Chapter Two · Chemical analysis · Chemistry. These are 10 questions from the Magmo3 bank on this lesson, from easy to hard. Solve each one, then open "Show answer and explanation". Magmo3 has 84 questions on this lesson, each with an explanation.
Phenolphthalein indicator shows which colours in acidic and in alkaline media, respectively?
Correct answer: (A) Colourless in acid and pink (red) in alkali.
Explanation: Phenolphthalein is colourless in acidic solution and turns pink (red) in alkaline solution.
50 mL of 1.0 M sodium chloride solution is diluted with distilled water to a final volume of 250 mL. The molarity of the diluted solution is:
Correct answer: (D) 0.2 M
Explanation: Using M₁V₁ = M₂V₂, M₂ = (1.0 × 50) / 250 = 0.2 M.
The molarity (M) of a solution is defined as the number of moles of solute dissolved in:
Correct answer: (C) one litre (1000 mL) of the solution.
Explanation: Molarity is the number of moles of solute dissolved in one litre (1000 mL) of solution.
For the titration of a strong acid against a strong base, which of the following indicators can be used to detect the end point?
Correct answer: (A) Either methyl orange or phenolphthalein, because the pH changes sharply over a wide range at the equivalence point.
Explanation: In a strong acid–strong base titration the pH jump is large, so either methyl orange or phenolphthalein can be used.
What volume of distilled water must be added to 50 mL of 2 M hydrochloric acid to dilute it to 0.5 M? (assume volumes are additive)
Correct answer: (A) 150 mL
Explanation: 2 M × 50 mL = 0.5 M × V2 → V2 = 200 mL total; water added = 200 − 50 = 150 mL.
A 0.585 g sample of pure sodium chloride is dissolved and treated with excess silver nitrate solution. The mass of silver chloride precipitate obtained is: (Na = 23, Cl = 35.5, Ag = 108)
Correct answer: (A) 1.435 g
Explanation: n(NaCl) = 0.585 / 58.5 = 0.01 mol = n(AgCl); mass = 0.01 × 143.5 = 1.435 g.
Which of the following indicators turns red in acidic medium and yellow in basic medium?
Correct answer: (D) Methyl orange
Explanation: The indicator table shows that Methyl orange is Red in acidic medium and Yellow in basic medium.
An impure sample of sodium hydroxide of mass 0.50 g is dissolved in water and completely neutralised by 100 mL of 0.1 M hydrochloric acid (NaOH + HCl → NaCl + H2O; NaOH = 40 g/mol). What is the percentage purity of the sodium hydroxide?
Correct answer: (C) 80%
Explanation: moles HCl = 0.1 × 0.1 = 0.01 = moles NaOH; mass NaOH = 0.01 × 40 = 0.4 g; purity = 0.4/0.5 × 100 = 80%.
When calculating the number of molecules of water of crystallization for anhydrous barium chloride combining with water, if the mass of anhydrous barium chloride is 2.2923 grams and the combined mass of water of crystallization is 0.398 grams, what is the exact percentage of water of crystallization?
Correct answer: (B) 14.79 %
Explanation: % Water of crystallization = (0.398)/(2.6903) × 100 = 14.79 %.
In the derivation for hydrated barium chloride in the text, how many molecules of water of crystallization are found to combine with one formula unit of BaCl2?
Correct answer: (C) 2.006 molecules
Explanation: 'The number of molecules of water of crystallization = (36.114)/(18) = 2.006 molecules', leading to BaCl2.2H2O.
The first 10 questions in every subject are free, each with an explanation.