Chapter_7_Powerpoint 2022 Flashcards
What is the formula mass?
The mass of a single molecule or formula unit
Example: The formula mass of a water molecule (H2O) is calculated as 2(1.01 u) + 1(16.00 u) = 18.02 u.
How do you calculate the percent composition of one element in a compound?
Percent composition = (mass of one element / mass of compound) x 100%
Example: For octane (C8H18), the percent composition of carbon is 84.09% and hydrogen is 15.91%.
What technique is used to measure the mass of molecules?
Mass spectrometry
This technique measures the mass of molecules by ionizing chemical species and sorting them based on their mass-to-charge ratio.
What is Avogadro’s Number?
6.02 x 10^23 units
This number is used to relate moles to particles, such as atoms or molecules.
How many grams are in one mole of carbon?
12.01 grams
The molar mass of carbon is equivalent to its atomic mass in grams.
What is the relationship between grams, moles, and particles?
Moles relate atoms to grams and particles
For example, 1 mole of CO2 (44.01 g) contains 6.02 x 10^23 molecules.
Differentiate between theoretical yield and actual yield.
Theoretical yield is the maximum amount of product that can be produced, while actual yield is the amount actually obtained from a reaction
Percent yield is calculated using the formula: (actual yield / theoretical yield) x 100%.
What is the formula mass of potassium carbonate (K2CO3)?
138.21 u
It is calculated as 2(39.10 u) + 1(12.01 u) + 3(16.00 u).
What is the percent yield if the theoretical yield is 50 g and the actual yield is 40 g?
80%
Percent yield = (40 g / 50 g) x 100%.
Fill in the blank: 1 atomic mass unit (u) = ______ g.
1.66 x 10^-24 g
What is the percent composition of hydrogen in water (H2O)?
11.19%
The calculation is based on the formula mass of water, which is 18.02 u.
What is the limiting reagent in a chemical reaction?
The reactant that is completely consumed first, limiting the amount of product formed
It determines the maximum yield of the reaction.
How do you convert grams of a substance to moles?
Use the formula: grams / molar mass
For NaCl, if you have 305 g, you divide by its molar mass (58.44 g/mol) to find moles.
Fill in the blank: The formula mass of carbon dioxide (CO2) is ______ g.
44.01 g
What is the mass in grams of 2.53 x 10^23 iron atoms?
23.5 grams Fe
Calculated using the relationship between atoms and moles, and then converting moles to grams.
True or False: The actual yield can never exceed the theoretical yield.
True
What is the mole ratio of H2 to O2 in the combustion of methane (CH4)?
2:1
The balanced equation is CH4 + 2 O2 → CO2 + 2 H2O.
What is the molar mass of NaCl?
58.44 g/mol
What is stoichiometry?
Using the amount of one material to predict the amount of another based on the balanced equation
It involves calculations using molar ratios from balanced chemical reactions.
Fill in the blank: The formula mass of magnesium oxide (MgO) is ______ g.
40.30 g
What does the term ‘excess reagent’ refer to?
The reactant that is not completely consumed in a reaction
It remains after the limiting reagent is used up.
How many grams of MgO can be produced from 5.24 g of MgCO3?
2.51 g
Calculation uses the stoichiometry of the reaction and molar masses.
What is the theoretical yield of a reaction?
The calculated maximum amount of product that can be formed from given reactants
What is the limiting reagent when 1.2 moles of potassium reacts with 15 moles of chlorine gas?
K is the limiting reagent
K is completely consumed, limiting the amount of product formed.
What is the excess reagent when 1.2 moles of potassium reacts with 15 moles of chlorine gas?
Cl2 is the excess reagent
Cl2 is not completely consumed, leaving some leftover after the reaction.
How many moles of potassium chloride can be produced from 1.2 moles of potassium?
1.2 moles KCl
Based on the reaction 2 K + Cl2 → 2 KCl.
How many moles of potassium chloride can be produced from 15 moles of chlorine gas?
30 moles KCl
Based on the stoichiometry of the reaction.
What is the limiting reagent when 30 moles of uranium react with 75 moles of fluorine gas?
F2 is the limiting reagent
F2 limits the amount of UF6 that can be produced.
How many moles of UF6 can be produced from 30 moles of uranium?
30 moles UF6
Based on the reaction U + 3 F2 → UF6.
How many moles of UF6 can be produced from 75 moles of F2?
25 moles UF6
Based on the stoichiometry of the reaction.
Using the recipe, how many turkey-and-cheese sandwiches can be made with 80 slices of bread, 18 slices of turkey, and 15 slices of cheese?
15 sandwiches
Limited by the number of cheese slices.
What is the theoretical yield?
The amount of a product that can form, based on the balanced equation
It is a calculated value, not the actual yield observed.
What is the actual yield?
The amount actually obtained
This is the measured amount after a reaction.
How is percent yield calculated?
Percent yield = (Actual yield / Theoretical yield) × 100%
This formula helps assess the efficiency of a reaction.
What can cause the actual yield to be lower than the theoretical yield?
Material sticks to container walls, unwanted side products, product lost during purification
These factors reduce the amount of product obtained.
What is the percent yield for a reaction with a theoretical yield of 240 grams and an actual yield of 180 grams?
75%
Calculated as (180 g / 240 g) × 100%.
What is the theoretical yield of SF6 from 120.0 kg of sulfur reacting with excess fluorine gas?
546.7 kg SF6
Based on the stoichiometry of the reaction S + 3F2 → SF6.
What was the percent yield for the production of SF6 if 480.2 kg was isolated?
87.84%
Calculated as (480.2 kg / 546.7 kg) × 100%.
What is the theoretical yield of magnesium oxide from 5.25 grams of MgCO3?
To be calculated based on stoichiometry
Requires the balanced equation MgCO3 → MgO + CO2.
What is the percent yield if 2.37 grams of MgO are obtained from the reaction starting with 5.25 grams of MgCO3?
To be calculated based on theoretical yield
Requires the theoretical yield value to compute.
What is the percent yield for a reaction starting with 14.2 g of C6H6 and isolating 13.7 g of C6H5Br?
To be calculated based on theoretical yield
Requires the theoretical yield value to compute.
