A student wants to know the concentration of acetic acid (HC2H3O2) in commercial vinegar in moles/liter. She dissolves 5.00 g NaOH in enough water to make 100.0 mL. Then she titrates 50.0 mL of commercial vinegar with the sodium hydroxide solution to the endpoint. What is the molarity of her NaOH solution? Write the balanced net ionic equation for acetic acid reacting with NaOH. To achieve the endpoint of the titration, the student uses 32.52 mL of her NaOH solution. What is the concentration of the acetic acid in the vinegar solution in moles/L? If the student were rushing through the titration and failed to stop adding NaOH solution at the endpoint, would her calculated molarity of the acetic acid be greater than or less than the actual value? Explain. Show your work for all calculations. Note: Your answer(s) must be provided in this text box. If you are unable to show your work adequately using the Rich Text Editor, complete your work on scratch paper. Upload a photo of your work in the “Comments” of this exam immediately after you have completed and submitted the exam. You can access the “Comments” through the grade book. Answers on scratch paper alone will not be scored.

The graph shows the speed distribution of molecules in a sample of gas at a certain temperature. A graph plots Number of Molecules against Speed. The graph shows a bell curve rising from the origin and falling to the horizontal axis with decreasing steepness. Which of the following graphs shows the speed distribution of the same molecules at a lower temperature (as a dashed curve)?

2 KClO3(s) → 2 KCl(s) + 3 O2(g) What is the percentage yield of O2 if 12.3 g of KClO3 (molar mass 123 g) is decomposed to produce 3.2 g of O2 (molar mass 32 g) according to the equation above?

The question refers to the 1 L flask shown in the figure. A diagram shows four flasks, each closed with a stopper. Flask A contains N 2 gas at 30 degrees Celsius temperature and 1 a t m pressure. Flask B contains N 2 gas at 50 degrees Celsius temperature and 0.5 a t m pressure. Flask C contains O 2 gas at 40 degrees Celsius temperature and 2 a t m pressure. Flask D contains O 2 gas at 40 degrees Celsius temperature and 0.5 a t m pressure. Which flask contains the sample with the greatest density?

The figure shows a particle view of a sample of H 2 O 2 aqueous. There are 10 circles. Each circle is labeled as H 2 O 2. A particle view of a sample of H2O2(aq) is shown above. The H2O2(aq) is titrated with KMnO4(aq), as represented by the equation below.   2 MnO4−(aq) + 5 H2O (aq) + 6 H+(aq) → 2 Mn2+(aq) + 5 O2(g) + 8 H2O(l)   Which of the following particle views best represents the mixture when the titration is halfway to the equivalence point? (H2O molecules and H+ ions are not shown.)

The reaction represented below has an equilibrium constant equal to 3.7 x 104.   HC₂H₃O₂(aq) + CN⁻(aq) ⇄ HCN(aq) + C₂H₃O₂⁻(aq)   Which of the following can be concluded from this information?

An ionic crystal is added to water and starts to dissolve as shown in the particulate representation below. Based on the orientation of the water molecules, what can be assumed about the charge of the hydrated particle indicated by the arrow? The figure shows a particle diagram of an ionic solid made of alternating large shaded circles and medium unshaded circles. Water molecules are represented by a small shaded circle and two smaller black circles. Ten water molecules surround the undissociated ionic crystal. To the right, one large shaded circle is surrounded by 5 H 2 O molecules oriented with the smaller black circles toward the large shaded circle. The medium unshaded circle is surrounded by 4 H 2 O molecules oriented with the small shaded circle toward the medium unshaded circle. An arrow points to the medium unshaded circle.

A student is assigned the task of determining the mass percent of zinc in a sample of brass, which is an alloy of copper and zinc. She places a piece of brass into excess hydrochloric acid, HCl. The copper does not react with hydrochloric acid, but the zinc does.Once the brass is completely reacted away, she precipitates out the zinc using excess NaOH according to this reaction:  Zn2+(aq) +  2OH-(aq) →  Zn(OH)2(s) The precipitate is filtered, washed, dried, and weighed to constant mass in a filter crucible. The data are shown in the table below. Mass of sample of copper-zinc alloy (brass) 2.36 g Mass of dry filter crucible 29.12 g Mass of filter crucible and precipitate (first weighing) 31.07 g Mass of filter crucible and precipitate (second weighing) 30.45 g Mass of filter crucible and precipitate (third weighing) 30.45 g Calculate the number of moles of Zn(OH)2 precipitate collected. Calculate the mass percent of zinc in the brass. Answers must be written in the space provided. Show your work.  Note: If you are unable to show your work adequately using the Rich Text Editor, complete your work on scratch paper. Upload a photo of your work in the “Comments” of this exam immediately after you have completed and submitted the exam. You can access the “Comments” through the grade book. Answers provided on scratch paper alone will not be scored.

What is the maximum number of moles of Al2O3 that can be produced by the reaction of 0.40 mol of Al with 0.40 mol of O2?

Suppose a solution was too concentrated for an accurate reading with the spectrophotometer. The concentrated solution was diluted by placing 1.00 mL of the concentrated solution in 4.00 mL of water. The solution was then placed in the spectrophotometer, an absorbance was obtained, and after a few calculations the molar concentration was calculated to be 3.5 × 10-6 M. What was the concentration of the original stock solution before dilution? (Assume volumes are additive.)