Sunday
May 1, 2016

# Homework Help: moles/solutions.

Posted by sarah on Sunday, September 17, 2006 at 7:25pm.

I have three questions. The first one I got an ansser of 6.02 X 10^23. The question is this.

How many molecules of sucrose (C-12,H-22, O-11) molecular weight, 342, would be present in one mole of sucrose?

The other two questions I have are related.

A) The molecular weight of glucose is 180 Daltons. To make a 1 M solution of glucose, you should do which of the following

q-Dissolve 180 mg (milligrams) of glucose in 1 L of water.

r-Dissolve 100 g of glucose in 1 L of water.

s-Dissolve 180 g of glucose in water, and then add more water until the total volume of the solution is 1 L (this is what I got)

t-Dissolve 1 g of glucose in 1 L of water.

u-Dissolve 180 g of glucose in 100 g of water.

I will ask the last question at another time. Am I on the right track?

I have three questions. The first one I got an ansser of 6.02 X 10^23. The question is this.

How many molecules of sucrose (C-12,H-22, O-11) molecular weight, 342, would be present in one mole of sucrose?

There are 6.02 x 10^23 molecules in a mol of anything.

The other two questions I have are related.

A) The molecular weight of glucose is 180 Daltons. To make a 1 M solution of glucose, you should do which of the following

q-Dissolve 180 mg (milligrams) of glucose in 1 L of water.

r-Dissolve 100 g of glucose in 1 L of water.

s-Dissolve 180 g of glucose in water, and then add more water until the total volume of the solution is 1 L (this is what I got) This is the correct answer. Good work!

t-Dissolve 1 g of glucose in 1 L of water.

u-Dissolve 180 g of glucose in 100 g of water.

ok, last question I have regarding this and I appreciate it. I am confused about this next one.

The molecular weight of glucose (C6, H12, O6) is 180 Daltons. To make a 0.5 solution of glucose, you hsould

l-dissolve 12 g of glucose in 1 L of water.

m-dissolve 180 g of glucose in a small volume of water, and then add more water until the total volume of the solution is 1 L.

n-dissolve 24 g of glucose in 1 L of water.

o-dissolve 90 g of glucose in a small volume of water and then add more water until the total volume of solution is 1 L. ( I think this is it.)

p-dissolve 0.5g of glucose in 1 L of water.

I assume you intended to write 0.5 M. If so your answer is correct. Good work again!
Just remember two things about molarity. One is that you ALWAYS dissolve the solute in a little water (assuming water is the solvent), THEN add water until the final volume is reached, in this case 1 L. The other thing to remember is that molarity = mols/L of solution. Thus, you want 0.5 M; therefore, you want 0.5 mol/L and 0.5 mol is 1/2 x 180 g/mol = 90 grams. The only part of your answer I might quibble about is that you don't need periods or commas between the elements and subscripts. We can't write subscripts on these boards, at least not easily, so we just write them in-line as C6H12O6. Everyone knows we mean subscript. For superscripts, such as 10 to the 3 power, we write 10^3 and denote the exponential part with the carat. Thanks for posting. Also, thanks for telling us what you think is the correct answer.