A buffer was prepared by mixing 0.200 moles of ammonia (Kb = 1.8x10-5) and 0.200 moles of ammonium chloride to form an aqueous solution with a total volume of 500 mL. 250 mL of the buffer was added to 50.0 mL of 1.00 M HCl. What is the pH of this second solution?

2NH 4 Cl(aq) + Pb(NO 3 ) 2 (aq) → 2NH 4 NO 3 (aq) + PbCl 2 (s)

This is a double replacement reaction, also called a double displacement, metathesis, or precipitation reaction, in which a precipitate (solid) is one of the products.

The general equation is  

AX + BY → AY + BX , where A and B are cations and X and Y are anions.

Explanation:

this is what i found let me know if its wrong or right