Buffers & Isotonic Solutions

Question 1

What is osmosis?

Answer 1

The passive movement of water molecules from a high water potential to a low water potential across a partially permeable membrane

Question 2

What is water potential?

Answer 2

The pressure exerted by water molecules as they collide with a membrane or container

Question 3

What are the units for water potential?

Answer 3

Pascals (Pa) or kilopascals (kPa)

Question 4

What is hydrostatic pressure?

Answer 4

The pressure exerted by a fluid at equilibrium at any point of time due to the force of gravity

Question 5

Describe an isotonic cell

Answer 5

• No net movement of water by osmosis

- No change in shape or size

Question 6

Describe a hypertonic cell

Answer 6

• Very low water potential
• Cytoplasm has a higher water potential than it’s surroundings
• Water moves out of the cell down the water potential gradient by osmosis

Question 7

Describe a hypotonic cell

Answer 7

• Very high water potential
• Cytoplasm has a linear water potential than it’s surroundings
• Water moves into cells down water potential gradient by osmosis

Question 8

What is a buffer?

Answer 8

An isotonic solution that maintains a constant pH by neutralising the effects of hydrogen ions

Question 9

How do you create isotonic solutions (buffer)?

Answer 9

• Weigh the compound

- Dissolve it in a solvent to create a solution that is the same concentration as the intracellular environment

Question 10

What is a cation?

Answer 10

A positively charge ion

Question 11

What is an anion?

Answer 11

A negatively charged ion

Question 12

How do you calculate the molecular mass of methane (CH4)?

Answer 12

Carbons atomic mass = 12
Hydrogens atomic mass = 1
12+1+1+1+1 = 16

Question 13

What is a mole?

Answer 13

An amount equal to the number of carbon atoms in exactly 12g of the carbon-12 isotope
- One mole contains 6.02214 x 10²³ atoms

Question 14

What is a solute?

Answer 14

In a solution of 2 substances, that which is present in the smaller amount

Question 15

What is a solution?

Answer 15

A ‘homogenous mixture’ of two (or more) substances

Question 16

What is a solvent?

Answer 16

In a solution of 2 substances, that substance which is present in the largest amount

Question 17

How do you calculate molecular mass?

Answer 17

Add up atomic masses of the elements

Question 18

How do you calculate the number of moles?

Answer 18

Mass of compound (g) / relative molecular mass of compound

Question 19

How do you calculate molarity (M)?

Answer 19

Moles of compound / volume (L)

Question 20

What is the equation used to prepare dilutions from stock solutions?

Answer 20

C1 x V1 = C2 x V2
C = concentration
V = volume
1 = stock solution 
2 = working solution

Question 21

What is the equation for percentage solutions?

Answer 21

W/v and v/v