Question

How many milliliters of a 0.640 M solution of KBr would be required to contain 17.2 grams of KBr

Please show mathmatics work, thank you

Answer 1

227 mL KBr

Step-by-step explanation:

To find the amount of milliliters KBr, you need to (1) convert grams to moles (via molar mass from values on periodic table), then (2) find the amount of liters KBr (via molarity equation using molarity and moles), and then (3) convert liters to milliliters. The final answer should have 3 sig figs to match the amount of sig figs in the given values.

(Step 1)

Molar Mass (KBr): 39.098 g/mol + 79.904 g/mol

Molar Mass (KBr): 119.002 g/mol

17.2 grams KBr 1 mole
----------------------- x ------------------ = 0.145 moles KBr
119.002 g

(Step 2)

Molarity (M) = moles / volume (L)

0.640 M = 0.145 moles / volume

(0.640 M) x (volume) = 0.145 moles

volume = (0.145 moles) / (0.640 M)

volume = 0.227 L

(Step 3)

0.227 L KBr 1,000 mL
------------------ x ----------------- = 227 mL KBr
1 L