One of the principles of the I2C standard, is that each device has a fixed address (range) baked in the chip. The datasheet of the integrated circuit specifies this address.
But it is not always so easy to find, and may e.g. even depend on the manufacturer of the chip (is the chip is made by multiple manufacturers.
Hence, it is useful to have a special Arduino sketch to scan for devices.
See https://playground.arduino.cc/Main/I2cScanner/
Code at: I2cScanner.ino
Comments: