Why is it important to fill the space below the tap in a burette with acid or alkali before beginning a titration?
Which reaction will distinguish between a primary and a secondary alcohol?
To give a more accurate result
The burette’s scale does not include this volume
To give concordant results
An incorrect volume would be recorded
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Which piece of equipment is not needed to make a 250 cm3 standard solution of sodium hydroxide?
Burette
Volumetric flask
Beaker
Balance
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A student was titrating a 25 cm3 sample of a solution of sodium hydrogen carbonate with 0.105 mol dm-3 hydrochloric acid. She wanted to reduce the percentage uncertainty in using the burette.
This could best be achieved by
Using more drops of the indicator
Repeating the titration several times and taking an average reading
Titrating a smaller volume of sodium hydrocarbonate solution
Titrating a larger volume of sodium hydrogen carbonate solution
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A student planned to carry out an experiment to measure the enthalpy change when magnesium displaces copper from copper(II) sulfate solution.
The method they followed was
50 cm3 of 0.20 mol dm-3 copper(II) sulfate solution was measured in a measuring cylinder and transferred to a polystyrene cup
A thermometer was placed in the cup and the initial temperature recorded
1.86 g of magnesium powder was added to the cup and the mixture was stirred
The final temperature was recorded
In this experiment
The copper(II) sulfate solution should be the excess reactant
The magnesium powder is all used up
It is unnecessary to weigh the magnesium powder so precisely
The measuring cylinder is the largest source of error
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A student investigates the intermolecular forces in various liquids by allowing the liquids to drain from a burette and observing the resulting deflections of the jet of liquid. The student uses a charged polyethene rod held near the jet.
Which statement is correct when comparing water and propanone, CH3COCH3?
Water deflects more than propanone
Propanone deflects more than water
Both liquids would deflect by the same amount
Neither liquid causes any deflection
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A student attempted to find the enthalpy of hydration of MgSO4.7H2O by measuring the enthalpies of solution of MgSO4 (s) and MgSO4.7H2O (s) and then completing a Hess cycle to find the missing enthalpy change:
MgSO4 (s) + 7H2O (l) → MgSO4.7H2O (s)
MgSO4 (s) + (aq) → MgSO4 (aq)
MgSO4.7H2O (s) + (aq) → MgSO4 (aq)
The measurements the student made were recorded as follows:
| Mass of solid / +0.01 g | Volume of water used / +0.05 cm3 | Temperature change / +1.0 oC |
MgSO4 (s) | 1.25 | 25.0 | +7.5 |
MgSO4.7H2O (s) | 2.55 | 25.0 | +2.0 |
From these results, the heat energy transferred by MgSO4 (s) would be
-39.19 J
-783.75 J
-1149.5 J
-1567.50 J
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A student attempted to find the enthalpy of hydration of MgSO4.7H2O by measuring the enthalpies of solution of MgSO4 (s) and MgSO4.7H2O (s) and then completing a Hess cycle to find the missing enthalpy change:
MgSO4 (s) + 7H2O (l) → MgSO4.7H2O (s)
MgSO4 (s) + (aq) → MgSO4 (aq)
MgSO4.7H2O (s) + (aq) → MgSO4 (aq)
The measurements the student made were recorded as follows:
| Mass of solid/ +0.01 g | Volume of water used / +0.05 cm3 | Temperature change / +1.0 oC |
MgSO4 (s) | 1.25 | 25.0 | +7.5 |
MgSO4.7H2O(s) | 2.55 | 25.0 | +2.0 |
Which of the statements is not correct about the data collected?
