If the Chromebook seems to be too quiet, too loud, or just won't produce sound at all, most likely, the volume can be adjusted via the keyboard.
1) If you are not hearing any sound, your volume is probably all the way down or muted. The button to the left highlighted in purple is the mute button. Once pressed, a notification on the screen should appear stating that you have either muted or unmuted the device.
2) The two keys highlighted in red are your volume decrease and volume increase buttons from left to right. If the volume decrease button is pressed enough times, that can result in silencing the device and to get the volume back simply hit the right hand key a couple times.