2: Water Flashcards

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1
Q

When are covalent bonds formed?

A

when two atoms share a pair of electrons

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2
Q

What happens if the nucleus of one of the atoms in a covalent bond is more attractive to the electrons than the other nucleus?

A

electrons are not shared equally

= part of the molecule has a slight positive charge and another part has a slight negative charge

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3
Q

What is the term for ‘when part of the molecule has a slight positive charge and another part has a slight negative charge’.

A

polarity

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4
Q

Are water molecules polar? Why?

A

yes:

  • hydrogen nuclei are less attractive to electrons than the oxygen nuclei
  • so the two hydrogen atoms have a slight positive charge and the oxygen atom has a slight negative charge
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5
Q

How many poles do water molecules have? What does this make them? What, therefore, do they show?

A

2 poles - therefore dipoles

- show dipolarity

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6
Q

What sort of bond forms between the positive pole of one water molecule and the negative pole of another?

A

a hydrogen bond

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7
Q

What happens when a hydrogen bond is made? What happens when a hydrogen bond is broken?

A
  • energy is released
  • energy is used

(this is true when any bond is made/broken)

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8
Q

What sort of energy is used to break hydrogen bonds in water? What does this explain?

A
  • heat energy

- why water is such a good coolant, and therefore why sweat is used as a coolant

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9
Q

What does evaporation of sweat remove from the body?

A

heat

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10
Q

How can the significance of hydrogen bonding in water be illustrated?

A

by comparing water with methane - a substance with similar molecular mass that has weaker intermolecular forces, no hydrogen bonds

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11
Q

State the 4 properties for which water and methane can be compared to illustrate the effect of hydrogen bonds.

A
  1. melting point
  2. specific heat capacity
  3. latent heat of vaporization
  4. boiling point
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12
Q

Contrast the melting point of water and methane. Explain the difference.

A
  • methane = -182°C
  • water = 0°C

ice melts at a much higher temperature: hydrogen bonds restrict the movement of water molecules and heat is needed to overcome this

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13
Q

Contrast the specific heat capacity of water and methane. Explain the difference.

A
  • methane = 2.2J per g per °C
  • water = 4.2J per g per °C

water’s heat capacity is higher: hydrogen bonds restrict movement so more energy is stored by moving molecules of water than methane

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14
Q

Contrast the latent heat of vaporization of water and methane. Explain the difference.

A
  • methane = 760 J/g
  • water = 2257 J/g

water has a much higher heat of vaporization: much heat energy is needed to break hydrogen bonds and allow a water molecule to evaporate

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15
Q

Contrast boiling point of water and methane. Explain the difference.

A
  • methane = -160°C
  • water = 100°C

water’s boiling point is much higher: heat energy is needed to break hydrogen bonds and allow water to change from a liquid to a gas.

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16
Q

What is the term used to describe a molecule that is attractive to water? What sort of bonds from between the two molecules?

A
  • hydrophilic

- intermolecular bonds

17
Q

Give general examples of a type of compound and a type of substance that is attractive to water?

A
  • molecule = ionic compounds
  • substances with polar molecules

both hydrophilic

18
Q

If a substance is not hydrophilic, what is it?

A

hydrophobic

19
Q

What does hydrophobic mean?

A

NOT ‘repelled by water’

but, ‘that water molecules are more strongly attracted to each other than to the non-polar molecules of hydrophobic substances’

20
Q

What sort of molecules are insoluble in water?

A

hydrophobic molecules

21
Q

Blood transports a variety of substances. How are most of the substances transported? What does the mode of transport of a substance depend on?

A
  • in the blood plasma

- depends on the substances solubility in water

22
Q

How is sodium chloride transported in the blood?

A

dissolved in the plasma as Na+ and Cl- ions

23
Q

How are glucose and amino acids transported in the blood?

A

both polar molecules so can be dissolved in the plasma

24
Q

How is oxygen transported in the blood?

A

red blood cells with haemoglobin (to which oxygen binds) are needed because oxygen is non-polar

25
Q

How are cholesterol and fats transported in the blood?

A

non-polar and insoluble in water:
- transported in small droplets called lipoproteins

lipoproteins = cholesterol and fat inside, coated by phospholipids and proteins