Question

a chemist prepares a solution of sodium thiosulfate (na₂s₂o₃) by measuring out 200. g of sodium thiosulfate into a 450. ml volumetric flask and filling the flask to the mark with water.
calculate the concentration in mol/l of the chemists sodium thiosulfate solution. be sure your answer has the correct number of significant digits.

Explanation:

Step1: Calculate the molar mass of \(Na_2S_2O_3\)

The molar mass of \(Na\) is \(22.99\ g/mol\), \(S\) is \(32.07\ g/mol\), and \(O\) is \(16.00\ g/mol\).

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Step2: Calculate the number of moles of \(Na_2S_2O_3\)

Use the formula \(n=\frac{m}{M}\), where \(m = 200.0\ g\) and \(M=158.12\ g/mol\)

$$n=\frac{200.0}{158.12}\approx1.265\ mol$$

Step3: Convert the volume of the flask to liters

The volume \(V = 450.0\ mL=0.4500\ L\)

Step4: Calculate the concentration of the solution

Use the formula \(c=\frac{n}{V}\), where \(n = 1.265\ mol\) and \(V = 0.4500\ L\)

$$c=\frac{1.265}{0.4500}\approx2.81\ mol/L$$

Answer:

\(2.81\ mol/L\)