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Unformatted text preview: Practice Problems for Chemistry 1A
First Examination A compound contains only carbon, hydrogen, nitrogen, and oxygen. Combustion of
0.157g ofthe compound produced 0.213g of C02 0.0310g ofHZO. In another
experiment,0. 103g of the compound produced 0.0230 g of NH 3 . What is the empirical
formula of the compound? Hint: Combustion involves reacting with excess 02. Assume
that all the carbon ends up inCOz and all the hydrogen ends up inHZO. Also assume that
all the nitrogen ends up in the NH 3 in the second experiment. This question is problem #3-4 7 from the text. The solution will be found inrthe "Solutions
Guide". A sample with an unknown amount of acetic acid (CH 3 COOH ) is analyzed by titration
with standard sodium hydroxide (NaOH). A volume of 50.0 mL of the unknown is
measured into a beaker. The solution is then titrated with a solution of 1.306 M NaOH .
The endpoint (The point at which all of the acetic acid is neutralized.) is reached after the
addition of 3 1 .66 mL of the standard sodium hydroxide solution. What is the
concentration of the acetic acid in moles per liter? CH3 CO0H(aq) + Na0H(aq) —> CH3 CO0Na(aq) +H20(l) VNaOH = ﬂ = 0.03166L #molsNaOH = 0.03166L x 1.306% = 4.135 x 10‘2mols From stoichiometry: 1 mol NaOH <=> 1 mol CH3COOH Thus, 4.135 X 10‘2molNa0H <=> 4.135 x 10‘2molCH3C00H VCH3C00H = ﬂ = 0.0500L [CH3C00H] = = 0.827M _____________________________________________________________________ _-_..-_--..__—__———___—_—_—________________________ A solution is prepared by dissolving 22.4g of MgCl 2 in 0.200 L of water. Calculate the
mole fraction of MgCl 2 (X Mgaz) in the solution. Given: The density of pure water is 1.00g/cm3. molsMgClz = mg = 0.235mol 95.22g/mol 3 "101st 0 = (0.200L0X(11(;032ang/:’llg>l<1.OOg/cm ) = 11.1m0 ls XMgC’z = W = 101.3355 = 00207 A. What is the name of NH 4 Cl ? ammonium chloride B. Write the formula for sodium phosphate. Na 3P04 C A sample of copper (Cu) weighs 6.93 g. How many moles of copper atoms does it
contain? #mols = gigging, = 0.109 D. Complete the following table:
Symbol: 69 Ga 3+
Number of protons: 31 (From periodic table.)
Number of neutrons: 38 (69-31=38)
Number of electrons: 28 (31-3=28, Ionic chg. is +3)
Atomic number: 31 ' Mass number: 69 (31+3 8:69) Practice Problems for Chemistry 1A
‘ First ExaminationPage #2 Balance the following oxidation-reduction equation in basic solution:
Cl2(g) —> Cl‘(aq) + Cl0‘(aq)
Solution: 20H‘(aq) + Clz(g) —> Cl‘(aq) + Clo—(aq) + H20(l)
This was homework problem 4. 58-b. See "Solutions 'Manual " for details. Multiple Choice. Circle the letter which represents the best response to each question.
Only one response is correct. No partial credit.
X indicates correct response. ‘
1. Which of the following atomic symbols is NOT correct?
X e. §4N Atomic number is 7, not 8.
Which of the following are alkaline earth halides?
a. NaI, KBr, LiF ‘-
X b. Can, MgBrz, SrIz
C. PbI2, PbBI'2, d. MgO, MgS, CaO
e. A1202, 111203, Ga2S3
3. The mass of 0.821 mol of a diatomic molecule is 131.3g. Identify the molecule.
X C. Brz
e. N2 ,
4. One mole of each of the following compounds is added to water in separate ﬂasks
to make 1.0 L of solution. Which solution has the largest total ion concentration?
7 g a. calcium carbonate 7 r r. _ r _. . X ' b. potassium phosphate K 3P04 will produce 4 ions.
c. potassium bromide
d. silver chloride
e. sodium chloride
5. For the reaction in aqueous solution that is shown below, (NH4)2C03(aq) + Ba(N0 3)2(aq) —> BaCO 3(s) +NH4N03(aq)
what is the balanced net ionic equation? 2
. _ a. 2(NH4)2C03(aq) + ZBa(N03)2(aq) —> ZBaCO 3(s) + 2NH4N03(aq)
X b. Ba2+(aq) + C0 §”(aq) —> BaC03(s)
0. Ba 2+(aq) + 2N0§(aq) —> Ba(N0 3)2(s)
d- NH 1(aq) + N0§(aq) -> NH 4N03(S)
e. (NH4)2C03(aq) + Ba(N03)2(aq) —> BaC03(s) + 2NH4N03(aq) E" ...
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