogen peroxide?
34.02 g/mol.
What is the empirical formula of a compound with a molar mass of 30.00 g/mol and an empirical formula of CH3?
To be determined through calculations.
What does X represent in determining the molecular formula?
The number you should multiply each of the subscripts by to determine the molecular formula.
What technique is used to determine the molar mass of new substances?
Mass spectrometry.
What happens to molecules in a mass spectrometer?
They break up into charged fragments when bombarded with electrons.
What is the molecular formula of butane with % C = 82.5% and % H = 17.5%?
To be determined through calculations.
Fill in the blank: The empirical formula gives the proportion of _______ of each element.
atoms
True or False: The empirical formula can provide the exact number of atoms in a compound.
False.
What is percentage composition?
The percentage, by mass, of each element in a compound
This concept is fundamental in chemistry for analyzing the composition of compounds.
How can you calculate the percentage composition of a compound by mass?
By using the formula: (mass of element / total mass of compound) x 100
Ensure both masses have identical units.
What is the total percentage of all elements in a compound?
100%
The percentages of each element in a compound must sum to 100%.
How do you calculate the percentage of orange skittles in a bag of 80g containing 25g of orange skittles?
Percentage = (25g / 80g) x 100
This method can be applied to find the percentage of any component.
Given a 500.00 mg tablet of Aspirin (C9H8O4) containing 300.00 mg carbon and 8.08 mg hydrogen, how do you find the percentage of oxygen?
First, calculate the mass of oxygen: 500.00 mg - (300.00 mg + 8.08 mg) = 191.92 mg. Then use the formula for percentage composition
The calculation illustrates how to determine the mass of an unmeasured component.
What is sodium carbonate commonly known as?
Soda ash
Sodium carbonate is used in various applications, including glass manufacturing and as a cleaning agent.
What experiment can be conducted to determine the percentage composition of sugar in bubble gum?
Chew the gum to dissolve the sugar, leaving behind the gum, and then calculate the percentage of sugar
This experiment illustrates practical application of percentage composition in everyday items.
True or False: The units of mass cancel out when calculating percentage composition.
True
This allows the final answer to be unitless.
Fill in the blank: The remaining mass of a compound after accounting for the known masses of its elements is called the _______.
mass of the unknown element
This concept is important for determining the composition of compounds with multiple elements.
What pages should be read for extra practice on percentage composition?
Pages 284-287
Additional practice questions are found on page 288.
What is the formula to convert mass to amount in moles?
Amount in moles (n) = mass (g) / Molar mass (g/mol)
This formula allows for the conversion of mass to moles using the molar mass of the substance.
How do you convert a mass of 1.5 kg of calcium carbonate to an amount in moles?
Use the formula: n = mass (g) / Molar mass (g/mol)
Convert 1.5 kg to grams (1.5 kg = 1500 g) and then apply the molar mass of calcium carbonate.
What is the rearranged equation to solve for mass when given amount in moles?
mass = amount in moles x molar mass
This rearrangement is essential for converting moles back to mass.
How do you convert 0.36 mol of sodium sulfate into mass in grams?
Use the formula: m = n x M
M is the molar mass of sodium sulfate.
What is the formula to calculate the number of entities from moles?
N = n x NA
N is the number of entities, n is the amount in moles, and NA is Avogadro’s number (6.02 x 10^23 entities/mol).
If you have 10 molecules of water, how many hydrogen and oxygen atoms are there?
There will be 20 hydrogen atoms and 10 oxygen atoms
Each molecule of H2O contains 2 hydrogen atoms and 1 oxygen atom.
How do you determine the number of chloride ions in 0.563 mol of calcium chloride, CaCl2?
Calculate using the formula: N = n x NA, with n = 0.563 mol and considering 2 chloride ions per formula unit
Each formula unit of CaCl2 has 2 chloride ions.
What is the first step to find the number of carbon, hydrogen, and oxygen atoms in a 26.5 g sample of benzaldehyde?
Calculate the molar mass of benzaldehyde
This is necessary to determine the number of moles from the mass.
