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# I can't figure out this Chemistry question. Can someone help?

How many grams of Na2SO4 must be dissolved in 2000.0 mL of solution to produce a solution that is 4.0-M?

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- davidLv 74 weeks ago
Roger's answer is probably correct, but I'm going to try to explain more.

... most of these problems start by doing the molar mass .... I will call that k (because M is used for something else.

M -- is molarity or concentration in moles / liters

=== now start canceling things

(4.0moles/1Liter) X (1L/1000mL) X (2000mL) X (k g/mole)

... sub the molar mass in place of k .. then just use a calculator .. --- good luck.

- Roger the MoleLv 74 weeks ago
(2.0000 L) x (4.0 mol/L) x (142.0421 g Na2SO4/mol) = 1136.34 g = 1100 g Na2SO4

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Probably because I was not taught the unit-factor method in HS. We did every problem using equations (gas laws) or by proportions. -- My older brother had a Schaum's outline of Chem. which I inhereted and everythng was done using proportions. For me, and some others, proportions MAKE SENSE.