Chapter 3 Flashcards
What is an aqueous solution?
Solution for which water is the solvent
Aqueous solutions are commonly used in chemistry as they involve water as the primary solvent.
What is Avogadro’s number (NA)?
Experimentally determined value of the number of entities comprising 1 mole of a substance, equal to 6.022 × 10^23 mol−1
Avogadro’s number is fundamental in converting between moles and particles.
What does the term concentrated refer to in a solution?
Qualitative term for a solution containing solute at a relatively high concentration
Concentrated solutions have a higher ratio of solute to solvent.
Define concentration in the context of solutions.
Quantitative measure of the relative amounts of solute and solvent present in a solution
Concentration can be expressed in various units, including molarity and percent by volume.
What does dilute mean when describing a solution?
Qualitative term for a solution containing solute at a relatively low concentration
Dilution results in a lower concentration of solute in the solution.
What is dilution?
The process of adding solvent to a solution in order to lower the concentration of solutes
Dilution is commonly performed in laboratory settings to achieve desired concentrations.
What does dissolved mean?
Describes the process by which solute components are dispersed in a solvent
Dissolution is essential for creating solutions where solutes are uniformly distributed.
What is the empirical formula mass?
Sum of average atomic masses for all atoms represented in an empirical formula
The empirical formula represents the simplest whole-number ratio of elements in a compound.
What is formula mass?
Sum of the average masses for all atoms represented in a chemical formula; for covalent compounds, this is also the molecular mass
Formula mass is used to calculate the mass of a specified amount of a substance.
Define mass percentage.
Ratio of solute-to-solution mass expressed as a percentage
Mass percentage is commonly used in chemistry to express the concentration of a solution.
What is mass-volume percent?
Ratio of solute mass to solution volume, expressed as a percentage
This measure is particularly useful in solutions where the volume is relevant for the solute’s concentration.
What is molar mass?
Mass in grams of 1 mole of a substance
Molar mass is essential for converting between grams and moles in stoichiometric calculations.
What does molarity (M) represent?
Unit of concentration, defined as the number of moles of solute dissolved in 1 liter of solution
Molarity is a crucial concept in preparing solutions and performing dilutions.
What is a mole?
Amount of substance containing the same number of atoms, molecules, ions, or other entities as the number of atoms in exactly 12 grams of 12C
The mole is a fundamental unit in chemistry for quantifying entities at the atomic or molecular level.
Define solute.
Solution component present in a concentration less than that of the solvent
Solutes can be solids, liquids, or gases that are dissolved in solvents.
Define solvent.
Solution component present in a concentration that is higher relative to other components
The solvent is often the major component of a solution and determines the phase of the solution.
What is volume percentage?
Ratio of solute-to-solution volume expressed as a percentage
Volume percentage is useful for expressing concentrations of liquids in solutions.
What is percent composition?
Percentage by mass of the various elements in a compound
Used to determine the contribution of each element to the total mass of the compound.
What does the formula for an ionic compound NOT represent?
The formula for an ionic compound does not represent the composition of a discrete molecule.
Why might the term ‘molecular mass’ be incorrectly used for ionic compounds?
Because the average masses of neutral atoms were used in computation, rather than the masses for cations and anions.
Fill in the blank: The formula for an ionic compound may not be correctly referred to as the _______.
[molecular mass]
What is the molecular mass (amu) for Acetaminophen C8H9NO2?
151.16 amu
What is the formula mass (amu) of Calcium phosphate Ca3(PO4)2?
310.18 amu
What unit is used to express formula mass?
amu
What is the atomic mass unit (amu) equivalent to?
Molar mass (g/mol)
The atomic mass unit is a standard unit of mass that quantifies mass on an atomic or molecular scale, equivalent to one twelfth of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state.
What is the estimated average of 4.7g potassium in moles?
0.12 moles
Calculation: 4.7 g x (1 mol K / 39.1 g K) = 0.12 mol K
How many moles of Be are in a 3.24 g thin-foil window?