The % uncertainty in the mass of MgSO4 (s) is greater than MgSO4.7H2O(s)
The uncertainty in the volume measurements is the same
The mass measurements are more accurate than the temperature measurements
The uncertainty in the thermometer readings is format('truetype')%3Bfont-weight%3Anormal%3Bfont-style%3Anormal%3B%7D%3C%2Fstyle%3E%3C%2Fdefs%3E%3Ctext%20font-family%3D%22math196da2f590cd7246bbde0051047%22%20font-size%3D%2216%22%20text-anchor%3D%22middle%22%20x%3D%226.5%22%20y%3D%2216%22%3E%26%23xB1%3B%3C%2Ftext%3E%3C%2Fsvg%3E){kind=small}
0.5 oC
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A student attempted to find the enthalpy of hydration of MgSO4.7H2O by measuring the enthalpies of solution of MgSO4 (s) and MgSO4.7H2O (s) and then completing a Hess cycle to find the missing enthalpy change:
MgSO4 (s) + 7H2O (l) → MgSO4.7H2O (s)
MgSO4 (s) + (aq) → MgSO4 (aq)
MgSO4.7H2O (s) + (aq) → MgSO4 (aq)
The measurements the student made were recorded as follows
| Mass of solid / +0.01 g | Volume of water used / +0.05 cm3 | Temperature change / +1.0 oC |
MgSO4 (s) | 1.25 | 25.0 | +7.5 |
MgSO4.7H2O (s) | 2.55 | 25.0 | +2.0 |
Which suggestion would reduce the overall measurement uncertainty in the experiment?
Use larger samples of the solids
Use smaller samples of the solids
Use a digital thermometer
Repeat the experiment several times
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A student attempted to find the enthalpy of hydration of MgSO4.7H2O by measuring the enthalpies of solution of MgSO4 (s) and MgSO4.7H2O (s) and then completing a Hess cycle to find the missing enthalpy change:
MgSO4 (s) + 7H2O (l) → MgSO4.7H2O (s)
MgSO4(s) + (aq) → MgSO4 (aq)
MgSO4.7H2O (s) + (aq) → MgSO4 (aq)
The measurements the student made were recorded as follows
| Mass of solid / +0.01 g | Volume of water used / +0.05 cm3 | Temperature change / +1.0 oC |
MgSO4 (s) | 1.25 | 25.0 | +7.5 |
c = 4.18 J K-1 mol-1
The overall uncertainty in calculating the heat energy change, q, for the MgSO4 (s) is:
13.5%
15.3%
16.9%
17.7%
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The enthalpy of neutralisation of hydrochloric acid takes place as follows
HCl (aq)+ NaOH (aq) → NaCl (aq)+ H2O (l)
State the most suitable piece of laboratory equipment for carrying out the experiment described.
Conical flask
Evaporating basin
Copper calorimeter
Polystyrene cup
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When a sample of sodium hydroxide, NaOH, is dissolved in 250 cm3 of distilled water. 25.0 cm3 of this solution is titrated against sulfuric acid with a concentration of 2.00 mol dm-3. Complete neutralisation takes place with 15.0 cm3 of sulfuric acid.
2NaOH + H2SO4 → Na2SO4 + 2H2O
What is the mass of the original sample of sodium hydroxide dissolved in 250 cm3 of distilled water?
1.20 g
12.0 g
2.40 g
24.0 g
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A sample of 2.76 g of ethanol was added to excess acidified aqueous potassium dichromate (VI). The reaction mixture was then boiled under reflux for one hour. The organic product was collected by distillation.
The yield of the product was 75.0%
What is the mass of the product collected?
1.9 g
2.1 g
2.7 g
3.6 g
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A student made up a standard solution of sodium hydrogen carbonate using a two decimal place balance and a 250 cm3 volumetric flask.
Which of the following steps would make the final concentration of the solution more accurate?
Using a dropping pipette to add water up to the graduated mark
Using a three decimal place balance
Using a 100 cm3 flask instead of a 250 cm3 flask
Adding a stopper and inverting the flask 10 times
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Zinc reacts with copper sulfate according to the following equation:
Zn(s) + CuSO4(aq) → Cu(s) + ZnSO4(aq)
Rates of reaction can be found by measuring how certain properties change during the course of the reaction.
Which of these properties could be used?
| Change in volume | Change in temperature | Change in colour |
A | ✓ | ✓ | ✓ |
B | ✓ | ✓ | × |
C | × | ✓ | ✓ |
D | ✓ | × | ✓ |
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25.0 cm3 of hydrochloric acid solutions reacts with 36.2 cm3 of 0.225 mol dm-3 sodium hydroxide solution.
What is the concentration of the acid?
