Chem 0100 Q1

Hydrogen peroxide, H₂O₂, decomposes at 25°C to yield water and oxygen. Write the balanced equation for this reaction.

• 2H₂O_2(l) → H₂O_(g) + O_2(g)

• H₂O_2(l) → H₂O_(g) + O_2(g)

• 2H₂O_2(l) → 2H₂O_(l) + O_2(g)

• 2H₂O_2(l) → 2H₂O_(g) + O_2(g)

What volume of water will be produced from the complete decomposition of 5 mL of H₂O₂? (A_r: H = 1; O = 16) Density of H₂O₂ = 1.450 gcm^-3; H₂O = 1.00 gcm^-3)

• 3.8 mL

• 24 cm³

• 16 mL

• 2.5 cm³

0.0012 moles of Na₂CO₃ were dissolved in distilled water in a 250.0 mL volumetric flask, and the solution made up to the mark. A 25.0 mL aliquot was taken and 40 mL of an HCl solution of unknown concentration was added. This resulting mixture required 16.5 mL of a 0.12 M NaOH solution for complete neutralization. (i) Why is Na₂CO₃ a primary standard?

• It is impure.

• It absorbs carbon dioxide from the atmosphere.

• It absorbs water from the atmosphere.

• It is stable and hence the strength does not change with time.

Give two specific reasons why NaOH is not considered to be a primary standard.

• It absorbs water from the atmosphere changes it's mass.

• It is not pure because it reacts with carbon dioxide on exposure to air.

• NaOH is used as a primary standard.

• NaOH has a high weight.

What is meant by the term "back titration"?

• Calculating the amount of solute required and making up the solution by dissolving this amount.

• Titrating original sample using a standard solution.

• Titrating excess standard reagent.

• Diluting a higher concentration to make a less concentration one.

Write the balanced equation for the reaction between Na₂CO₃ and HCl.

• Na₂CO_3(aq) + 2HCl_(aq) → 2NaCl_(aq) + CO_2(g) + HCl_(aq)

• 2Na₂CO_3(aq) + HCl_(aq) → 4NaCl_(aq) + CO_2(g) + H₂O_(l)

• Na₂CO_3(s) + 2HCl_(aq) → 4NaCl_(aq) + CO_2(g) + H₂O_(l)

• Na₂CO_3(aq) + 2HCl_(aq) → 2NaCl_(aq) + CO_2(g) + H₂O_(l)

0.0012 moles of Na₂CO₃ were dissolved in water in a 250.0 mL volumetric flask, and the solution made up to the mark. A 25.0 mL aliquot was taken and 40 mL of HCl solution of unknown concentration was added. This resulting mixture required 16.5 mL of a 0.12 M NaOH solution for complete neutralization. Calculate the number of moles of HCl that reacted with the 25.0 mL aliquot of the Na₂CO_3(aq).

• 0.0012 moles HCl

• 0.0024 moles HCl

• 0.00012 mol HCl

• 0.00024 mol HCl

0.0012 moles of Na₂CO₃ were dissolved in water in a 250.0 mL volumetric flask, and the solution made up to the mark. A 25.0 mL aliquot was taken and 40 mL of HCl solution of unknown concentration was added. This resulting mixture required 16.5 mL of a 0.12 M NaOH solution for complete neutralization. Calculate the number of moles of HCl that reacted with the NaOH.

• 0.12 mol/16.5 mL

• (16.5 mL x 0.12 mol)/1000 mL

• 0.12 mol/1000 mL

• (0.12 mol/ 16.5 mL) x 1000 mL

0.0012 moles of Na₂CO₃ were dissolved in water in a 250.0 mL volumetric flask, and the solution made up to the mark. A 25.0 mL aliquot was taken and 40 mL of HCl solution of unknown concentration was added. This resulting mixture required 16.5 mL of a 0.12 M NaOH solution for complete neutralization. Calculate the molarity of the HCl(aq).

• 0.06 M HCl solution

• 0.00006 M HCl solution

• 0.00222 M HCl solution

• 0.00198 M HCl solution

Calculate the energy required to excite an electron from the n = 2 to the n = 4 level in atomic hydrogen. What is the maximum wavelength of light that causes this excitation?

• 4.09 x 10^-19 J, 486 nm

• 4.09 x 10^-18 J, 426 nm

• 2.09 x 10^-18 J, 496 nm

• 2.09 x 10^-19 J, 506 nm