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CHEMISTRY 101 Name ______________________________ Hour Exam II March 28, 2023 Signature ___________________________ McCarren Section _____________________________
“Obstacles don’t have to stop you. If you run into a wall, don’t turn around and give up. Figure out how to climb it, go through it, or work around it.” – Michael Jordan
This exam contains 17 questions on 10 numbered pages. Check now to make sure you have a complete exam. You have one hour and thirty minutes to complete the exam. Determine the best answer to the first 15 questions and enter these on the special answer sheet. Also, circle your responses in this exam booklet. Show all of your work and provide complete answers to questions 16 and 17.
1-15 (30 pts.) _________
16 (18 pts.) _________
17 (12 pts.) _________
Total (60 pts) _________
Useful Information: 1 L = 1000 mL (exactly)
Always assume ideal behavior for gases (unless explicitly told otherwise).
PV = nRT R = 0.08206 L·atm/mol·K
K = C + 273 NA = 6.022 × 10^23 = 1 mole
Standard temperature and pressure (STP) is 1.0 atm and 273 K.
Solubility Rules:
- Most nitrate salts are soluble.
- Most salts of sodium, potassium, and ammonium cations are soluble.
- Most chloride salts are soluble. Exceptions: silver(I), lead(II), and mercury(I) chloride.
- Most sulfate salts are soluble. Exceptions: calcium, barium, and lead(II) sulfate.
- Most hydroxide salts can be considered insoluble. Soluble ones: sodium, potassium, ammonium, and calcium hydroxide.
- Consider sulfide, carbonate, and phosphate salts to be insoluble. Soluble ones: sodium, potassium, and ammonium.
Hour Exam II Page No. 2
Part 1: Multiple Choice
- Which is true about a limiting reactant?
The limiting reactant always is the reactant that…
a. can produce less product. b. has the largest coefficient in the balanced equation. c. remains in the container after the reaction is complete. d. has the greatest molar mass. e. has the smallest number of moles before the reaction.
- Consider the following balanced equation which shows acetylene gas burning in oxygen. Balance the equation in standard form (using lowest whole number coefficients) and give the coefficient in front of the oxygen gas.
C 2 H 2 (g) + O 2 (g) CO 2 (g) + H 2 O(g)
a. 1 b. 2 c. 3 d. 4 e. 5
Consider the equation shown below for the reaction between solid sulfur (S 8 ) and solid carbon to form liquid CS 2. Use this reaction to answer the next two questions.
S 8 (s) + 4C(s) 4CS 2 (l)
- Each time 2.50 moles of S 8 react, __________ moles of CS 2 form. a. 2.50 moles b. 5.00 moles c. 7.50 moles d. 10.0 moles e. 12.5 moles.
- Each time 65.0 grams of CS 2 forms, _________ moles of S 8 were required. a. 0.214 moles b. 0.427 moles c. 0.853 moles d. 3.41 moles e. 54.7 moles
Hour Exam II Page No. 4
As seen in a lecture demonstration, magnesium metal reacts with oxygen gas to produce solid magnesium oxide according to the balanced equation below.
2Mg(s) + O 2 (g) 2MgO(s)
The image below shows the contents of a reaction container holding some magnesium and some oxygen. The labeled particles of different sizes each represent one mole of magnesium and one mole of oxygen, respectively. Use this information and the balanced equation to answer the next three questions.
- How many moles of magnesium oxide are formed in this reaction? a. 2 moles b. 6 moles c. 4 moles d. 8 moles e. 10 moles
- How many moles of excess reactant are left-over after this reaction? a. 0 moles (Both reactants are completely consumed.) b. 2 moles c. 4 moles d. 6 moles e. 8 moles
- Is mass conserved in this reaction? Choose the best answer and explanation. a. No: There are fewer particles in the container after the reaction. b. No: The overall mass of the magnesium oxide product formed is less than the total mass of the magnesium and oxygen present before the reaction. c. No: The atoms of magnesium react to form magnesium oxide. d. Yes: The same number of oxygen atoms and the same number of magnesium atoms are present before and after the reaction. e. Yes: Particles of oxygen gas are present both before and after the reaction.
