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Practice calculating number of moles of a substance given the concentration and volume of a solution.

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How many moles of glucose are there in $\\var{a}$L of a $\\var{0.25 * b}$M (mol/L) solution?

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[[0]] moles

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How many moles of glucose are there in $\\var{25 * c}$mL of a $\\var{0.25 * d}$M (mol/L) solution?

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[[0]] moles

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To answer these questions, 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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#### a)

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How many moles of glucose are there in $\\var{a}$L of a $\\var{0.25 * b}$M (mol/L) solution?

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Solution:

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Putting our numbers into the formula, we find that there are

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$\\var{a} \\times \\var{0.25 * b} = \\var{a * 0.25 * b}$ moles

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of glucose in $\\var{a}$L of a $\\var{0.25 * b}$M (mol/L) solution.

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#### b)

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How many moles of glucose are there in $\\var{25 * c}$mL of a $\\var{0.25 * d}$M (mol/L) solution?

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Solution:

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Our formula uses the volume of liquid in litres so first we have to convert $\\var{25 * c}$mL to a volume in litres. There are 1000ml in 1L so $\\var{25 * c}$mL is equal to

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$\\dfrac{\\var{25 * c}}{1000} = \\var{25 * c / 1000}$L.

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Putting our numbers into the formula, we find that there are

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\\begin{align}\\var{25 * c / 1000} \\times \\var{0.25 * d} & = \\var{(25 * c / 1000) * 0.25 * d} \\text{ moles} \\\\ & = \\var{precround(((25 * c / 1000) * 0.25 * d),2 )} \\text{ moles to 2 d.p.}\\end{align}

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of glucose in $\\var{25 * c}$mL of a $\\var{0.25 * d}$M (mol/L) solution.

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