0.360 mol Be
3.24 g x (1 mol Be / 9.01 g Be) = 0.360 mol Be
How is the molar amount of a substance calculated?
By dividing its mass (g) by its molar mass (g/mol)
Molar amount is a key concept in chemistry for quantifying substances.
What is the sequence for converting units from mass to atoms?
mass (grams) –> moles –> atoms (molecules)
This sequence is essential for stoichiometric calculations in chemistry.
To convert mass (grams) to moles, what operation is performed?
Divide mass (grams) by molar mass (g/mol)
Molar mass is specific to each substance and is typically expressed in grams per mole.
How do you convert moles to atoms (molecules)?
Multiply moles by Avogadro’s number
Avogadro’s number is approximately (6.022 imes 10^{23}) particles per mole.
What is the mass of argon in a liter of air 9.2 x 10^-4 mol Ar?
0.04 g Ar
9.2 x 10^-4 mol Ar x (39.95 g Ar / 1 mol Ar) = 0.04 g Ar
This is calculated based on the molar mass of argon and the amount in moles.
What is the mass of 2.561 mol of gold?
504.4 g
Calculate the number of Au atoms in a quantity of gold that weighs 15.00 g. What is the result?
4.586 × 10^22 Au atoms
How many copper atoms are in 5.00 g of copper wire?
4.74 x 10^22 atoms Cu
5.00 g (1 mol / 63.55 g ) (6.022 x 10^23 atoms / 1 mol) = 4.74 x 10^22
How many moles of glycine molecules are contained in 28.35 g of glycine C2H5O2N?
0.378 mol glycine
28.35 g (1 mol / 75.07 g) = 0.378 mol
Calculation of moles is based on the molar mass of glycine.
How many moles of sucrose, C12H22O11, are in a 25-g sample of sucrose?
0.073 mol
This is calculated using the molar mass of sucrose.
Vitamin C is a covalent compound with the molecular formula C6H8O6. The recommended daily dietary allowance of vitamin C for children aged 4–8 years is 1.42 x 10^−4 mol. What is the mass of this allowance in grams?
0.0250 g
1.42 x 10^-4 mol (176.124 g / 1 mol) = 0.0250 g
What is the mass of 0.443 mol of hydrazine, N2H4?
14.2 g
The mass is calculated using the molar mass of hydrazine.
A packet of an artificial sweetener contains 40.0 mg of saccharin (C7H5NO3S). Given that saccharin has a molar mass of 183.18 g/mol, how many saccharin molecules are in a 40.0 mg (0.0400 g) sample of saccharin? How many carbon atoms are in the same sample?
1.31 x 10^20 C7H5NO3S molecules & 9.17 x 10^20 C atoms
0.0400 g (1 mol / 183.18 g) (6.022 x 10^23 / 1 mol) = 1.31 x 10^20
1.31 x 10^20 (7 C atoms / 1 C7H5NO3S molecule) = 9.17 x 10^20
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How many hydrogen atoms are in 9.213 g of C4H10?
9.545 × 10^23 atoms H
What is the percent composition of a compound containing 7.34 g C, 1.85 g H, and 2.85 g N in a 12.04-g sample?
61.0% C, 15.4% H, 23.7% N
% C = (7.34 g / 12.04 g) x 100% = 61.0%
% H = (1.85 g / 12.04 g) x 100% = 15.4%
% N = (2.85 g / 12.04 g) x 100% = 23.7%
Calculate the percent composition of a 24.81-g gaseous compound that contains 3.01 g C, 4.00 g O, and 17.81 g Cl.
12.1% C, 16.1% O, 71.79% Cl
The percent composition is calculated based on the mass of each element relative to the total mass of the sample.
To calculate the percent composition, the masses of C, H, and O in a known mass of C9H8O4 are needed. It is convenient to consider 1 mol of C9H8O4 and use its molar mass (180.159 g/mole, determined from the chemical formula) to calculate the percentages of each of its elements:
60.00% C, 4.476% H, 35.52% O
% C = ((9 mol C x 12.01 g/mol) / 180.159 g/mol) x 100% = 60.00%
% H = ((8 mol H x 1.008 g/mol) / 180.159 g/mol) x 100% = 4.476%
% O = ((4 mol O x 16.00 g/mol) / 180.159 g/mol) x 100% = 35.52%
To three significant digits, what is the mass percentage of iron in the compound Fe2O3?
