Bio practical-4 pH and dilutions

bio 1107

What are buffers made out of?

conjugate base and weak acid

What is a buffer?

are solutions that minimize change in pH

When a solution is more basic (alkalinity) what does it have a higher concentration in?

OH-

When a solution is more acidic, it has a higher concentration in…what?

H+

How to determine a hydrogen conjugate base

1 hydrogen

How do determine weak acid

2 hydrogens

Cohesion

attraction between like molecules

ex: surface tension

Adhesion 

Attraction between different substances 

ex: water droplets sticking to glass 

what is very good solvent?

water

why is water a good solvent?

water self-ionizes o yield H+ ions

H₂O (l) → H+ (aq) + OH- (aq)

what does [H+] mean and what does it determine?

molarity of hydrogen ion

• how acidic or basic a solution is

How do you find pH?

pH =-log[H+]

How do you find hydrogen ion concentration

[H+]= 10^-pH

What unit must [H+] be in before finding pH? 

Molarity (M)

pH meter reminders

• pH meters must remain submerged at all times

  • Keep the pH meter in the holding solution if not being used, or in the experimental solution

• Remember to rinse the base of the meter with distilled water over the liquid waste container before and after each use 

• Make sure the correct one is connected to your iPad

  • Use the ID number on the back of the pH meter

What is the pH of a solution with a concentration of 0.7 M hydrogen ions?

pH = -(log(0.7))

pH = -(-0.15)

pH = 0.15

What is the concentration of [H+] present in a solution with a pH of 11.0?

[H+] = 10^-11 = 1.0 x 10^-11

What does weak acid absorb?

excess OH-

Conjugate base absorbs what?

excess H+

What are the 3 main buffers in human body

Carbonic Acid-Bicarbonate Buffer

Phosphate Buffer

Protein BUffer

What is the purpose of Dilutions? 

Make a less concentrated solution from a more concentrated stock solution 

How are dilutions done?

• adding more solvent (typically water)

What can dilutions NOT do

• can NEVER increase the concentration

What formula can you use for dilutions?

C₁ x V₁ = C₂ x V₂

C₁ - initial concentration (of the stock solution)

V₁ - initial volume (of the stock solution needed to make the diluted solution)

C₂ - final concentration (of the diluted solution)

V₂ - final volume (of the diluted solution)

How would you prepare 400 mL of a 0.2 M hydrochloric acid from a concentrated stock of HCl with a concentration of 8.0 M?

(8.0 M)(?) = (0.2 M)(400 mL)

(8.0 M)(?) = 80

V₁ = 10 mL of HCl is needed to make the dilution

How much 0.5 M sodium chloride solution can you prepare if you start with 150 mL of a 2.0 M NaCl stock solution?

(2.0 M)(150 mL) = (0.5 M)(?)

300 = (0.5)(?)

V₂ = 600 mL of the NaCl solution can be prepared