AP Chemistry Unit 3 2nd Half Quiz

The student mixed each of the four compounds with water. Only one of the four did not dissolve. Which of the following was the compound that did not dissolve?

Pentane

A 50mL sample of C6H14(l) is mixed with a 50mL sample of H2O(l) and the mixture is shaken vigorously. The two liquids do not stay mixed but instead form two separate layers. The density of hexane is 0.66g/mL and the density of water is 1g/mL. A 1g sample of I2(s) is added to the mixture which is shaken again. Which of the following best predicts what happens to the I2(s)?

I2 will be found mainly in the top layer because it will dissolve more in C6H14(l)

Which of the following questions about the components in a mixture could be investigated with paper chromatography?

Do the components have different molecular polarities?

A student prepared four solutions of known [Cu2+] and measured the absorbance of each solution using the same cuvette. The graph shows the data for two absorbance measurements done for each solution. Which of the following identifies the most likely error that affected the absorbance recorded for the solution with [Cu2+] ≈7 E-3 M in the second trial?

A fingerprint was left on the side of the cuvette facing the detector.

Fe3+(aq) + KSCN(s) → FeSCN2+(aq) + K+(aq)
To determine the moles of Fe3+(aq) in a 100. mL sample of an unknown solution, excess KSCN(s) is added to convert all the Fe3+(aq) into the dark red species FeSCN2+(aq), as represented by the equation above. The absorbance of FeSCN2+(aq) at different concentrations is shown in the graph below.
If the absorbance of the mixture is 0.20 at 453 nm, how many moles of Fe3+(aq) were present in the 100. mL sample? (Assume that any volume change due to adding the KSCN(s) is negligible.)

4×10^-6mol

An ionic crystal is added to water and starts to dissolve as shown in the particulate representation above. Based on the orientation of the water molecules, what can be assumed about the charge of the hydrated particle indicated by the arrow?

The particle is positively charged, because the oxygen atoms in water are attracted to it.

How many mL of 10.0M HCl are needed to prepare 500mL of 2.00M HCl?

100.0mL

Which of the following is the best piece of laboratory glassware for preparing 500.0mL of aqueous solid solution?

Volumetric flask

The diagram above represents the photoelectric effect for a metal. When the metal surface is exposed to light with increasing frequency and energy of photons, electrons first begin to be ejected from the metal when the energy of the photons is 3.3×10^-19J. Using the wavelength information provided, what is the color of the light?

Orange

N2 molecules absorb UV light but not visible light. I2 molecules absorb both UV light. Which of the following statements explains the observations?

visible light does not produce transitions between electronic energy levels in the N2 molecules but does produce transitions in the I2 molecule