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Answer the following question. Please enter your answer as a decimal, not as a fraction. Give your answer to 2 decimal places.

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Clicking on 'Show steps' will provide you with some prompts to break down the question into smaller parts.

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If you would like to see how to do this question, click on 'Reveal answers' at the bottom of the page.

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1) First calculate how many litres there are in $\\var{100 * a}$ml.

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2) Using the volume in litres you calculated in step 1, work out how many moles of glucose you would need to make a $\\var{0.5 * b}$M solution.

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3) Using the number of moles of glucose required which you calculated in step 2, work out the mass of glucose needed using the molecular weight ($\\var{glucose}$).

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Glucose ($C_6H_{12}O_6$) has a molecular weight of $\\var{glucose}$, what mass of glucose would you need to dissolve in $\\var{100 * a}$ml of water to get a $\\var{0.5 * b}$M solution?

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[[0]] grams

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We can break this question up into parts. First we need to know how many moles of glucose we need to make a $\\var{0.5 * b}$M solution using $\\var{100 * a}$ml of water. The calculate this we use the formula

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$\\text{volume of liquid (in litres)} \\times \\text{concentration (in mol/L)} = \\text{number of moles of substance}$.

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This formula uses the voume in litres so we have to convert $\\var{100 * a}$ml to a volume in litres. There are 1000ml in 1L so $\\var{100 * a}$ml is equal to 

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$\\dfrac{\\var{100 * a}}{1000} = \\var{100 * a / 1000}$L.

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Putting our numbers into the formula, we find that we need 

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$\\var{100 * a / 1000} \\times \\var{0.5 * b} = \\var{(100 * a / 1000) * 0.5 * b}$ moles

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of glucose. Finally, to work out the mass of glucose we need, we use the formula

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$\\text{molecular weight} \\times \\text{number of moles} = \\text{mass of substance (in grams)}$.

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We are told that glucose has a molecular wight of $\\var{glucose}$ and we have calculated that we need $\\var{(100 * a / 1000) * 0.5 * b}$ moles of glucose. Putting these numbers into the formula, we find that we need

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$\\begin{align}\\var{glucose} \\times \\var{(100 * a / 1000) * 0.5 * b} & = \\var{glucose * ((100 * a / 1000) * 0.5 * b)} \\text{ grams} \\\\ & = \\var{precround((glucose * ((100 * a / 1000) * 0.5 * b)), 2)} \\text{ grams to 2 d.p.}\\end{align}$

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of glucose to make a $\\var{0.5 * b}$M solution using $\\var{100 * a}$ml of water.

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Molecular weight of glucose

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Practice at a longer calculation to work out how much glucose is needed to make a solution of a given concentration.

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