Gen Chem Problems

[goodie]

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Hey,

Im working on problems for gen chem and have 2 that have stumped me 😕 Any help would be awesome!
1) What is the molarity of C6H12O6 in an aqueous solution that is prepared by dissolving 14.19g sample of impure C6H12O6 in water to make a 1200mL solution. Assume that the sample is 81% C6H12O6 by mass. I know C6H12O6 is a sugar and wont dissociate but i cant figure out how to set up the equation.

2)A 4.6008g sample of hydrate NiSO4 was heated to driev off all of teh water of hydration. The remaining solid weighed 2.7088g. If NiSO4 x H2O rprestn teh forumal of teh hydrate then waht is the value of x? No idea for this one

Thanks again for any help! 🙂

 

[ushaseos]

1) 81% of 2g = grams of sugar. Convert to moles, divide by .002 L to get molarity. I am guessing we are going to ignore the density of the solution and presume it is the same as water since a density for the solution isn't given.

2) a)Calculate moles of NiSO4 from the 2.7088 moles.
b) 4.6008 - 2.7088 = grams of water evaporated. Divide by 18g/mol to find moles of water evaporated
c) Divide the value in b) by a) and calculate the number of water molecules hydrating each NiSO4

If this isn't clear PM me your email and I'll try to email you a PDF of the solutions

 

[MissingTooth]

2)A 4.6008g sample of hydrate NiSO4 was heated to driev off all of teh water of hydration. The remaining solid weighed 2.7088g. If NiSO4 x H2O rprestn teh forumal of teh hydrate then waht is the value of x? No idea for this one

My chemistry is a little rusty but i'll give it a shot. The first step is to find how much water you evaporated away. To find that you take 4.6008 g of hydrate NiSO4 and subtract 2.7088g of NiSO4. You should end up with 1.892 g of H2O. Convert both masses into moles by dividing by the molar mass:

2.7088g NiSO4 / 154.7560 g/mol of NiSO4 = 0.017504 mol of NiS04

1.892 g of H20 / 18 g/mol = 0.105111 mol of H20

Now take the smaller value and divide both numbers by it.

0.017504 / 0.017504 = 1 mol of NiSO4

0.10511 / 0.017504 = 6.00509 mol of H20

The formula is NiS04 6H20

 

[goodie]

Thank you both for the help! I understand #2 but am a bit confused still about #1...ill PM you about that ushaseos. One last question i came upon I couldn't figure out was this one:


3) An aqueous stock solution is 36% HCl by mass an its density if 1.18g/L. What volume of this solution (in mL) is required to make 1.25L of 1.15 mol/L HCL?

Thank again!