placement new operator help

Code:

#include <iostream>
using namespace std;

class addition 
{
    int a, b;

    public:
      addition() 
      {
             a=0;
             b=0;
      }

      addition(int x, int y) 
      {
          a = x;
          b = y;
      }

      void show() 
      {
          cout << a << " ";
          cout << b << "\n";
      }

      addition operator+(addition op2);
};

addition addition::operator+(addition op2)
{
     addition temp;
     temp.a = op2.a + a;
     temp.b = op2.b + b;
     return temp;
}

int main()
{
    char* buf=new char[100];
     addition* a1=new (buf) addition(1,3);//placement new operator   
     return 0;
}

Queries:
i. Is it possible to create object at a memory location on heap? i.e. let's say memory locaiton 2134433 present on heap....If yes, pl provide the code?

ii. In the above code, what is the use of placement new opearator as we dont know address of memory location where object is getting creating?