Which of the following statements about solutions is incorrect?
A solution is a homogeneous mixture.
The solvent is always the component in the largest amount.
Adding solvent changes the number of moles of solute.
Molarity expresses concentration as moles of solute per liter of solution.
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A chromatogram of two compounds, A and B, is shown above.
The Rf value of compound B is
0.21
0.44
0.65
1.54
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The distance that an amino acid moves on a chromatogram depends on
the intermolecular forces between the amino acid and the stationary phase.
the intermolecular forces between the amino acid and both the mobile and stationary phases.
the intermolecular forces between the solvent and the stationary phase.
the intermolecular forces between the solvent and both the mobile and stationary phases.
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1 markWhich of the following describes the correct procedure to prepare 0.25 L 0.100 M Na2CO3 (aq)?
(The molar mass of Na2CO3 is 106 gmol-1)
Dissolve 1.06 g of Na2CO3 (s) in a small amount of distilled water and dilute to 0.25 L.
Dissolve 2.65 g of Na2CO3 (s) in a small amount of distilled water and dilute to 0.25 L.
Add 1.06 g of Na2CO3 (s) to 0.25 L of distilled water.
Add 2.65 g of Na2CO3 (s) to 0.25 L of distilled water.
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1 markA 5.23 g sample of anhydrous K2SO4 (molar mass 174.3 gmol-1) is dissolved in 1.75 L of solution.
What is the molarity of the solution, to three significant figures?
0.0221
0.0171
0.0300
0.0111
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1 markWhich of the following solutions contains the greatest number of moles of Cl- ions?
25 mL of 0.10 M CaCl2
10 mL of 0.15 M NaCl
20 mL of 0.20 M SrCl2
10 mL of 0.10 M KCl
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A sample of cyclohexene contaminated with cyclohexanol is separated by column chromatography.
Hexane is used as the mobile phase and silica gel as the stationary phase.
Which statement correctly explains why cyclohexene has a shorter retention time than cyclohexanol?
Cyclohexene and cyclohexanol have different polarities.
Cyclohexene is polar due to the C=C.
Cyclohexanol is held in the mobile phase for longer.
Cyclohexanol can form hydrogen bonds with the silica gel.
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Four pure dyes, A through D, are spotted on chromatography paper as indicated in the diagram below.
An unknown dye, X, is spotted on a separate piece of chromatography paper. Both papers are then developed in chromatography chambers. The developed chromatograms are shown above.
Based on the results of the paper chromatography experiment, which of the four dyes is most likely to be dye X?
Dye A
Dye B
Dye C
Dye D
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Compound | Formula | Boiling point (oC) | Density (g/mL) |
|---|---|---|---|
Pentane | C5H12 | 36 | 0.63 |
Heptane | C7H16 | 98 | 0.68 |
A student obtains a mixture of the liquids pentane and heptane, which are miscible in all proportions.
Which of the following techniques would be best for separating the components of this mixture, and why?
Distillation, because the liquids would boil at different temperatures owing to the difference in strength of their intermolecular forces.
Filtration, because the different densities of the liquids would allow one to pass through the filter paper while the other would not.
Column chromatography, because the higher molar mass of octane would cause it to move down the column faster than hexane.
Paper chromatography, because the liquids would move along the stationary phase at different rates owing to the difference in polarity of their molecules.
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Under which condition is a solution most likely to form?
When solvent-solute interactions are weaker than solvent-solvent interactions.
When solvent-solute interactions are stronger than solvent-solvent interactions.
When solute-solute interactions are stronger than solvent-solvent interactions.
When all interactions (solvent-solvent, solute-solute, and solvent-solute) are equally strong.
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A 50.2 g sample of barium hydroxide is dissolved in 1.25 L of solution.
What is the concentration of hydroxide ions, to three significant figures?
0.234 M
0.366 M
0.469 M
0.732 M
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Ascorbic acid has the chemical formula C6H8O6.
How many millilitres of a 0.0653 M solution of ascorbic acid would be required to obtain 4.90 g of ascorbic acid?
27.8
426
550
2350
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Equal volumes of solutions in two different vessels are represented above. (Water molecules are not shown).
If vessel 1 represents a CaCl2 (aq) solution, then vessel 2 could represent an aqueous solution of
CaCl2 with the same molarity as the solution in vessel 1.
CaCl2 with half the molarity of the solution in vessel 1.
KCl with the same molarity as the solution in vessel 1.
KCl with half the molarity of the solution in vessel 1.
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Which of the following diagrams represents a heterogeneous mixture?
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A thin-layer chromatography (TLC) experiment was conducted using a silica gel-coated TLC plate (a polar material) and a solvent mixture of 95% dichloromethane (DCM) and 5% methanol.
The sample mixture contained two polar food additives.
The relative polarities of the solvents used in this and similar experiments are:
Chloroform 0.26
DCM 0.31
Methanol 0.76
Based on this information, which change to the solvent mixture would likely increase the Rf values of the food additives in a subsequent experiment?
Decreasing the percentage of methanol.
Increasing the percentage of methanol.
Replacing DCM with chloroform.
Replacing methanol with chloroform.
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