# Calculate molar concentration of 500 cm^3 glucose solution with mass part 5%

• Chemistry
• tedytodl
In summary: No, I am saying that I know the chemical formula for a substance, but I don’t know how to calculate its molecular weight.

#### tedytodl

New poster has been reminded to show their work on schoolwork problems
Homework Statement
The question is:
Calculate molar concentration of 500 cm^3 glucose solution with mass part 5%. Density of the solution is 1g/cm^3.
Relevant Equations
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We can't help until you show some effort. What have you learned about calculating molar concentrations? Have you solved similar problems in the past? What don't you understand about the problem?

tedytodl and jim mcnamara
phyzguy said:
We can't help until you show some effort. What have you learned about calculating molar concentrations? Have you solved similar problems in the past? What don't you understand about the problem?
I found the solution mass which is 500 g. Then I found the glucose mass (25 g). And now I don’t know how to continue. I know I have to find the M(C6H12O6) in order to find the amount of the solute and then the concentration. This is where I am stuck.

phyzguy said:
We can't help until you show some effort. What have you learned about calculating molar concentrations? Have you solved similar problems in the past? What don't you understand about the problem?
The formulas I use are:
m(solution) = V x p
m(C6H12O6) = w(solution) x m (solution)
And this is where I struggle:
n(C6H12O6) = m(C6H12O6)/M(C6H12O6)
c = n/V

What is the weight of one mole of glucose? So how many moles is 25g of glucose?

tedytodl said:
I found the solution mass which is 500 g.

Beware: that's assuming density of the solution is 1 g/mL. The more concentrated the solution, the less likely it is to be true. The only way to be sure is to check the density of the solution in density tables - you can google them, or - if the question is from the course - they were probably handed to you or are in a recommended book.

For 5% glucose solution error you are making assuming its density is 1 g/mL is a little below 2%.

How do you calculate molar mass of a substance knowing its formula?

@Borek, the problem gives the density at 1 g/cm^3.

phyzguy said:
the problem gives the density at 1 g/cm^3.
Ah, good point. Still, worth of noting it is only an approximation.

tedytodl said:
The formulas I use are:
m(solution) = V x p
m(C6H12O6) = w(solution) x m (solution)
And this is where I struggle:
n(C6H12O6) = m(C6H12O6)/M(C6H12O6)
c = n/V
Are you really saying that you know the chemical formula for a substance and you don’t know how to calculate its molecular weight?

## 1. What is the formula for calculating molar concentration?

The formula for molar concentration is M = n/V, where M is the molar concentration in mol/L, n is the number of moles of solute, and V is the volume of the solution in liters.

## 2. How do I convert mass percent to moles?

To convert mass percent to moles, you first need to determine the mass of the solute present in the solution. Then, divide the mass of the solute by its molar mass to get the number of moles. This can be written as: n = (mass of solute / molar mass of solute).

## 3. What is the molar mass of glucose?

The molar mass of glucose, also known as dextrose, is 180.16 g/mol.

## 4. How do I convert volume from cm3 to L?

To convert volume from cm3 to L, simply divide the volume in cm3 by 1000. This is because 1 L = 1000 cm3.

## 5. What is the molar concentration of a 500 cm3 glucose solution with mass percent 5%?

To calculate the molar concentration of this solution, we first need to convert the volume from cm3 to L. This can be done by dividing 500 cm3 by 1000, which gives us 0.5 L. Next, we need to calculate the number of moles of glucose present in the solution. This can be done by multiplying the mass percent (5%) by the total mass of the solution (500 cm3 x 5% = 25 g). Then, divide the mass of glucose by its molar mass (25 g / 180.16 g/mol = 0.139 mol). Finally, divide the number of moles by the volume in liters to get the molar concentration: M = 0.139 mol / 0.5 L = 0.278 mol/L.