69.9% Fe
Empirical formulas are derived from experimentally measured element masses by what 3 steps?
- Deriving the number of moles of each element from its mass
- Dividing each element’s molar amount by the smallest molar amount to yield subscripts for a tentative empirical formula
- Multiplying all coefficients by an integer, if necessary, to ensure that the smallest whole-number ratio of subscripts is obtained
A sample of the black mineral hematite, an oxide of iron found in many iron ores, contains 34.97 g of iron and 15.03 g of oxygen. What is the empirical formula of hematite?
The empirical formula is Fe2O3
Step 1:
34.97 g Fe (1 mol / 55.85 g) = 0.6261 mol Fe
15.03 g O (1 mol / 16.00 g) = 0.9394 mol O
Step 2:
0.6261 / 0.6261 = 1.000 mol Fe
0.9394 / 0.6261 = 1.500 mol O
Step 3:
2 (Fe1O1.5) = Fe2O3
What is the empirical formula of a compound if a sample contains 0.130 g of nitrogen and 0.370 g of oxygen?
N2O5
What is the most convenient mass of elements to calculate when determining empirical formula from percent composition?
100 g
This is because the scale for percentages is 100, simplifying calculations.
The bacterial fermentation of grain to produce ethanol forms a gas with a percent composition of 27.29% C
and 72.71% O. What is the empirical formula for this gas?
Step 1:
27.29% C = 27.29 g C / 100 g compound = 27.29 g C
72.71% O = 72.71 g O / 100 g compound = 72.71 g O
Step 2:
27.29 g C (1 mol/ 12.01 g) = 2.272 mol C
72.71 g O (1 mol/ 16.00 g) = 4.544 mol O
Step 3:
2.272 mol C / 2.272 = 1 mol C
5.544 mol O / 2.272 = 2 mol O
The empirical formula is CO2.
What is the empirical formula of a compound containing 40.0% C, 6.71% H, and 53.28% O?
CH2O
Nicotine, an alkaloid in the nightshade family of plants that is mainly responsible for the addictive nature of cigarettes, contains 74.02% C, 8.710% H, and 17.27% N. If 40.57 g of nicotine contains 0.2500 mol nicotine, what is the molecular formula?
C10H14N2
Step 1:
Assume a convenient, a 100-g sample of nicotine yields the following molar amounts of its elements: 74.02 g C, 8.710 g H, 17.27 g N
Step 2:
74.02 g C (1 mol / 12.01 g) = 6.163 mol C
8.710 g H (1 mol / 1.01 g) = 8.624 mol H
17.27 g N (1 mol / 14.01 g) = 1.233 mol N
Step 3:
6.163 mol C / 1.233 = 5 mol C
8.624 mol H / 1.233 = 7 mol H
1.233 mol N / 1.233 = 1 mol N
C5H7N = 81.13 amu (empiricial forumla mass)
Step 4:
40.57 g nicotin / 0.2500 mol nicotine = 162.3 g/mol (molar mass)
Step 5:
162.3 g/mol / 81.13 amu = 2 formula units
Step 6:
2 (C5H7N) = C10H14N2
What is the molecular formula of a compound with a percent composition of 49.47% C, 5.201% H, 28.84% N, and 16.48% O, and a molecular mass of 194.2 amu?
C8H10N4O2
What is the formula for molarity (M)?
Molarity (M) = mol solute divided by L solution
Molarity is a common unit of concentration in chemistry, indicating the number of moles of solute per liter of solution.
A 355-mL soft drink sample contains 0.133 mol of sucrose (table sugar). What is the molar concentration of sucrose in the beverage?
