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1
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2
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- The sum of the atomic masses for all the atoms represented in the
chemical formula of a compound.
- AKA formula mass, molecular mass,
molecular weight
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3
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- Number of particles in atomic mass in grams of an element.
- Number of molecules/formula units in the molar mass in grams of a
compound
- 6.02 x 1023 particles.
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4
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- How many water molecules are in one drop of water? (One drop of water is 1/20 of a mL,
and the density of water is 1.0 g/mL.)
- How many hydrogen atoms are in a drop of water?
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5
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- Nitrogen fixation in the root nodules of peas and other legumes occurs
with a reaction involving a molybdenum containing enzyme named
nitrogenase. This enzyme contains
two Mo atoms per molecule and is 0.0872% Mo by mass. What is the molar mass of the enzyme?
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6
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- Simplest formula for a compound.
- Can be determined from percent composition data and combustion analysis.
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7
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- A compound of Ca, C, N, and S was subjected to quantitative analysis and
formula mass determination, and the following data were obtained. A 0.250 g sample was mixed with NaCO3
to convert all of the Ca to 0.160 g of CaCO3. A 0.115 g sample of the compound was
carried through a series of reactions until all of its S was changed to
0.344g of BaSO4. A
0.712 g sample was processed to liberate all of its N as NH3,
and 0.155 g NH3 was obtained.
The formula mass was found to be 156. Determine the empirical and molecular
formulas of this compound.
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8
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- (mass part/mass whole) x 100(%)
- An aqueous solution of acetic acid is 20 percent by weight Acetic acid
has a density of 1.0269 g/mL. How
many moles of acetic acid are contained in 35 mL of this solution?
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9
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- Mole solute/ Liter solution
- For Dilution -- M1V1 = M2V2
- A chemist wants to prepare 0.25 M HCl.
Commercial HCl is 12.4M.
How many mL of the concentrated acid does the chemist require to
make up 1.50 L of the dilute acid?
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10
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- Disulfur dichloride S2Cl2, is used to vulcanize
rubber. It can be made by
treating molten sulfur with gaseous chlorine
- S8(l) + 4 Cl2(g) à 4 S2Cl2(g)
- Calculate the mass of S2Cl2 that can be produced
by reacting 15.0 g of S8 with excess chlorine gas.
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11
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12
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- The potassium salt of benzoic acid, potassium benzoate (KC7H5O2)
can be made by the action of potassium permanganate on toluene (C7H8)
as follows
- C7H8 + 2KMNO4 à KC7H5O2 + 2MnO2
+ KOH + H2O
- If the yield of potassium benzoate cannot realistically be expected to
be more than 71%, what is the minimum number of grams of toluene needed
to achieve this yield while producing 11.5 g of potassium benzoate?
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13
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- One of the steps in the commercial process for converting ammonia to
nitric acid involves the conversion of NH3 to NO:
- 4 NH3(g) + 5 O2(g) à 4
NO(g) + 6 H2O(g)
- How many grams of NO form when 1.50 g of NH3 reacts with 1.85
g of O2?
- Which reactant is the limiting reactant and which is the excess
reactant?
- How much of the excess reactant remains after the limiting reactant is
completely consumed?
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14
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15
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16
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17
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- A 35.49 mL sample of 0.2430 M H2SO4 is mixed with
65.33 mL of a 0.4199 M sample of KOH.
Determine the concentration of all ions in solution, the pH, and
pOH.
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18
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- A noncarbonated soft drink contains an unknown amount of citric acid, H3C6H5O7. If 100.0 mL of the soft drink requires
33.51 mL of 0.01024 M NaOH to neutralize the citric acid completely,
what is the concentration of citric acid in the soft drink in
moles/liter (M)? In
equivalents/liter (N)?
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19
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- Suppose you are given a 4.554 g sample that is a mixture of oxalic acid,
H2C2O4, and another solid that does not
react with sodium hydroxide. If
29.58 mL of 0.5501 M NaOH is required to titrate the oxalic acid in the
4.554 g sample, what is the weight percent of oxalic acid in the
mixture?
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20
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- A vitamin C tablet was analyzed to determine whether it did in fact
contain, as the manufacturer claimed, 1.00 g of the vitamin. A tablet was dissolved in water to
form a 100.00 mL solution, and a 10.00 mL sample was titrated with
iodine (as KI3, potassium triiodide). It required 10.10 mL of 0.0521 M I3-1
to reach the stoichiometric point in the titration. Given that vitamin C, C6H8O6,
is oxidized to dehydroascorbic acid, C6H6O6
and triiodide, I3-1, is reduced to iodide, I-1,
write a balanced equation for the reaction and determine whether the
manufacturer’s claim is correct?
(MW vitamin C = 176 g/mol)
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21
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- Some compounds can be decomposed quantitatively with water or acid to
give known compounds. Suppose you
have a 0.643 g sample of a compound known to be composed of C, H, Al,
and Cl. Furthermore, you know
that it is composed of some number of CH3 groups and chlorine
atoms per aluminum atom. The
formula could be written as (CH3)xAlCly. To find x and y you decompose the
sample with acid in water. The CH3
portion is evolved as methane gas, CH4, and the chloride ions
remain in the water. The chloride
ions are precipitated as AgCl by adding AgNO3 to the
solution. The data collected in
the experiment are given here.
What are the values of x and y?
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22
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- (CH3) xAlCly ¾® x CH4(g) + Al3+(aq) + y Cl-(aq)
- 0.643g 0.222g ½
-
AgNO3
- ¯
-
AgCl(s)
- 0.996g
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23
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- A 19.264 gram sample of a mixture of MgCl2 and CsCl is
dissolved in water and treated with excess AgNO3 so that ALL
the chloride precipitates as AgCl.
The mass of dried AgCl is 43.668 grams. Calculate the:
- a) mass percent chlorine
- b) mass CsCl
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24
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- A 3.111g mixture of two hydrates, CuSO4·4H2O and Na2CO3·4H2O is
heated until all of the water of crystallization is driven off. The anhydride mixture that results
weighs 2.027 g.
- a. Calculate the percent water in the original mixture.
- b. Calculate the grams of CuSO4 in the original mixture.
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Notes
