Water & its properties

Hydrogen bonds are important for the physical and chemical properties of water.

How do hydrogen bonds form in water?

Electronegative (–) oxygen atoms are attracted to the electropositive (+) hydrogen atoms A of adjacent water molecules.

Electronegative (–) oxygen atoms are attracted to the electropositive (+) hydrogen atoms B within the same water molecule.

Electropositive (+) oxygen atoms are attracted to the electronegative (–) hydrogen atoms C of adjacent water molecules.

Electropositive (+) oxygen atoms are attracted to the electronegative (–) hydrogen atoms D within the same water molecule.

Water has many properties that are important for living organisms.

Which property of water molecules explains why small animals, such as pond skaters, are able to move over the surface of water without sinking?

A Adhesion

B Buoyancy

C Cohesion

D Density

17* The thermal properties of water allow organisms to live in an environment with relatively small changes in temperature. These properties also make water efficient as a coolant, e.g. in sweating or by absorbing large amounts of heat.

Outline how other properties of water are essential for sustaining life on Earth.

Additional answer space if required.

Which of the following statements about water transport in plants is/are correct?

1 Transpiration happens as a consequence of the need for gas exchange. 2 There are cohesive forces between water molecules because they form hydrogen bonds with one another. 3 Water is drawn up the stem due to adhesive forces between water molecules.

A 1, 2 and 3

B only 1 and 2

C only 2 and 3

D only 1

Your answer

Water moves by osmosis in living organisms.

Define osmosis.

Plants rely on osmosis for support.

Explain the importance of osmosis in plant support.

The apparatus shown in Fig. 16 can be used to demonstrate osmosis.

When the capillary tube with visking tubing bag was placed in solution Y, the level of solution X inside the capillary tube rose from 10.5 mm to 26.5 mm.

The ruler used to measure the distance along the capillary tube was accurate to the nearest 0.5 mm.

Calculate the percentage uncertainty of the measurement.

What conclusions can be drawn about the composition of solutions X and Y ?

Explain why it was necessary to calculate percentage change in mass.

The students identified replicate 3 of the potato in 0.7 mol dm^–3 sucrose as anomalous. (ii)

Suggest a practical error by the students that might have caused this result to be anomalous and explain the likely effect of this error.

Use Table 16 to identify which plant cells contained the highest concentration of sucrose.

Justify your conclusion.

Water has many properties that are essential for living organisms.

Explain how properties relating to the density of water contribute to the survival of organisms.