0.375 M
Step 1:
Convert mL to L
355 mL (1 L / 1000 mL) = 0.355 L
Step 2:
0.133 mol / 0.355 L = 0.375 M
A teaspoon of table sugar contains about 0.01 mol sucrose. What is the molarity of sucrose if a teaspoon of sugar has been dissolved in a cup of tea with a volume of 200 mL?
0.05 M
How much sugar (mol) is contained in a modest sip (~10 mL) of the soft drink with a molarity of 0.375
0.004 mol sugar
Step 1:
Convert mL to L
10 mL (1 L / 1000 mL) = 0.01 L
Step 2:
mol solute = M x L solution
0.375 x 0.01 L = 0.004 mol sugar
Distilled white vinegar is a solution of acetic acid, CH3CO2H, in water. A 0.500-L vinegar solution contains 25.2 g of acetic acid. What is the concentration of the acetic acid solution in units of molarity?
0.84 M acetic acid
Step 1:
Use molar mass of solute to obtain the amount of solute in moles
CH3CO2H = 60.052 g/mol (molar mass)
25.2 g (1 mol / 60.052 g) = 0.42 mol solute
Step 2:
M = mol solute / L solution
0.42 mol / 0.500 L = 0.84 M
Calculate the molarity of 6.52 g of CoCl2 (128.9 g/mol) dissolved in an aqueous solution with a total volume of 75.0 mL.
0.674 M
How many grams of NaCl are contained in 0.250 L of a 5.30-M solution?
77.4 g NaCl
Step 1:
mol solute = M x L
5.30 M x 0.250 L = 1.325 mol NaCl
Step 2:
Convert moles to mass (grams)
1.325 mol (58.44 g / 1 mol) = 77.4 g NaCl
How many grams of CaCl2 (110.98 g/mol) are contained in 250.0 mL of a 0.200-M solution of calcium chloride?
5.55 g CaCl2
The concentration of acetic acid in white vinegar was determined to be 0.839 M. What volume of vinegar contains 75.6 g of acetic acid (CH3CO2H)?
1.50 L solution
Step 1:
Find molar mass
CH3CO2H = 60.05 g
Step 2:
mass (grams) –> moles —> solution (L)
75.6 g (1 mol / 60.05 g) (1 L / 0.839 mol) = 1.50 L solution
What volume of a 1.50-M KBr solution contains 66.0 g KBr?
0.370 L
What is the first step in determining the volume of solution containing a given mass of solute?
Convert mass (grams) to moles
Use the molar mass of the solute for the conversion.
After converting mass to moles, what is the next step in determining the volume of solution?
Convert moles to solution (L)
This typically involves using the molarity of the solution.
Fill in the blank: To determine the volume of solution containing a given mass of solute, you go from _______ to moles to solution (L).
mass (grams)
What is the formula that defines molarity?
n = M x L
Where n is the number of moles of solute, M is the molarity, and L is the volume in liters.
In the formula n = M x L, what does ‘n’ represent?
The number of moles of solute.
In the formula n = M x L, what does ‘M’ represent?
The molarity of the solution.
In the formula n = M x L, what does ‘L’ represent?
The volume of the solution in liters.
What is the dilution equation?
C1V1 = C2V2
What unit of concentration does the dilution equation use?
Molarity
What unit of volume is used in the dilution equation?
Liters
If 0.850 L of a 5.00-M solution of copper nitrate, Cu(NO3)2, is diluted to a volume of 1.80 L by the addition of water, what is the molarity of the diluted solution?
2.36 M
Step 1:
C1 = 0.850 L
V1 = 5.00 mol/L
C2 = ?
V2 = 1.80 L
Step 2:
C2 = (C1 x V1) / V2
C2 = (0.850 L x 5.00 mol/L) / 1.80 L = 2.36 M
What is the concentration of the solution that results from diluting 25.0 mL of a 2.04-M solution of CH3OH to 500.0 mL?
0.102 M CH3OH
What volume of 0.12 M HBr can be prepared from 11 mL (0.011 L) of 0.45 M HBr?
