Final answer:
The hydroxide ion concentration [OH−] in a 0.870 M solution of Sr(OH)2 is 1.74 M, as Sr(OH)2 dissociates to produce two OH− ions for every formula unit.
Step-by-step explanation:
The hydroxide ion concentration [OH−] in a 0.870 M solution of Sr(OH)2 can be found by considering that Sr(OH)2 is a strong base that fully dissociates in water.
Since Sr(OH)2 produces two OH− ions for every formula unit that dissociates, the concentration of [OH−] will be twice the concentration of the Sr(OH)2 solution. Thus, the value of [OH−] in a 0.870 M solution of Sr(OH)2 is:
[OH−] = 2 × [Sr(OH)2] = 2 × 0.870 M = 1.74 M