QUESTION 1
Question 1.1 [2 marks]
To find the molecular formula from the empirical formula and the molar mass, we can follow these steps:
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Calculate the molar mass of the empirical formula \( \text{Mg}_3\text{Si}_2\text{H}_3\text{O}_8 \):
- Molar mass of Mg = 24.31 g/mol
- Molar mass of Si = 28.09 g/mol
- Molar mass of H = 1.01 g/mol
- Molar mass of O = 16.00 g/mol
\[ \text{Molar mass of } \text{Mg}_3\text{Si}_2\text{H}_3\text{O}_8 = (3 \times 24.31) + (2 \times 28.09) + (3 \times 1.01) + (8 \times 16.00) \]
\[ = 72.93 + 56.18 + 3.03 + 128.00 = 260.14 , \text{g/mol} \]
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Divide the molar mass of the compound by the molar mass of the empirical formula:
\[ \frac{520.8}{260.14} \approx 2 \]
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Multiply the empirical formula by this factor (2):
\[ \text{Molecular formula} = \text{(Mg}_3\text{Si}_2\text{H}_3\text{O}_8\text{)}_2 = \text{Mg}_6\text{Si}_4\text{H}6\text{O}{16} \]
Answer: B. \( \text{Mg}_6\text{Si}_4\text{H}6\text{O}{16} \)
Question 1.2 [2 marks]
Bromothymol blue is typically used as an indicator in the titration of a strong base and a weak acid, as it changes color in a pH range that corresponds to the transition from acidic to neutral and into basic conditions.
Answer: B. Weak base and a strong acid
Question 1.3 [2 marks]
An exothermic reaction is characterized by the release of energy, where the products have less potential energy than the reactants. This means that the enthalpy change (\(\Delta H\)) is negative.
Answer: B. \(\Delta H\) is negative and the products have less potential energy than the reactants.
1 answer