A pure substance refers to an element or a compound that has no component of another compound or element. Pure substances are made of only one type of atom or molecule. Hydrogen gas and pure iron are examples of pure substances. Hydrogen consists of hydrogen atoms only while iron consists of only iron atoms. Mixing two pure substances results in a mixture. To separate the two, scientists use a method known as filtration. Mixtures can either be homogeneous or heterogeneous. The measure used to determine how pure a substance may be called purity. Besides hydrogen and iron, other pure substances include gold, diamonds, sugar, and baking soda.

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The concentration of HCl can be determined by titration with a primary standard such as Na2CO3 (sodium carbonate). The titration

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Answer:

The concentration of HCl is 0.275 M

Explanation:

Step 1: Data given

Mass of Na2CO3 = 0.521 grams

Molar mass of Na2CO3 = 105.99 g/mol

Volume of HCl = 35.7 mL

Step 2: The balanced equation:

2HCl + Na2CO3 → 2NaCl + CO2 + H2O

CO3(2-) + 2H+ ---> H2O + CO2

Step 3: Calculate moles of Na2CO3

Moles Na2CO3 = mass Na2CO3 / Molar mass Na2CO3

Moles Na2CO3 = 0.521 grams / 105.99 g/mol

Moles Na2CO3 = 0.0049 moles

Step 4: Calculate moles of HCl

For 1 mol of Na2CO3 consumed, we need 2 moles of HCl

moles of HCL = 2 * 0.0049 = 0.0098 moles HCl

Step 5: Calculate molarity of HCl

Molarity = number of moles of HCl / Volume (liters)

Molarity = 0.0098 moles / 0.0357 L

Molarity = 0.275 M

The concentration of HCl is 0.275 M

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