A solution containing \(4.4\,\mathrm{g}\) of an organic acid is exactly neutralised by \(25.0\,\mathrm{cm^3}\) of \(2.0\,\mathrm{mol\,dm^{-3}}\) sodium hydroxide. The acid has one \(\mathrm{COOH}\) group in each molecule.
What is the empirical formula of the acid?
Correct Answer: \( \boxed{\mathrm{B}} \)
Moles of sodium hydroxide:
\(\mathrm{2.0\times\frac{25.0}{1000}=0.0500\,mol}\)
The acid contains one \(\mathrm{COOH}\) group, so it reacts with sodium hydroxide in a \(1:1\) ratio.
Moles of acid:
\(\mathrm{0.0500\,mol}\)
Molar mass of the acid:
\(\mathrm{\frac{4.4}{0.0500}=88\,g\,mol^{-1}}\)
The molecular formula with \(M_r=88\) is \(\mathrm{C_4H_8O_2}\), whose empirical formula is:
\(\mathrm{C_2H_4O}\)
Therefore, the correct answer is (B).
Three equations are listed. \(x,\ y\) and \(z\) are all whole numbers.
1 \(x\mathrm{Al}+y\mathrm{O_2}\rightarrow z\mathrm{Al_2O_3}\)
2 \(x\mathrm{Mg}+y\mathrm{O_2}\rightarrow z\mathrm{MgO}\)
3 \(x\mathrm{Na}+y\mathrm{O_2}\rightarrow z\mathrm{Na_2O}\)
Which equations can be balanced if \(x=4\) and \(z=2\)?
Correct Answer: \( \boxed{\mathrm{A}} \)
Substitute \(x=4\) and \(z=2\) into each equation.
Therefore, equations 1 and 3 can be balanced, so the correct answer is (A).
What is the empirical formula of butanoic acid?
Correct Answer: \( \boxed{\mathrm{A}} \)
The molecular formula of butanoic acid is:
\( \mathrm{C_4H_8O_2} \)
The empirical formula is the simplest whole-number ratio of the atoms.
Divide each subscript by 2:
\( \mathrm{C_4H_8O_2 \div 2 = C_2H_4O} \)
Therefore, the empirical formula is \( \mathrm{C_2H_4O} \), so the correct answer is (A).
