What is the difference between the speed of an object, the velocity of an object and the acceleration of an object?

Speed is the rate of change of distance(basically how much distance(m) has been covered in a particular time(s)). Velocity is the rate of change of displacement( change of distance in a particular direction with respect to time) , and acceleration is the rate of change of velocity per unit of time.

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%