0.326 mol dm-3
0.155 mol dm-3
1.55 x 10-4 mol dm-3
3.26 x 10-4 mol dm-3
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Silver nitrate solution reacts with aqueous potassium iodide to form silver iodide and potassium nitrate. Which separation technique could be used to recover the silver iodide?
distillation
chromatography
filtration
crystalllisation
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The enthalpy change of a chemical reaction can be found using the following relationship:
q = mcΔT
In this expression, which of the following is true?
m represents the amount of substance in moles
The temperature is measured in Centigrade
c is the specific heat capacity of the substance
The unit of q is kJ
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In an acid-base titration, what is the point at which the indicator changes colour known as?
the titre
the end point
the equivalence point
neutralisation point
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The enthalpy of solution of hydrated copper (II) sulfate can be determined by measuring the temperature changes when a known amount of copper (II) sulfate is added to a fixed volume of water in a calorimeter.
What assumption is not made when calculating the enthalpy change?
there are negligible heat losses in the calorimeter
the specific heat capacity of the solution is the same as water
the density of solution is the same as water
the copper (II) sulfate dissolves completely
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The variation of reaction rate with temperature can be investigated using the reaction between sodium thiosulfate solution and hydrochloric acid. The thiosulfate solution is heated to different temperatures and the acid is added to start the reaction. A precipitate of sulfur makes the solution opaque. Placing a cross drawn on paper under the flask enables the ‘end’ of the reaction to be measured using a stopwatch.
Which of the following steps are necessary for each run in the investigation ?
| The same volume of sodium thiosulfate should be used | The temperature should be measured before adding the acid | The temperature should be measured at the end of the reaction |
A | ✓ | ✓ | ⨯ |
B | ✓ | ✓ | ✓ |
C | ✓ | ⨯ | ✓ |
D | ✓ | × | ⨯ |
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A student used the following method to make a 250 cm3 standard solution of 0.150 mol dm-3 propanedioic acid.
Measure out 3.9000 g of propanedioic acid on a 4 decimal place balance.
Transfer the propanedioic acid to a 250 cm3 beaker.
Add approximately 50 cm3 of distilled water.
Stir the mixture to dissolve the propanedioic acid.
Transfer the solution to a 250 cm3 volumetric flask.
Add distilled water to the mark.
Stopper and invert the flask.
If necessary, add more distilled water to the volumetric flask so that the meniscus is at the mark.
After analysis, the propanedioic acid standard solution was determined to be 0.154 mol dm-3.
Which of the following would not account for the concentration of the propanedioic acid standard solution being less than 0.150 mol dm-3?
Using a 4 decimal place balance instead of one that measures to 2 decimal places
Rinsing the weighing boat into the beaker
Rinsing the beaker into the flask
Having the top of the meniscus level with the mark in the volumetric flask
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A titration experiment was set up to determine the relative formula mass, Mr, anunknown monoprotic acid, HA.
HA + NaOH → NaA + H2O
2.52 g of HA is used to make a 250 cm3 aqueous solution.
25.0 cm3 of 0.136 mol dm–3 aqueous sodium hydroxide is added to a conical flask.
The aqueous sodium hydroxide is titrated with the acid solution, HA (aq).
The titration results are as follows.
| Rough | 1 | 2 | 3 | 4 |
Initial volume / cm3 | 0.00 | 0.45 | 2.50 | 2.55 | 0.05 |
Final volume / cm3 | 28.30 | 27.90 | 29.70 | 29.60 | 27.35 |
What is the identity of the unknown monoprotic acid?
HCl
HBr
HNO3
CH3CH2COOH
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Potassium carbonate can form hydrates of the general formula K2CO3.xH2O
A titration experiment was set up to determine the number of moles of water of crystallisation in the hydrated potassium carbonate sample.
A 250 cm3 solution was made by dissolving 3.672 g of a potassium carbonate hydrate in water.
The solution was titrated with 0.18 mol dm-3 hydrochloric acid.
The titration results are shown in the table.
| Rough | 1 | 2 | 3 |
Initial volume / cm3 | 0.00 | 0.45 | 2.50 | 2.55 |
Final volume / cm3 | 26.30 | 25.20 | 27.15 | 26.85 |
What is the correct value for x in the formula of this potassium carbonate hydrate, K2CO3.xH2O?
1
1.5
2
5
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A student carried out an experiment to find the enthalpy change for a reaction between zinc and copper(II) sulfate solution.