What symbols represent the following quantities: amount in moles, mass, and molar mass?
n for amount in moles, m for mass, M for molar mass
These symbols are standard in chemical calculations.
What is Avogadro’s Constant?
6.02 x 10^23 entities/mol
This constant is used to convert between moles and number of entities.
Fill in the blank: The molar mass of NaOH is _______ g/mol.
[molar mass of NaOH]
The specific molar mass must be calculated based on the atomic weights of sodium, oxygen, and hydrogen.
What is Avogadro’s Constant?
6.02 x 10^23 entities/mol
Define a mole.
The amount of substance containing 6.02 x 10^23 entities.
How many atoms are in one mole?
6.02 x 10^23 atoms
What is the relationship between moles and grams for carbon-12?
1 mole = the number of atoms in 12 g of carbon-12 isotope
What is molar mass?
The mass, in grams per one mole of a substance, measured in g/mol.
How do you calculate the molar mass of a compound?
Add together the molar mass of each individual atom in the compound.
Fill in the blank: The molar mass of water (H2O) is _______.
18.015 g/mol
What is the molar mass of nitrogen gas (N2)?
14.007 g/mol x 2 = 28.014 g/mol
How is the number of formula units in a sample calculated?
Use the unit conversion factor N_A = 6.02 x 10^23 entities/mol.
True or False: 1 mole of sodium chloride contains 6.02 x 10^23 formula units of NaCl.
True
What analogy is used to represent the size of a mole?
The Green Pea Analogy
What is the molar mass of (NH4)3PO4?
The sum of the molar masses of its constituent atoms.
How many entities are in 5 moles of NaCl?
5 x 6.02 x 10^23 entities
List the steps to calculate molar mass.
- Write the chemical formula
- Determine the number of atoms or ions of each element
- Use atomic molar masses from the periodic table
- Communicate in g/mol
What does the symbol ‘N_A’ represent?
Avogadro’s Constant
Fill in the blank: Molar mass is measured in _______.
g/mol
What is the mass of one mole of hydrogen atoms?
1.008 g/mol
How many peas would cover a large city like New York to a depth of 1 meter?
10^15 peas
How many peas would cover half of Ontario to a depth of 1 meter?
10^18 peas
What is the Law of Definite Proportions?
A specific compound always contains the same elements in definite proportions by mass.
Define quantitative analysis.
The process of measuring the quantity of a substance in a sample, providing numerical data.
Define qualitative analysis.
The process of identifying substances present in a sample, no measurements are involved.
What is stoichiometry?
The study of the relationships between the quantities of reactants and products involved in chemical reactions.
What does the term ‘relative atomic mass’ refer to?
The mass of an element that would react with a fixed mass of a standard element, currently Carbon-12.
Define atomic mass unit (amu).
A unit of mass defined as 1/12 the mass of a carbon-12 atom.
What is an isotope?
Atoms of an element that have the same number of protons but a different number of neutrons.
True or False: Isotopes of an element react chemically in different ways.
False.
What is isotopic abundance?
The percentage of an isotope in a sample of an element.
What is the significance of the atomic mass of carbon depicted in the periodic table?
It accounts for the naturally occurring isotopes and their relative abundance.
Calculate the average atomic mass of chlorine using the isotopes Cl-35 and Cl-37 with their respective abundances.
Average atomic mass = (0.7553 * 35) + (0.2447 * 37).
Fill in the blank: The only difference between carbon monoxide (CO) and carbon dioxide (CO2) is the ratio of ______ to ______.
Carbon to Oxygen.
What are the properties of a substance dependent on?
- The quantities of each element
- The elements the compound is composed of.
What is the atomic mass of an isotope calculated by?
atomic mass = (% abundance of isotope 1)(mass of isotope 1) + (% abundance of isotope 2)(mass of isotope 2)
What was the atomic mass assigned to hydrogen by Dalton?
1.
Where is Canada’s standard kilogram kept?
In a vault at the National Research Council in Ottawa.
What is the melting point of carbon monoxide?
-199 °C.
True or False: Carbon dioxide has a sweet taste.
False.
What do protons and neutrons represent in atomic structure?
- Protons: Red
- Neutrons: Blue.
