Chemistry help? (solution concentrations)
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Chemistry help? (solution concentrations)

[From: ] [author: ] [Date: 11-05-03] [Hit: ]
5 L = 0.10834 mol / 0.5 L =0.21668 M With sig figs its 0.217 M Cl-.Question 2:You need to determine the moles of acetic acid in 20 mL.......
2/1 = 2 = mol ratio for Cl to MgCl2

0.0981 mol NaCl x (1 mol Cl / 1 mol NaCl) = 0.0981 mol Cl
0.00512 mol MgCl2 x (2 mol Cl / 1 mol MgCl2) = 0.01024 mol Cl

Step 4. Add the amount of moles of Cl and divide by volume of solution in liters to find the molarity (M, mol/L).

(0.0981 mol + 0.01024 mol) / 0.5 L = 0.10834 mol / 0.5 L = 0.21668 M

With sig figs it's 0.217 M Cl-.



Question 2:

You need to determine the moles of acetic acid in 20 mL.

Pre-step: Find the MW of acetic acid (CH3COOH). See the problem above for the steps. But the MW of acetic acid is 60 g/mol. You'll also need to convert 250 mL to liters, which is 0.25 L.

Step 1. Convert the mL to g by taking the volume and multiplying by the density.

20 mL acetic acid x 1.049 g/mL acetic acid = 20.98 g acetic acid

Step 2. Convert the g into mol. Do so by taking the mass and dividing by the MW.

20.98 g acetic acid / 60 g/mol acetic acid = 0.350 mol acetic acid

Step 3. Calculate M by taking the mol and diving by final volume of the solution in L.

0.350 mol / 0.25 L = 1.4 M



Question 3:

Step 1. Determine the number of moles in each solution. Do so by multiplying the volume of the solution, in L, by the M.

.03590 L x 1 mol/L = .03590 mol KBr
.060 L x .600 mol/L = .0360 mol KBr

Step 2. Add up the two values to get the total number of moles.

0.03590 + 0.0360 = 0.0719 mol KBr

Step 3. Divide the moles by the volume of the solution in L to get M.

0.0719 mol KBr / 0.050 L = 1.438 M KBr

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