9 This question is about acids.
Hydrogen chloride and ethanoic acid both dissolve in water. All hydrogen chloride molecules ionise in water.
Approximately 1% of ethanoic acid molecules ionise in water.
9-1 A solution is made by dissolving 1 g of hydrogen chloride in 1 dm3 of water.
Which is the correct description of this solution? [1 mark]
ANSWER
a dilute solution of a strong acid
9-2 Which solution would have the lowest pH? [1 mark]
ANSWER
1.0 mol/dm3 hydrogen chloride solution.
A student investigated the concentration of a solution of sodium hydroxide by titration with a 0.0480 mol/dm3 ethanedioic acid solution.
This is the method used.
Measure 25.0 cm3 of the sodium hydroxide solution into a conical flask using a 25.0 cm3 pipette.
Add two drops of indicator to the sodium hydroxide solution.
Fill a burette with the 0.0480 mol/dm3 ethanedioic acid solution to the 0.00 cm3 mark.
Add the ethanedioic acid solution to the sodium hydroxide solution until the indicator changes colour.
Read the burette to find the volume of the ethanedioic acid solution used.
9-3 Suggest two improvements to the method that would increase the accuracy of the result. [2 marks]
ANSWER
swirl the solution,
Use of white tile (under the flask) which will indicator clear visibility of color change;
Add ethanedioic acid drop wise near the endpoint;
Repeat and calculate mean.
9-4 Ethanedioic acid is a solid at room temperature.
Calculate the mass of ethanedioic acid (H2C2O4) needed to make 250 cm3 of a solution with concentration 0.0480 mol/dm3
Relative formula mass (Mr): H2C2O4 = 90 [2 marks]
ANSWER
Since the concentration is given in mol/dm3, therefore,
Now by using,
The student found that 25.0 cm3 of the sodium hydroxide solution was neutralised by 15.00 cm3 of the 0.0480 mol/dm3 ethanedioic acid solution.
The equation for the reaction is:
H2C2O4 + 2 NaOH → Na2C2O4 + 2 H2O
9-5 Calculate the concentration of the sodium hydroxide solution in mol/dm3. [3 marks]
ANSWER
Step1: Calculating Moles of ethanedioic acid solution,
Step 2: Now seeing the balanced equation, we need to identify molar ratio
H2C2O4 : NaOH = 1:2
Therefore, moles of NaOH is
