The ph of a solution prepared by mixing 40.0 ml of 0.125 m mg(oh)2 and 150.0 ml of 0.125 m hcl is

The balanced chemical reaction is:

Mg(OH)2  +  2HCl  -->  MgCl2  +  2H2O

So we can see that 2 moles of HCl reacts for every 1 mole of Mg(OH)2.

moles HCl left = 0.125 M * 0.150 L – (0.125 M * 0.040 L) * 2

moles HCl left = 0.00875 mol

So the concentration of H+ ion is:

[H+] = 0.00875 mol / (0.150 L + 0.040 L)

[H+] = 0.046 M

So the pH is:

pH = - log 0.046

pH = 1.34

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.