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Solutions and biomolecules
8 MDCAT Chemistry questions with answers and explanations.
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A solution has 2 moles of A and 3 moles of B. What is the mole fraction of A?
- 1 0.4
- 2 0.6
- 3 0.67
- 4 2
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Osmotic pressure of a dilute solution is directly proportional to its:
- 1 Concentration
- 2 Colour
- 3 Density only
- 4 Volume
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Correct answer: Concentration
Osmotic pressure = cRT, so it increases with the concentration of solute.
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Dissolving a non-volatile solute in a solvent causes the vapour pressure of the solvent to:
- 1 Increase
- 2 Decrease
- 3 Stay the same
- 4 Become zero
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Correct answer: Decrease
According to Raoult's law, the vapour pressure is lowered in proportion to the mole fraction of the solute.
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What mass of NaCl is in 500 mL of a 0.1 M solution? (Na = 23, Cl = 35.5)
- 1 5.85 g
- 2 2.925 g
- 3 0.585 g
- 4 29.25 g
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Correct answer: 2.925 g
Moles = 0.1 x 0.5 = 0.05 mol. Mass = 0.05 x 58.5 = 2.925 g.
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Glucose is classified as:
- 1 A ketohexose
- 2 An aldohexose
- 3 A disaccharide
- 4 A polysaccharide
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Correct answer: An aldohexose
Glucose has six carbons and an aldehyde group, so it is an aldohexose.
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What colour does starch give with iodine solution?
- 1 Red
- 2 Blue-black
- 3 Green
- 4 Yellow
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Correct answer: Blue-black
Iodine forms a blue-black complex with starch.
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Fats are esters of fatty acids with:
- 1 Glycerol
- 2 Glucose
- 3 Ethanol
- 4 Glycine
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Correct answer: Glycerol
A fat, or triglyceride, is formed from one glycerol molecule and three fatty acids.
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An amino acid exists mainly as a dipolar ion in water. This ion is called a:
- 1 Zwitterion
- 2 Carbocation
- 3 Free radical
- 4 Carbanion
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Correct answer: Zwitterion
A zwitterion has both a positive NH3+ group and a negative COO- group in the same molecule.