Lecture 4: Water, concentrations, acids and bases

Question 1

Mole?

Answer 1

Quantity used to measure an amount of substance.

Question 2

Calculating number of moles?

Answer 2

n (moles) = mass (grams) / molecular weight (Da)

Question 3

Avogadros number?

Answer 3

6.022 x 10^23

Question 4

Calculating concentration?

Answer 4

C (concentration) = n (number of moles of substance) / volume (litres)

Question 5

pH values?

Answer 5

14 is basic, 7 is neutral, 0 is acidic

Question 6

Disassociation of water?

Answer 6

Water can disassociate resulting in hydronium ions and hydroxide ions. Changes in concentration of these ions can have a great effect on living organisms.

Question 7

What is equation for disassociation of water?

Answer 7

2H20 = hydronium ion (H30+) + hydroxide ion (OH-)

Question 8

Coordinate covalent bonds?

Answer 8

The hydronium ion is actually a coordinate covalent bond, where both electrons in the bond with the additional H+ come from water itself. The third proton can be exchanged with other ions with a net negative charge (e.g. OH- group to make H20) or molecules with a lone pair (e.g. NH3 to make NH4+)

Question 9

How to measure acidity of a solution?

Answer 9

Measured by the concentration of H30+ ions present.

Question 10

Acid?

Answer 10

Acids are substances which tend to donate a proton (H+).

Question 11

Base?

Answer 11

Bases are substances which tend to accept a proton (H+).

Question 12

Acid and Base equation.

Answer 12

HA (acid) + OH- (base) = A- (salt) + H20 (water)

Question 13

Normal average pH value for body fluids?

Answer 13

7.4

Question 14

What is pH threshold?

Answer 14

if body pH gets below 6.8 or above 8.0, you could die.

Question 15

What is a buffer?

Answer 15

The buffer system absorbs protons by removing them from hydronium ions through a reaction with a salt ion. The buffer can also donate protons by generating hydronium ions when the pH gets too high.