0.041 L
Step 1:
C1 = 0.45 M
V1 = 0.011 L
C2 = 0.12 M
V2 = ?
Step 2:
V2 = (C1 x V1) / C2
V2 = (0.45 M / 0.011 L) / 0.12 M = 0.041 L
A laboratory experiment calls for 0.125 M HNO3. What volume of 0.125 M HNO3 can be prepared from 0.250 L of 1.88 M HNO3?
3.76 L
What volume of 1.59 M KOH is required to prepare 5.00 L of 0.100 M KOH?
0.314 L
Step 1:
C1 = 1.59 M
V1 = ?
C2 = 0.100 M
V2 = 5.00 L
Step 2:
V1 = (C2 x V2) / C1
V1 = (0.100 M x 5.00 L) / 1.59 M = 0.314 L
What volume of a 0.575-M solution of glucose, C6H12O6, can be prepared from 50.00 mL of a 3.00-M glucose solution?
0.261 L
What is the formula for mass percentage?
Mass percentage = (mass of component / mass of solution) x 100%
This formula is used to calculate the concentration of a component in a solution.
A 5.0-g sample of spinal fluid contains 3.75 mg (0.00375 g) of glucose. What is the percent by mass of glucose in spinal fluid?
0.075%
Step 1:
Convert mg to g
3.75 mg (1g / 1000 mg) = 0.00375 g
Step 2:
Mass percentage = (mass of component / mass of solution) x 100%
% glucose = (0.00375 g glucose / 5.0 g spinal fluid) x 100% = 0.075%
A bottle of a tile cleanser contains 135 g of HCl and 775 g of water. What is the percent by mass of HCl in this cleanser?
14.8%
“Concentrated” hydrochloric acid is an aqueous solution of 37.2% HCl that is commonly used as a laboratory reagent. The density of this solution is 1.19 g/mL. What mass of HCl is contained in 0.500 L of this solution?
221 g HCl
Step 1:
Convert L to mL for proper cancellation
0.500 L (1000 mL / 1 L) = 500 mL
Step 2:
Volume of solution –> mass of solution —> mass of HCl
(multiply by density g/mL) (multiply by mass percent as ratio: g HCl / g solution)
500 mL solution (1.19 g solution / 1 mL solution) (37.2 g HCl / 100 g soltuion) = 221 g HCl
What volume of concentrated HCl solution contains 125 g of HCl?
282 mL
What is the formula for volume percentage?
Volume percentage = (volume solute / volume solution) x 100%
This formula is used to express the concentration of a solute in a solution as a percentage of the total solution volume.
Rubbing alcohol (isopropanol) is usually sold as a 70%vol aqueous solution. If the density of isopropyl alcohol is 0.785 g/mL, how many grams of isopropyl alcohol are present in a 355 mL bottle of rubbing alcohol?
195 g isopropyl alchol
Step 1:
Isopropanol volume is 70% of the total solution volume.
Multiplying the isopropanol volume by its density yields the requested mass: (70 mL isopropy alcohol / 100 mL solution) <– add this to the volume percentage equation
Step 2:
355 mL solution (70 mL isopropy alcohol / 100 mL solution) (0.785 g isopropyl alcohol / 1 mL isopropyl alcohol) = 195 g isopropyl alchol
Wine is approximately 12% ethanol (CH3CH2OH) by volume. Ethanol has a molar mass of 46.06 g/mol and a density 0.789 g/mL. How many moles of ethanol are present in a 750-mL bottle of wine?
1.5 mol ethanol
What does ppm stand for?
Parts per million
Used to express very dilute concentrations of substances.
What is the formula for calculating parts per million (ppm)?
ppm = (mass solute / mass solution) x 10^6
This formula is used to determine the concentration of a solute in a solution.
What does ppb stand for?
Parts per billion
Used to express extremely dilute concentrations of substances.
What is the formula for calculating parts per billion (ppb)?
ppb = (mass solute / mass solution) x 10^9
This formula is used to determine the concentration of a solute in a solution at a billion parts.
