Gold and hydrochloric acid
1 answer:
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The pH of a buffer solution containing acid of pKa 7.5 will be 8.1.
The pH of a solution indicates its acidity or basicity. A pH below 7 is acidic, while pH above 7 is basic. 7 is considered as the neutral value.
A buffer is a solution that has the ability to resist the change in pH when an acid or a base is added to it. The natural example of buffer is blood.
According to the question, pKa of acid = 7.5
If concentration of base is x then, concentration of acid will be x/4.
According to the Henderson–Hasselbalch equation,
pH = pKa + log [A⁻] / [HA]
pH = 7.5 + log []
pH = 7.5 + log 4 ⇒ 7.5 + 0.602
pH = 8.1
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Answer:
Option f: an addition of HCl will exceed the buffer capacity. The option d is also correct since it is a consequence of the option f.
Explanation:
The pH of the buffer solution before the addition of HCl is:
The hydrochloric acid added will react with the potassium fluoride as follows:
H₃O⁺(aq) + F⁻(aq) ⇄ HF(aq) + H₂O(l)
The number of moles (η) of potassium fluoride (KF) and the HF before the addition of HCl is:
The number of moles of the HCl added is 0.408 moles. Since the number of moles of HCl is bigger thant the number of moles of KF, the moles of HCl that remains after the reaction is:
Hence, the KF is totally consumed after the reaction with HCl and thus, exceding the buffer capacity.
We can calculate the pH after the addition of HCl:
HF(aq) + H₂O(l) ⇄ F⁻(aq) + H₃O⁺(aq) (1)
The number of moles of HF after the reaction of KF with HCl is:
And the concentration of HF after the reaction of KF with HCl is is:
Now, from the equilibrium of equation (1) we have:
(2)
By solving equation (2) for x we have:
x = 0.0187
Finally, the pH after the addition of HCl is:
Therefore, the addition of HCl will exceed the buffer capacity and thus, lower the pH by several units. The correct option is f: an addition of HCl will exceed the buffer capacity. The option d is also correct since it is a consequence of the option f.
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Answer:
1. Molarity of MgSO₄ = 0.6 M
2. Molarity of AgNO₃ = 0.06 M
3. volume of acetic acid = 250 mL
4. Molarity of NaCl= 2.3 M
5. Mass of C₁₂H₂₂O₁₁ = 4.1 g
6. Mass of C₁₀H₈ (naphthalene) = 77 g
7. mass of ethanol = 11 g
8. Mass of DDT = 0.011 mg
Explanation:
Ans 1.
Data given
mass of MgSO₄ = 403
Volume of solution = 5.25 L
Solution:
First we will find mole of solute
no. of moles = mass in grams / Molar mass . . . . . .(1)
Molar mass of MgSO₄ = 24 + 32 + 4(16)
Molar mass of MgSO₄ = 120 g/mol
Put values in equation 1
no. of moles = 403 g / 120 g/mol
no. of moles = 3.36 mol
Now to find molarity
Formula used
Molarity = No. of moles of solute / solution in L . . . . . . (2)
Put Values in above equation
M = 3.36 mol / 5.25 L
M = 0.64
So, round the figure to two significant digits.
Molarity of MgSO₄ = 0.64 M
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Ans 2.
Data given
mass of AgNO₃ = 1.24 g
Volume of solution = 125 mL
convert mL to L
1000 mL = 1 L
125 mL = 125/1000 = 0.125
Solution:
First we will find mole of solute
no. of moles = mass in grams / Molar mass . . . . . .(1)
Molar mass of AgNO₃ = 108 + 14 + 3(16)
Molar mass of AgNO₃ = 170 g/mol
Put values in equation 1
no. of moles = 1.24 g / 170 g/mol
no. of moles = 0.0073 mol
Now to find molarity
Formula used
Molarity = No. of moles of solute / solution in L . . . . . . (2)
Put Values in above equation
M = 0.0073 mol / 0.125 L
M = 0.06
So, round the figure to two significant digits.
Molarity of AgNO₃ = 0.06 M
______________________
Ans 3.
Data Given:
volume of acetic acid = 500 mL
% solution of acetic acid (M)= 50%
volume of acetic acid needed = ?
Solution:
formula used
percent of solution = volume of solute/ volume of solution x 100
Put Values in above formula
50 % = volume of solute / 500 mL x 100
Rearrange the above equation
volume of solute = 50 x 500 mL /100
volume of solute = 250 mL
So, volume of acetic acid = 250 mL
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Ans 4
Data Given:
Molarity of NaCl (M1) = 6 M
Volume of NaCl (V1) = 750 mL
convert mL to L
1000 ml = 1 L
750 ml = 750/1000 = 0.75 L
Volume of dilute solution (V2)= 2 L
Molarity of dilute solution (M2) = ?
Solution:
Dilution Formula will be used
M1V1 = M2V2 . . . . . . (1)
Put values in equation 1
6 M x 0.75 L = M2 x 2 L
Rearrange the above equation
M2 = 6 M x 0.75 L / 2 L
M2 = 2.25 M
So, round the figure to two significant digits.
Molarity of NaCl= 2.3 M
_________________________
Ans 5.
Data Given:
Molarity of C₁₂H₂₂O₁₁ = 0.16 M
Mass of C₁₂H₂₂O₁₁ (m) = ?
Volume of dilute solution = 75 mL
convert mL to L
1000 ml = 1 L
75 ml = 75/1000 = 0.075 L
Solution:
As we know
Molarity = no.of moles/ liter of solution . . . . . . .(1)
we also know that
no.of moles = mass in grams / molar mass . . . . . (2)
Combine both equation 1 and 2
Molarity = (mass in grams / molar mass) / liter of solution . . . . (3)
Molar mass of C₁₂H₂₂O₁₁ (Sucrose) = 12(12) +22(1) +11(16)
Molar mass of C₁₂H₂₂O₁₁ (Sucrose) = 144 +22 + 176
Molar mass of C₁₂H₂₂O₁₁ (Sucrose) = 342 g/mol
Put values in equation in equation 3
0.16 M = (mass in grams / 342 g/mol) / 0.075 L
Rearrange the above equation
mass in grams = 0.16 mol/L x 0.075 L x 342 g/mol
mass in grams = 4.104 g
So, round the figure to two significant digits.
Mass of C₁₂H₂₂O₁₁ = 4.1 g
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The remaing portion is in attachment
