How much sr(oh)2 • 8 h2o (m = 265.76) is needed to prepare 250.0 ml of solution in which [oh–] = 0.100 m?

We start from the concentration of OH- given then multiply this to the desired volume of the solution to obtain the number of moles OH- needed.

0.100 mol OH- / L soln ( 0.250 L) = 0.025 mol OH-

We then use the relation of OH ions with the OH ions formed when Sr(OH)2 • 8 H2O is dissolved in water to calculate the number of moles of the compound needed. Finally we multiply the value with the molar mass given to obtain the number of grams needed.

0.025 mol OH- (1 mol Sr(OH)2 • 8 H2O / 2 mol OH-) (265.76 g / 1 mol) = 3.322 g Sr(OH)2 • 8 H2O needed

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant. 

Answer(28.02g/mol);