Acids And Bases

Question 1

What would be the resulting pH if one drop (0.05mL) of 1.0 M HCL were added to one liter of pure water (assume initial pH 7.0)?
A) 2.7
B) 4.3
C) 5.0
D) 7.0 ( there would be no significant change)
E) 9.7

Answer 1

B) 4.3
As HCl is a strong acid, the final concentration of protons would be the same as the concentration of HCl added. I.e 1.0 M x (0.05 mL)/(1000mL)=5x10-5 M. Taking the negative log, the pH would be 4.3.

Question 2

What is the resulting pH if 1 mL of 10 M HCl is added to 1 liter of 0.1 M sodium phosphate buffer (pH 7.00). The pka of sodium phosphate is 6.82.
A) 6.82
B) 6.98
C) 7.01
D) 7.19
E) cannot be determined

Answer 2

A) 6.82
Initially, 7.00=6.82+log (HPO4-^2-)/(H2PO4^-1)=0.1, then solving from (HPO4-^2-)=0.1M = H2PO4^-1+ 1.51(HPO4-^2-),thus HPO4-^-1 =0.1M/ 2.51= 0.04 M or 0.04 mol in 1 litre. Thus, HPO4-^2-=0.1-0.04= 0.06M ( 0.06 mol in 1 litre)
Adding 10 mol (0.1 mol) of HCl will titrate the amount of HPO4-^2- to HPO4-^-1, so the final ratio would be (0.06-0.01)/(0.04+0.01)=0.05/0.05= 1
Since log (1) =0, the final pH will be 6.82

Question 3

Which if the below statements is false?
A) phosphate is an important intracellulat buffer
B) bicarbonate is an important extracellular buffer
C) many biomolecules can behave as buffers
D)a buffer is the least effective when a solution pH is the same as the buffers pka
E) le chateliers principle is important for pH regulation in the body

Answer 3

D) a buffer is least effective when the solution pH is the same as the buffers pka

Question 4

Which of the below statements is false?
A) the charge of biomolecules varies with pH
B)water is able to self ionize
C) in aqueous solutions the concentration of OH- and H+ is always equal to 10 ^-7 M.
D) a buffer is the most effective when the solution pH is the same as the buffers pka
E) carbon, nitrogen, oxygen, and hydrogen are some of the most abundant elements in living things

Answer 4

C)in aqueous solutions the concentration of OH- and H+ is always equal to 10^-7