The student used a measuring cylinder to place 70 cm3 of 0.500 mol dm–3 copper(II) sulfate solution into a polystyrene cup.
The student recorded the temperature at one-minute intervals for three minutes.
At the fourth minute the student added 2.00 g of zinc powder and stirred the mixture, but did not record the temperature.
The student recorded the temperature at one-minute intervals for a further eight minutes.
After plotting a graph of their results, the student determined that the temperature change, ΔT, for the reaction was 21.70 oC.
Assume that the density of the solution is 1 g cm-3 and the specific heat capacity of the solution is 4.18 J K-1 g-1.
What is the enthalpy change for this reaction between zinc and copper(II) sulfate solution?
181.4 kJ mol-1
-181.4 kJ mol-1
207.6 kJ mol-1
-207.6 kJ mol-1
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When 1.383 g of impure potassium chloride is dissolved in 25.0 cm3 of water the temperature decreases from 22.23 oC to 20.02 oC.
The molar enthalpy of dissolution for potassium chloride is 17.30 kJ mol-1
The specific heat capacity of water is 4.18 J K−1 g−1
What is the percentage purity of potassium chloride used?
72.0%
13.9%
68.4%
76.0%
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2.65 g of magnesium sulfate is added to 35.0 cm3 of water with an initial temperature of 296.7 K.
The specific heat capacity of water is 4.18 J K−1 g−1.
The enthalpy change of solution for magnesium sulfate is -75.1 kJ mol-1.
What was the final temperature of the magnesium sulfate solution?
284.3 K
295.7 K
308.0 K
319.4 K
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The reaction between the aqueous copper(II) ion and concentrated hydrochloric acid proceeds according to the following equilibrium. The equilibrium is endothermic in the forward direction.
[Cu(H2O)6]2+ (aq) + 4Cl- (aq) ⇌ CuCl42- (aq) + 6H2O (l)
The tetrachlorocuprate(II) ion, CuCl42-, produces a yellow colour in solution.
Which of the following statements is not correct?
Adding more drops of hydrochloric acid will change the colour of the reaction mixture from blue to green
Placing the test tube in a warm water bath will change the colour of the reaction mixture from blue to green
Placing the test tube in an ice bath will change the colour of the reaction mixture from green to yellow
Adding drops of water will change the colour of the reaction mixture from yellow to green
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Two students were asked to use a continuous monitoring method to investigate the effect of changing the concentration of hydrochloric acid on the rate of reaction between hydrochloric acid and calcium carbonate powder.
Student 1 decided to place the reaction vessel on a balance and measure the mass lost over time.
Student 2 decided to connect the reaction vessel to a gas syringe and measure the volume of gas produced over time.
Which is the correct explanation for which student will obtain more accurate results for acid concentrations from 0.1 mol dm-3 to 2.0 mol dm-3?
Student 1 because no product will be lost
Student 1 because they are measuring the mass that remains
Student 2 because they are measuring the volume of gas produced
Student 2 because some product will be lost
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A student investigates the intermolecular forces in cyclohexane, ethanol, propanone and water by allowing the liquids to drain from a burette and observing the resulting deflections of the jet of liquid. The student uses a charged polyethene rod held near the jet.
Which statement about the deflections is correct?
Deflection of cyclohexane is caused by the attraction of the delocalised electrons above and below the ring and the positive charge of the rod
Water is deflected the most because it has the lowest mass
Propanone is the least deflected polar molecule
Ethanol is more deflected than water due to stronger hydrogen bonding
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An experiment was set up to determine the identity of an unknown volatile liquid, X, as shown in the diagram.
A hypodermic syringe was used to inject a sample of the unknown volatile liquid X into a gas syringe in an oven, where it vapourised.
Mass of hypodermic syringe | 232.941 g |
Mass of hypodermic syringe and liquid X | 233.175 g |
Oven temperature | 98.0 oC |
Atmospheric pressure | 98.57 kPa |
Gas volume produced | 85.0 cm3 |
Using the information in the table, what is the identity of the unknown volatile liquid, X?
The gas constant R = 8.31 J K–1 mol–1
Cyclohexane
Hexane
2-methylpent-1-ene
Butanoic acid
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