Chemistry math problems?
a) 2.0 m KCL in water (density of H2O is 1g/cm^3)
b) 15% NaOH by mass in water ( d=1g/cm^3)
c) 25% NaOH by mass in CH3OH (d=0.79g.cm^3)
d) 0.10 mole fraction of C6H12O6 in water (d=1g/cm^3)
2) Which solvent, water, or hexane (C6H14) , would you choose to dissolve each of the following?
a) NaCl
b) HF
c) octane (C8H18)
d) (NH4)2SO4
Answer:
1) a) 2M KCl MW 74.551
you want 100ml of solutions so you want
0.2 moles /0.1L = 2M KCl or you want 0.2 moles KCl dissolved in 100 ml water
0.2 moles * 74.551 g/mole = 14.91 g
take 14.91 g KCl and dissolve in 100 ml of H20 to form a 2M solution
b) 15% NaOH solution by mass means 15g NaOH/ (Total mass) *100 = weigh percent
Total mass = mass water + mass NaOH = 100 g
Mass NaOH = 15 g ==> mass H2O = 85 g = 85ml (d= 1 g/ml)
take 15 g NaOH and dissolve in 85ml H2O and you will have a 15% NaOH solution by mass in water.
c) 25% NaOH solution by mass in CH3OH (d= 0.79g/ml)
25g NaOH/(Total weight)*100 = weight percent
Total Weight = 25g NaOH + Weight CH3OH = 100g
Weight CH3OH = 75g ==> 94.94 ml (d = .79 g/ml)
Take 25 g NaOH and dissolve in 94.94 ml of CH3OH and you will have a 25% NaOH solution by mass of NaOH
Decant the solution off into a 100 graduated cylinder until you have 100 ml total soution.
d) I leave this to you - It's just 0.1 moles of C6H10O6 in 0.9 moles H2O
0.9 moles H2O should be close to 100 ml of H2O
2) a) ionic - water
b) ionic - water
c) non-polar - hexane
d) ionic - water
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