How many milliliters of water will need to be added to 10.0mLof a 2.5 M solution

Question

How many milliliters of water will need to be added to 10.0mLof a 2.5 M solution to dilute it to a concentration of 1.5 M? What is the percent solution by mass if32g of CaCL_2 is added to 220.0 g of water? How many grams of MgBr_2 will be needed to be added to 300.0 g of water to create a solution that is 5.0% by mass? Determine the amount of water that will be added to 22gof sodium flouride to prepare a solution that is 15% by mass. What is the percent by volume of a solution, if 20.0 mL of glycerol is dissolved in 500.0 mLof water? How many grams of water is needed to make a 3.0 %ethanol, C_2H_5OH, solution? The volume of ethanol available is 50.0 mL

Explanation / Answer

Problem 7.

Apply Dilution law so

M1*V1 = M2*V2

M1 = 2.5, M2 = 1.5 the initial volume = 10 mL, final V = ?

V2 = M1*V1/M2 = (2.5)(10)/(1.5) = 16.66667 mL required

we already have 10 mL, so assuming, the volumes are additive, we need to add 16.667 - 10 = 6.667 mL of liquid

Question 12.

Mass for 3% ethanol

assume 3% is by mass

so

% ethanol = 3%

3% = mass of ethanol / total mass * 100%

3% = mass of ethanol / ( mass of water + mass of ethanol ) * 100%

mass of ethanol = D*V = 0.789*50 = 39.45 g of ethanol

substitute

3% = 39.45 / ( mass of water + 39.45 ) * 100%

mass ofwater = 39.45/0.03 -39.45 = 1,275.55 g of water

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