Hour Exam II Page No. 5
Consider the reaction between aqueous magnesium nitrate and aqueous potassium hydroxide as shown below. Use this reaction to answer the next three questions.
Mg(NO 3 ) 2 (aq) + 2KOH(aq) Mg(OH) 2 (s) + 2KNO 3 (aq)
- Select the balanced complete ionic equation for this reaction.
a. Mg+2(aq) + 2NO 3 - (aq) + 2K+(aq) + 2OH-(aq) Mg(OH) 2 (s) + 2K+(aq) + 2NO 3 - (aq)
b. Mg+2(aq) + (NO 3 - ) 2 (aq) + 2K+(aq) + 2OH-(aq) Mg(OH) 2 (s) + 2K+(aq) + (NO 3 - ) 2 (aq)
c. Mg+2(aq) + 2NO 3 - (aq) + K+(aq) + OH-(aq) Mg(OH) 2 (s) + K+(aq) + NO 3 - (aq)
d. Mg+(aq) + NO 3 - (aq) + K+(aq) + OH-(aq) MgOH(s) + K+(aq) + NO 3 - (aq)
e. Mg+2(aq) + NO 3 - (aq) + K+(aq) + OH-(aq) Mg(OH) 2 (s) + K+(aq) + NO 3 - (aq)
- When a 100.0 mL solution of 0.200 M aqueous magnesium nitrate is mixed with 100.0 mL of 0.200 M aqueous potassium hydroxide, which ion limits the amount of product that can be produced? a. The magnesium ion b. The potassium ion c. The nitrate ion d. The hydroxide ion e. Both magnesium ion and the hydroxide ion limit the amount of product.
- After mixing the two solutions in #12, which ions are remaining in the solution after the reaction? a. magnesium and potassium ions b. magnesium and hydroxide ions c. nitrate and potassium ions d. nitrate, potassium, and hydroxide ions e. magnesium, nitrate, and potassium ions
Hour Exam II Page No. 7
Part 2: Free Response
- Recall the lab activity in which you observed the combinations of several aqueous solutions. Use the solubility rules on the equation sheet to help answer the following questions related to these solutions.
a. The table below shows possible combinations of aqueous solutions of several salts. For each combination, determine whether or not a precipitate formed. Write “ppt” or “no” in each of the boxes below accordingly.
b. For each combination above which resulted in the formation of a precipitate, give the balanced molecular and net ionic equations in the space below. Be sure to include all phases and charges as required, and label which is the molecular equation and which is the net ionic equation.
Please go on to the next page.
iron(III) nitrate sodium sulfate potassium chloride
calcium nitrate
sodium carbonate
Hour Exam II Page No. 8
c. Give a particle picture diagram for the balanced complete ionic equation for the combination of calcium nitrate and sodium sulfate from the table in part a. In your particle picture, be sure to include: All particles in aqueous solutions before and after Any solid present after the reaction (if a solid is formed) Charges on substances in ion form, where applicable
Please go on to the next page.
Hour Exam II Page No. 10
c. In another scenario, you find an unknown white solid which consists of a bicarbonate compound and some unknown cation X consisting of an ion of one element. This compound reacts with sulfuric acid according to the balanced equation below and similarly inflates a balloon.
H 2 SO 4 (aq) + 2XHCO 3 (s) 2H 2 O(l) + 2CO 2 (g) + X 2 SO 4 (aq)
This reaction occurs when 50.0 mL of 0.100 M H 2 SO 4 and 0.680 g of the unknown solid react completely, with no excess reactant remaining. What is the identity of X? Show work to support your answer.
STOP. You have reached the end of the exam. Nothing written after this page will be graded.
Hour Exam II Page No. 11
SCRATCH PAPER Nothing written on this page will be graded.
