Question

A 150.0 ml buffer solution is 0.110 moll−1 in (ch₃)₂ nh and 0.130 moll⁻¹ in (ch3)₂ nh₂br . what mass of hcl will this buffer neutralize before the ph falls below 9.95?

Answer 1

To find the mass of HCl that a buffer can neutralize before the pH falls below 9.95, use the Henderson-Hasselbalch equation and calculate changes in the buffer components' ratios.

Step-by-step explanation:

To determine the mass of HCl that a buffer solution can neutralize before the pH falls below 9.95, we need to utilize the Henderson-Hasselbalch equation. The buffer contains dimethylamine ((CH3)2NH) and its conjugate acid, dimethylammonium bromide ((CH3)2NH2Br).

The Henderson-Hasselbalch equation is given by:

pH = pKa + log ( [A−]/[HA] )

In which [A−] is the concentration of the base and [HA] is the concentration of the acid. Since we're given the pKa of dimethylamine is 10.70, we can calculate the moles of HCl that will change the ratio of [A-] to [HA] to the point where pH drops to 9.95.

The calculation steps are:

1. 
   
3. Calculate the moles of (CH3)2NH and (CH3)2NH2Br in the buffer.
4. 
   
6. Use the Henderson-Hasselbalch equation to find the new ratio of [A-]/[HA] that corresponds to pH 9.95.
7. 
   
9. Find out the change in moles of (CH3)2NH2Br needed to reach the new ratio.
10. 
    
12. Convert the change in moles to mass of HCl since each mole of HCl will react with one mole of (CH3)2NH to form one mole of conjugate acid.

The equivalent mass of HCl required to neutralize the buffer can then be calculated in grams using the molar mass of HCl, which is approximately 36.46 g/mol.