What should be done before measuring an unknown ph of a

Question

Assignment Questions

Question 1: The pH of a solution describes its acidity or alkalinity: Describe how pH and H3O+ concentration are related and explain why diluting an acid raises the pH, but diluting a base lowers the pH.

Question 2: Based on the equation below, which ion plays the role of hydrogen-ion donor (acid) and which ion plays the role of hydrogen-ion acceptor (base) in PBS?

H₂PO₄^-(aq) H+(aq) + HPO₄^2-(aq)

Question 3:  Which ions are being produced by this process, assuming that each of the chemical compounds dissociate into their constituent parts once they are dissolved in water?

Question 4: Using this webpage below calculate (to 2 decimal places) the molecular mass for each of the compounds used to make PBS (the values here differ slightly from the periodic table found in your text book due to rounding errors).

Question 5: As previously stated, the concentration of NaCl, KCl and Phosphate in working strength 1 x PBS is 0.137M NaCl, 0.012M Phosphate, 0.027M KCl,  pH 7.4  How do they compare to the concentrations you calculated for 10x PBS?

 Watch the following videos

• "Using an Electronic Balance" from Bio-Rad tutorials:
• "Using a pH Meter" from Bio-Rad tutorials:
• "Making a PBS solution" from Community College Consortium for Bioscience Credentials:

Question 6:  What is the first thing to do after putting a weighing boat on the balance?

Question 7:  If you have excess reagent on the weighing boat, what should you avoid doing and why?

Question 8:  If you had the choice between a 1 liter beaker and a 1 liter graduated cylinder, which one should you use to measure volumes with maximal precision when making 1 liter of PBS? (you can perform an internet search to find this if you are not sure of the answer)

Question 9:  What should be done before measuring an unknown pH of a solution using a pH meter?

Question 10:  Why do you think the protocol does not say to dissolve compounds directly in 1 liter of water?

Question 11: The PBS protocol above says to adjust pH to 7.4 with HCl. What does this imply on the pH of 10x PBS before adjusting the pH, would it be greater or smaller than 7.4?

Question 12: The last step in the protocol is to autoclave the 10x PBS solution. Why do you think this step is important? Look up the definition of autoclave if you are unsure what it means.

Question 13: Taking into account your response to question 5, now that you have made a 10x PBS solution, describe how you would prepare 1 liter of 1x working solution PBS, including which glassware you would use. Will you need to adjust the pH again?

Attachment:- Question 5.rar