Moles VI – Titrations

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Question 1

A solution of sodium hydroxide contained 0.250 mol dm-3. Using phenolphthalein indicator, titration of 25.0 cm3 of this solution required 22.5 cm3 of a hydrochloric acid solution for complete neutralisation.

  1. write the equation for the titration reaction.
  2. what apparatus would you use to measure out (i) the sodium hydroxide solution? (ii) the hydrochloric acid solution?
  3. what would you rinse your apparatus out with before doing the titration ?
  4. what is the indicator colour change at the end-point?
  5. calculate the moles of sodium hydroxide neutralised. Ans: 0.00625 moles
  6. calculate the moles of hydrochloric acid neutralised. Ans: 0.00625 moles
  7. calculate the concentration of the hydrochloric acid in mol/dm3(molarity). Ans: 0.278 mol dm-3

Question 2

A solution made from pure barium hydroxide contained 2.74 g in exactly 100 cm3 of water. Using phenolphthalein indicator, titration of 20.0 cm3 of this solution required 18.7 cm3 of a hydrochloric acid solution for complete neutralisation. [atomic masses: Ba = 137, O = 16, H = 1)

  1. write the equation for the titration reaction.
  2. calculate the molarity of the barium hydroxide solution.
  3. calculate the moles of barium hydroxide neutralised. Ans: 0.0032 mol 
  4. calculate the moles of hydrochloric acid neutralised. Ans: 0.0064 mol 
  5. calculate the molarity of the hydrochloric acid. Ans: 0.342 mol dm-3

 

Question 3

25 cm3 of a solution of 0.1 moldm-3 NaOH reacts with 50 cm3 of a solution of hydrochloric acid. What is the molarity of the acid?

Ans: 0.05 mol dm-3

 

Question 4

25.0 cm3 of a 0.10 moldm-3 solution of sodium hydroxide was titrated against a solution of hydrochloric acid of unknown concentration. 27.3 cm3 of the acid was required. What was the concentration of the acid?

Ans: 0.092  mol dm-3

 

Question 5

10 cm3 of a solution of NaCl react with 15 cm3 of  a 0.02 moldm-3 solution of AgNO3. What is the concentration of the NaCl solution in g dm-3?

Ans: 1.76 g dm-3

 

Question 6

25 cm3 of a 0.1 moldm-3 solution of an acid HxA reacts with 75 cm3 of a 0.1 moldm-3 solution of NaOH. What is the value of x?

Equation: HxA + xNaOH → + NaxA + xH2O

Ans: 3

 

Question 7 

A solution of hydrochloric acid of volume 25.0 cm3 was pipetted onto a piece of marble which is calcium carbonate. When all action had ceased, 1.30g of the marble had dissolved. Find the concentration of the acid

Equation: CaCO3 + 2HCl → CaCl2 + CO2 + H2O

Ans: 1.04 mol dm-3

 

Question 8

What volume of 0.1 moldm-3 hydrochloric acid would be required to dissolve 2.3 g of calcium carbonate?

Equation: CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)

Ans: 459 cm3

 

Question 9

2.05 g of the carbonate of an unknown alkali metal (X2CO3) required 8.9 cm3 of 2.0 moldm-3 hydrochloric acid to completely dissolve it. What was the relative atomic mass of the metal and which metal was it?

Equation: X2CO3(s) + 2HCl(aq) → 2XCl(aq) + CO2(g) + H2O(l)

Ans: 85.2, Rb

 

Question 10

3.2 g of hydrated sodium carbonate, Na2CO3.xH2O, was dissolved in water and the resulting solution was titrated against 1.0 moldm-3 hydrochloric acid. 22.4 cm3 of the acid was required. What is the value of x?

Ans: 10