Question

8. (12 pts) A recipe for 1.00L of a 10X concentrated stock of a buffer solution calls for:

80.00g NaCl (58.44 g/mol)        2.00g KCl (74.55 g/mol)       2.00g KH₂PO₄ (136.08 g/mol)

(Note: the quantities above are the amounts used to prepare the 10X concentrated stock.)

a) What are the concentrations of each component in the 10X stock?

Express in molar.

NaCl:   _______________                  KCl: _______________             KH₂PO₄: _______________

b) What are the concentrations of each component in 1X buffer (e.g. diluted for use)?

Express in millimolar (mM).

NaCl:   _______________                  KCl: _______________             KH₂PO₄: _______________

c) Explain the steps (including calculations and measurements) involved in preparing 250.0mL of 1X solution by diluting the 10X concentrated stock.

(Note: this question is NOT asking how to prepare the 10X buffer – assume you already have this).

8. (12 pts) A recipe for 1.00L of a 10X concentrated stock of a buffer solution calls for:

80.00g NaCl (58.44 g/mol)        2.00g KCl (74.55 g/mol)       2.00g KH₂PO₄ (136.08 g/mol)

(Note: the quantities above are the amounts used to prepare the 10X concentrated stock.)

a) What are the concentrations of each component in the 10X stock?

Express in molar.

NaCl:   _______________                  KCl: _______________             KH₂PO₄: _______________

b) What are the concentrations of each component in 1X buffer (e.g. diluted for use)?

Express in millimolar (mM).

NaCl:   _______________                  KCl: _______________             KH₂PO₄: _______________

c) Explain the steps (including calculations and measurements) involved in preparing 250.0mL of 1X solution by diluting the 10X concentrated stock.

(Note: this question is NOT asking how to prepare the 10X buffer – assume you already have this).

Answer 1

Q8

a)

mol of NaCl = mass/MW = 80/58.44 = 1.36892 mol

mol of KCl = mass/MW= 2/74.55 = 0.02682 mol

mol of KH2OI4 = mass/Mw = 2/136.08 = 0.01469 mol

then, for molarity, since this is 1 L,

M = mol / V = mol/ 1

M of NaCl = 1.36892 mol/L

M of KCl = 0.02682 mOL/L

M of KH2OI4 = = 0.01469 mol/L

B)

CONCENTRATION OF EACH COMPENT IN 1X BUFFER

ratio is:

1/10 so it must decreas by a factor of 10

M of NaCl = 0.136892 mol/L

M  of KCl = 0.002682 mOL/L

M  of KH2OI4 = = 0.001469 mol/L

c) Explain the steps (including calculations and measurements) involved in preparing 250.0mL of 1X solution by diluting the 10X concentrated stock.

Use the stcok solution

M1V1 = M2V2

1*250 = 1/10*V2

V2 = 2500 mL required for dilution